CHAPTER ONE

Yucca Mountain Site Characterization Project

Background on the Project

Located 100 miles northwest of Las Vegas, Nevada, on remote and arid Federal land, Yucca Mountain has been the subject for many years of studies to support a determination of whether it should be developed as a geologic repository for spent nuclear fuel and high-level radioactive waste. If a repository is developed there, the Office of Civilian Radioactive Waste Management (OCRWM) will accept spent nuclear fuel and high-level radioactive waste from the sites where it is currently stored, transport it to Yucca Mountain, and emplace it in the repository.

Site characterization studies of Yucca Mountain have generated a huge volume of information regarding the safety and suitability of the site. Ensuring the integrity of this information, evaluating it, and presenting it to other parties is a significant task. By the time site characterization ends, approximately $4 billion and nearly 20 years of effort will have been invested in studies of Yucca Mountain and the design of a repository tailored to its features.

Aerial view of Yucca Mountain

State of Nevada showing Yucca Mountain

OCRWM is close to the end of the site characterization phase. The Secretary of Energy will draw upon the data we have produced, along with other sources, to determine whether this information is sufficient to recommend to the President that a repository be developed at the site. If the Secretary does recommend the site for development, and if the President submits the recommendation to Congress, the Nuclear Waste Policy Act (NWPA) gives the State of Nevada an opportunity to disapprove the designation. If Nevada does disapprove, Congress must act if the site is to be designated for repository development. If the site is designated, the Department of Energy (DOE) must submit a license application to the Nuclear Regulatory Commission (NRC) for authorization to construct a repository. Upon the completion of construction and other regulatory requirements, NRC would issue a license authorizing facility operations.


Statutory process for Site Recommendation

To accomplish the work planned for Fiscal Year 2000, OCRWM allocated $281.2 million of its appropriation of $351.2 million to the Yucca Mountain Site Characterization Project. The distribution was as follows: $70.6 million was allocated to core science; $61.4 million to site suitability, licensing, and performance assessment; $66.3 million to design and engineering; $1.3 million to National Environmental Policy Act compliance; $30.0 million to operations and construction; $35.2 million to project management; and $16.4 million was allocated to external oversight and payments-equal-to-taxes.

Core science

In Fiscal Year 2000, the Yucca Mountain Site Characterization Project focused on preparing the analysis and documentation needed to support the Secretary of Energy's determination on site recommendation.

We placed priority during the year on obtaining data to reduce key uncertainties about the factors important to repository performance and to refining our models of how the engineered and natural barrier systems would perform. Testing and monitoring enabled us to better define the range of variability in natural processes at the site and to confirm predictions we made through modeling.


Yucca Mountain Project Fiscal Year 2000 budget (dollars in millions)

Consistent with our plan to provide an adequate technical basis for a decision on site recommendation, many of our investigations have been completed or are nearing completion. However, site evaluation and repository design are continuous processes, and if the determination is made to go forward with repository development, confirmatory testing and monitoring activities are expected to continue until repository closure. New information will be evaluated for its effect on system and subsystem performance as part of an ongoing learning process. Design and operating decisions will be modified based on feedback from these evaluations, as well as other technological and policy developments.

Test facilities
During Fiscal Year 2000, we continued to conduct site investigations at many existing testing facilities at the Yucca Mountain site and its vicinity. In addition, we developed specialized facilities to accommodate testing that will further reduce uncertainty about repository performance.

The hub of our testing activities is an underground Exploratory Studies Facility - an underground tunnel, the main loop of which is 7.6 meters (25 feet) in diameter and nearly 8 kilometers (5 miles) long. Transecting the main loop is a "cross-drift" tunnel, 5 meters (16.5 feet) in diameter and 2.8 kilometers (1.67 miles) long, which gives us direct access to the central and western portions of the proposed repository block, and to the geologic strata where approximately two-thirds of the waste emplacement tunnels would lie. Testing related to rock properties, groundwater flow, water seepage, and the effects of heat from waste packages is or will be located in the cross-drift.

We have constructed a number of alcoves and niches within the Exploratory Studies Facility to house additional hydrologic and heat-related tests. We began excavation of Alcove 8, a cross-over alcove located in the cross-drift above the main drift tunnel, in January 2000. Niche 3 is located off the main loop approximately 17 meters (56 feet) directly below Alcove 8. Together, these areas constitute a facility for testing flow properties in the portion of the Topopah Spring Formation that lies immediately above the potential repository horizon.


Exploratory Studies Facility cross-section

During site characterization we have obtained geologic and geochemical data from more than 350 boreholes drilled from within the underground facilities, more than 450 boreholes drilled from the surface, and more than 250 pits and trenches. Monitoring wells have yielded hydrologic data, and Global Positioning System stations have measured small movements in the earth's surface.

The test facility at Busted Butte is an important site in the vicinity of Yucca Mountain, as it offers direct access to a rock formation similar to that beneath the repository site.

The rock being tested at Busted Butte is the Calico Hills non-welded vitric hydrogeologic unit. By studying pathways, quantities, and rates of water movement through this rock, we learn about the physical and chemical processes involved in radionuclide transport from the repository to the water table. In addition, we have excavated blocks of rock from the Busted Butte facility for off-site laboratory testing.


Exploratory Studies Facility and alcoves

Understanding the unsaturated zone
At Yucca Mountain, the unsaturated zone is the area of rock that lies between the surface and the deep, regional water table. The repository would be located in this zone, about 300 meters (1,000 feet) below the surface and about 300 meters (1,000 feet) above the water table.

Our performance assessments have identified seepage of water into emplacement tunnels and onto waste packages as a primary cause of waste package degradation and eventual release of radionuclides. Determining under what conditions, in what quantities, and at what rate(s) water would seep into excavated underground openings (drifts) and onto waste packages is, therefore, of prime importance. Unsaturated zone tests focus on collecting data on the flow of groundwater through the unsaturated rock overlying the potential repository, seepage into drifts, and the potential for water flow and radionuclide transport through the unsaturated rock beneath the potential repository horizon to the water table.


Underground alcoves and niches

The Drift Seepage Peer Review Panel, which was convened to review the Project's approach and assess the potential for seepage into drifts, submitted its report at the end of Fiscal Year 1999. In Fiscal Year 2000, we implemented a plan to address the Panel's recommendations by modifying planned tests and conducting additional tests and modeling efforts to further reduce uncertainties associated with groundwater flow and seepage in the unsaturated zone.

Major hydrologic experiments designed to determine seepage parameters were conducted at several underground test locations in the Exploratory Studies Facility. These tests investigated seepage phenomena under two general types of conditions: (1) ambient conditions, in which passive measurements of the amount of natural seepage of water into test areas are conducted, and (2) forced injection or surface application, in which water is introduced into test media (rock of the repository horizon) and the resulting seepage is monitored. This latter testing condition yields information on what is termed the "drift seepage threshold," or the minimum amount of percolation required to produce seepage into drifts. The preliminary calculations of threshold value indicate that it would be orders of magnitude higher than the currently assumed percolation flux, and thus no seepage into the drift would occur.

Specific aspects of this plan include conducting seepage testing in untested portions of the potential repository horizon (the lower lithophysal zone), incorporating better controls over evaporation due to tunnel ventilation (which can affect seepage testing) through the use of hydrologic bulkheads to isolate test areas, and employing lower water release rates and longer test durations to simulate ambient conditions more realistically.

Ambient deep percolation and seepage tests, passive moisture monitoring, and observations of deep percolation and seepage continued to be performed in the main loop in Alcove 7, which crosses the Ghost Dance Fault approximately 220 meters (726 feet) below the surface. During Fiscal Year 2000, the third year of monitoring, no natural seepage was detected within the alcove. This is consistent with results obtained the two previous years and demonstrates that, even in regions with pervasive fracturing associated with through-going faults, seepage into excavated underground openings under present-day percolation fluxes is not expected.


Yucca Mountain stratigraphy and repository layout

A similar test, begun in Fiscal Year 1999 and continued through Fiscal Year 2000, is being conducted in the cross-drift. There, a long section of the tunnel (more than a kilometer) has been isolated behind dual hydrologic bulkheads to allow this portion of the tunnel to re-equilibrate to ambient conditions by isolating it from the effects of ventilation. The objective of this isolation is to observe if seepage into the tunnel occurs under the "high infiltration zone" as determined from the Project's surface infiltration model. To date, temperature and relative humidity within the isolated section have returned to ambient conditions, but no active seepage has been reported. A capillary barrier effect due to tunnel excavation appears to be diverting water around the drift opening.

Forced-flow experiments that were completed in Niches 2 and 4 and are ongoing in Niche 3 enable us to investigate how underground openings similar to waste emplacement tunnels alter the groundwater flow field, possibly diverting water into surrounding rock. Using several niches at repository depth in the Topopah Spring tuff and one alcove closer to the surface in Tiva Canyon tuff, experiments examined the distribution and amount of seepage that might occur in waste emplacement drifts. Seepage tests in the Topopah Spring tuff involved introducing water above a niche and observing the resulting seepage in the opening. Again, the completed testing confirmed the existence of a capillary barrier. This diversion may play an important role in limiting the contact of water with waste packages.

Crossover collection system at Niche 3

Unlike most of the Exploratory Studies Facility, which is dry due to ventilation, Niche 3 is isolated from ventilation and, consequently, has high humidity (and correspondingly high capillary pressure) that closely simulates expected post-closure repository conditions. Test-bed improvements, such as the use of Niche 3, ensure that unnatural hydrologic effects due to evaporation are minimized and that an accurate determination of the seepage threshold is obtained. Based on the water-release seepage tests that have been completed, it appears unlikely that ambient percolation fluxes (that is, fluxes of water through the unsaturated zone that are not thermally perturbed), and/or current climatic conditions, would produce seepage into drifts. If the threshold is high, seepage may not be likely even with higher percolation fluxes.


Lower lithosphysal cross-section

Experiments to simulate flow that might result from extremely high rainfalls in a future climate that is wetter and cooler than at present took place in Alcove 1, located near the north portal of the Exploratory Studies Facility. Water was applied at the surface (via a drip-irrigation system) and its eventual arrival was monitored in the testing alcove approximately 30 meters below. It took 58 days for water to travel from the surface to the collection system, but once flow had been established, changes in the rate at which water was applied at the surface produced corresponding changes in seepage into the alcove within a few days. After equilibrium was established for the final flow rate, a lithium bromide tracer was added and monitored. The results provided insight into near-surface infiltration processes, diffusion mechanisms, and seepage into underground openings.

Systematic hydrological testing of lower lithosphysal unit

After a test hiatus of six months, the second phase of the experiment in Alcove 1 was started. The flow and transport experiment was repeated by establishing equilibrium at several different flow rates. After equilibrium was established, a seepage response for each new flow rate was observed after only 2 to 3 days. However, the first breakthrough of the tracer took 30 days. The results suggest that piston flow is a possible fracture flow mechanism - that is, flow of the tracer from the surface to the alcove requires that the water in the fracture must drain or be displaced in order to see tracer in the alcove. This understanding of the flow mechanism reduces uncertainty in the groundwater flow model for the unsaturated zone.

Investigation of the possible presence of "bomb-pulse" chlorine-36 (produced by nuclear testing conducted during the 1950s and 1960s) at proposed repository depths has been ongoing since Fiscal Year 1998. Because evidence of chlorine-36 raises questions about "fast pathways" for groundwater traveling from the surface, the Project commissioned a peer review panel to address the matter. We subsequently conducted enhanced geologic sampling and additional modeling integration work. We are awaiting final results of a study to determine if the chlorine-36 signal reported by Project investigators at two fault zones within the Exploratory Studies Facility can be corroborated by independent laboratories. Preliminary results were inconclusive, with samples analyzed by the Lawrence Livermore National Laboratory showing no evidence of bomb-pulse chlorine-36; this appears to contradict earlier positive findings by Los Alamos National Laboratory using samples from nearby, but not identical, locations, and using different chlorine-36 extraction procedures. Scientists from the two laboratories are conducting tests to eliminate the possibility of errors due to rock sampling and sample processing procedures. Final results are expected in Fiscal Year 2001.

Partially completed hydrology test area in Niche 3

Understanding the saturated zone
Beneath the unsaturated zone lies the saturated zone, approximately 300 meters below the repository level. This is the region in which rock pores and fractures are saturated with groundwater. Because radionuclides could migrate through this zone, we need to understand its characteristics.


Nye County Early Warning System drilling activities

In Fiscal Year 2000, we continued to integrate our efforts with the Nye County Early Warning Drilling Program. Nye County, the county within which the Yucca Mountain site is located, is drilling a series of boreholes as part of an early warning system that could also support performance confirmation monitoring if a repository is developed at the site. Nye County is conducting its drilling program in cooperation with, and with funding from, OCRWM.

One of the goals of the Nye County program is to provide geologic and hydrologic information that is needed but currently not available. The targeted area, located in a very complex hydrogeologic system, is one of the least understood hydrogeologic systems in the vicinity of Yucca Mountain. The issues to be investigated are the origin of the spring deposits, the geology of the area, and the recharge and groundwater flow patterns. During Fiscal Year 2000, Nye County completed drilling a second phase of boreholes and made preparations to begin the planned third phase.

Project scientists accompanied Nye County scientists during sample collection and hydrologic testing. Information from rock and groundwater samples collected during and after drilling has been integrated into our conceptual model of the saturated zone. Stratigraphic data from the drilling program and information about the flow and transport properties of the alluvium and valley fill aquifer have been incorporated into our site-scale model. Further information on the Early Warning Drilling Program can be found on Nye County's web site: http://www.nyecounty.com/ewdpmain.htm.

To obtain data on local and regional water table elevations and fluctuations through time, we continued to take measurements at the network of 22 water-monitoring boreholes drilled by the Project. We developed workbooks based on the geophysical and geological logs obtained from the boreholes. These workbooks provide data on the stratigraphy and hydrology that enable us to refine process models for the natural barrier system at the site.

A particular area of focus in Fiscal Year 2000 was Borehole SD-6, which was drilled in Fiscal Year 1999 along the crest of Yucca Mountain. This borehole was the principal well used for hydraulic testing. Borehole SD-6 provides data on the western portion of the mountain for design and hydrologic modeling efforts. Initial tests have been completed, and the borehole is now being prepared for long-term hydrologic testing, with results expected in Fiscal Year 2001.

Borehole SD-6

We continued to use data from the saturated zone boreholes to assess the seasonal transient effect of precipitation and evaporation, as well as the effects of local and regional water use and potential impacts on repository operations. These ongoing measurements helped us determine the range of variability in the natural environment, and we used the information to calibrate the regional and site-scale groundwater models. Among other things, these measurements will be used to validate simulations of transient seasonal effects for these models.

In Fiscal Year 2000, we initiated a second tracer complex test to collect data to better understand the flow and radionuclide transport through the alluvial portion of the transport pathway in the aquifer. The data from the initial single-well test, which is currently under way, will provide information on colloid transport that would be included in the saturated-zone flow and radionuclide transport models prepared at the time of a potential site recommendation. A multi-well tracer test is planned to begin in Fiscal Year 2001.

Building on the C-Well tracer-testing program completed in Fiscal Year 1999, we analyzed and incorporated the data obtained from tracer testing into the saturated-zone models which will be used for a potential site recommendation. The C-Well tests yielded critical data on the hydraulic properties of the volcanic aquifer, an estimate of flow and transport properties of materials in the aquifer, and laboratory confirmation of the transport properties of those materials from core samples. Test results indicate the range of variability in the flow properties of the hydrogeologic and hydrostratigraphic units within the aquifer and the influence of fracture density on flow rates. These data will be used to test and improve models for radionuclide transport.

Phase I tracer test in Busted Butte test alcove

Understanding the effects of heat on repository system performance
Long-term studies have addressed how heat generated by the radioactive decay of waste would alter the surrounding environment and waste packages. Heat-induced changes in mechanical properties; rock, water, and gas chemistry; and site hydrology would affect the rate at which waste packages degrade and radionuclides are released and the mechanisms and pathways through which radionuclides would be transported. For example, as water is vaporized by heat, salts would precipitate and the vaporized water would move away as a gas. Salts could then be redissolved by moisture that condenses and returns, making the water a more concentrated and corrosive fluid that could accelerate waste package degradation. To closely examine these phenomena, DOE's Lawrence Berkeley, Lawrence Livermore, Sandia, and Los Alamos National Laboratories have completed two tests and are currently conducting a third test within the rock using electric heaters to simulate heat generated by waste. Very different in scale, all three tests contribute significant data on the effects of thermally driven hydrologic, chemical, and mechanical processes in rock. Scientists use these data to develop and test models of how the engineered and natural barriers of a potential repository system at Yucca Mountain would respond to heat. Information gained during Fiscal Year 2000 led to extensive design and engineering work to integrate the results from thermal studies into the design in support of a potential site recommendation.

The three major thermal testing activities are the large block test at Fran Ridge and the single heater test, both of which have been completed, and the drift scale test now in progress. Both the single heater test and the drift scale test are located in the Exploratory Studies Facility.

• The large block test at Fran Ridge generated data on how heat affects the movement of moisture through the rock, the mechanical and chemical responses of the rock to heat, the behavior of metals to be used in potential repository design, and microbial behavior in the heated rock. This test involved heating a large block cut out of the exposed host rock. Heaters operated from February 1997 until March 1998; cool-down was completed in September 1998, as scheduled. Post-heating data collection and most of the analyses were completed in Fiscal Year 1999.

In Fiscal Year 2000, we used the data to prepare analysis and model reports on thermally induced, coupled hydrologic, chemical, and mechanical processes. Results from this heater test indicate that under the test conditions, groundwater in the block flowed by gravity below the heated region, with fractures acting as the dominant flow conduit. Microbes that were injected into the heater holes were found in observation holes below the heated horizon. Results also indicate the potential presence of a "heat pipes" effect - a process that could offset the redistribution of water in the rock above waste packages in a potential repository in which the temperature reaches the boiling point. These findings provide vital information on how heat emitted by waste could affect coupled thermal-hydrologic processes that, in turn, would affect flow and transport in the rocks. This information is needed to develop models for the near-field environment, waste packages, and engineered barrier system.

• The single heater test was a small-scale underground test, which began in August 1996. This pilot test was performed to gather data for planning the drift scale test, as well as to obtain initial data on the thermal-mechanical-hydrologic-chemical processes that would be induced by heat from radioactive decay of radioactive waste. One heater, approximately 5 meters long, heated a 21-cubic-meter (27-cubic yard) volume of rock over a period of 10 months. Instrumentation included more than 300 temperature sensors that continuously fed data through cables to a computer that recorded approximately 700 channels of information. Additional equipment monitored moisture distribution and mechanical responses within the rock.

Testing ended in Fiscal Year 1998. The results from this test provided preliminary information on the thermal-mechanical-hydrologic-chemical behavior of the rocks at the potential repository horizon. During Fiscal Year 2000, the results were incorporated into process model reports to support a possible site recommendation.

• The drift scale test is the largest test of its kind in the world. It is being carried out in an underground alcove approximately 48 meters (156 feet) long, with a diameter approximately the scale of an actual emplacement drift. The rock is being heated for four years by electric heaters placed in the walls and along the floor of the tunnel. The heaters within the drift generate heat similar to that expected from actual canisters of spent nuclear fuel. The test is designed to heat an estimated 15,000 cubic meters (about 19,600 cubic yards) of rock to a temperature above 100 degrees centigrade. The test is instrumented extensively with temperature sensors, mechanical sensors, hydrologic sensors, and sampling locations to collect water and gas samples throughout the heated rock.

Remote-controlled video and infrared cameras monitor this test, and from remote locations we can continuously modify system parameters and retrieve data by telephone. Automation allows more accessible, consistent, and reproducible testing, and it also allows scientists to spend their time analyzing data instead of physically collecting them. This automated system is supplemented by a limited amount of manual sampling.


Major thermal testing activities

The heaters were turned on in early Fiscal Year 1998. After four years, they will be turned off, and the cool-down will be monitored for another four years. The resulting data will be utilized to assist in developing performance confirmation activities to ensure that a potential repository would be appropriately monitored.

Significant results from the single heater test and the drift scale test include the identification of conduction as the dominant heat transfer mechanism. Both of these tests indicate that rock porewater mobilized by the heat tends to drain by gravity, via fractures in the rock mass, to below the heated region rather than staying perched above it, a phenomenon also evident from the results of the large block test discussed above. As in the single heater test, mechanical response within the rock near the drift scale test proved to be less than expected. Also, the water and gas samples indicate that the evolution of carbon dioxide gas during the heating directly affects the chemistry of the condensed water. Current models of the water and gas chemistry provide good matches to the observations that have been made in the drift scale test, supporting model validation efforts.


1m x 1m block from Busted Butte ready for shipment to a national laboratory

Laboratory and field testing
Another important line of inquiry is determining the pathways, mechanisms, and rates at which radionuclides could travel if the waste packages are breached and the radionuclides are transported to the accessible environment. Current studies examine how phenomena such as the solubility limits of specific radionuclides; sorption, dispersion, and diffusion during their transport; and dilution could reduce concentrations of radionuclides in groundwater and minimize potential doses in the accessible environment.

For the unsaturated zone, tests using tracer elements as surrogate radionuclides to measure sorption were conducted in the Busted Butte facility, which provides direct access to the Calico Hills Formation. This important geologic unit features rock that is similar to that below the potential repository host rock. The Calico Hills Formation below the potential repository is on the potential radionuclide transport pathway from the repository to the water table. Measurements with surrogate radionuclides were made to demonstrate that sorption data collected in laboratory experiments are applicable to site-scale transport modeling. Laboratory tests using actual radionuclides were conducted to augment measurements in the Busted Butte tests.

In other tests at Busted Butte, we investigated colloidal migration using polystyrene microspheres, a surrogate for colloids. Colloids are minute particles that may be transported by groundwater. If these particles are composed of radionuclides, or have radionuclides attached to them, they may enhance the transport of radionuclides into the environment. The colloidal materials tested include iron oxides and clay minerals. The Busted Butte tests were designed in three phases in sequence, with increasing test-block sizes and thus with increasing complexity of flow and transport processes. The increasing test-block sizes allow us to bridge the scale-range of available test data and examine the applicability of the results from these tests along with those from laboratory tests. This capability is important to the development of models of groundwater flow and radionuclide transport at the Yucca Mountain site.

In Fiscal Year 2000, we completed phases 1A and 1B of the Busted Butte tests referred to above and continued with phase 2. The results of the tests will be incorporated in the unsaturated zone flow and transport models the Project developed for a possible site recommendation. We also initiated laboratory tests on radionuclide transport using three large blocks cut from the Busted Butte test rock units. These block tests are verification tests, and are being conducted using actual radionuclides of the type contained in waste that would be emplaced in a potential repository.

For the saturated zone, sorption measurements were made in the alluvium samples collected in cooperation with the Nye County Early Warning Drilling Program. In Fiscal Year 2000, we assessed the available data collected through Fiscal Year 1999, and developed flow and transport models, which were summarized in the saturated zone process model report prepared for a potential site recommendation.

To fill in the gaps in the information for flow and transport properties through the saturated zone, in Fiscal Year 2000 we started a tracer test at one well in the alluvial portion of the saturated zone. This single-well alluvial tracer test is the first at what will become a multi-well testing complex for a multi-year test designed to determine the flow and radionuclide transport characteristics of the alluvial part of the saturated zone pathway.

To increase confidence in our measurements of radionuclide transport parameters, we continued to evaluate data about radionuclides in the groundwater of other DOE sites and to use them to verify our transport model. Those sites are the Nevada Test Site, the Hanford site in Washington, and the Idaho National Engineering and Environmental Laboratory. Observations from these analogue sites were incorporated in the saturated and unsaturated radionuclide transport models that will be used in developing a possible site recommendation.

Building a regional groundwater model
We continued work on a major project that began in 1997 to develop a combined regional flow model, sharing data bases with the Nevada Test Site; the U.S. Geological Survey; the Bureau of Indian Affairs; Nye, Inyo, Lincoln, and Clark Counties in Nevada; the National Park Service; the U.S. Air Force; and the Nevada State Engineer's Office. The model will incorporate the best features of two independently produced models. The Test Site's model, which was developed to study existing contamination, focuses on transport phenomena at the Test Site. Our model is a tool for simulating and evaluating the effects of climate change on the regional water table.

Fiscal Year 2000 activities included refinement of this regional hydrologic framework model with newly available data. This effort is providing a more comprehensive model, closely calibrated to observations of actual conditions at the site, both steady-state and transient. The steady-state model is scheduled to be completed by early Fiscal Year 2002; the transient model should be completed by the end of Fiscal Year 2002.

Building a three-dimensional model of the site
Data from site investigations were interpreted and extrapolated to build and refine a three-dimensional, integrated model of site geology and hydrogeology. This is, in effect, a picture of what we know about rock layers; faults; rock properties such as porosity and hydraulic conductivity; and mineralogy, including the presence of zeolites (minerals to which some radionuclides can sorb and which, therefore, have the potential to retard radionuclide migration). This integrated site model represents geologic features within an area of 65 square miles and a volume of 185 cubic miles, to a depth of 13,000 feet, as interpreted from data taken from boreholes drilled from the surface of the site to depths of up to 6,000 feet, data from drifts, and other sources such as gravity, seismic lines, and magnetic data. The site model was the basis of the site description presented in the viability assessment and will also be used in preparing a possible site recommendation; it is the framework for hydrologic studies and repository design investigations.

The data input, methodologies, and assumptions used to construct the latest version of the three-dimensional model were documented in a report that was completed in early Fiscal Year 2000. Updating of the site model was begun in Fiscal Year 2000 to incorporate only qualified data and to address comments we have received in technical reviews. The model documentation update will be completed in Fiscal Year 2001. The update includes a comprehensive validation and estimation of spatial uncertainty that will provide important information for users of the model.

The repository safety strategy

The repository safety strategy summarizes DOE's completed, ongoing, and planned efforts to develop and integrate the information needed to make a safety case, to NRC and the interested public, that a potential repository system that may be recommended for approval at Yucca Mountain will protect public health and safety. The strategy is a living document, now undergoing its fifth revision, to incorporate new information and lessons learned from ongoing investigations and analyses of the natural and engineered barriers of a waste disposal system. The safety case, as the product of that strategy, will be at the heart of a possible license application to build a potential repository at Yucca Mountain.

The post-closure safety case will be used as the conceptual framework for a possible site recommendation, and for a subsequent license application if the site recommendation is approved. The post-closure safety case is a forecast, based on total system performance assessments, of how the repository system will perform after it is closed, considering potentially disruptive processes and events together with differing approaches to increase safety margins and demonstrate defense in-depth. The safety case currently relies, among other things, on multiple barriers to mitigate uncertainties in repository performance and on understanding gained from relevant natural analogues to the Yucca Mountain site. It also recognizes the value of performance confirmation testing and monitoring to verify the continuing validity of the assumptions, data, and analyses used in evaluating long-term performance.

Although the repository safety strategy continues to focus on a safety case demonstrating that multiple natural and engineered barriers will work together to enhance post-closure safety performance, details of the resulting safety case have evolved as our work has progressed. The safety case will continue to evolve in the future with additional information and in response to the evolving regulatory framework for the potential repository system.

In Fiscal Year 2000, we continued to update the repository safety strategy to more clearly recognize the advantages of Yucca Mountain's natural waste isolation barriers and features that favor performance of engineered barriers. The revised strategy identifies what we now believe to be the factors most important to evaluating repository system performance and what information we still need to complete the safety case. These principal factors include the limited seepage of water into the emplacement drifts, the performance of the drip shield and waste package, the low solubility limits of dissolved and colloid-associated radionuclides in Yucca Mountain water, the retardation of radionuclide migration in the unsaturated and saturated zones, the dilution of radionuclide concentrations during migration, the improvement of conversion factors for projecting doses in the biosphere, and better assessment of the probability of igneous activity and its effects on the repository.

Together, the safety case assumptions and the principal factors constitute a conceptual framework for assessing overall repository system performance. In Fiscal Year 2000, this framework helped scientists and engineers focus data collection, analysis, and modeling on factors important to demonstrating that the performance of natural barriers, the waste package, and other engineered barriers will satisfy regulatory standards for protecting the public.

To reduce uncertainties about performance of the potential repository, we conducted field and laboratory tests, analyzed data, assessed alternative designs, and conducted performance assessments to determine which uncertainties matter most and which are most sensitive to new information that could be obtained from further field and laboratory testing. These efforts have allowed for the identification of potential vulnerabilities and the corresponding need for additional measures to be taken to ensure that elements of the safety case are implemented.

Total System Performance Assessment integrates natural barriers and engineered systems

In Fiscal Year 2000, we also began to develop a safety strategy and safety case for the pre-closure phase of a geologic repository. At Yucca Mountain, the pre-closure safety case would incorporate technical specifications; surveillance; industry precedent and experience; and an integrated safety analysis addressing, among other things, the proposed system's safety margin and defense-in-depth against conservative design basis events. The pre-closure case is based on the utilization of accepted nuclear industry technologies and practices, systematic reviews of facility designs to address safety-related site characteristics, and a test and evaluation program to verify compliant repository operation.

The ability to retrieve disposed waste and bring it back to the surface if necessary for storage, repackaging, and/or relocation, is also an essential element of the pre-closure safety case. DOE must anticipate the possibility that retrieving disposed waste packages may be required at any time during the pre-closure monitoring period, and the repository design includes features that would facilitate retrieval.

Performance assessment

To assess the anticipated performance of a potential repository at Yucca Mountain, analysts have built detailed mathematical models to represent the features, events, and processes that could affect repository performance. The results of performance assessment analyses are a major component of the repository safety case that will underlie a possible site recommendation and will be refined for a license application if the site is approved.

For Yucca Mountain, the performance assessment provided not only a means for estimating anticipated performance, but also a framework for organizing and describing the site and the repository design. The performance assessment integrated information from site investigations, laboratory studies, expert judgment, and repository design into a set of numerical models that represent the total repository system. The total system model was used to simulate how a potential repository at the site might perform under a range of conditions over thousands of years after it was closed. We used it to evaluate repository system performance against risk-informed, performance-based regulatory criteria, to determine the contribution from each engineered barrier to performance, and to identify uncertainties in our understanding of performance. We then determined how to reduce the uncertainties by evaluating how sensitive they are to new information from scientific studies, or how we might compensate for uncertainties by enhancing design.

The result was an estimate of the radiation dose a person might receive from radioactive waste, if it were emplaced within Yucca Mountain, thousands of years in the future. That dose must not exceed regulatory standards if the potential repository is to be demonstrated to be safe and licensed by NRC.

In Fiscal Year 2000, we completed the refinement of models used to examine the natural system to reflect new information from site investigations and laboratory studies, advances in modeling physical processes at the site, and an enhanced repository design. Performance assessments were done on an enhanced repository design alternative to examine the effects of design changes and their relative effect on the principal factors.

Documenting the foundation for determining site suitability
If a determination of site suitability is to be made, accepted, and understood, our performance assessment models must be defensible, and their bases must be traceable. To ensure that they are, we continued to update models and to fully document them in process model reports and supporting analysis and model reports in Fiscal Year 2000. These reports, reviewed by experts and supported by expert elicitation, build the technical basis for our total system performance assessment for a possible site recommendation.

Process model reports describe the technical basis for all models and submodels for each of the major physical processes that would govern performance of the repository system. The reports present the technical information needed to ensure that models are defensible and that data and references can be traced to their sources. The subject areas addressed in the process model reports are the integrated site model, the flow of water and transport of radionuclides in the unsaturated zone, flow and transport in the saturated zone, the near-field environment around waste packages, waste package degradation, waste form degradation, degradation of the engineered barrier system and flow and transport through it, the biosphere, and potentially disruptive events.

Supporting analysis and model reports provide analysis of site and laboratory data, incorporation of these data into detailed process-level models, and abstraction of process-level modeling results into submodels for inclusion in the overall system-level model.

Developing the performance confirmation program
Under NRC's licensing criteria, if a repository is developed at Yucca Mountain, DOE must conduct a testing program to confirm the assumptions, data, and analyses that are the basis for the safety case presented in the license application. NRC's regulation also requires that a repository be kept open for at least 50 years after the start of waste emplacement. Our plans would not preclude its being kept open for at least 125 years, and, with a reasonable expectation of appropriate maintenance, indefinitely. To enable scientists to make the necessary observations, the repository would be monitored by remote-sensing devices, and data from these devices would be continually evaluated by computer programs and scientific investigators.

The performance confirmation program we are developing encompasses monitoring, testing, and analyses. In Fiscal Year 2000, we continued to define the current physical conditions against which short-term performance would be compared and the tests and related activities necessary to monitor performance. The performance confirmation program entails two groups of activities: process confirmation and post-closure simulation. Monitoring factors would include air temperature and relative humidity; the presence and types of radioactive gases; soil and rock temperature, stress, deformation, and displacement; and moisture, vapor, and fluid temperature and conditions in the zone altered by heat generated by radioactive decay of waste.

Design and engineering

Since the release of the Viability Assessment of a Repository at Yucca Mountain in December 1998, the primary objective of the Program's scientific and technical work has been to reduce uncertainty in our predictions of repository performance. A substantial body of design work will be part of the foundation for a Secretarial determination on a possible site recommendation.

In Fiscal Year 2000, by selecting the reference design and a set of operating modes to be used for a possible site recommendation, OCRWM met one of its performance targets in the Secretary of Energy's Fiscal Year 2000 performance agreement with the President. Our repository design is evolving to better manage thermal loads and to reduce uncertainty. It is a flexible and robust design that can accommodate changes resulting from technical advances or future changes in priority. The design can accommodate various operational modes, including adjusting the period of ventilation, varying fuel staging and loading into waste packages, and adjusting waste package spacing to manage thermal loads. Adjustments in ventilation and waste package spacing can reduce temperature and humidity.


Repository design concept

Because water is the primary means of transport by which radionuclides could leave the repository site, design and operating modes evaluated for a possible site recommendation decision take advantage of natural and engineered barriers that work in a complementary manner to provide a high level of confidence. In other words, overall, the integrated repository system would perform well even if some individual barriers are not completely effective. The evaluated design is expected to be effective for more than 10,000 years.

Design work is closely integrated with performance assessment modeling and core science data collection and testing. Integration with performance assessment ensures that the models appropriately reflect the range of conditions associated with the latest designs and that designers consider where design enhancements might reduce uncertainties in predictions of repository system performance. Integration with core science ensures that designs are supported by data on the natural features of the site and information on potential climate and seepage conditions.

Selecting the reference design
Materials to be emplaced in a repository would contain various types of radionuclides. Our studies indicate that the natural features of the Yucca Mountain site could contain most of them for long periods of time, but a small fraction appears to be mobile. Under some conditions they could be transported from the potential repository by water. The engineered barriers we are designing, together with the natural barriers of the site, would limit the amount of water that contacts radionuclides and the rate of release of radionuclides from the engineered system.

In Fiscal Year 2000, we evaluated the enhanced design alternatives selected in Fiscal Year 1999 as a reference design for a possible site recommendation. We recognized that temperature - that is, how hot a repository would be as a consequence of heat generated by spent nuclear fuel, and where that heat would be distributed - may have a profound effect on the cumulative uncertainty in predictions of long-term repository system performance. Therefore, in Fiscal Year 2000, we evaluated a design that permits use of more intensive thermal management techniques than the viability assessment reference design. These techniques include thermal blending of fuel assemblies, closer spacing of the waste packages with wider spacing of the emplacement drifts, and ventilation options.

Designing waste packages
The primary component of the engineered barrier system is the waste package. The waste package has been designed to use materials that perform well under anticipated conditions at Yucca Mountain. Waste packages will make a major contribution to the potential repository system's ability to isolate waste and retard the migration of radionuclides. While several waste package designs will ultimately be needed to accommodate the different waste forms and packaging, including the necessary criticality safety measures, the primary features—the thickness of the inner and outer barrier walls—are similar.

The waste package design consists of two concentric cylinders in which the waste forms would be placed. The inner cylinder would be composed of stainless steel (Alloy 316NG). The outer cylinder would be made of a corrosion-resistant nickel-based alloy (Alloy 22). The corrosion-resistant material of the outer cylinder would protect the underlying structural material from corrosion, while the structural material of the inner cylinder would support the thinner, corrosion-resistant material. A titanium drip shield, which is another component of the engineered barrier system, would be placed over the waste package before the repository is closed. When combined with a titanium drip shield, the Alloy 22 outer cylinder would be the second corrosion barrier protecting the waste from contact with water. The use of two distinctly different corrosion-resistant materials reduces the probability that any single environmental effect could cause the failure of both materials.


Evolving waste package design

In Fiscal Year 2000, a subset of waste package designs was evaluated to support a possible site recommendation. Through a sensitivity analysis, it was determined which waste package designs best represent the widest array of design configurations and waste forms. The analysis also determined which design criteria would be evaluated. The analysis resulted in the selection of four waste package designs which demonstrate likely compliance with anticipated regulatory requirements. The design analysis illustrated that the selected waste package designs performed their containment functions for anticipated design basis events.

The Disposal Criticality Analysis Methodology Topical Report was updated in September 2000 to address concerns raised by NRC. The report describes how waste packages would be evaluated to demonstrate criticality safety during the post-closure period. This report represents the methodology that would be applied if a license application is prepared to demonstrate that a criticality event would not exceed regulatory requirements.

Much effort was spent in Fiscal Year 2000 evaluating the impact of stress corrosion cracking on waste package performance. Residual stresses are a common by-product of fabrication processes such as forming, machining, and welding. Under certain environmental conditions, these residual stresses can accelerate localized corrosion and cause premature failure of the material. Because stress corrosion cracking is the principal potential mechanism that could lead to early waste package failure, closure welds were redesigned, and a 10 mm Alloy 22 lid between the outer and inner lids was added on the top end of the waste package. This lid provides additional protection against cracking in the closure weld area. The outer barrier of the waste package and closure weld would be subjected to an annealing process to mitigate the stresses that may have been induced during the fabrication of the waste package. The closure weld area for the middle lid would be subjected to a laser peening process to mitigate the weld stresses.

Laboratory testing to support design
Experimental testing investigates the long-term corrosion and degradation processes that would affect waste package materials. The data obtained enable modelers to predict waste package lifetime under repository conditions. Testing began in 1996 and will be conducted for at least 5 years, with a possible extension up to 10 years, for a total of 15 years.

Waste package design - close up

In Fiscal Year 2000, waste package materials degradation experiments and modeling were performed at Lawrence Livermore National Laboratory; the General Electric Corporate Research and Development Center; McDermott Technology, Inc.; and Atomic Energy of Canada, Ltd. Long-term tests continued on corrosion-resistant materials, Alloy 22, and titanium. Short-term tests focused on galvanic protection, crevice corrosion, stress corrosion cracking, aging and phase stability, and microbiologically influenced corrosion. Results have shown that, for the materials selected, general and localized corrosion should not limit the life of the waste package. Stress corrosion cracking and aging and phase stability have been identified as warranting further investigation, and those investigations are being conducted. In the closure welds of the waste package, stress mitigation techniques, which aid in minimizing the potential for stress corrosion cracking, have also been identified and are being implemented in some of the experiments. Current estimates indicate that the waste package lifetime may be 10,000 years or longer.

Emplacement drift with waste packages and drip shields

Waste forms themselves (spent nuclear fuel assemblies and vitrified high-level waste) are part of the engineered barrier system, as they serve to contain radionuclides. To determine the degradation behavior of waste form material, in Fiscal Year 2000 we continued long-term tests on commercial spent nuclear fuel and vitrified high-level waste. Investigations of the condition of commercial spent nuclear fuel cladding after storage, and its degradation thereafter, are ongoing, and new models are being developed. Studies of colloids and fuel oxidation, as well as investigations of in-package chemistry and radionuclide solubility, also continued in Fiscal Year 2000.

Long-term tests of waste forms began about 15 years ago and are planned to continue until 2020. Waste form testing and modeling are being performed at DOE's Pacific Northwest, Lawrence Livermore, Argonne, Sandia, and Los Alamos National Laboratories, and at the Idaho National Engineering and Environmental Laboratory. In addition to generating data that can be used to characterize mechanisms for waste form degradation, these tests yield data for establishing parameters for empirical models. The results have reduced uncertainties in models of waste form degradation. Continued confirmation testing will help to further reduce uncertainties about the physical processes most important to repository performance.


National laboratories supporting the Yucca Mountain Project

Engineering studies
In Fiscal Year 2000, we performed a pre-closure safety assessment of the site recommendation design to examine design basis events that could occur above and below ground at a repository before it is permanently closed and to calculate potential radiation doses to the public and repository workers. The assessment would be used to establish specifications for acceptance of waste forms and design criteria for the potential repository that mitigate and reduce any potential impacts.

Developing specifications for DOE spent nuclear fuel and immobilized plutonium
In addition to commercial spent nuclear fuel, OCRWM would also accept for disposal spent nuclear fuel managed by DOE. This fuel consists of more than 250 types, the characteristics of which vary widely. During Fiscal Year 2000, we continued to work closely with DOE's National Spent Nuclear Fuel Program in the Office of Environmental Management to develop specifications for a suite of standardized canisters that would accommodate all types of DOE-owned spent nuclear fuel. The Office of Environmental Management funds this work.

Analyses to demonstrate the viability of disposal have been performed or are in progress for seven groups of DOE spent nuclear fuel (excluding naval spent nuclear fuel). In general, the amount of DOE-owned spent nuclear fuel that would be allowed per canister is a function of the physical size and weight limitations of the canister. Insoluble neutron absorbers (gadolinium compounds and alloys) would be required for criticality control within the canister for some of the DOE-owned spent nuclear fuel groups.

Because OCRWM would also accept plutonium waste forms in a repository, criticality analyses were conducted. It was determined that the criticality potential of the immobilized plutonium ceramic would be effectively controlled by the neutron absorbers, gadolinium and hafnium, which are fabricated into the waste form itself. The addition of these neutron absorbers would mitigate the risk of criticality events under normal circumstances.

Designing repository surface facilities
Repository surface facilities would support the excavation, construction, loading, and ventilation of repository tunnels. Surface facility operators would receive spent nuclear fuel and high-level radioactive waste and package it for disposal. Shipping casks containing waste would be received from rail or truck carriers at the Carrier Preparation Building. Waste would be removed and loaded into waste packages in the Waste Handling Building, where waste packages would be welded shut. Low-level waste generated during waste handling operations would be prepared for disposal. Vehicles used to transport sealed waste packages to a holding area and then to emplacement drifts would be serviced at the Transporter Maintenance Building. Major surface facilities would also include a Waste Treatment Building for site-generated waste, site utilities, and other support facilities, such as warehouses, maintenance shops, and administrative facilities.

During Fiscal Year 2000, work on design of surface facilities supported development of engineering design files for the possible site recommendation, including design descriptions. The reference design includes descriptions of the Waste Handling Building, the Waste Treatment Building, the carrier/cask transportation system, and the balance of plant facilities. Descriptions of these facilities include building and operating systems, waste handling operations and processes, and waste package loading and welding.


Repository surface and subsurface layouts

Documenting the design to support a possible site recommendation
The repository design consists of design packages for each of the major repository subsystems, such as the materials handling system, the carrier/cask transport system, and the disposal container handling system. The system description documents that we have developed for major repository subsystems related to safety are an important part of the documentation that would support a possible site recommendation.

In Fiscal Year 2000, system description documents were developed for all possible major repository subsystems. The entire suite of documents will constitute life-cycle records of possible repository development and will be retained as permanent records. The documents are part of the technical baseline. They specify requirements and criteria for possible repository subsystems and describe the resulting design.

Environmental Impact Statement

Draft environmental impact statement
The NWPA requires that a final environmental impact statement (EIS) be included in the "comprehensive statement" that would accompany the Secretary of Energy's possible site recommendation to the President.

In Fiscal Year 2000, we built upon the foundation established by the Draft Environmental Impact Statement for a Geologic Repository for the Disposal of Spent Nuclear Fuel and High-Level Radioactive Waste at Yucca Mountain, Nye County, Nevada, which was published in July 1999. The draft EIS provides background, data, and analyses that can help decision makers and the public understand the potential environmental impacts that could result from the proposed action: constructing, operating and monitoring, and eventually closing a repository at Yucca Mountain. It also examined the potential environmental impacts of transporting waste from around the country to the potential repository.

The draft EIS also analyzed the consequences of continued storage of spent nuclear fuel and high-level radioactive waste at current sites under a "no-action" alternative that provides a basis for comparison with the proposed action. The draft EIS identified the proposed action as DOE's preferred alternative, because the analyses did not identify any potential environmental impacts that would be a basis for not proceeding with the proposed action. The draft EIS was released in hard copy and as a CD-ROM. It is posted on our web site at http://www.rw.doe.gov/.

Draft EIS public meeting in Las Vegas, Nevada

We provided a 199-day public comment period from August 13, 1999, through February 28, 2000. During the public comment period, we held 21 public hearings: 10 in Nevada and 11 in cities around the United States. Completing these public hearings fulfilled another one of OCRWM's performance targets in the Secretary of Energy's Fiscal Year 2000 performance agreement with the President. Excluding DOE staff and DOE contractor representatives, 2,224 individuals attended those hearings and over 700 provided comments. By the close of the comment period we had received more than 11,000 comments either in writing or orally during the public hearings.

Draft EIS hearing locations

In addition to incorporating the technical updates resulting from ongoing scientific investigations, we spent the remainder of the fiscal year evaluating the public comments to address the public's concerns and continued work toward finalizing the EIS. We will incorporate a number of updates that are based on the public comments and technical improvements, including improved census data, the addition of potential State route maps and transportation data, a new transportation appendix, and additional baseline data. We have also continued our interactions with stakeholders, particularly the affected units of local government, to address their concerns related to the EIS. All public comments and DOE's responses will be incorporated in a Comment Response Document that will be contained in Volume 3 of the final EIS, which would accompany a possible site recommendation to the President.

In May 2001, DOE issued a Supplement to the Draft EIS to provide information on repository design enhancements and operating modes which have evolved since the issuance of the draft EIS. The supplement evaluates the potential environmental impacts of the updated design and repository modes information. We solicited public comment and held three public hearings on the supplement. As with the draft EIS, public comments received will be considered in the development of the final EIS, and our responses to comments incorporated into the Comment Response Document.

Yucca Mountain EIS process
The National Environmental Policy Act of 1969 (NEPA) specifies steps that Federal agencies must follow when developing an EIS. The process encourages early public involvement in defining the scope and content of the EIS, and it requires Federal agencies to provide opportunities for public comment on the draft EIS.

The NWPA, as amended, includes specific provisions on how NEPA applies to a proposed repository at Yucca Mountain. The NWPA states that the Secretary need not consider in the EIS the need for a repository, alternatives to geologic disposal, or any sites other than Yucca Mountain. Nonetheless, we evaluated a "no-action" alternative in order to provide a basis for comparison with the proposed action: to construct, operate and monitor, and close a repository at Yucca Mountain.

The regulatory framework for repository development

The NWPA of 1982 directed DOE to issue general guidelines for selecting repository sites for site characterization and assigned NRC responsibility for licensing geologic repositories and the Environmental Protection Agency (EPA) responsibility for setting generic radiological protection standards for repositories. The 1987 Nuclear Waste Policy Amendments Act limited characterization of candidate repository sites to Yucca Mountain. The Energy Policy Act of 1992 directed EPA to develop site-specific radiation standards for a repository at Yucca Mountain, and it directed NRC to revise its repository licensing criteria to be consistent with EPA's standards. Between February and November 1999, NRC, EPA, and DOE released proposed regulations that reflect site-specific criteria for a repository at Yucca Mountain. The proposed regulations reflect a shift away from a generic evaluation to a site-specific evaluation that relies on an overall systems approach to repository performance. The specific standards established by EPA and implemented by NRC in its licensing criteria will be central to evaluating the technical suitability of Yucca Mountain as a repository site.

DOE siting guidelines
When DOE issued repository siting guidelines at 10 CFR 960 in 1984, multiple sites were under consideration for a repository. The 1987 Nuclear Waste Policy Amendments Act identified Yucca Mountain as the sole site to be studied. In December 1996, DOE published a Notice of Proposed Rulemaking, proposing to modify its guidelines by adding a site-specific subpart for evaluating the suitability of the Yucca Mountain site. The proposed approach would require an assessment of how the total repository system would perform and a comparison of that predicted performance with the permissible radiation doses for members of the public living near Yucca Mountain. It would not contain requirements relative to how individual subsystems of the repository would perform.

After evaluating the comments we received, and in light of EPA's proposed radiation standards and NRC's proposed licensing criteria, both described below, we revised our 1996 proposal. It was published for public comment in the Federal Register at 10 CFR 963, General Guidelines for the Recommendation of Sites for Nuclear Waste Repositories; Yucca Mountain Site Suitability Guidelines, on November 30, 1999. We held public hearings in Pahrump and Las Vegas, Nevada, on February 2 and February 3, 2000, respectively. The comment period closed on February 28, 2000. Transcripts of these hearings, as well as written comments and documents submitted by the public, may be obtained at the Yucca Mountain Science Center, via the OCRWM web site page at http://www.rw.doe.gov/, or by calling (1-800) 967-3477.

On May 4, 2000, DOE submitted to NRC, for its review and concurrence, a draft notice of final rulemaking for the proposed 10 CFR 963. The draft notice includes responses to the major comments raised by members of the public. NRC conducted a similar review and granted concurrence on the general repository siting guidelines at 10 CFR 960 in 1984. The draft notice is also available on the OCRWM web site.

EPA radiation protection standards
EPA's site-specific radiation standards for a repository at Yucca Mountain, as required by the Energy Policy Act of 1992, establishes limits on annual radiation doses to individual members of the public from repository releases, based on and consistent with the findings and recommendations of the National Academy of Sciences (NAS). NAS issued its report, Technical Bases for Yucca Mountain Standards, in 1995. On August 27, 1999, EPA published in the Federal Register a proposed rule, 40 CFR 197, Environmental Radiation Protection Standards for Yucca Mountain, Nevada, for site-specific health and safety standards.

On June 5, 2001, EPA adopted the final rule that sets forth the standards for the Yucca Mountain site. EPA's final rule is divided into two subparts:

• Subpart A sets standards for the period of repository operations and monitoring before the facility is closed. Specifically, DOE must ensure that no member of the public in the general environment would receive more than an annual dose of 15 millirems (mrem/year) from management and storage of radioactive materials that occur inside the repository and outside the repository but within the Yucca Mountain site.



• Subpart B sets three separate standards after the repository is closed: the individual protection standard limits doses to 15 mrem/year from all pathways of radionuclide travel at 18 km from the repository, assuming no human intrusion into the repository occurs; the groundwater protection standard sets a separate limit of 4 mrem/year for contamination of groundwater at a specific point of compliance; and the human intrusion standard sets a 15 mrem/year limit for an individual at 18 km from an inadvertent intrusion into the repository.

DOE must demonstrate that any releases from the repository would not exceed any of the three standards for 10,000 years following disposal.

NRC licensing regulation
On February 22, 1999, NRC published in the Federal Register its proposed licensing criteria, 10 CFR Part 63, for the disposal of spent nuclear fuel and high-level radioactive wastes in a proposed geologic repository at Yucca Mountain, Nevada. The proposed rule is based on overall performance objectives for the pre-closure and post-closure phases of the repository as the measures of acceptable repository performance, removing the previous performance requirements for each subsystem of a repository, and the technical criteria for siting and engineering. It would require that DOE demonstrate compliance with overall performance objectives through an integrated safety analysis of pre-closure operations and a performance assessment for long-term post-closure performance. The public did have an opportunity to comment during a public comment period in Fiscal Year 1999.

Project management

Project technical baseline changes
The repository system we are designing continues to evolve as our understanding of the natural setting grows and as we continue to enhance design concepts for engineered barriers. In Fiscal Year 2000, we produced or revised several technical baseline documents that define our understanding of the natural and engineered components of a repository system and ensure their thorough integration. Systems studies were completed to support decision making on technical changes.

We also modified the work breakdown structure to reflect technical changes. In Fiscal Year 2000, the most significant change was the incorporation of an enhanced design alternative into the technical baseline documents, providing for a more flexible design that could address a wider range of thermal management options that would permit achievement of a range of post-closure temperatures. In our modifications, we continued to upgrade web-based information management tools to support integrated technical, cost, and schedule planning. We established a comprehensive data base of environment, safety, and health requirements to clearly articulate, for ourselves and for oversight agencies, the tasks and responsibility assignments for the activities we conduct to ensure the health and safety of the public and our workers.

We expanded and updated the Monitored Geologic Repository Requirements Document to include requirements for all Project activities and products. The document reflects the evolving repository design concepts and provides further documentation of statutory, regulatory, and other requirements for the design of the repository system. Many of the changes were based on technical recommendations from within the Program and resulted from our increased interactions with the Nuclear Waste Technical Review Board (NWTRB) and NRC.

We revised the document, now titled the Yucca Mountain Site Characterization Project Requirements Document, to include requirements applicable to the proposed repository facilities; the overall environment, safety, and health program; a potential site recommendation determination; a potential license application; and potential subsequent licensing documentation. In the revised document, we continued to refine the requirements for a repository design to include features associated with thermal management and emplacement operations that allow for a range of thermal design options.

Project cost and schedule baseline changes
The Project uses a "rolling-wave" schedule that has more detail in the early years and less detail in the later years. Each year the Project updates its planning and schedules the next increment of work in detail. This allows us to identify the skill mix and hours needed to perform the planned work. During the Fiscal Year 2000 update of its multiyear plan, the Project planned and baselined work activities for a possible site recommendation.

In Fiscal Year 2000, as part of the Project's implementation of DOE's integrated safety management initiative, the Project successfully integrated a risk-based prioritization matrix into the planning process, which helps us prioritize work based on public and worker health and safety. The matrix allowed the Project to identify the work it should fund to complete its mission safely. OCRWM is committed to ensuring that each employee has a safe and healthy work environment.

Protecting workers, the public, and the environment

Fostering a nuclear safety culture
We have an outstanding safety record. Our standards/requirements identification and occupational health and safety documents provide program elements, methods, and processes to identify and implement Federal and State laws, regulations, standards, and DOE directives applicable to safety and health. These documents also define safety and health responsibilities for the protection of workers, the public, and Project property in order to achieve the goals and objectives of the OCRWM worker protection program. In addition, the workers' experience has been incorporated in the planning process to increase worker and facility safety and protection.

In Fiscal Year 2000, we worked to foster the safety culture that NRC demands of potential licensees for nuclear facilities. This includes compliance with safety requirements, revision and implementation of more than 50 safety and health procedures, and development of detailed work orders and hazard analysis. It also requires personal accountability, continuous self-assessment and improvement, avoiding complacency, regular and critical reviews of work, and feedback of lessons learned. In Fiscal Year 2000, we built accountability into operating procedures and maintained it through annual employee appraisals; a policy calling for application of progressively more severe disciplinary measures, if necessary; and a "Time Out For Safety" policy that empowers employees to take immediate action whenever they have a safety concern. Other management tools included additional training on environment, safety, and health requirements; continuing development of root cause analyses of incidents that compromise safety; involving workers in training and tasks to incorporate their prior experiences to identify hazards; and clearly defining roles and responsibilities for all actions. Performance indicators and self-assessments supported a process of continuous improvement. In Fiscal Year 2000, while the incidence of reporting and evaluating "near-miss" events rose, harm to employees remained well below the DOE average.

Posted safety precautions at the main portal of Yucca Mountain

Mine rescue team at the national competition, Las Vegas, Nevada

Also, during Fiscal Year 2000, we developed a Condition/Issue Identification and Reporting/Resolution System to centralize tracking, trending, and reporting of safety and health conditions/issues and opportunities for improvement. The system provides problem identification and resolution and supports the integrated safety management core function by providing feedback and continuous improvement. The system is available for use by all employees, and more than 950 conditions/issues have been entered into the system. We met the Secretary's requirement that all DOE sites have an integrated safety management system in place and verified by September 30, 2000. More information on the integrated safety management system can be found in Chapter 3.

Environmental protection
OCRWM is committed to performing its work at the Yucca Mountain site in a manner that minimizes adverse environmental impacts. We, therefore, developed an environmental program before site characterization activities began to ensure compliance with all applicable Federal, State, and local environmental statutes and regulations and DOE orders.

In Fiscal Year 2000, although major underground excavation projects ended, scientific studies continued. In support of work both above and below ground, our environmental staff continued to meet responsibilities that ranged from training new employees to be aware of their environmental obligations to reclaiming approximately three hectares (7.5 acres) of disturbed areas at which site characterization activities had been completed.

Environmental compliance
Obtaining and maintaining required environmental permits is critical to every activity undertaken to characterize Yucca Mountain. These permits cover activities such as those associated with air quality; underground injection of tracers for drilling; drinking water, wastewater discharge, and water use; and land management.

In Fiscal Year 2000, we maintained compliance with more than 40 environmental permits, plans, and procedures; and our environmental program continued to evolve to address new regulatory requirements. As required to maintain these permits, we continued to submit quarterly and annual compliance reports to the Nevada Division of Environmental Protection and other regulating agencies. An area of particular interest within the environmental compliance program is historic preservation. In compliance with the Programmatic Agreement between DOE and the Advisory Council on Historic Preservation, consultation and interactions with 17 Native American Tribes and organizations continued. In January 2000, at a regularly scheduled update meeting with Tribal representatives, OCRWM presented the draft EIS, described the draft statement's findings, including specific actions that would preserve Native American cultural resources, and formally received their comments.

Environmental field surveillance

Compliance verification
To ensure that the conditions and requirements of all environmental permits, plans, and procedures are being fulfilled and applicable regulations are met, DOE's Office of Environment, Safety, and Health conducts frequent, unannounced surveillance field checks. In Fiscal Year 2000, surveillance personnel conducted 610 environmental field surveillances that showed compliance with environmental regulations.

Functioning in concert with the permitting process, pre-activity land access surveys are undertaken to inventory and protect ecological and cultural resources in areas proposed for surface-disturbing activities. Specially trained personnel thoroughly examine these areas before work begins to identify important plant and animal species, such as the desert tortoise, and items of archaeological significance (primarily Native American artifacts in the Yucca Mountain vicinity). In Fiscal Year 2000, 11 pre-activity land access surveys were conducted.

Data collection and monitoring
As stewards of the environment and in compliance with the conditions of our permits, we monitor air quality, meteorology, water quality, terrestrial ecosystems, and cultural resources (archaeological and Native American) to determine potential impacts from site characterization activities. To date, no significant adverse environmental impacts have been detected.

In Fiscal Year 2000, data collection continued to support repository design, biosphere modeling, total system performance assessment, and responding to comments on the draft EIS. We also maintained land access and land withdrawal agreements and right-of-way reservations with the Bureau of Land Management, the U.S. Air Force, the National Park Service, and the U.S. Forest Service so that scientific studies could continue at Yucca Mountain and remote sites in southern Nevada and California.

Additional information on these and other environmental program activities can be found in the Site Environmental Report, which is published annually and available upon request.

External oversight

As noted above, NRC plays a statutory role in the Civilian Radioactive Waste Management Program: It is responsible for licensing the potential repository and for issuing licensing criteria to govern licensing. NRC's regulations also ensure that the spent fuel casks meet strict regulatory design standards and regulate the protection of shipments against radiological sabotage.

NRC shares transportation oversight with the U.S. Department of Transportation (DOT). DOT's role in regulating spent fuel shipment strategy is broad and covers all aspects of actual transportation, including route selection, vehicle condition, placarding, driver training, package marking, labeling, and other shipping documentation.

The NWTRB was created by Congress to oversee our scientific and technical work. Composed of distinguished experts appointed by the President, it acts as a full board through five panels organized around site characterization; the repository; the waste management system; the environment, regulations, and quality assurance; and performance assessment.

Meetings held in Fiscal Year 2000 with NRC and the NWTRB are listed in Appendix E. Publications the NWTRB issued in Fiscal Year 2000 are listed in Appendix F.

Interactions with NRC
Under the NWPA, if the Secretary of Energy recommends to the President that the Yucca Mountain site should be developed as a repository, the recommendation must include preliminary comments from NRC on whether our site characterization analysis and proposed waste form appear sufficient to serve as the foundation for a license application. If Yucca Mountain is designated as the site for a geologic repository, DOE must submit a license application to NRC. The work we have done to prepare for a determination on site recommendation also contributes to development of a potential license application, but the information supporting a potential license application would be more comprehensive.

If the site is designated, the licensing process must be completed within three years as required by Congress and will involve the review of thousands of documents. None of the facilities previously licensed by NRC approaches a geologic repository in terms of the timeframe for which safe performance must be demonstrated. Consequently, work to develop the basis for a potential license application began some years ago, and our interactions with NRC have been important to developing a mutual understanding of both NRC's expectations and our plans for presenting documentation of our findings and analyses. To facilitate communication, NRC representatives work on site at the Project and report on information and events of interest to NRC staff.

NRC's strategic planning calls for early identification and resolution of issues at the staff level before a license application is submitted. To provide feedback on key issues, NRC has developed nine issue resolution status reports that define criteria for resolving each issue and report on its status, including areas of agreement and NRC staff's comments. In August 2000, NRC issued Revision 3 of its Issue Resolution Status Report on Evolution of the Near Field Environment. In September 2000, NRC issued Revision 3 of the Report on Total System Performance Assessment and Integration and the Report on Repository Design and Thermal Mechanical Effects. In September 2000, NRC also issued Revision 2 of its Issue Resolution Status Report on Radionuclide Transport.

Tour of Yucca Mountain by Richard Meserve, NRC Chairman

In Fiscal Year 2000, NRC provided comments on the draft EIS for Yucca Mountain during the comment period for that document. On May 4, 2000, NRC received for review DOE's draft notice of final rulemaking addressing theYucca Mountain site suitability guidelines (10 CFR 963).

Fiscal Year 2000 technical exchange meetings with NRC addressed criticality, pre-closure design and safety, total system performance assessment, the unsaturated zone, igneous activity, and container life and source term. In addition, through management and quality assurance meetings, we kept NRC informed of our overall progress and ensured that issues needing management attention were addressed.

As we move closer to potential licensing, quality assurance issues become more central and, therefore, are an important topic of discussion with NRC. We are working to resolve concerns about quality assurance; and, in Fiscal Year 2000, NRC continued to closely monitor our progress. More information on our quality assurance program is presented in Chapter 3.

For some years, NRC and DOE have been planning for an electronic licensing support network that would meet NRC's requirements for electronic access to the unprecedented volume of documents required for a repository licensing proceeding. This early planning facilitates clarification of important technical issues. NRC's rulemaking on the licensing support network provides guidelines for the use of web-based technology to promote access to supporting documents, which is expected to make NRC's review of the potential license application faster.

More information about NRC is available through its web site at http://www.nrc.gov/.

Interactions with the NWTRB
Pursuant to the NWPA, as amended, the NWTRB must report its findings, conclusions, and recommendations to Congress and the Secretary of Energy at least twice a year. In April 2000, the Board released its Report to the U.S. Congress and the Secretary of Energy, summarizing its calendar year 1999 activities.

In its April report, the NWTRB stressed the importance of meaningful quantification of uncertainties and the use of additional methodologies, such as analysis of natural analogues, in conjunction with performance assessments. The NWTRB emphasized the benefits of simpler designs and advocated continued work on lower temperature repository designs, suggesting that lower temperatures will lessen the effects of thermally driven disturbances and may reduce uncertainty about repository performance. In our June 2000 response to the NWTRB, we emphasized the flexibility of the repository design concept that balances technical and programmatic considerations and accommodates a wide range of operational parameters. The operational parameters could be manipulated to reduce repository temperatures, if that mode was preferred in the future.

In Fiscal Year 2000, the full NWTRB held three meetings, all of which OCRWM attended. The first addressed uncertainty, the repository safety strategy, and scientific progress. The second focused on repository design and geochemistry. The third focused on the total system performance assessment and science and technical issues. In addition, the NWTRB's Waste Management System Panel held a meeting on spent nuclear fuel transportation issues.

In late 2000 correspondence, the NWTRB indicated that the site recommendation can be made at any time, depending in part on how much uncertainty policymakers are prepared to accept. The current uncertainties regarding waste package and repository performance were of concern to the NWTRB, and are related to the high temperatures of the waste package design. The Program is working to baseline a new schedule to evaluate lower temperature repository designs.

More information about the NWTRB and the text of correspondence between the NWTRB and OCRWM's Director are available on the NWTRB's web site at http://www.nwtrb.gov/.

Relations with affected parties

Under the NWPA, the State of Nevada and the affected units of local government are entitled to exercise oversight of site characterization activities and to receive financial assistance for this purpose. Affected units of local government include Nye County and nine contiguous counties, including Inyo County in California. In Fiscal Year 2000, Congress continued to provide financial support for oversight efforts by the 10 affected counties and the State of Nevada; Congress provided $5.43 million to the counties and $500,000 to Nevada.

The NWPA also gives the State and Nye County the authority to conduct independent investigations and to receive funding for an onsite representative. The State has never designated such a representative, but Nye County has, and its representative continued to oversee our work in Fiscal Year 2000. As reported previously, Nye County implemented its Fiscal Year 2000 initiative to drill boreholes near Amargosa Valley, Nevada. Continued sampling and data collection are yielding information about water flow and fault structure in the saturated zone. OCRWM provided Nye County $4.13 million in Fiscal Year 2000 for this program. Information about Nye County's oversight program can be found through its web site at http://www.nyecounty.com/.

During Fiscal Year 2000, we continued interactions with the 10 affected counties and the State. Project staff hosted two meetings in Las Vegas, Nevada, with county representatives. We also provided Project updates to the county commissions, boards of supervisors, and State and local government committees. We conducted 22 site tours for community, county, and State officials.

We continued funding our payments-equal-to-taxes agreement with the State of Nevada and Nye, Clark, Esmeralda, Lincoln, and Inyo Counties. Under Section 116(c)(3)(A) of the NWPA, these payments are intended to compensate for taxes that affected entities would have collected on site characterization and the development and operation of a repository if they were authorized to tax Federal Government activities. A total of $9.5 million was provided in Fiscal Year 2000, of which $8 million went to Nye County.


Financial support for affected units of local government and the state of Nevada

In Fiscal Year 1998, the Project and the University and Community College System of Nevada entered into a cooperative agreement for conducting scientific studies that could augment our own studies on the Yucca Mountain site. Under this agreement, up to $40 million may be applied to such studies through Fiscal Year 2003; through Fiscal Year 2000, $18 million has been approved for 27 tasks. Subjects of the studies include rain accumulation in the Yucca Mountain area, fluid inclusion in rock fracture fillings, water infiltration through the site, and seepage into drifts and potential waste packages. Studies will also contribute geochemical data for development of the single regional groundwater model described above.

Yucca Mountain Site Characterization Project outreach

Students at Yucca Mountain Science Center

During Fiscal Year 2000, we maintained an active communications program to provide timely and accurate information about the Yucca Mountain Site Characterization Project to stakeholders, interested groups, and other members of the public through a variety of means. A major opportunity for formal public involvement was a series of public hearings on the Project's draft EIS. Between September 1999 and February 2000, we held hearings in 21 cities across the United States. In Fiscal Year 2000, we also conducted two public hearings in Nevada on DOE's proposal to amend its guidelines for evaluating the suitability of Yucca Mountain.

We promoted two-way communications with technical audiences and the general public through a tour program, speakers' bureau, and exhibits at key events. In Fiscal Year 2000, we conducted 204 tours of Yucca Mountain, briefing more than 4,200 visitors about the status of activities at Yucca Mountain. Our exhibit was seen at 29 conferences and events held throughout the United States. Through our speakers' bureau, we made 91 presentations to civic, educational, and professional groups, reaching more than 5,800 people.

We answered more than 15,000 phone calls on our toll-free information line, and shipped 9,130 documents to 880 requestors worldwide. Our three Nevada Science Centers provided information to 6,837 visitors.

Through our educational activities, we reached more than 10,000 Nevada students in kindergarten through twelfth grade, as well as more than 300 teachers and parents. These activities included workshops on energy, geology, and environmental studies; field trips to Yucca Mountain; geology merit badge workshops for Girl and Boy Scouts; science discovery days; classroom presentations; and participation in the JASON Project, a nationwide, interactive science program.


Science Center activities

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