Development of accumulator computational aid for determining RCS injection volume

Reactor coolant system (RCS) injection using accumulator is an important strategy for both emergency operating procedure (EOP) and severe accident management guideline (SAMG) of pressurized water reactor (PWR) nuclear power plant. Once accumulator injection starts, the operator is requested to close the accumulator isolation valve to avoid nitrogen gas flow into RCS as the water level is low. Current accumulator water level indication system is not designed for this purpose. In emergency operating procedure, it relies on the steam generator pressure to close the accumulator isolation valve.The purpose of this paper is to develop a computational aid for estimating RCS injection volume of accumulator. First of all, simple accumulator model is verified using the plant data during a station blackout incident of Maanshan nuclear power plant. An isentropic expansion model is found better than adiabatic expansion model. Then, a computational aid is developed based on this model. Using this computational aid, the accumulator water level can be judged directly from the accumulator pressure. This computational aid can be applied for typical PWR nuclear power plants in both emergency operating procedure and severe accident management guideline.