A Gamma-Ray Scanner for Nuclear Spent-Fuel Cask Safeguards

 

Dr. A.J. Caffrey

Idaho National Laboratory

The increasing use of dry-storage casks for spent nuclear reactor fuel suggests the need for cask safeguards methods in addition to tamper-resistant tags and seals.  At present, if a cask seal fails, perhaps due to weather exposure, its contents cannot be verified without reopening the cask.

At Idaho National Laboratory, we are developing a gamma-ray scanner system to confirm the presence or absence of spent-fuel bundles in dry-storage cask slots.  The monitoring system uses a well-collimated Ge detector to view spent-fuel bundle slots from the cask’s flat end cap.  The cask’s filled and empty slots are distinguished by the peak-to-Compton background ratios of fission and activation product gamma rays.

We have conducted scanner test experiments on a Westinghouse MC-10 spent fuel cask partially filled with pressurized-water commercial reactor fuel bundles.  The peak-to-Compton background ratios for 60Co gamma rays have proved to be a reliable indicator of full and empty fuel slots.  Gamma rays from 137Cs and 154Eu fission products also were used to analyze the data and interpret the results.   In addition, the technique may also provide a unique gamma-ray spectral fingerprint of individual spent-fuel bundles to monitor if tampering has occurred since the last cask inspection.