Influence of Passive Containment Cooling System on containment thermal hydraulic transients during a postulated severe accident

Abstract

The nuclear reactor containment is an important safety system that acts as an ultimate barrier to prevent the release of radioactive fission products to the environment in case of a Severe Accident (SA). The containment system of advanced nuclear reactors is expected to be designed to meet the challenges posed by severe accidents. The response of containment to pressure and temperature build-up during a SA with core melt needs to be assessed to ascertain its structural integrity and leak tightness. The focus of this paper is on analysing the influence of a natural circulation based conceptual Passive Containment Cooling System (PCCS) on the containment pressure and temperature transients in a 220 MWe Pressurized Heavy Water Reactor (PHWR) and highlighting its role as an additional energy management feature. The scenario considered is a Large Break Loss of Coolant Accident (LBLOCA) along with failure of Emergency Core Cooling System (ECCS), moderator and calandria vault water cooling systems. A validated, lumped parameter computer code called Thermal Hydraulics of Containment (THYCON) containing a PCCS model is used for the analysis. The mathematical formulations relevant to the present analysis, solution methodology, validation and benchmarking exercises of THYCON and PCCS model with available experimental and numerical works is presented. It is then applied to analyse the influence of the conceptual PCCS on the long-term containment transients during a postulated SA. Parametric studies are conducted to elucidate the influence of location and operating conditions of PCCS. The key findings are presented and discussed in this paper.