Development of Multiphysics Tests for Verification of Dry Storage Cask Content via the BERRU Framework

Spent nuclear fuel contains fissile isotopes of uranium and plutonium that can present a proliferation concern. Dry cask storage is a popular method for the interim storage of spent fuel assemblies, but once a dry cask is sealed, its contents are no longer directly accessible for verification. Consequently, there is a need for nondestructive analysis techniques to verify dry cask content for nonproliferation security. Since spent fuel assemblies are sources of radiation and heat, any malicious diversion of cask contents should result in observable deviations from the radiation dose and temperature profiles predicted by nominal case calculations. Such deviations between measurements and calculations, therefore, can inform when there may be malicious diversion of the cask content. To examine the potential for a neutronics-based test (based on two-dimensional neutron diffusion) and a thermal-based test (based on one-dimensional heat transfer) for verifying dry cask content, we consider two different methods of applying “single-physics” measurements and predictions in complementary manners, and also develop a multiphysics test. Although neither approach provides a high level of confidence, we find that the latter method gives better results and can be recommended as the preferred approach for future development. We close with a sketch of a potential validation pathway for the multiphysics testing methodology.