Effects of residual stress by weld overlay cladding and PWHT on the structural integrity of RPV during PTS

Udagawa, Makoto; Katsuyama, Jinya  ; Onizawa, Kunio 

In order to assess the structural integrity of a reactor pressure vessel (RPV), it is assumed that a surface crack resides through the cladding at the inner surface of the vessel. It is, therefore, important to precisely evaluate stress intensity factor (SIF) taking the residual stress due to weld overlay cladding and post-weld heat treatment (PWHT) into account. In this study, we performed a numerical simulation based on thermal-elastic-plastic-creep analysis using finite element method to evaluate residual stress distribution near the cladding layer produced by weld overlay cladding and PWHT. The tensile residual stress of about 400 MPa occurs in the cladding at room temperature after the PWHT. The residual stress distributions under the normal operating conditions (pressure and temperature) of RPV were also evaluated. The effect of residual stress and evaluation methods on SIF behavior for various crack size were studied under several PTS conditions such as SBLOCA, MSLB and LBLOCA.