CHARACTERIZATION OF IN-SERVICE THERMAL AGING EFFECTS IN BASE METALS AND WELDS OF THE PRESSURE VESSEL OF A DECOMMISSIONED PWR PRESSURIZER, AFTER 27 YEARS OF OPERATION

摘要

In 2012, after the replacement of the Pressurizer ofthe Ringhals 4 nuclear power plant, sections of thedecommissioned pressurizer pressure vessel were cut byRinghals and made available to a group of members ofthe FROG?* Aging Network for investigations onthermal aging. At its decommissioning date, thiscomponent had been in operation for more than ~ 27years (close to 190 000 h) at a temperature close to350°C.The cut sections included pieces of the welds and of theadjacent base metals (BM) between the lower shell ringand the bottom dome. The original base materials of thepressure vessel wall were SA533 Gr B Cl1 plates. TheEnd of Manufacturing Report (EOMR) for the Pressurizerwas also made available, and acceptance tests resultswere retrieved, for comparison with the properties after27 years of operation.Tensile tests and Charpy impact tests were performed inthe in-service-aged conditions. The program wascompleted by some detailed microstructuralinvestigations, including fractographic examinations,Auger electron spectroscopy of grain boundaries, andatom probe tomography observations.The paper presents the results of these investigations andshows that the effects of thermal aging on the ductilebrittletransition temperature are not significant for basematerials and heat affected zone. Some effects aremeasured for weld metals (WM). In the discussion, themeasured embrittlement is related to the variation oftensile properties and the chemical composition of thematerials, in terms of impurity content (phosphorus) andother elements (nickel) of the WM chemical composition.