Development of a U.S. Nuclear Waste Repository Research Program in Salt

With the United States rethinking its strategy for the management and disposal of defense high-level radioactive waste and civilian used nuclear fuel (UNF), it is an opportune time to evaluate the near-term and long-term options and requirements for the U.S. geologic repository program. In this paper, we outline a research program investigating the behavior of salt when subjected to thermal loads like those that would be present in a high-level-waste (HLW) repository. This program builds upon the knowledge base developed as a result of previous repository program efforts and the successful licensing and operation of the Waste Isolation Pilot Project Transuranic waste repository. We present a preliminary evaluation of a conceptual repository design that, in principle, exploits the positive attributes of salt as a disposal medium while balancing heat management issues against other considerations such as efficiency of disposal operations and cost. The coupled thermal-mechanical behavior of the intact and crushed salt, which influences and is influenced by the liberation and movement of water present in the salt and hydrous minerals, will ultimately control the thermal and hydrochemical conditions in the repository and at the waste package. To address key scientific issues, we advocate a combination of laboratory-scale investigations, a thermal test in the field for a configuration that replicates a small portion of our conceptual repository design, and numerical simulations conducted to develop a validated model that can be used for future repository design or performance assessment purposes. Accompanying this testing program would be a broader set of investigations that we advocate be conducted in the context of an iterative and adaptive process for systematically reducing uncertainties as we build a science-based safety case for HLW disposal in salt.