Evolution of the possibility to use the emergency feedwater system of units 5 and 6 in WWER-1000 for management of BDBA - loss of-site power with subsequent failure of the primary residue heat removal system

This paper presents some of the main results of the thermal-hydraulic analysis of selected variants of the beyond design basis accident 'Loss of off-site power with subsequent failure of the residual heat removal system line TQ40'. The objective of the analyses was to evaluate the possibility to cool the primary circuit down to 150 oC and and to maintain it in this state for at least 24 hours by the operation of the emergency feedwater system. The calculated pressures and temperatures were plotted against the existing pressure-temperature limitations and checked against the Hydro press protection setpoint (author)