Extending SBO coping capability: An improved auxiliary feedwater system

A novel way to increase the station blackout (SBO) coping capability for pressurized water reactors is presented and evaluated for Advanced Pressurized Reactor 1400 (APR1400). The technical solution proposed is to install an electric direct current (DC) generator coupled to the shaft of a turbine-driven pump (TDP). The new system, named turbine-driven pump - DC (TDP-DC), works as a complement to the plant class 1E batteries, and it is meant to extend the plant coping time beyond present 8-h capacity. Assessment is performed using the one-dimensional multi-dimensional analysis of reactor safety (MARS-KS) system code by evaluating the plant response over an assumption of only one TDP-DC available. The test has been conducted for two conditions: SBOs with/without a reactor coolant pump (RCP) seal loss-of-coolant-accident (LOCA). For both cases, it is assumed to have a mature nuclear core (after three refueling cycles) and a degradation of 20% in efficiency of the only turbine driver working. Results shows that, in 2.7 h from SBO onset, the new TDP-DC system is capable of supporting all electrical loads required during SBO. It is proven that the TDP-DC can extend the plant SBO coping time from 8 to 20 h for the most limiting case of SBO with RCP seal LOCA. In addition, it is revealed that the coping time can be extended beyond 32 h for SBO without RCP seal LOCA.