Implementation of a Modified Spent Fuel Attribute Tester for WWER-1000 in Ukraine

IAEA needs a rugged spent fuel attribute tester, SFAT, for verifying spent fuel assemblies of the Ukrainian WWER-1000 reactors. Spent fuel verification using the existing Improved Cerenkov Viewing Device is becoming more and more difficult and sometimes impossible due primarily to the increasing number of long cooling time, low burnup assemblies and damaged fuel in closed bottles. Other complicating factors include dummy assemblies in the ponds, different storage configurations, difficult-to-access and poor quality of the pond water. The task to develop a SFAT device for the 11 Ukrainian WWER-1000 facilities has been performed under the Finnish Support Programme (FINSP) to the IAEA safeguards under the Task FIN A 1073. The task made use of the experience gained on designing and implementing SFAT devices in Finland. Based on agreed user requirements, a series of measurement campaigns were jointly organized by the IAEA Safeguards Department, Ukrainian NPP operators and the FINSP first at the Zaporozhye and Khmelnitski NPPs and finally in 2001 at the Rovno and the South Ukraine NPPs. Several hardware configurations were tested to take into account the measurement conditions including pond lattice geometry, fuel storage conditions, relatively high background radiation and the design of the upper part of the WWER-1000 fuel assembly. The best results were achieved using a large CZT detector, an optimized collimation and precise positioning using the refueling machine. The system is now ready for routine inspection use at 9 of the 11 VVER-1000 NPPs. During the development of the method, special attention was paid to minimize intrusion and to maximize efficiency of the procedure while ensuring compliance with the national and the facility level safety regulations in Ukraine.