An In Situ Safeguards Verifier for Spent CANDU-Type Fuel Bundles Stored on Stacked Trays

The safeguards verification of irradiated fuel bundles requires not only physically identifying them but also confirmation through spent-fuel-specific attributes. Performing such measurements situ in view of the very high radiation levels that exist. This paper describes a verifier for CANDU-type spent-fuel bundles, which has been designed, developed, and used for more than a decade. The associated equipment testing for an extended period was carried out at the Karachi Nuclear Power Plant (KANUPP). The verifier or its variant in one form or other is routinely utilized for the verification of fuel bundles at other CANDU stations as well. It comprises a room temperature CdZnTe semiconductor detector embedded in a shield-collimator assembly, the electromechanical scanning mechanism plus the data acquisition and analysis electronics. In addition to the hardware, the development of appropriate data acquisition software also contributed to the efficient functioning of this safeguards equipment. The working principle of the equipment and the verification methodology used for bundles of different cooling time ranges are described. As the use of this equipment involves the handling of a massive shield assembly over the irradiated fuel tray stacks in the storage bay, its inherent industrial safety features are described. Radiation safety measures for handling the contaminated components of the equipment are also outlined. In conclusion, savings in the costly inspection time affected through the development and implementation of the verifier are emphasized. inwithout isolating the bundles could be extremely challenging