BEPU Analysis of an Extended SBO Accident in a Typical Three-Loop PWR

In line with the guidelines of the IAEA SSG-2 Safety Guide and the Instruction IS-37 of the Spanish Nuclear Safety Council (CSN), this work focuses on the analysis, using the BEPU methodology, of the uncertainties associated with a design extension condition scenario. The study is applied to a typical three-loop PWR reactor under a Station Blackout accident in which the emergency diesel generators are unavailable and the recovery of off-site power is not assumed. Under these conditions, a key component for maintaining core integrity is the turbine-driven pump of the auxiliary feedwater system. Once the battery supplying this system is depleted, a mobile pump may be deployed, thereby extending the time available to recover off-site power and maintain system integrity. The analysis focuses on three figures of merit (FoMs) considered to be of particular interest: the peak cladding temperature, the pressure difference between the primary and secondary systems, and the loss of primary inventory through the relief valves. The results show that no critical values that would significantly destabilize the system are exceeded, and they identify the uncertainty parameters that have the greatest impact on each of the three FoMs.

Keywords: BEPU, LEPL, SBO, DEC, PWR, Mobile Pump.