Comparison of effluent and inlet header breaks for an SRS reactor LOPA

The loss-of-pumping accident (LOPA) is a design-basis accident for Savannah River Site (SRS) reactors. The LOPA is defined as a double-ended guillotine break in a secondary cooling water pipe. The secondary cooling line break is termed inlet or effluent depending on break location. Upon break detection, the emergency shutdown procedure begins, the reactor scrams, the secondary cooling pump motors trip, the primary cooling pump alternating-current motors switch off, and the direct-current motor drive engages. Secondary cooling gravity flow continues flooding the building after the secondary cooling pumps are off. The emergency cooling system (ECS) activates before the dc motors flood out. Break detection time, header flooding rate, and flooding locations are different for the inlet and effluent header breaks because of different break locations. Inlet and effluent header break primary coolant temperature transients differ because primary and secondary cooling pumps continue during a break detection and reactor scram time delay for the effluent header case, whereas the pumps trip off almost immediately for the inlet header case. Design-basis accident reactor core power limits are calculated for both the inlet and effluent header breaks.