Total loss of feedwater accident for VVER-1000/V446 NPP with operator action

Abstract

The main purpose of this study is to analyse the response of VVER-1000/V446 Nuclear Power Plant (NPP) during Total Loss of Feedwater (TLFW) accident categorised as a Beyond Design Basis Accident (BDBA). During the accident, working fluid level decreases in all Steam Generators (SGs) which interrupts heat removal and the primary side pressure increases. Accordingly, Pressuriser (PRZ) Pulse Safety Devices (PSDs) discharge the inventory of primary side which could lead to core damage, if not managed properly. The certain strategy called the Feed & Bleed (F&B) recovery procedure could be employed to prevent core damage. In this study, the primary side F&B strategy is investigated to demonstrate core cooling capability of the reactor. The results are compared with those reported in Bushehr NPP unit 1 Final Safety Analyses Report (FSAR) and relatively good agreement is observed between them. Moreover, based on a set of sensitivity analyses the threshold of operators' action time to initiate the mitigation strategy and the least required equipment to manage the accident are determined. It is observed that one PRZ PSD is capable of reducing the pressure of the primary side and at least one High-Pressure Injection System (HPIS) pump is required to rescue the core.