Modeling and Testing of Wireless Diamond Radiation Detector Prototype for Dry Spent Fuel Canister Monitoring

There is a need to ensure safe storage of spent nuclear fuel for long periods (decades to a century) using dry storage canisters (DSCs). Over extended interim storage, an aging management program is implemented involving monitoring of the DSC to verify the functionality of its safety features. One area of interest is establishing if the conditions within a DSC can be determined, preferably by a self-contained system, because opening sealed canisters and making penetrations are not feasible. Radiation Monitoring Devices, Inc. is developing a system that detects damaged fuel rod cladding by sensing and quantifying the amount of Kr-85 present using a diamond sensor. Kr-85 is produced as a fission product in the fuel during operation and diffuses throughout a fuel pellet. A crack in the cladding of a fuel rod will provide a release path for this noble, radioactive gas and, if detected, provide a telltale sign of the integrity of the fuel. Knowledge of a cladding breach requires different protocols to be followed for transportation, repackaging or reprocessing. We present work on modeling the magnitude of the Kr-85 signal depending on the amount and type of shielding around the detector, and the thresholds chosen to record coincidence counts from the two diamond substrates. We also present results from testing a prototype in a mock-up of a NUHOMSTM EOS canister transition rail segment manufactured by Orano TN. The prototype uses a wireless ultrasonic power and data transmission system provided by Sandia National Laboratories (SNL) to supply power to the system through a curved steel wall and transmit the detector signal back out. Finally, a discussion is provided of the fitting of the system in the DSC basket assembly and how the system is designed to survive immersion in dilute boric acid, vacuum drying, and helium backfilling. The system must meet challenging requirements including operation at 200 °C and under high radiation conditions. SNL is managed and operated by National Technology & Engineering Solutions of Sandia, LLC (NTESS) under Department of Energy’s (DOE) National Nuclear Security Administration (NNSA) contract DE-NA0003525.