Center for Nuclear Waste Regulatory Analyses

Progress continued toward the development of the nation's first high-level waste (HLW) geologic repository. The assistance provided to the U.S. Nuclear Regulatory Commission (NRC) by the Center for Nuclear Waste Regulatory Analyses (CNWRA), located at SwRI, played a major role in assuring that the proposed repository will protect public health and safety, as well as the environment. The CNWRA also helped government and industry - who are faced with an immediate need for interim storage pending a decision on HLW disposal - evaluate interim storage solutions. In addition, the number and variety of projects outside the nuclear arena continued to grow. Support to the petroleum industry expanded in both the exploration and distribution sectors.

CNWRA researchers are examining the spatial patterns of fractured rock and their effects on fluid movement and contaminant transport. Networks of interconnected fractures, such as the oil-filled fractures from a breached oil field in Oklahoma shown here, form the primary pathways for the movement of groundwater, hydrocarbons, and even toxic chemicals or radioactive wastes. Staff have developed specialized statistical simulation and flow modeling approaches to simulate radioactive contaminant transport for application at other sites.

The CNWRA accelerated laboratory testing, numerical analyses, and field investigations to resolve key technical issues related to the proposed repository at Yucca Mountain, Nevada. Nine major documents detailing the status of repository issues and required research are helping to meet the NRC objective of resolving these issues by mid-2002. At that time, DOE expects to apply for a license to begin construction of the repository. The Yucca Mountain Review Plan, also completed this year, provides methods for reviewing DOE's license application and criteria for judging the acceptability of DOE's conclusions regarding pre- and post-closure safety. This plan will be used in 2001 to develop preliminary comments on the sufficiency of DOE's at-depth site characterization and waste form proposal, which DOE plans to submit to the president of the United States in mid-2001.

During the review of the DOE license application, NRC and CNWRA staff will use the Total-system Performance Assessment (TPA) code to estimate the peak expected radiation dose to nearby inhabitants during a 10,000-year regulatory period, based on a number of radiation release scenarios. Recent DOE modifications to the design of metallic spent fuel canisters, coupled with the addition of a titanium shield to protect the canisters from water and the removal of crushed-rock backfill to reduce temperatures, have led the CNWRA to develop an enhanced TPA code that more readily incorporates and evaluates alternative designs for the repository. To further facilitate the use of the improved code, analysts developed a graphical user interface enabling Monte Carlo simulations that display results on a standard web browser.

Integrated, three-dimensional models are the foundation of many geological investigations. The CNWRA-developed computer code 3DStress(tm) is used to evaluate both seismic risks and preferential flow paths that result from the interaction of rock stresses on geologic structures such as faults and fractures. This figure displays the tendency of faults to open (dilate) under unequal stress conditions. Because the orientation of these faults varies, some parts of the faults allow rapid movement of fluids such as water, oil, and gas (magenta and purple tones), while others resist flow (green and yellow tones).

Waste container performance is important to the DOE strategy for safely disposing the nation's high-level radioactive waste. CNWRA staff are investigating the processes that contribute to long-term corrosion of the containers. The CNWRA is determining extremely low corrosion rates using sensitive analytical techniques. In addition to developing techniques for long-life prediction, scientists are developing long-lasting sensors that can function in a highly aggressive environment that includes alternating wet and dry conditions, high temperatures, seismicity, and ionizing radiation. Various long-life sensors are being evaluated to monitor parameters that control localized corrosion processes during an extended period of performance. In addition, the release of radionuclides from the waste containers is being investigated by measuring the dissolution rates of spent nuclear fuel and high-level waste glass. Using a variety of analytical instrumentation available at SwRI, scientists are evaluating the effect of the complex chemistry resulting from container corrosion on the dissolution rate of the waste glass.

The CNWRA is developing a Preclosure Safety Analysis (PCSA) tool capable of independently reviewing the DOE Integrated Safety Analysis of the proposed repository for the 30- to 100-year period of operations before permanent closure. The PCSA focuses specifically on the waste-handling process. When completed, the tool will be used to perform systematic hazard, event sequence, and consequence analyses. The software will conduct failure mode and effects analyses, what-if analyses, event tree and fault tree analyses, and radiological dose calculations. Results from the tool will be used to review the DOE safety analyses, thus ensuring the safety of the public and workers during operation of the facility.

CNWRA scientists conducted an extensive independent assessment of safety issues associated with the treatment and vitrification of high- and low-level radioactive wastes stored in the underground tanks at the Hanford Reservation in Washington. Staff reviewed HLW glass-melter safety issues, proprietary process information, and pretreatment processes such as ultrafiltration, process tank cooling systems, and off-gas treatment facilities. As part of this activity, a mass-balance software tool was developed that enables a quick and comprehensive assessment of the distribution of various chemicals used in the treatment processes. This, combined with thermodynamic analysis software, enables rapid and accurate assessments of the potential for explosion or criticality.

The CNWRA staff provided technical support to the NRC for licensing independent spent nuclear fuel storage casks and facilities. A safety evaluation report was completed that documents CNWRA and NRC staff evaluations of the Private Fuel Storage Facility (PFSF), which is proposed by a utility consortium. If licensed, the PFSF would be constructed on the reservation of the Skull Valley Band of Goshute Indians in Utah. Staff extensively evaluated the site characteristics and proposed design of the PFSF. In addition, the CNWRA evaluated a probabilistic seismic hazard assessment, including all structures that may handle or store nuclear materials at the site. Beginning this year, the CNWRA is assisting the NRC in preparing positions for the hearing of safety issues before the Atomic Safety and Licensing Board, which is reviewing the license application based on several contentions filed by the state of Utah.

CNWRA hydrologists have developed methods for integrating satellite imagery, field data collection, and geographic information system technology to develop physical frameworks for groundwater and watershed hydrologic models. This figure shows results of a watershed model, overlain on a satellite image, indicating how surface features affect the distribution of infiltration. Excess infiltration is the difference between precipitation and the amount of water infiltrated.

The CNWRA supports the NRC in activities associated with decontamination, dismantling, and license termination at sites contaminated with radioactive materials. During the past year, SwRI scientists assessed the likely effects of long-term erosion at a site heavily contaminated with buried wastes, evaluated dose receptor characteristics for this site, and explored the use of a geographical information system database to assist regulatory decision-making at the site. They are also developing technology to assess various approaches to cleaning up contaminated groundwater and estimating the costs of cleanup. In addition, staff evaluated the potential environmental effects of two commercial metal alloy production facilities contaminated by thorium and uranium. The CNWRA continues to develop an increasingly broad capability to solve environmental problems, such as developing and reviewing environmental impact statements, and assessing specific environmental problems.

Internal corrosion of gas pipelines can occur from a combination of condensed water, brine from formation water, and microorganisms. Under the sponsorship of GRI and the Pipeline Research Council International (PRCI), the CNWRA has constructed a unique facility that simulates the conditions inside natural gas pipelines to study the effects of microorganisms on corrosion, under high pressure. External corrosion and stress corrosion cracking, which can lead to pipeline failures, have been observed under disbonded polymeric coatings on natural gas pipelines. SwRI scientists also developed a numerical model to evaluate the chemistry of the environment and resulting corrosion under a disbonded coating. When completed, the model will provide better evaluations of the adequacy of corrosion protection in the disbonded region.

To develop a capability to predict the structural complexity of natural fault and extension fracture systems, CNWRA geologists are combining geometric and kinematic modeling, numerical simulation, physical analog modeling, and detailed examination of field analogs to analyze the development of complex structural systems. In a recent project for an oil company, geologists integrated physical analog modeling and field analyses to characterize the development of the key fault geometries and structural patterns that control migration, trapping, leakage, and compartmentalization of hydrocarbons in extensional, contractional, and strike-slip tectonic settings. Comparisons between analog modeling results and field analogs enabled the staff to examine the progressive structural evolution of normal fault systems, including localized zones of distributed deformation related to lateral and vertical displacement gradients on faults similar to those in structurally complex hydrocarbon exploration settings.

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