Analysis of Fuel Handling System for Fuel Bundle Safety During Station Blackout in 500 MWe PHWR Unit of India

Abstract

Situations of Station Blackout (SBO) i.e. postulated concurrent unavailability of Class Ill and Class IV power, could arise for a long period, while on-power refuelling or other fuel handling operations are in progress with the hot irradiated fuel bundles being any where in the system between the Reactor Building to the Spent Fuel Storage Bay. The cooling provisions for these fuel bundles are diverse and specific to the various stages of fuel handling operations and are either on Class Ill or on Class I1 power with particular requirements of instrument air. Therefore, during SBO, due to the limited availability of Class II power and instrument air, it becomes difficult to maintain cooling to these fuel bundles. However, some minimal cooling is essential, to ensure the safety of the bundles. As discussed in the paper, safety of these fuel bundles in the system and/or for those lying in the liner tube region of the reactor end fretting is ensured, during SBO, by resorting to passive means like 'stay-put', 'gravity-fill', 'D2O-steaming' etc. for cooling the bundles. The paper also describes various consequences emanating from these cooling schemes.