Influence of Steam Generator Inventory on Severe Core Damage Behaviour During Loss of Coolant Accident with SBO for VVER 1000 (V320)

ABSTRACT

Severe accident analysis of a reactor is an important aspect in evaluation of source term. This in turn helps in emergency planning and Severe Accident Management (SAM). The analyses have been carried out for VVER-1000 (V320) reactor following Loss Of Coolant Accident (LOCA) along with Station Blackout (SBO) and maintaining Steam Generator (SG) Inventory. During SBO the feed pump stops due to loss of power supply. Assessment on core degradation and natural circulation has been done in case the feed water is continued from external power sources which can be considered as a part of SAM. For establishment of natural circulation flow in the degraded core (a higher order of resistance due to blockages etc. as compared to healthy plant) sufficient steam inventory is required which again depends on the break sizes. The assessment is hence carried out for three break sizes in cold leg (covering medium and small break), as they results in different steam water inventory during the course of accident. Unavailability of hydro accumulator is also considered for this study as unavailability leads to worst core conditions. Integral code computer code ASTEC V1.3, jointly developed by ISRN, France, and GRS, Germany) is used for analyzing the transients. In this paper, ASTEC predictions have been studied for the in-vessel phase of the accident. The predictions of different severe accident parameters like natural circulation flow, primary and secondary behaviour, hydrogen and core status (corium production etc.) have been compared.

Keywords: Nuclear reactor,Severe accident management, LOCA and SOB, Thermal hydraulic analysis, Severe code damage.

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