Control of decay heat removal through alternate system in PFBR

In the Prototype Fast Breeder Reactor (PFBR) decay heat is removed directly from the reactor core through Safety Grade Decay Heat Removal (SGDHR) circuit. Operation Grade Decay Heat Removal (OGDHR) system offers an alternate decay heat removal path using the heat removal capacity of the main heat transport system. It is preferred path during planned shutdown and also during plant upset conditions when at least one secondary sodium system, steam water system and offsite power are available. Besides removing the decay heat, this system decreases the reactor coolant temperature at a controlled rate and it is able to maintain the plant at cold shutdown condition for fuel handling or maintenance for up to 30 days. This alternate decay heat removal system of PFBR is described in the paper along with system dynamics, analysed based on in-house developed thermal hydraulics code, sequence of the system deployment, system operation and control.

► An alternate decay heat removal system is described.
► The plant dynamics is analysed and strategy of deploying OGDHR is worked out during reactor SCRAM and planned shutdown.
► System control and instrumentation are described to maintain isothermal condition in plant for prolonged durations after reactor SCRAM and planned shutdown.