Operating strategy of SGDHRS during long term decay heat removal operation in an FBR

Following events like Station Blackout, the reactor is shutdown and the decay heat is removed using a passive decay heat removal system known as Safety Grade Decay Heat Removal System (SGDHRS). The SGDHRS removes heat from the hot pool through a sodium to sodium heat exchanger (DHX) and ejects to ambient air through a sodium to air heat exchanger (AHX). During long term decay heat removal operation, it is essential to maintain the sodium temperature above its freezing point to keep the system in healthy condition. For this, three different SGDHRS operating strategies are investigated. Out of all the three strategies, the strategy of closing the AHX dampers sequentially is found to be the best one. With this strategy, the decay heat removal operation can be continued for more than 10 days without any risk of sodium freezing. The paper discusses the mathematical models used, operating strategies studied and the results obtained. (author)