The effect of primary pump coastdown characteristics on loss-of-flow transients without scram in EBR-II

Abstract

A series of loss-of-flow (LOF) tests without scram (unprotected) is planned for the Experimental Breeder Reactor II (EBR-II) to demonstrate the inherent shutdown capability of the reactor during an LOF event. The purpose of this paper is to discuss in detail the unprotected LOF transient analysis, the validation of the EBR-II reactivity feedback modeling, and the significance of pump coastdown characteristics on peak reactor temperatures. The tests as designed are limited by the fuel-cladding eutectic temperature of the fuel elements, and in order to meet the required temperature limit, the initial power and flow of all the tests are 16.7 and 20% of their rated values, respectively. To further reduce peak temperature, the primary tank temperature is to be decreased to 338°C from the nominal 371°C. The results show that primary flow coastdown rate and the capacity of the auxiliary pump have dramatic effects on the reactor temperatures. The impact of secondary flow depends somewhat on test conditions. When the auxiliary pump is in operation, the effect of secondary flow behavior on the reactor temperature becomes less significant during an unprotected LOF event.