Numerical modeling of FBR safety grade decay heat removal system and its validation

A numerical code has been developed for simulating natural circulation based decay heat removal system of a typical pool type sodium cooled fast reactor. The code consists of one-dimensional numerical models of a sodium–sodium shell and tube heat exchanger (DHX) dipped in a pool of sodium, finned tube type sodium to air heat exchanger (AHX), intermediate circuit connecting the two heat exchangers, a tall stack over the AHX and dampers for regulating natural draft air flow through the AHX. The code simulates steady state and transient natural circulation flow development in the DHX primary, intermediate and air circuits following any transients in the source temperature or in the air circuit. The code has been validated against in-house experiments conducted in a 355 kW natural circulation test loop SADHANA under various operating conditions. With the validated code, the performance of decay heat removal system has been evaluated at various source temperatures.