Emergency core cooling during an SRS reactor LOPA

The loss-of-pumping accident (LOPA) is a Savannah River site (SRS) reactor design-basis accident. The most limiting LOPA is caused by a double-ended guillotine break in a secondary cooling system inlet header and is the topic of this discussion. Upon break detection, the reactor scrams and the secondary cooling water pumps and alternating-current (ac) primary pump motors trip off. The direct-current (dc) motors continue to drive the primary pumps at about one-third capacity. Gravity flow through the broken header continues flooding the building after the cooling pumps are off. The emergency cooling system (ECS) is activated prior to flood-out of the dc motors. The design-basis accident reactor power limit ensures the reactor will shut down safely should a LOPA occur. The simulated LOPA has five phases: steady state, ac coastdown, dc flow, dc coastdown, and fully developed ECS flow. Analyses of LOPAs have shown that ECS is the most limiting phase of the accident. This paper concentrates on the role of ECS in LOPA limits.