Abstract
In the framework of severe accident research activity developed by ENEA, a MELCOR nodalization of a generic Pressurized Water Reactor of 900 MWe has been developed. The aim of this paper is to present the analysis of MELCOR code calculations concerning two independent unmitigated large break loss of coolant accident transients, occurring in the cited type of reactor. In particular, the analysis and comparison between the transients initiated by an unmitigated double-ended cold leg rupture and an unmitigated double-ended hot leg rupture in the loop 1 of the primary cooling system is presented herein. This activity has been performed focusing specifically on the in-vessel phenomenology that characterizes this kind of accidents. The analysis of the thermal-hydraulic transient phenomena and the core degradation phenomena is therefore here presented. The analysis of the calculated data shows the capability of the code to reproduce the phenomena typical of these transients and permits their phenomenological study. A first sequence of main events is here presented and shows that the cold leg break transient results faster than the hot leg break transient because of the position of the break. Further analyses are in progress to quantitatively assess the results of the code nodalization for accident management strategy definition and fission product source term evaluation.
Highlights
Following the Fukushima accident events, a particular attention on unmitigated Nuclear Power Plant (NPP) accidents and their mitigation has been addressed by the International Scientific Community [13]
With respect to the activities dedicated to the unmitigated transient analysis in Light Water Reactors (LWR) (e.g. [6,7,8]), the aim of this paper is to present the results of the analysis of MELCOR 2.1 calculations concerning two independent unmitigated Large Break Loss of Coolant Accident (LBLOCA) transients, occurring in the cited type of reactor
Because of the position of the break in the hydraulic circuit and the consequent faster blowdown, the CL1 accident is predicted to be characterized by a complete temporary core uncovery during the blowdown phase and a lower collapsed coolant level increase during the reflooding phase
Summary
Following the Fukushima accident events, a particular attention on unmitigated Nuclear Power Plant (NPP) accidents and their mitigation has been addressed by the International Scientific Community [13] This interest has induced the study of different unmitigated accidents in order to understand their progression and, starting from a thermal hydraulic analysis of the transient, to evaluate their consequences in terms of core damage and fission products release. The analysis and comparison between the transients initiated by an unmitigated doubleended Cold Leg (CL) rupture and an unmitigated double-ended Hot Leg (HL) rupture in the loop 1 of the Primary Cooling System (PCS) is presented This activity has been performed focusing on the in-vessel phenomenology that characterizes this kind of accidents. The thermalhydraulic phenomena analysis, deeply affecting the evolution of both of the transients, and the core degradation processes, caused due to the unmitigated postulated accidents, are here presented
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