Formulation and Evaluation of Candidate Materials for Encapsulating Spent Nuclear Fuel in a Dry Storage Canister for Final Repository

Statement of the problem The U.S. nuclear reactors have produced over 86,000 metric tons of spent nuclear fuel that is currently stored in over 3,200 Dual Purpose (storage and transport) Canisters (DPCs). The DPCs are not designed for use in the final repository necessitating the costly ($20 billion) transfer of the spent fuel to repository canisters. As a more economical alternative, the U.S. Department of Energy is considering an option to fill the current DPCs with a material to limit the ingress of water, reduce the potential for criticality and make the canisters safe for direct placement in a final repository. The goal of the research proposed under this SBIR grant is to study geopolymer materials for their ability to limit water ingress and meet other repository requirements to enable direct placement of DPCs in a repository. • General statement of how this problem is being addressed The objective of this Phase 1 project is to research the effectiveness of four geopolymer materials as Dual Purpose Cask (DPC) filler material to enable DPCs to be directly deposited in a final repository, to avoid repackaging them into long-term storage canisters. The approach is to experimentally and analytically examine geopolymers to address repository requirements for criticality avoidance, chemical and thermal stability, homogeneity and consistency, rheological properties, material availability and cost, weight and radiation shielding, and operational considerations. • What is to be done in Phase I Four different formulations of geopolymers will be fabricated at a bench-top level, experimentally tested and numerically analyzed for their suitability as Dual Purpose Cask fillers. Testing includes density, heat stability, leaching in water after 180 days, water absorption, volume of permeable voids, and hydraulic permeability. Numerical analyses will be performed to study their shielding properties and long-term degradation mechanisms due to radiation. The results will be assessed against criteria established by the U.S. Department of Energy for the direct placement of DPCs in a final repository which include criticality avoidance, chemical and thermal stability, homogeneity and consistency, rheological properties, material availability and cost, weight and radiation shielding, and operational considerations. • Commercial Applications and Other Benefits Geopolymers that prove useful as filler material for dual purpose canisters to be placed in a final geological repository also are very attractive materials for radiation shielding applications. Geopolymer shielding material applications include shielding low-level waste facilities, spent fuel cask supplementary shielding, burial containers for low-level radioactive waste, supplementary shielding for a variety of operations at nuclear plants, and encapsulation for nuclear and radioactive materials at government nuclear sites. Improvements in shielding result in improved safety with lower radiation dose to workers and the public, and they reduce the cost of operations of nuclear facilities. Improved safety inspires more favorable public acceptance