VVER-1000 SFAT: Final Report on Task FIN A 1073 of the Finnish Support Programme to the IAEA Safeguards

IAEA needed a rugged spent fuel attribute tester, SFAT, for verifying spent fuel assemblies of the Ukrainian VVER-1000 reactors in line with IAEA safeguards measurement standards and criteria of verification. Spent fuel verification using the existing Improved Cerenkov Viewing Device is becoming more and more difficult and sometimes impossible primarily due to the increasing cooling time of low burnup assemblies and damaged fuel in closed bottles. Other complicating factors include dummy assemblies in the ponds, different storage configurations, difficult access and variation in the quality of the pond water. The task to develop a SFAT device for the eleven Ukrainian VVER-1000 facilities has been accomplished 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 the agreed user requirements, a series of measurement campaigns were joint lyorganized by the IAEA Safeguards Department, Ukrainian Nuclear Power Plant Operators and the FINSP first at the Zaporozhye and Khmelnitski NPPs and finally in 2001 at the Rovno and South Ukraine NPPs. Several hardware configurations were tested to take into account the measurement conditions including pond lattice geometry, fuel storage conditions, high background radiation and the design of the upper part of the VVER-1000 fuel assembly. The best results were achieved using a large CZT detector, an optimized collimation and precise positioning using the refuelling machine. The system is now ready for routine inspection use at nine of the eleven Ukrainian VVER-1000 units. During the development of this verification method, special attention was paid to minimizing intrusiveness and maximizing efficiency of the procedure while ensuring complianc ewith national and facility level safety regulations in Ukraine.