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 is developing 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. All of the Phase II technical objectives were successfully accomplished. These involved the fabrication of diamond detectors, fabrication and characterization of diamond spectrometers for detecting beta particle radiation in a gamma-ray background at high temperature up to 200oC, fabrication of stacked detectors an developing a coincidence detection technique for rejection of gamma rays signals, evaluated and compared various detector configurations and operating parameters, design of packaging and tungsten shielding suitable for use in a commercial casks, and the design of rad-hard, high temperature electronic circuitry. The Phase II research and development has demonstrated the approach and built a foundation for continuing to advance the technology towards commercialization. In Phase IIB, we will perform the engineering development to reach the pre-production prototype stage for integration into a commercial cask for testing and evaluation by Orano Inc., a commercial manufacturer of nuclear waste casks. This effort will include: Optimizing the detector configuration, operating parameters and shielding, building electronic circuitry based on the Phase II design, producing an integrated system with detector and front-end electronics compatible with the space limitations and internal structural components in a commercial cask, and testing in a realistic simulated environment. As with Phase II, the Phase IIB effort will be carried out in collaboration with Draper Laboratories (Cambridge, MA).Commercial Applications and Other Benefits: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.