STRUCTURAL ASPECTS OF THE ENVIRONMENTALLY ASSISTED CRACKING OF WWER-440 DISSIMILAR WELD JOINTS

This paper deals with the environmentally assisted cracking assessment of the WWER 440 MWe (PWR type) reactor pressure vessel safe-end: this part of the primary circuit was tested in the framework of the LBB ev aluation. The basic metallographic microstructures occurring in the we ldment are described in detail. Particular attention is driven to the ferrite-austenite transition region, containing microstructural elemen ts which can embrittle the material during nuclear power plant service . CT specimens were loaded in both static and cyclic regimes in a high temperature primary circuit environment to assess the stress corrosio n cracking and corrosion fatigue. The stress corrosion cracking tests showed negligible susceptibility to the crack initiation. It is shown that the fusion boundary may be a barrier which can effectively preven t the crack from growing under the static loading. The crack growth ra te was in the range 10(-10) ms(-1), which can not lead to critical cra ck propagation during the nuclear power plant operation. The results o f corrosion fatigue tests showed that the fusion boundary is the weake st area of the weldment. Nevertheless, the kinetics are well below tho se shown in the published ASME XI curve. Copyright (C) 1996 Elsevier S cience Ltd.