[en] The presentation briefly addresses three topics. First, science has played an important role throughout the history of the WIPP project, beginning with site selection in the middle 1970s. Science was a key part of site characterization in the 1980s, providing basic information on geology, hydrology, geochemisty, and the mechanical behavior of the salt, among other topics. Science programs also made significant contributions to facility design, specifically in the area of shaft seal design and testing. By the middle 1990s, emphasis shifted from site characterization to regulatory evaluations, and the science program provided one of the essential bases for certification by the Environmental Protection Agency in 1998. Current science activities support ongoing disposal operations and regulatory recertification evaluations mandated by the EPA. Second, the EPA regulatory standards for long-term performance frame the scientific evaluations that provide the basis for certification. Unlike long-term dose standards applied to Yucca Mountain and proposed repositories in other nations, the WIPP regulations focused on cumulative releases during a fixed time interval of 10,000 years, and placed a high emphasis on the consequences of future inadvertent drilling intrusions into the repository. Close attention to the details of the regulatory requirements facilitated EPA's review of the DOE's 1996 Compliance Certification Application. Third, the scientific understanding developed for WIPP provided the basis for modeling studies that evaluated the long-term performance of the repository in the context of regulatory requirements. These performance assessment analyses formed a critical part of the demonstration that the site met the specific regulatory requirements as well as providing insight into the overall understanding of the long-term performance of the system. The presentation concludes with observations on the role of science in the process of developing a disposal system, including the importance of establishing the regulatory framework, building confidence in the long-term safety of the system, and the critical role of the regulator in decision making.

[en] Despite decades of international consensus that deep geological disposal is the best option for permanent management of long-lived high-level radioactive wastes, no repositories for used nuclear fuel or high-level waste are in operation. Detailed long-term safety assessments have been completed worldwide for a wide range of repository designs and disposal concepts, however, and valuable insights from these assessments are available to inform future decisions about managing radioactive wastes. Qualitative comparisons among the existing safety assessments for disposal concepts in clay, granite, salt, and unsaturated volcanic tuff show how different geologic settings can be matched with appropriate engineered barrier systems to provide a high degree of confidence in the long-term safety of geologic disposal. Review of individual assessments provides insights regarding the release pathways and radionuclides that are most likely to contribute to estimated doses to humans in the far future for different disposal concepts, and can help focus research and development programs to improve management and disposal technologies. Lessons learned from existing safety assessments may be particularly relevant for informing decisions during the process of selecting potential repository sites.

[en] This paper provides a summary of observations drawn from twenty years of personal experience in working with regulatory criteria for the permanent disposal of radioactive waste for both the Waste Isolation Pilot Plant repository for transuranic defense waste and the proposed Yucca Mountain repository for spent nuclear fuel and high-level wastes. Rather than providing specific recommendations for regulatory criteria, my goal here is to provide a perspective on topics that are fundamental to how high-level radioactive waste disposal regulations have been implemented in the past. What are the main questions raised relevant to long-term disposal regulations? What has proven effective in the past? Where have regulatory requirements perhaps had unintended consequences? New regulations for radioactive waste disposal may prove necessary, but the drafting of these regulations may be premature until a broad range of policy issues are better addressed. In the interim, the perspective offered here may be helpful for framing policy discussions.

No abstract available

[en] Demonstrating compliance with the applicable regulations for the Waste Isolation Pilot Plant (WIPP) requires an assessment of the long-term performance of the disposal system. Scenario development is one starting point of this assessment, and generates inquiry about the present state and future evolution of the disposal system. Scenario development consists of four tasks: (1) identifying and classifying features, events and processes (FEPs), (2) screening FEPs according to well-defined criteria, (3) forming scenarios (combinations of FEPs) in the context of regulatory performance criteria and (4) specifying of scenarios for consequence analysis. The development and screening of a comprehensive FEP list provides assurance that the identification of significant processes and events is complete, that potential interactions between FEPs are not overlooked, and that responses to possible questions are available and well documented. Two basic scenarios have been identified for the WIPP: undisturbed performance (UP) and disturbed performance (DP). The UP scenario is used to evaluate compliance with the Environmental Protection Agency's (EPA's) Individual Dose (40 CFR Section 191-15) and Groundwater Protection (40 CFR Section 191-24) standards and accounts for all natural-, waste- and repository-induced FEPs that survive the screening process. The DP scenario is required for assessment calculations for the EPA's cumulative release standard (Containment Requirements, 40 CFR Section 191-13) and accounts for disruptive future human events, which have an uncertain probability of occurrence, in addition to the UP FEPs

No abstract available

[en] Published analyses of geologic repositories indicate potential for excellent long-term performance for a range of disposal concepts. Estimates of peak dose may be dominated by different radionuclides in different disposal concepts. Thermal loading issues can be addressed by design and operational choices. Impact of waste form lifetime on estimates of peak dose varies for different disposal concepts.

[en] Full text: The recognition that the endpoint of spent fuel management practices will be deep geologic disposal of radioactive wastes leads to questions about how alternative options for spent nuclear fuel (SNF) management might affect performance of a geologic repository. Do some options for SNF management simplify the siting and design of a geologic repository? Do some geologic disposal concepts favor specific SNF management practices? Do some SNF management options favor specific geologic disposal concepts? Are some waste forms inherently preferable than others for geologic disposal? Given the historical difficulty in many nations associated with siting and licensing geologic repositories for permanent disposal of SNF and high-level radioactive waste (HLW), are there activities that the spent fuel management community could or should undertake today to facilitate future disposal operations? Long-term repository safety is, in general, independent of specific treatments of SNF or HLW other that its packaging. However, multiple aspects of the form in which the waste will be disposed are relevant to repository design and performance, including waste volume, radionuclide content, thermal power, waste package size, and waste form and package lifetime in a range of geologic environments. Consideration of how these factors impact repository performance suggests that choices made now regarding SNF management may affect future flexibility in repository siting and design. In the U.S., due to the absence of a final disposal site (since the suspension of the Yucca Mountain Project in 2009), nuclear utilities have been storing SNF at their nuclear reactor sites using dual purpose casks. These casks are large and, depending on the burn-up of the SNF contained therein, can also be very hot. This current practice can have significant implications for transportation and, ultimately, disposal. This paper shall discuss these implications based on the current U.S. practice and will suggests ways in which these implications can be addressed. The principal message that we intend to convey is the need for careful planning while implementing upfront and temporary SNF management practices because of their potential costly implications to transportation and disposal. An integrated view of the entire back end of the nuclear fuel cycle (interim storage, transportation, and disposal) upfront during the planning phases is paramount to develop and implement an effective SNF management program.Sandia National Laboratories is a multimission laboratory operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DENA-0003525. This abstract is Sandia publication 2017-5723A.

[en] Published results of safety assessments for deep geologic disposal of high-level radioactive waste and spent nuclear fuel in the United States, Sweden, France, Switzerland and other nations provide insight into those aspects of the waste form that are most important to the long-term performance of the repository system. Hypothetical modifications to the wastes, such as might result from new technologies for processing spent fuel and advances in the design of nuclear reactors and waste forms have the potential to impact long-term performance. This paper reviews relevant results of existing safety assessments for a range of disposal concepts and provides observations about how hypothetical modifications to the waste (e.g. changes in radionuclide inventory, thermal loading and durability of waste forms) might impact results of safety assessment models. Disposal concepts considered include geologic repositories in both saturated and unsaturated environments. (authors)

[en] A deep borehole repository is one of the four geologic disposal system options currently under study by the U.S. DOE to support the development of a long-term strategy for geologic disposal of commercial used nuclear fuel (UNF) and high-level radioactive waste (HLW). The immediate goal of the generic deep borehole repository study is to develop the necessary modeling tools to evaluate and improve the understanding of the repository system response and processes relevant to long-term disposal of UNF and HLW in a deep borehole. A prototype performance assessment model for a generic deep borehole repository has been developed using the approach for a mined geological repository. The preliminary results from the simplified deep borehole generic repository performance assessment indicate that soluble, non-sorbing (or weakly sorbing) fission product radionuclides, such as I-129, Se-79 and Cl-36, are the likely major dose contributors, and that the annual radiation doses to hypothetical future humans associated with those releases may be extremely small. While much work needs to be done to validate the model assumptions and parameters, these preliminary results highlight the importance of a robust seal design in assuring long-term isolation, and suggest that deep boreholes may be a viable alternative to mined repositories for disposal of both HLW and UNF. (authors)