Abstract
The integrity of the containment will be challenged during a severe accident due to pressurization caused by the accumulation of steam and other gases and possible ignition of hydrogen and carbon monoxide. Installation of a passive filtered venting system and passive autocatalytic recombiners allows control of the pressure, radioactive releases, and concentration of flammable gases. Thermal hydraulic analysis of the containment equipped with dedicated passive safety systems after a hypothetical station blackout event is performed for a two-loop pressurized water reactor NPP with three integral severe accident codes: ASTEC, MELCOR, and MAAP. MELCOR and MAAP are two major US codes for severe accident analyses, and the ASTEC code is the European code, joint property of Institut de Radioprotection et de Sûreté Nucléaire (IRSN, France) and Gesellschaft für Anlagen und Reaktorsicherheit (GRS, Germany). Codes’ overall characteristics, physics models, and the analysis results are compared herein. Despite considerable differences between the codes’ modelling features, the general trends of the NPP behaviour are found to be similar, although discrepancies related to simulation of the processes in the containment cavity are also observed and discussed in the paper.
Highlights
The accident at the Fukushima Dai-ichi nuclear power plant (NPP) made utilities review the plants’ safety systems and procedures
The modelling follows the same pattern as in the ASTEC and MELCOR codes; the containment is divided into thermal hydraulic volumes connected by junctions with addition of heat structures which act as heat sinks
The modular accident analysis program (MAAP) code, for example, uses simpler phenomenological models to reduce the running times, while MELCOR and ASTEC rely on more complicated numerics at the expense of the duration of the analysis
Summary
The accident at the Fukushima Dai-ichi nuclear power plant (NPP) made utilities review the plants’ safety systems and procedures. The reports and papers published in the open literature, some of them listed in [1,2,3,4], support the interest of nuclear facilities for such systems to restrict radioactive releases out of the NPPs. Influence of safety systems on containment behaviour is examined by calculating a station blackout event without any recovery actions with three integral severe accident codes: ASTEC, MELCOR, and MAAP. The objectives of calculations are to analytically confirm the ability of passive containment safety systems to mitigate accident consequences and to justify the applicability of, currently, the most popular severe accident codes for such analyses.
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