Proposed methodology for Passive Autocatalytic Recombiner sizing and location for a BWR Mark-III reactor containment building

Abstract

The Stress Tests accomplished by the European nuclear plants assume to be a complementary and comprehensive review of the safety of nuclear facilities, taking into account the events occurred in Fukushima Daiichi. The analysis of Passive Autocatalytic Recombiners (PARs) installation in Cofrentes NPP (BWR Mark III, 1092 MWe) was a requirement emerged from those tests and developed by Iberdrola Engineering and Construction jointly with Universidad Politécnica de Madrid (UPM). The study established a methodology for location and number of PARs for being installed to minimize the risk arising from an hydrogen release and its distribution in containment building during a severe accident (SA). In this paper, the implementation of this methodology was deeply analyzed for Cofrentes NPP.The proposed methodology presented herein for PARs installation analysis is divided in four steps: identification of the most limiting scenarios to be simulated with a severe accident code (MAAP4) in order to obtain mass and energy sources (step 1); hydrogen distribution analysis in containment with a 3D containment code (GOTHIC 8.0) (step 2 and 3); and PAR sizing and location analysis (step 4). The most limiting scenarios chosen for a BWR were: Station Blackout (SBO); Total Loss of Feed Water (TLOFW); and Loss of Coolant Accident (LOCA). Several sensitivity analyzes of different PAR sizes and configurations were accomplished, and the most suitable PARs configuration was determined. This optimal configuration consisted in a total of 53 PARs: 47 units placed inside the containment and 6 units in the drywell. For data analysis, an in-house code was developed, providing combustion and deflagration data in a clear and accurate way, showing the combustion windows and their span.The proposed methodology was established as accurate enough for analysing PARs installation within containment applied to a BWR Mark III. The fact of having a very detailed 3D GOTHIC model allowed creating a strategy of implementation based on the preferred hydrogen pathways and areas of accumulation.