Predicted and measured response of the EBR-II plant to large steam pressure changes

Abstract

Three tests were performed on the Experimental Breeder Reactor II (EBR-II) plant in which the steam pressure was ramped down by about 8, 16 and 32% of the initial 8806 kPa value, held constant, and then ramped back up to this value. Measured data from all three tests are provided along with a comparison with results from a numerical simulation of the down-ramp portion of the most severe test. The measured change in reactor inlet temperature was only about 25 to 30% of the change in steam drum saturation temperature. This relationship is very important in limiting power and temperature changes caused by steam system blowdowns in liquid metal reactor designs, such as the EBR-II, which utilize (large) negative temperature coefficients to enhance controllability and safety. These test results suggest that it appears possible to design an LMR plant in which reactivity feedbacks protect the reactor during a loss-of-heat-sink accident, without risking overly severe consequences during a steam pressure reduction accident.