The primary circuit untightening subsystem is designed to ensure reliable water flow from atmospheric ECCS tanks and natural circulation of coolant along the circuit ‘reactor-emergency pool’. This system operates during LOCAs when the primary circuit pressure decreases to 0.6 MPa. The system consists of two independent trains with redundancy of 2 x 100%. Each train comprises two pipelines and valves connecting the primary hot and cold legs to the emergency pool located in the lower part of the containment. This provides long term residual heat removal after the ECCS accumulator tanks and atmospheric tanks are emptied. The system train includes untightening valve units, pipeline and valves for connecting the refueling pool with the emergency pool, repair valves, and a screen filter.