Best Estimate Analysis for RHR Pump Failure in Two Loops PWR

Abdul Wasay Khan


This paper presents an examination of the consequences of a hypothetical failure of the Residual Heat Removal (RHR) system during the shutdown operating mode, in a two loops Pressurized Water Reactor (PWR).

The purpose of the analyses presented in this paper is to determine: (i) the time window for the operator to put the standby train in operation (ii) the time for the pressurizer Power Operated Relief Valve (PORV) opening & (iii) the time window for the start of boiling of the core coolant. A best estimate analysis of this scenario has been performed using the system code RELAP5/mod3.4 for a two-loops PWR. The RHR train in operation is assumed failed at Reactor Coolant System (RCS) average temperature (~447.15K) and at pressure (~2.94MPa).

The results of the analysis show that RCS becomes solid at 3490 seconds. After solidification the RCS pressure overshoots to pressurizer PORV setpoint. There is a time window of less than 1 h (3530 seconds) for the operator to put the standby RHR train in operation. The pressurizer pressure reaches in 3560 seconds to PORV opening set point (3.92 MPa) and boiling in RCS starts at 9195 seconds (~2.6 h). The pressure rise caused by the expansion of the RCS inventory is thus kept within acceptable limits for at least 2.6 h. After this time, the average primary circuit temperature reaches saturation and vapor production in the RCS increases, causing the PORV to remain permanently open.



PWR shutdown; RHR isolation valve; RELAP5; accident analysis; deterministic safety analysis


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