Center for Nuclear Waste Regulatory Analyses

Faults in the Earth's crust are sources of potentially damaging earthquakes that threaten the safety and stability of a geologic repository at Yucca Mountain. Here, a hidden fault is simulated by two opposite-moving "plates" beneath sand. Resulting deformation is illustrated by distortion of the grid. Analyses of modeling experiments such as this provide insight into the potential deformation and seismicity of hidden faults near Yucca Mountain.

For nearly 10 years, the Center for Nuclear Waste Regulatory Analyses (CNWRA) at SwRI has been the U.S. Nuclear Regulatory Commission's (NRC) primary source of technical assistance and research in support of the high-level radioactive waste (HLW) management regulatory program under the Nuclear Waste Policy Act. As a result of federal budget reductions in the HLW program in 1995, the NRC permitted the CNWRA to offer its technical expertise to other areas within the NRC, as well as to foreign governments and private industries. Despite this shift, HLW research and development is expected to remain stable in coming years, driven by the nuclear industry's need for a disposal site and a congressional mandate for the development of an underground geological repository.

This year, the CNWRA has focused on preparations for the U.S. Department of Energy (DOE) 1998 assessment of the viability of the proposed repository site at Yucca Mountain, Nevada. The DOE is the government agency responsible for siting, designing, and operating the repository. Preparations include developing criteria and methods to assess the adequacy of both the repository site characterization and the design efforts conducted by the DOE through a variety of research, analysis, technical exchange, and inspection activities. If the site is found to be viable, the CNWRA will assist the NRC in evaluating the adequacy of the DOE license application for the repository, scheduled to be submitted in 2002. These technical reviews will determine whether the site can adequately protect the radiological health and safety of the public in future millennia.

Total system performance assessment (TSPA) has emerged as the organizing methodology and integrating element of the U.S. HLW program. An important CNWRA activity this year has been the critical review of the DOE TSPA, including independent calculations of key processes likely to affect repository performance. As part of the overall performance assessment program, CNWRA staff members evaluated the effects of thermal loading, groundwater infiltration rate, thermohydrological properties, ventilation, and backfill on repository performance. These studies provide feedback to DOE regarding the defensibility of its safety evaluation and also help prioritize future CNWRA work.

Using coupled moisture flux and energy balance simulations, scientists estimate hydrologic infiltration into fractured bedrock in an arid environment, identifying areas of high infiltration (reds) and lower infiltration (blues). Here, infiltration is calculated as a function of climatic parameters, hydraulic properties, alluvium depth, and erosion.

Performance assessment calculations by the CNWRA and other organizations have shown that the movement of water from precipitation through various rock layers to the repository horizon, then downward and off site to potential drinking water sources, is among the most crucial factors affecting repository safety. Consequently, resources have been directed toward understanding shallow infiltration and deep percolation of groundwater. The CNWRA staff performed a definitive series of one-dimensional simulations of groundwater infiltration. From these results, formulas were developed that relate infiltration to meteorological and geological factors that can be measured, bounded, or predicted for the repository site.

Because of volcanism's possible impact on repository performance, its probability and potential consequences continue to spur intensive field and numerical investigations. The CNWRA has taken an innovative approach that uses geologically similar active volcanoes as analogs to volcanic activity that has occurred near Yucca Mountain and which may recur in the future. Results of this research -- at volcanoes in Nicaragua, Mexico, and far east Russia -- were used to make preliminary calculations of the effects of volcanism on repository performance and to aid in the development of appropriate regulations. In related activity, CNWRA staff members visited Indonesia at the request of the International Atomic Energy Agency to evaluate the risks of volcanism to foreign nuclear power plants.

CNWRA staff members developed a computer code called MULTIFLO^TM that calculates chemical reactions along flow paths in a multiphase, multicomponent, nonisothermal, partially saturated, porous medium. The initial version of the two-module program was released for internal testing and use by the CNWRA and NRC staff. The two modules treat mass and energy transport and general electrochemical migration, respectively. In addition to playing a critical role in modeling the behavior of the near-field environment of the proposed repository, MULTIFLO has potential applications in the environmental remediation and oil and gas industries.

Using the CNWRA-developed MULTIFLOTM code, engineers model reactive chemical transport through porous media. Combining multiphase, nonisothermal flow with chemistry and electrochemistry, the code predicts changes to host media caused by water-rock interactions, evaporative heating, and corrosion. In this example, fluid injected into solid rock (blues) follows flow paths indicated by the arrows. Red indicates areas of rock dissolution.

Significant advances have been made in understanding the potential for microbial influences on corrosion of radioactive waste containers. This capability, relatively new to both the HLW program and SwRI, has potential applications in other industries as well. Discussions are under way with representatives of the oil and gas industry and the U.S. Navy to identify research needs in this area. The CNWRA staff has also extended its knowledge of nuclear reactor pressure vessels in analyzing the potential for fracture and thermal embrittlement of long-lived nuclear waste containers.

The CNWRA completed work on software to evaluate the tendency of faults and fractures to dilate or slip, depending on the orientation and magnitude of in situ stresses. Originally developed to evaluate the behavior of faults in the vicinity of Yucca Mountain, 3DStress^TM is also a useful tool for the international oil and gas exploration industry, to help predict sealing of faults, migration of fluids, fault trapping potential, and reservoir anisotropy, all of which are important in risk assessment and production planning.

An innovative program called 3DStressTM has been developed at SwRI to analyze the tendencies of faults and fractures to slip or dilate. Here, 3DStress highlights in purple the region of maximum dilation tendency along the flank of a salt dome. Sand and shale layers surrounding salt domes such as those in the Gulf of Mexico region often contain trapped oil and gas. Information regarding dilation tendencies on salt dome flanks can be used to assess the risk of trap leakage.

The Center recently integrated two important document management systems -- the Regulatory Program Database and the Technical Reference Document System. The resulting Consolidated Document Management System has generated considerable interest at the NRC as a potential base for a large-scale Licensing Support System (LSS), which would provide access to documents related to the proposed geologic repository. To test the viability of such a system, the CNWRA initiated an LSS Pilot Project that produced a world wide web interface to access HLW program and technical documents.

The CNWRA played a significant role in supporting the NRC as final preparations were made for the DOE to begin operations at the West Valley Demonstration Project in upstate New York. Over the next several years, the project will oversee the conversion of liquid and semi-solid forms of HLW to solid monoliths of glass encased in large stainless steel cylinders. The CNWRA prepared safety evaluation reports for critical aspects of the West Valley facilities and provided technical support to the NRC as it oversaw the DOE operational readiness review that preceded hot, or radioactive, operations.

The Center continues to expand its services in radioactive waste management to other nations. Software originally developed for the Swedish Radiation Protection Institute (SSI) for assessing the radiological safety of an integrated HLW encapsulation, transportation, and disposal system was upgraded this year. With SSI approval, the CNWRA will provide the software and associated training to the Russian waste management community. In addition, the CNWRA provided technical and management reviews of key aspects of the United Kingdom and Canadian HLW disposal programs.

1996 Annual Report SwRI Home