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Project PISA: Phosphorus Influence on Steel Ageing

01 Jan 2008-

AbstractThe 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.

Topics: Reactor pressure vessel (52%)

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Book ChapterDOI
01 Jan 2013
Abstract: 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.

References
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Journal ArticleDOI
Abstract: The thermodynamics of co-segregation and precipitation of P and alloying elements (transition metals M and carbon) involved in temper embrittlement of steels are studied quantitatively on the basis of the regular solution model for co-segregation. The equations of this model are fitted to the available Auger data for grain boundary segregation in high purity iron-base alloys and commercial steels, allowing the determination of the intrinsic segregation energies ΔGi o and of the binary βP gb, βc gb and ternary βPC gb, sMP gb interaction coefficients in the grain boundaries. This analysis shows that Ni, Cr, and Mo do not segregateper se in iron whereas Mn does weakly, and that the segregation of these elements is essentially driven by that of P through the strongβMP gb attractive interaction energyat the boundaries. This energy, which increases in the order Ni, Mn, Cr, Mo, is remarkably close to the bulk values βMP B in the corresponding phosphides as calculated on the basis of solubility data. The scavenging of P by M elements with largebulk M-P interactions is shown to play a determining role in low Mo and high (12 pct) Cr steels. The beneficial role of carbon is complex since it drives Mo to the grain boundaries due to the large Mo-C attraction, but it also strongly opposes P segregation due to the large repulsive P-C interaction.

137 citations


Journal ArticleDOI
Abstract: Russian reactor pressure vessel steels have been studied in three conditions: initial, irradiated and annealed. It has been established that irradiation induces both intergranular as well as intragranular phosphorus segregation. Fractographic studies demonstrated that brittle intergranular and ductile intergranular fracture surfaces of Charpy specimens appear as a result of intergranular and intragranular segregation, respectively. Transmission electron microscope (TEM) studies have revealed radiation-induced precipitates on interface boundaries to which intragranular phosphorus segregation occurs. Auger electron spectroscopy (AES) has been applied to detect phosphorus enrichment of fracture surfaces in the regions of brittle and ductile intergranular fractures.

43 citations


Journal ArticleDOI
Abstract: Results of phosphorus, copper and nickel effect on radiation induced yield stress increase and ductile-to-brittle transition temperature (DBTT) shift are presented. The synergetic interaction between phosphorus and nickel is observed. The results of Russian VVER-440 and VVER-1000 surveillance programs and results of research programs on reactor pressure vessel (RPV) steel irradiation in surveillance channels of power reactors are discussed. The basic regularities of VVER-440 and VVER-1000 RPV steel are discussed. Trend curves for VVER-440 and VVER-1000 RPV steels are developed. The annealing effectiveness for VVER-440 and VVER-1000 RPV steel grades was compared. DBTT recovery of VVER-1000 RPV steels was found to be much lower than for VVER-440 RPV steels. Nickel was supposed to increase the post-irradiation residual DBTT shift of VVER-1000 type steels. Models for prediction of the post-irradiation residual DBTT shift of VVER-440 and VVER-1000 type steels were suggested.

34 citations


Journal ArticleDOI
Abstract: Grain-boundary segregation in the Fe–P–C system has been examined using Auger Electron Spectroscopy on specimens which were cooled slowly to various intermediate temperatures after equilibration at 600°C, and then quenched prior to examination. The aim was to monitor the segregation of phosphorus and carbon through temperature ranges which offered the extremes of both solutes having long-range lattice mobility to that where only carbon was mobile. This approach revealed new complexities in the segregation process. It was found that phosphorus continued to segregate during the early stages of both furnace and air cooling, i.e. when long-range lattice diffusion remained possible. At intermediate temperatures, when the mobility of phosphorus was limited, an apparently competitive process occurred between the solutes, i.e. phosphorus de-segregated whilst the grain-boundary concentration of carbon increased. At temperatures less than approximately 200°C, carbon segregation continued under furnace cooling but not under air cooling but in neither case did phosphorus continue to de-segregate. A theoretical framework is developed which can account qualitatively for these segregation characteristics.

30 citations