Long-cooled spent fuel verification using a digital Cerenkov viewing device

A joint Canadian/Swedish programme in support to the IAEA has developed a non-intrusive, non- destructive analytical instrument to verify long-cooled fuel in storage ponds. The handheld instrument, operated above the water surface, consists of an ultraviolet (UV) light transmitting lens, a UV band-pass filter, a charge-coupled device mounted in a camera head, a computer system based upon the PC/104-plus format, a liquid crystal display and a wearable liquid crystal heads-up display. The instrument was developed with specific imaging software to assist in the operation and verification of the spent fuel. The quantum efficiency of the charge-coupled device at the peak sensitivity of the detector, 300-nm, is 52%, which is a factor of 6 higher than the detector used in a previous instrument. The measurement objective is to verify that fuel has not been diverted and is radioactive (IAEA method H). This is achieved by measuring the Cerenkov glow from the spent fuel. The Cerenkov glow is produced by high-speed charged particles generated by gamma rays that interact with the water (Compton effect) adjacent to the fuel rods to produce light at very low intensities. Fission products emit these gamma rays, which is indicative of spent fuel. The verification is currently done using the Mark IVe Cerenkov viewing device. However, the IAEA requires a non-intrusive instrument that is capable of detecting fuel with a burnup of 10,000 MWd/t U and a cooling time of 40 years. This is beyond the capability of the Mark IVe CVD. The recently developed digital Cerenkov viewing device was successfully tested at the Central Interim Storage Facility for Spent Nuclear Fuel (CLAB) on PWR non-fuel and spent fuel, long- cooled BWR spent fuel and very long-cooled and low burnup Agesta PHWR fuel