Robust Kr-85 Detectors for New Waste Cask Design

Dry cask storage systems (DCSS) are used to store spent nuclear fuel from nuclear power plants. Without a long term storage solution in place, storage for decades in casks may be required. High burnup fuel rods may become brittle over time presenting problems for eventual transport of the spent fuel from reactor sites to a central storage facility. It is desired to passively determine the structural integrity of spent fuel assemblies by monitoring conditions inside the casks including temperatures, pressures, corrosion products and radioactive decay elements. The presence of Kr-85, a high yield, long-life fission product gas, in the outer envelope of a dry storage cask is an indicator of a fuel rod cladding breach. RMD will investigate radiation detectors for monitoring beta particle emissions from Kr-85 radiation while inside storage casks. In particular, the design goal is to detect beta particles in the presence of strong background gamma rays. Diamond is a wide band gap semiconductor that can operate at elevated temperatures and under high radiation conditions, and with intrinsic properties that enable high count rate detection. Detectors were fabricated from synthetic diamond samples, both polycrystalline and single crystal. Their sensitivity to beta particles from Kr-85 and photons (such as from Cs-137) were measured. Operating a stack of two diamond detectors in coincidence was found to be an effective technique for discriminating between beta and gamma interactions. And most impressively, the diamond detectors were found to operate with low noise even at elevated temperatures. RMD will optimize the diamond devices and determine a final detector assembly. A significant effort will involve pushing the detector design to operate under harsher conditions, through more in-depth testing with collaborators, particularly under higher radiation conditions. From design and evaluation, RMD will initiate construction of complimentary electronics. Finally, there will be further outreach to specialists in the field who can ensure that the sensor is adaptable to plans for future waste storage (and other nuclear fuel cycle needs). In addition to monitoring status of nuclear waste inside storage casks, non-destructive evaluation, particle physics and homeland security are also possible areas that would benefit from a rad hard beta particle detector, which could operate at elevated temperatures if need be. Bore hole logging is another high temperature detector application. Due to its high density of nuclei, diamond is promising for fast neutron detection. Diamond detectors are also well suited for tissue equivalent dosimeter applications.