PARTIAL DEFECT DETECTION IN LWR SPENT FUEL USING A DIGITAL CERENKOV VIEWING DEVICE

Previous studies on the detection of partial defects focussed on the detection of a small number of missing or substituted fuel rods in a spent fuel assembly. Attention has now been directed to the diversion of fifty percent or more fuel rods, which is considered to be a more credible diversion scenario. The diversion of fifty percent of the fuel rods in a fuel assembly by rod substitution using stainless steel or zirconium rods should cause a decrease in the total Cerenkov light output from the fuel assembly. Studies were carried out in the laboratory and in the field to determine the ability of the digital Cerenkov viewing device (DCVD) to detect this expected decrease in Cerenkov light intensity. Because there are no real examples of LWR fuel with fifty percent rod substitution, a spent fuel assembly was modelled using ORIGEN-ARP, GEANT4 and ZEMAX to produce a Cerenkov light intensity at the detector of the DCVD. The preliminary laboratory, field and modelling results on the ability of the DCVD to detect partial defects will be given.