DEVELOPMENT OF A ROBUST PROCEDURE FOR THE EVALUATION OF STRIATION SPACINGS IN LOW CYCLE FATIGUE SPECIMENS TESTED IN A SIMULATED PWR ENVIRONMENT

A pressurized water reactor primary environment can have a deleterious effect on the fatigue lifetime of austenitic stainless steels. There is a need to develop a greater understanding behind the effect of a pressurized water reactor primary environment on the fatigue behaviour of austenitic stainless steels. One of the ways that we can improve our mechanistic understanding is by carrying out striation spacing analysis. Striation counting is a widely used technique in fatigue failure investigations where it is typically used to infer information on crack progression, including the estimation of propagation rates and number of applied loading cycles. Standardised procedures for performing striation counting are uncommon, especially for environmental fatigue in a high temperature pressurized water reactor primary water environment where differences in fracture surface morphology and oxide coverage can lead to additional complications in performing an analysis. One of the main goals of the EU Horizon 2020 INCEFA-SCALE project is to develop an improved mechanistic understanding of fatigue in these systems through extensive characterisation of laboratory tested specimens. As part of this work, this paper describes the development of a standardised and robust striation counting procedure for the low cycle fatigue of austenitic stainless steels operating in both air and simulated pressurized water reactor environments. Additionally, results are presented from round robin exercises that involved eight partners of the INCEFA-SCALE consortium

A52M/SA52 Dissimilar Metal RPV Repair Weld : Experimental Evaluation and Post-Weld Characterizations

Aging management of the existing fleet of nuclear power plants is becoming an increasingly important topic, especially as many units are approaching their design lifetimes or are entering long-term operation. As these plants continue to age, there is an increased probability for the need of repairs due to extended exposure to a harsh environment. It is paramount that qualified and validated solutions are readily available. A repair method for a postulated through cladding crack into the low alloy steel of a nuclear power plant’s reactor pressure vessel has been investigated in this study. This paper is part of larger study that evaluates the current possibilities of such repair welds. The present paper documents the weld-trials and method selection. A parallel paper describes numerical simulations and optimization of weld parameters. The presented weld-trial represents a case where a postulated crack has been excavated and repaired using a nickel base Alloy 52M filler metal by gas metal arc welding-cold metal transfer with a robotic arm. A SA235 structural steel has been used as a base material in this weld-trial. No pre-heating or post-weld heat treatment will be applied, as it would be nearly impossible to apply these treatments in a reactor pressure vessel repair situation. While Alloy 52M presents good material properties, in terms of resistance to environmentally assisted degradation mechanisms, such as primary water stress corrosion cracking, it is notoriously difficult to weld. Some difficulties and challenges during welding include a sluggish weld puddle, formation of titanium and/or aluminium oxides and its susceptibility to lack of fusion defects and weld metal cracking, such as ductility dip cracking and solidification cracking. Moreover, gas metal arc welding-cold metal transfer is not traditionally used in the nuclear industry. Nonetheless, it presents some interesting advantages, specifically concerning heat input requirements and automation possibilities, as compared to traditional welding methods. The mechanical properties, in terms of indentation hardness, and microstructure of a weld-trial sample have been evaluated in this study. The fusion boundary and heat affected zone were the main areas of focus when evaluating the mechanical and microstructural properties. Detailed microstructural characterization using electron backscatter diffraction and nanoindentation were performed across the weld interface. Based on these results, the gas metal arc welding cold metal transfer is seen as a potential high-quality weld method for reactor pressure vessel repair cases.acceptedVersionPeer reviewe

INCEFA-PLUS Findings on Environmental Fatigue

INCEFA-PLUS is a five year project supported by the European Commission HORIZON2020 programme. The project concluded in October 2020. 16 organisations from across Europe have combined forces to deliver new experimental data which is being used to develop improved guidelines for assessment of environmental fatigue damage to ensure safe operation of nuclear power plants. Within INCEFA-PLUS, the effects of mean strain and stress, hold time, strain amplitude and surface finish on fatigue endurance of austenitic stainless steels in light water reactor environments have been studied experimentally. This document constitutes a Reference Book compiling the research developed within the INCEFA-PLUS Project. It provides a comprehensive overview of the tasks performed, and it also presents the background and the assumptions taken to develop the INCEFA-PLUS experimental and analytical works. It compiles and orders documents and contributions from INCEFA-PLUS partners.This project has received funding from the Euratom research and training program 2014-2018 under grant agreement No 662320