Severe Accident Analysis of a Generic Integral Pressurized Water Reactor with MELCOR

Abstract

Small modular reactors (SMRs) are increasingly recognized as a carbon-free energy generation option. As an evolution on current operating water cooled reactors, integral pressurized water reactors (iPWRs) are one of the technologies close to widespread deployment. Thus, a broad understanding of possible iPWR accident scenarios/behavior is important to support both safety and licensing, and emergency preparedness. The iPWRs use a small containment vessel submerged in an external cooling pool as part of passive safety features, which can affect accident progression and radionuclide source terms. This study uses the MELCOR severe accident analysis code to assess three accident scenarios in a generic iPWR design. The base case is a station blackout with loss of steam generator feed water and the decay heat removal system, which is one of the more challenging postulated accident conditions. The second case adds a small leak in the operating pool surrounding the containment vessel, thus degrading containment cooling. The third scenario maintains an intact operating pool, but instead includes a failure of the containment isolation system, opening containment directly to the environment. The analysis compares accident progression and radionuclide releases for the three cases over 72 hours and provides insight on the iPWR passive safety system performance.