Center for Nuclear Waste Regulatory Analyses

In 1997, the Center for Nuclear Waste Regulatory Analyses (CNWRA) at SwRI celebrates its 10th year as the U.S. Nuclear Regulatory Commission's (NRC) federally funded research and development center. Established in 1987, the CNWRA is the NRC's primary source of technical assistance and research support to the national high-level radioactive waste (HLW) management regulatory program. More recently, this role has expanded significantly, with the CNWRA now providing technical assistance to the NRC on the Hanford, Washington, Tank Waste Remediation System, site decommissioning, spent fuel storage and transportation, and uranium recovery programs. The CNWRA also is applying its diverse earth sciences and engineering skills to problem solving for foreign governments and private industries.

In 1997, the Department of Energy completed a five-mile, 25-foot-diameter tunnel called the Exploratory Studies Facility near Yucca Mountain, Nevada. SwRI scientists played a vital role in design reviews and assessments and are conducting independent evaluations of anticipated test results.

Activities in the HLW program accelerated this year in preparation for a review of the Department of Energy (DOE) assessment in 1998 of the viability of the proposed repository site at Yucca Mountain, Nevada. This viability assessment is a key decision point for the DOE, the government agency responsible for siting, designing, developing, and operating the repository. In addition, Congress will use the results of the assessment to determine whether to proceed with the proposed repository. The CNWRA will play a leading role in the independent technical assessment of the adequacy of site characterization, design, and performance of the repository. Beginning in 1997 and continuing through receipt of the assessment late in 1998, CNWRA and NRC staff are working to resolve technical issues related to repository performance and to develop criteria for evaluating the acceptability of the site for permanent disposal of HLW.

In recent years, total system performance assessment has emerged as the organizing methodology and integrating element of HLW programs throughout the world. A major revision of the NRC/CNWRA Total-system Performance Assessment code, a part of that methodology, was completed this year. Version 3.1 will be used to study the sensitivity of repository performance to various processes and parameters and will provide an independent assessment of repository performance as part of the viability review. Because of their importance to decisions that affect human health and safety and the environment, CNWRA computer codes are developed and maintained under a rigorous configuration control system.

Improved understanding of shallow infiltration and deep percolation of groundwater continued as the focus of hydrology studies at the CNWRA. One-dimensional simulations of groundwater infiltration serve as a guide for defining field investigations of stream profiles, soil depth, and infiltration parameters, and the type and extent of vegetative cover in the vicinity of the proposed repository. The results of these investigations and calculations will be combined to establish the range of both the average infiltration rates and the potential for focused recharge that may accelerate the movement of water to and through the repository area.

Field investigations and analytical evaluations culminated in producing an upper range for the probability of renewed volcanism at the proposed HLW repository site. The CNWRA spatio-temporal model uses geological and geophysical information, as well as the locations and ages of known volcanoes in the region, to produce the estimate. Studies of analog sites in the U.S. and abroad have built confidence in this model. Future work will focus on the potential consequences of volcanism, guided by sensitivity studies that show the repository cross section affected by the intrusion, the waste particle size distribution, and the ratio of incorporation of waste into the volcanic ash. These characteristics are expected to have the greatest influence on the radiological hazard of volcanic disruption of the proposed repository. Efforts continued toward transferring the technology acquired in probabilistic volcanological risk assessment to evaluation of other critical facilities such as nuclear reactors, geothermal energy systems, and port and dock facilities in the Americas, eastern Europe, and Asia.

The CNWRA-developed multicomponent, multiphase reactive transport computer code MULTIFLO^TM was enhanced significantly, copyrighted, and employed in two diverse program areas this year. First, MULTIFLO^TM was used to study the nature and extent of changes in the near-field environment of the proposed HLW repository. The effects of heat-generating HLW on the moisture content of the rock mass, precipitation of minerals that could alter the permeability of the surrounding rock, and the acidity and chemical composition of water contacting the waste containers have been quantified using this powerful computer code. In addition, CNWRA scientists transferred this complex technology to model coupled hydrochemical processes accompanying in situ recovery of copper from underground ore bodies. Studies for two mining companies have evaluated critical parameters affecting the technical viability and economics of in situ mining of specific ore deposits. As part of a program funded by the Gas Research Institute, MULTIFLO^TM will also be used to evaluate the environment around coated gas-transmission pipelines to help mitigate corrosion and stress corrosion cracking of these pipelines.

The Engineered Barrier System Performance Assessment Code (EBSPAC) has been developed by the CNWRA to model processes affecting the performance of HLW containers and release of radionuclides to the near-field environment. EBSPAC was extensively revised and reissued this year to incorporate enhanced material models, near-field hydrothermal and geochemical conditions, dry-air oxidation and aqueous corrosion models, and dry-air oxidation and dissolution of the spent fuel waste form. It includes the DOE advanced conceptual design for emplacement of waste packages in backfilled or unbackfilled underground storage rooms, double-walled containers of different materials, and horizontal emplacement of wastes in the underground storage rooms. A multiyear experimental program is being conducted to provide data to verify the models used in this code.

A multiyear laboratory, field, and computational study of the effects of repeated earthquakes on underground structures was completed and documented. A two-phase parametric study of the sensitivity of repository performance to thermomechanical and seismic processes also was completed. This work supports evaluations of the adequacy of the DOE repository design to provide for safe operations, allow for retrieval of wastes for 100-150 years, and ensure long-term structural integrity of the underground openings following repository closure.

The Institute is assisting the NRC through assessments of radiological health and safety aspects of the Hanford Tank Waste Remediation System near Hanford, Washington. Underground tanks, organized in "farms," store highly radioactive liquids and sludges until they can be transferred, processed, and converted into forms for permanent disposal. Ports into the tops of tanks in one such farm are shown here.

The CNWRA began offering professional services to the oil and gas industry this year. Two geomechanical evaluations were completed: an examination of approaches to estimating in situ stresses in geological basins, and numerical analysis of deformation in and around salt bodies that may form targets for exploration and development. Downstream support also is being provided in two projects initiated late this year with the Gas Research Institute and the Pipeline Research Committee International. Both projects aim to evaluate long-term corrosion and safety of gas transmission pipelines.

In the international arena, the CNWRA trained the staff of Gosatomnadzor, the Russian federal agency responsible for radiation safety, in the use of the computer code the CNWRA previously developed for the Swedish Radiation Protection Institute. This code is used for assessing the radiological safety of integrated HLW encapsulation, transportation, and disposal systems. Support also continued for the United Kingdom Environmental Agency in the area of radioactive waste management.

1997 Annual Report SwRI Home