Modeling Hydrogen Explosion in Level 1 PSA

Abstract

Extension of the operational lifetime beyond 40 years is currently a noteworthy project in the field of nuclear safety in France, especially for 900-MW(electric) reactors that will be the first ones to go through the fourth periodic safety review. For 1300-MW(electric) reactors, the safety studies have already been engaged. Probabilistic Safety Assessments (PSAs) play an important role in this process, including assessment of the robustness of the plants against internal and external hazards. Among the hazards, internal explosion induced by hydrogen accumulation due to leakage of pipes and/or singularities, or failure of venting systems in the battery rooms is now taken into account in the PSA developed by the licensee (EDF). The PSAs are then reviewed by IRSN, which is the French Technical support organization. To achieve this purpose, IRSN develops its own Level 1 PSA studies. This paper takes into account the most recent developments of the IRSN analyses, especially regarding the Bayesian quantification of the hydrogen leak frequency derived from an original method developed by Sandia National Laboratories.

Keywords:

• Probabilistic safety assessment
• hydrogen explosion
• Bayesian model

Acknowledgments

The authors wish to thank Angélique Pasco and Marc Henrio (IRSN) for precious support during on-site walkdown.

Notes

^a This is true only for seaside NPPs.

^b More recently, one minor hydrogen explosion was observed in the turbine room of one French NPP. None of these events led to any consequence on the core. As mentioned before, these events cannot be shared without the consent of the French licensee (except the events presented in Ref. 18) and are therefore not included in this paper, which mainly focuses on the methodology.

^c In these figures, the relative section of the leak corresponds to the leak section divided by the pipe/component section. A 100% relative section corresponds therefore to a complete rupture of the pipe/component.