Performance of cooling system of a fast reactor sub-assembly storage facility during station blackout

Abstract

In this work, using a specifically developed CFD model, design of a cooling system for an upcoming fresh fuel storage facility with 22 kW of decay heat generation and its availability have been optimized in the event of equipment failure and station blackout. Parameters such as air temperature, concrete temperature, velocity of air and time taken by air to escape from the storage have been used to compare the performances of various designs of the cooling system. From the analysis of a pre-designed system without any backup equipment, it is observed that in absence of suction blower, contaminated air escapes through the upper inlets after 100 s. With an intention to stop this escape of contaminated air, we analyzed two upgraded designs; one with the backup equipment and another with relocated upper inlets. The results show that with backup equipment, -which starts within 100 s, the temperatures of the fuel sub-assemblies and concrete are maintained within the safe limit. With the relocation of upper inlets, the contaminated air remains in the storage vault, but the temperature of the air in the vicinity of the concrete ceiling reaches the safety limit of 338 K in 500 s. Hence, we suggest a safe limit of 400 s for starting up the backup system. The modification in inlet positions and integration of backup equipment for cooling of the nuclear inventories during station blackout prevents release of contaminated air and retains the temperature within safe limits.