Thermomechanical Analysis of a Reactor Pressure Vessel under Pressurized Thermal Shock Caused by Inadvertent Actuation of the Safety Injection System

M Annor-Nyarko,Hong Xia,Abiodun Ayodeji,George Bakos

doi:10.1155/2022/5886583

Abstract

The damage induced pressurized thermal shock (PTS) may pose to a reactor pressure vessel (RPV) is a critical safety requirement assessed as part of the ageing management programme of pressurized water reactors (PWRs). A number of researches have studied PTS initiated mainly by postulated accidents such as loss of coolant accidents (LOCAs). However, investigations on PTS-induced threat on RPV caused by inadvertent actuation of the safety injection, a frequent anticipated transient, have not been thoroughly studied. In this paper, a simplified multistep analysis method is applied to study the thermomechanical status of a two-loop PWR under PTS loads caused by inadvertent actuation of the safety injection system. A direct-coupling thermomechanical analysis is performed using a three-dimensional (3D) RPV finite element model. A 3D finite element submodel (consisting of the highiest stress concentration area in the RPV) and an assumed crack are then used to perform fracture mechanics analysis. Subsequently, the critical integrity parameter-stress intensity factor (SIF) is estimated based on FRANC3D-M-integral method coupled in the multistep simulation. The material fracture toughness of the vessel is computed based on the master curve method with experimental fracture toughness data. The results obtained from the direct coupling stress analysis in comparison with sequential coupling approach demonstrate the effectiveness of the proposed multistep method. Also, comparing SIF results obtained with that calculated based on the conventional virtual crack-closure technique (VCCT) and extended finite element method (XFEM) show good agreement. This study provides a useful basis for future studies on anticipated transient-induced crack propagation and remaining service life prediction of ageing reactor pressure vessels.

Highlights

IntroductionA typical PWR’s safety injection system (SIS) consists of four pumps classified as high-pressure safety injection (HPSI) pumps
Direct ermomechanical Analysis. e direct thermomechanical coupling simulation using the numerical model and assumed boundary conditions defined in Section 3.3 was executed in Abaqus commercial software following the simplified multistep simulation procedure shown in Figure 3. e direct simulation process computed the thermomechanical stresses by the simultaneous coupling of the thermal and pressure loads of the selected PTS transient (Figure 2). is modeling and simulation were to estimate the highest stress concentration area in the finite element (FE)
Inadvertent actuation of the safety injection system is a critical anticipated transient that frequently occurs in the lifetime of PWRs. is anticipated transient induces PTS that may have an effect on the structural health of an ageing PWR's RPV; it is important to estimate the RPV material’s thermomechanical status under such asymmetric cyclic loads

Summary

Introduction

A typical PWR’s SIS consists of four pumps classified as high-pressure safety injection (HPSI) pumps. Two inlets pumps of the SIS are linked through power-operated isolation valves to a refueling water storage tank (RWST). The shutdown margin pump’s outlets are connected to the inlets of the two HPSI pumps. Ese pump outlets are linked to a pipe header with discharge channels connected to the cold or hot legs of the coolant system. Following the operation of the injection system, the high-pressure pumps cause the cooling water from the RWST to be released into the core of the reactor [18]. Transient incidents that cause the unintentional injection of cooling water directly into the RPV’s downcomer give rise to high pressurizer levels. The recurrent inadvertent actuation of the SIS during the operational service life of PWR either by a reactor operator error or by a control system misfunction may induce high thermal stresses in the nozzles or inner vessel wall [4, 5]

Methods

Results

Conclusion