The increasing age of European nuclear power plants and envisaged extensions of reactor pressure vessel (RPV) lifetimes up to 80 years require the accurate prediction and management of RPV neutron irradiation embrittlement. LONGLIFE (“Treatment of long term irradiation embrittlement effects in RPV safety assessment”) is a collaborative project of the seventh Framework Programme of EURATOM. This project has been initiated as the next step forward towards obtaining an improved understanding of irradiation effects in RPV steels under conditions representative of long term operation (LTO) of RPVs. Phenomena that might become important at high neutron fluences (such as late-blooming effects and flux effects) must be considered in detail as part of the process of upgrading safety assessments and embrittlement surveillance procedures to underwrite the safety of LTO of RPVs. The work starts with the collection and evaluation of plantspecific information and data, such as target neutron fluences for LTO and the chemical compositions of the materials. This includes a survey of available results of RPV materials data from decommissioned plants of validating surveillance data and specific irradiation effects relevant for LTO. Microstructural data are obtained from different techniques with the aim of assessing the adequacy of current dose-damage models with respect to their relevance to the mechanisms of irradiation damage associated with LTO of RPVs. Complementary mechanical tests are performed in order to address gaps in existing experimental data. Microstructural data pertaining to the evolution of Manuscript received June 7, 2011; accepted for publication April 4, 2012; published online December 17, 2012. Helmholtz-Zentrum Dresden-Rossendorf HZDR, D-01314 Germany (Corresponding author), e-mail: e.altstadt@hzdr.de Helmholtz-Zentrum Dresden-Rossendorf HZDR, D-01314 Germany. AREVA NP GmbH, Erlangen, D-91052 Germany. Copyright VC 2012 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. 3 Effects of Radiation on Nuclear Materials: 25th Volume STP 1547, 2012 Available online at www.astm.org DOI:10.1520/STP104113 Copyright by ASTM Int'l (all rights reserved); Fri Aug 29 03:32:26 EDT 2014 Downloaded/printed by Edith Reschke (Helmholtz-Zentrum Dresden-Rossendorf) pursuant to License Agreement. No further reproductions authorized. irradiation damage are correlated with changes in mechanical properties, and the most important influencing factors will be identified. Surveillance guidelines for LTO of RPV base materials and welds will be developed as one of the principal outputs of the project. The scope of work and the project structure are outlined in the paper. Two LTO relevant phenomena—late blooming effect and flux effect—are discussed in more detail.

Long Term Irradiation Phenomena in RPV Steels—The LONGLIFE Project

The integrity of the pressure vessel is vital to the safe operation of a nuclear reactor. It is therefore necessary to monitor or predict the changes in the reactor pressure vessel (RPV) material during operation. Exposure to irradiation (or elevated temperatures) causes the segregation of phosphorus to internal grain boundaries in RPV steels. This, in turn, encourages brittle intergranular failure of the material. The PISA project had the objective of reducing the uncertainties associated with the impact of this failure mechanism on the properties of the RPV, both during service and at the end-of-life. This report presents the experimental results on the segregation of P and C during irradiation and thermal treatments, and the associated mechanical property changes, generated within PISA. The new data cover a range of bulk P levels, irradiation temperatures and fluences, steel types and product forms. In all cases only modest increases of P level on the grain boundary have been observed in commercial steels. Segregation is higher in pre-strained than in unstrained material. In addition a model for P segregation under irradiation has been developed, and shown to be capable of fitting the experimentally observed changes in P level after irradiation. Significant insight into the development of the microstructure under irradiation has thereby been obtained. Overall, the data and modelling together indicated that relatively small amounts of segregation are likely to occur under most reactor operational conditions in homogeneous commercial steels, and an (unexpectedly) small amount of additional embrittlement likely to derive from this process during reactor service. How to obtain EU publications Our priced publications are available from EU Bookshop (http://bookshop.europa.eu), where you can place an order with the sales agent of your choice. The Publications Office has a worldwide network of sales agents. You can obtain their contact details by sending a fax to (352) 29 29-42758. The mission of the JRC is to provide customer-driven scientific and technical support for the conception, development, implementation and monitoring of EU policies. As a service of the European Commission, the JRC functions as a reference centre of science and technology for the Union. Close to the policy-making process, it serves the common interest of the Member States, while being independent of special interests, whether private or national.

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Ballesteros Avila Antonio

Papers

Project PISA: Phosphorus Influence on Steel Ageing