Towards a defensible safety case for deep geologic disposal of DOE HLW and DOE SNF in bedded salt.

Abstract

The primary objective of this study is to investigate the feasibility and utility of developing a defensible safety case for disposal of United States Department of Energy (U.S. DOE) high-level waste (HLW) and DOE spent nuclear fuel (SNF) in a conceptual deep geologic repository that is assumed to be located in a bedded salt formation of the Delaware Basin. A safety case is a formal compilation of evidence, analyses, and arguments that substantiate and demonstrate the safety of a proposed or conceptual repository. A safety case also provides the necessary structure for organizing and synthesizing existing knowledge in order to help DOE prioritize its future research and development (R&D) activities. We conclude that a defensible initial safety case for potential licensing could be readily compiled by capitalizing on the extensive technical basis that exists from prior work on the Waste Isolation Pilot Plant (WIPP), work on other repository development programs, and the work published through international efforts in salt repository programs such as in Germany.It should be emphasized that the DOE has not made any decisions regarding the disposition of DOE HLW and DOE SNF. This study provides additional information that could be used to inform DOE's decision making regarding management of this waste. Furthermore, the safety case discussed herein is not intended to either site a repository in the Delaware Basin or preclude siting in other media at other locations. Rather, this study simply presents an approach for accelerated development of a safety case for a potential DOE HLW and DOE SNF repository using the currently available technical basis for bedded salt. This approach includes a summary of the regulatory environment relevant to disposal of DOE HLW and DOE SNF in a deep geologic repository, the key elements of a safety case, the evolution of the safety case through the successive phases of repository development and licensing, and the existing technical basis that could be used to substantiate the safety of a geologic repository if it were to be sited in the Delaware Basin. We also discuss the potential role of an underground research laboratory (URL).

Deep Borehole Disposal Safety Analysis.

“…The safety case is an essential management and communication tool throughout the project lifetime, in particular during the following key phases: site selection, site characterization and facility design, licensing, construction, operations, closure, and post-closure. Two primary roles of the safety case are (MacKinnon et al 2012, Section 3, adapted from National Research Council 20032):…”

Temperature response and brine availability to heated boreholes in bedded salt

“…In the United States, the Vadose Zone Journal USDOE Office of Nuclear Energy is funding research into the generic feasibility of HLW disposal in geologic repositories within competent crystalline rock formations, lowpermeability argillaceous formations, and salt formations (UFD Campaign, 2012). Geologic salt formations may be an ideal host media for a HLW repository due to salt's extremely low permeability in the far field, high thermal conductivity, and self-healing capability (Hansen & Leigh, 2011;MacKinnon, Sevougian, Leigh, & Hansen, 2012). These characteristics have led to the selection of salt for two lowand intermediate-level waste repositories, the Waste Isolation Pilot Plant (WIPP), in New Mexico, USA, and the Morsleben Mine in Germany.…”

Probabilistic Performance Assessment vs. the Safety Case Approach

“…For instance, the safety case concept, as currently practiced in the U.S., no longer includes key components of the safety case such as the assessment basis and the iterative process of update and revision of the evidence, analyses and arguments. Instead, the safety case is reduced to a process of site selection, site characterization, and repository design serving the basis for evaluating the pre-closure and post-closure safety [16]. However, the safety case approach is much more than the extension to pre-closure safety of the PPA approach which, by U.S. regulations, is limited to evaluating post-closure safety.…”