RELAP5 analysis of an EOP based on mobile pumps, at a generic VVER-1000 NPP in case of a total loss of the primary heat sink (for DBDA conditions)

Full text of publication follows: The loss of the primary heat sink is one of the most relevant DBDA scenarios. If the capability to remove heat from the primary side cannot be restored, the primary side will be subjected to high pressure for a long period of time. The actuation of the ECCS will be inhibited, PS inventory will be lost, finally the core will be in dryout conditions. The EOP which is investigated in this paper proposes to utilize mobile pumps (e.g. using fire brigade trucks) to make additional sources of feedwater available and thereby restore the primary heat sink at least for a limited period of time. After a certain time (which should be determined by calculations) of this measure, the PORV-valve and/or the gas-removal system should be opened to lower the pressure in the primary side and actuate the ECCS (primary side bleed and feed mode). The calculations indicate that this procedure is capable of saving the plant, or at least extending the grace period. Three cases are presented: the effect of only primary side feed and bleed, the beneficial effect of utilising mobile pumps first, and a scenario which assumes no operator action. (authors)