Partial defect verification of spent fuel assemblies by PDET: Principle and field testing in Interim Spent fuel Storage Facility (CLAB) in Sweden

A Design Study of the Parallel-Slit Ring Collimator for Fast Neutron Emission Tomography of Spent Fuel

“…Because of the thousands of metric tons of heavy metal being discharged from nuclear reactors globally, countries like Finland and Sweden are taking the lead to develop underground repositories to store their used nuclear fuel [2], [3]. The IAEA has developed safeguards approaches under integrated safeguards for encapsulation plants and geological repositories [4].…”

“…Several attempts have been made by the IAEA and its Member States to develop technologies to detect diversions of pins from a spent fuel assembly and to determine whether pins have gone missing or have been replaced with dummy or fresh fuel pins. This mode of verification is known as partial defect detection [2]. The IAEA partial defect test addresses a diversion scenario where irradiated pins are extracted from the fuel assembly or the pins are replaced with un-irradiated material, and no subsequent irradiation after the fuel rod substitution is envisaged.…”

“…For these devices, the performance criteria for verifying the integrity of a spent fuel assembly means detecting a diversion of 50% of the material in an assembly with high confidence (90%) [6]. The DCVD is less accurate in measuring fuel with long cooling times, low burnup, or in dirty pool conditions [2]. The DCVD also cannot detect a single replaced fuel rod and is limited in scenarios in which random pins are missing because adjacent fuel pins can cause the device to register a false negative [2], [8].…”

“…The DCVD is less accurate in measuring fuel with long cooling times, low burnup, or in dirty pool conditions [2]. The DCVD also cannot detect a single replaced fuel rod and is limited in scenarios in which random pins are missing because adjacent fuel pins can cause the device to register a false negative [2], [8]. FDET measurements use both the passive neutron and gamma emissions from the spent fuel assembly to characterize it and cannot be employed to independently verify pin diversion [9].…”