In recent years, within the fusion long-term programmes, attention has been devoted to the charac... more In recent years, within the fusion long-term programmes, attention has been devoted to the characterization of Chromium (Cr) alloys, in view of their elevated corrosion resistance, low activation properties and high-temperature mechanical strength. As part of the European Fusion Programme, an activity has been launched in 1999 with the aim of exploring the potential of Cr alloys as structural materials in fusion reactors, for example, as first wall or blanket materials. Recent investigations have focused attention on two commercially available materials: high-purity 99.7% Cr (DUCROPUR) and Cr alloyed with 5% Fe and 1%Y203 (DUCROLLOY), both of which have shown excellent low activation characteristics. The mechanical properties of these two alloys, in both as-received and heat-treated conditions, have been characterized at SCK•CEN by means of tensile, instrumented impact and static three-point bend tests, using standard and sub-size specimens. Tensile tests have also been carried out on samples irradiated at 300 °C in the BR2 reactor in Mol up to an accumulated dose of about 0.5 dpa.
Rachid Chaouadi, 1 Albert Fabry, 1 Eric van Walle, 1 and Jose Van de Velde1 Fracture Toughness of... more Rachid Chaouadi, 1 Albert Fabry, 1 Eric van Walle, 1 and Jose Van de Velde1 Fracture Toughness of the Ni-Modified A302-B Plate of the ... ON Ni-MODIFIED A302-B PLATE 163 The BR3 reactor, the sister of the Yankee Rowe PWR reactor, was put into operation in 1963 and ...
Effects of Radiation on Materials: 17th International Symposium
The aim of the current study is the application of local micromechanical models to predict crack ... more The aim of the current study is the application of local micromechanical models to predict crack initiation in ductile materials. Two reactor pressure vessel materials have been selected for this study: JRQ IAEA monitor base metal (A533B Cl.1) and Doel-IV weld material. Charpy impact tests have been performed in both un-irradiated and irradiated conditions. In addition to standard tensile tests, notched tensile specimens have been tested. The upper shelf energy of the weld material remains almost un-affected by irradiation, whereas a decrease of 20% is detected for the base metal. Accordingly, the tensile properties of the weld material do not reveal a clear irradiation effect on the yield and ultimate stresses, this in contrast to the base material flow properties. The tensile tests have been analyzed in terms of micromechanical models. A good correlation is found between the standard tests and the micromechanical models, that are able to predict the ductile damage evolution in these materials. Additional information on the ductility behaviour of these materials is revealed by this micromechanical analysis.
Effects of Radiation on Materials: 17th International Symposium
In-service embrittlement of the welds at the Doel I and II pressure vessels displays an apparent ... more In-service embrittlement of the welds at the Doel I and II pressure vessels displays an apparent "outlier" behaviour as compared to the predictions of US NRC Regulatory Guide 1.99 Rev.2. This issue is being addressed by asystematic R&D effort, supplementary to the mandatory surveillance programmes. The status of this effort is reviewed in this paper. The anomalous trends can be outlined as follows. Extensive characterization of the chemical composition of representative test specimens reveals that these low nickel welds, although being nominally identical (same fabrication practice, heat treatment, microstructure,...), do feature an appreciable variability of their bulk copper content - covering a range of 0.13% to 0.35%. High copper Charpy-V weld specimens are however not available in the surveillance capsules. The variability could be identified only because the weld part of some HAZ (heat affected zone) Charpy-V specimens, as well as some tensile specimens, consist of the high copper melt. For the low copper contents, (0.13-0.18%), the 41 J Cv transition temperature shift, as obtained from seven capsules exposed in the neutron fluence range of 1 to 3.9 1019 n/cm 2 (>1 MeV), is rather constant, but significantly larger than predicted (by US NRC Regulatory Guide 1.99 rev.2).This has caused some concern on the upper bound shift to be adopted, given the possibility of higher copper content in the actual pressure vessel welds. High copper samples were manufactured by applying the stud welding reconstitution technique to remnants of the HAZ specimens, and the results cannot be distinguished from the low copper data. Such insensitivity to copper, confirmed by tensile and hardness measurements, is at odds with current literature knowledge and with Regulatory guidelines. A further anomaly observed for this type of weld metal is an appreciable sensitivity to thermal ageing. The surveillance results will be evaluated in accordance with the USNRC Regulatory guide-lines, and the embrittlement trends described above will be thoroughly evaluated from a micromechanical perspective, in the light of a high resolution microstructural investigation.
Effects of Radiation on Materials: 17th International Symposium
Charpy-size tensile specimens have been reconstituted starting from broken Charpy specimens. Prec... more Charpy-size tensile specimens have been reconstituted starting from broken Charpy specimens. Precautions have been taken to prevent fracture in the weld regions of the reconstituted specimens. Careful qualification of the tensile properties of the reconstituted tensile bars has been established and is in agreement with test results on ASTM/E8-size tensile specimens. The tensile properties of the unirradiated weld material of the Belgian PWR Doel 2 and of the unirradiated base metal of the German BWR Philippsburg 1 have been determined using this methodology. Both the resulting yield and maximum loads are in agreement with the actual expectations. Qualification to apply the technique on irradiated specimens is in preparation.
This study aims at assessing the applicability of the Master Curve procedure to the measurement o... more This study aims at assessing the applicability of the Master Curve procedure to the measurement of the reference temperature for three well-characterised reactor pressure vessel steels (22NiMoCr37, JSPS, JRQ). The following aspects of the methodology were investigated, using statistical tools such as the Generalised Maximum Likelihood (GML) and Monte Carlo methods: independence of To from test temperature and specimen type (configuration/dimensions); formula given in ASTM E1921 for evaluating the standard deviation of the reference temperature, and possibile expressions for estimating the standard deviation of the other Weibull parameters (m and Kmin); proposed relationships for estimating the median toughness and standard deviation for To(aTo) in the case of mulfi-temperature Master Curve analysis. In reference to the three Reactor Pressure Vessel Steels (RPVS) investigated, the independence of To was assessed from the test temperature (within the range prescribed by the following revision of the ASTM standard, To 9 50 ~ and, as far as C(T) specimens are concerned, from the sample dimensions; the well-known 10-15 ~ difference was however found between PCCv and C(T) geometries. Furthermore, using the Monte Carlo method, we assessed the relationship proposed by the ASTM standard for estimating the standard deviation of the reference temperature, which results fairly conservative; an alternative analytical function has been proposed. Clear trends have also been identified for the standard deviation of m (with respect to the number of valid data r) and Kmin (with respect to the median toughness). Finally, the proposed relationships for estimating Kjc,med and CrTo for the multi-temperature analysis have been validated by comparison with the results of the Monte Carlo method: an excellent agreement was found in terms of ~rTo (better than 0.2 ~
Fracture of Nano and Engineering Materials and Structures, 2006
In this paper it is described the work performed on the steel coming from a Spanish BWR Nuclear P... more In this paper it is described the work performed on the steel coming from a Spanish BWR Nuclear Power Plant (NPP) vessel currently operating in order to analyse its structural integrity assessment from different procedures. The classical procedures for the characterization of the cuasistatic fracture behaviour in the ductile to brittle transition region [1] are based on conservative correlations obtained from Charpy impact tests. In this work, on the contrary, direct measurements of cuasistatic KJC fracture toughness were performed. The results were analysed according to the recent Master Curve methodology [2] in order to obtain the Reference Temperature, T0, describing fairly the response of the material in such a region.
Mössbauer spectra (MS) at room temperature have been collected for non-irradiated Eastern- and We... more Mössbauer spectra (MS) at room temperature have been collected for non-irradiated Eastern- and Western-type nuclear reactor pressure vessel (RPV) steels. All samples showed a typical Mössbauer spectrum for steels with a low alloy-element concentration. Analysis with distributed hyperfine parameters revealed that the spectra consist of two magnetically split subspectra and that only for the Western-type RPV steels a small doublet
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1996
An advanced positron lifetime setup is described, particularly suited to perform measurements on ... more An advanced positron lifetime setup is described, particularly suited to perform measurements on irradiated nuclear reactor pressure vessel steel. The equipment exists of three BaF,-detectors operated in triple coincidence mode to avoid the very disturbing 60Co-contribution in the lifetime spectra. The use of BaF, scintillators gives rise to an acceptable efficiency and a time resolution well below 300~s.
The RESQUE project aims at optimising and normalising reconstitution techniques and is now in its... more The RESQUE project aims at optimising and normalising reconstitution techniques and is now in its final phase. The project belongs to the AGE-cluster, that also involves the REFEREE project being used as an input to RESQUE. At FISA '97 the reference data on non-reconstituted specimens were presented together with a set of recommendations on temperature measurements (WP1, WP2). Now, the
In the nuclear field, the importance of direct fracture toughness measurements on RPV materials h... more In the nuclear field, the importance of direct fracture toughness measurements on RPV materials has been nowadays widely recognized, as opposed to Charpy-based estimations. However, sample dimensions have to be kept small in order to optimize the use of available material (often in the form of previously broken Charpy specimens) or, in the case of new irradiations, make effective use of the limited space available inside irradiation facilities. One of the most appealing geometries for fracture toughness measurements is the miniature Compact Tension specimen, MC(T), which has the following dimensions: B = 4.15 mm, W = 8.3 mm, cross section 10 × 10 mm². Four MC(T) specimens can be machined out of a broken half Charpy, and in the case of irradiation ten MC(T) samples occupy approximately the same volume as a full-size Charpy specimen. The MC(T) geometry was already successfully applied and qualified for fracture toughness assessments in the ductile-to-brittle transition regime, using the Master Curve method (ASTM E1921-03). A further, comprehensive investigation is presented in this report, aimed at assessing the applicability of MC(T) specimens to measure fracture toughness in fully ductile (upper shelf) conditions. In this study, 18 1TC(T) and 20 MC(T) specimens have been tested at different temperatures from three RPV steels and one low-alloy C-Mn steel. The results obtained clearly show that MC(T) samples exhibit lower fracture toughness properties, both in terms of initiation of ductile tearing (according to various test standards) and resistance to ductile crack propagation (J-R curve). The reduction of tearing resistance might be attributed to work hardening prevailing over loss of constraint in the uncracked ligament in a side-grooved specimen, or to the inadequacy of J-integral to represent ductile crack extension in very small specimens. Both arguments will have to be verified with further investigations.
The Charpy test plays a fundamental role in the nuclear field for evaluating the neutron embrittl... more The Charpy test plays a fundamental role in the nuclear field for evaluating the neutron embrittlement of the reactor pressure vessel, specifically in the framework of the so-called Enhanced Surveillance Approach, developed at SCK·CEN and aimed at extracting as much information as possible from Charpy impact tests performed with an instrumented striker. Careful analysis of the instrumented force/deflection traces allows defining important parameters which can help investigate material characteristics such as flow properties, microcleavage fracture stress, crack arrest behavior and alternative characteristic (index) temperatures. For this advanced approach to be successfully applied, confidence in the quality of instrumented force values must be high; as a consequence, extensive research has been performed in order to establish an optimal procedure for the verification of instrumented Charpy strikers. Various approaches will be described in this paper and their applicability and effectiveness discussed. A procedure based on the comparison between yield stresses measured from tensile tests and calculated from instrumented Charpy curves has recently been adopted at SCK·CEN as the recommended in-house procedure for verifying instrumented strikers. This method has shown that for all strikers investigated, the so-called “dynamic” calibration (based on the equalization of dial and calculated energies) yields the most accurate results.
Broken Charpy specimens from the surveillance program of a Belgian nuclear power plant are used t... more Broken Charpy specimens from the surveillance program of a Belgian nuclear power plant are used to obtain the fracture toughness in the transition regime using the master curve concept. Two approaches are used. The first one is based on the reconstitution of Charpy specimens that are subsequently precracked and tested in three-point bending. The second approach is an innovative one that makes use of miniature Compact Tension specimens, which are machined from the broken pieces of the original Charpy specimens. Both approaches lead to consistent results. The recently developed miniature Compact Tension design has the advantage to use less material and is less costly in terms of machining operation. For the material investigated in this research, the current regulation, based on a semi-empirical approach to obtain the lower bound fracture toughness, is demonstrated to be conservative as compared to the direct fracture toughness determination.
In recent years, within the fusion long-term programmes, attention has been devoted to the charac... more In recent years, within the fusion long-term programmes, attention has been devoted to the characterization of Chromium (Cr) alloys, in view of their elevated corrosion resistance, low activation properties and high-temperature mechanical strength. As part of the European Fusion Programme, an activity has been launched in 1999 with the aim of exploring the potential of Cr alloys as structural materials in fusion reactors, for example, as first wall or blanket materials. Recent investigations have focused attention on two commercially available materials: high-purity 99.7% Cr (DUCROPUR) and Cr alloyed with 5% Fe and 1%Y203 (DUCROLLOY), both of which have shown excellent low activation characteristics. The mechanical properties of these two alloys, in both as-received and heat-treated conditions, have been characterized at SCK•CEN by means of tensile, instrumented impact and static three-point bend tests, using standard and sub-size specimens. Tensile tests have also been carried out on samples irradiated at 300 °C in the BR2 reactor in Mol up to an accumulated dose of about 0.5 dpa.
Rachid Chaouadi, 1 Albert Fabry, 1 Eric van Walle, 1 and Jose Van de Velde1 Fracture Toughness of... more Rachid Chaouadi, 1 Albert Fabry, 1 Eric van Walle, 1 and Jose Van de Velde1 Fracture Toughness of the Ni-Modified A302-B Plate of the ... ON Ni-MODIFIED A302-B PLATE 163 The BR3 reactor, the sister of the Yankee Rowe PWR reactor, was put into operation in 1963 and ...
Effects of Radiation on Materials: 17th International Symposium
The aim of the current study is the application of local micromechanical models to predict crack ... more The aim of the current study is the application of local micromechanical models to predict crack initiation in ductile materials. Two reactor pressure vessel materials have been selected for this study: JRQ IAEA monitor base metal (A533B Cl.1) and Doel-IV weld material. Charpy impact tests have been performed in both un-irradiated and irradiated conditions. In addition to standard tensile tests, notched tensile specimens have been tested. The upper shelf energy of the weld material remains almost un-affected by irradiation, whereas a decrease of 20% is detected for the base metal. Accordingly, the tensile properties of the weld material do not reveal a clear irradiation effect on the yield and ultimate stresses, this in contrast to the base material flow properties. The tensile tests have been analyzed in terms of micromechanical models. A good correlation is found between the standard tests and the micromechanical models, that are able to predict the ductile damage evolution in these materials. Additional information on the ductility behaviour of these materials is revealed by this micromechanical analysis.
Effects of Radiation on Materials: 17th International Symposium
In-service embrittlement of the welds at the Doel I and II pressure vessels displays an apparent ... more In-service embrittlement of the welds at the Doel I and II pressure vessels displays an apparent "outlier" behaviour as compared to the predictions of US NRC Regulatory Guide 1.99 Rev.2. This issue is being addressed by asystematic R&D effort, supplementary to the mandatory surveillance programmes. The status of this effort is reviewed in this paper. The anomalous trends can be outlined as follows. Extensive characterization of the chemical composition of representative test specimens reveals that these low nickel welds, although being nominally identical (same fabrication practice, heat treatment, microstructure,...), do feature an appreciable variability of their bulk copper content - covering a range of 0.13% to 0.35%. High copper Charpy-V weld specimens are however not available in the surveillance capsules. The variability could be identified only because the weld part of some HAZ (heat affected zone) Charpy-V specimens, as well as some tensile specimens, consist of the high copper melt. For the low copper contents, (0.13-0.18%), the 41 J Cv transition temperature shift, as obtained from seven capsules exposed in the neutron fluence range of 1 to 3.9 1019 n/cm 2 (>1 MeV), is rather constant, but significantly larger than predicted (by US NRC Regulatory Guide 1.99 rev.2).This has caused some concern on the upper bound shift to be adopted, given the possibility of higher copper content in the actual pressure vessel welds. High copper samples were manufactured by applying the stud welding reconstitution technique to remnants of the HAZ specimens, and the results cannot be distinguished from the low copper data. Such insensitivity to copper, confirmed by tensile and hardness measurements, is at odds with current literature knowledge and with Regulatory guidelines. A further anomaly observed for this type of weld metal is an appreciable sensitivity to thermal ageing. The surveillance results will be evaluated in accordance with the USNRC Regulatory guide-lines, and the embrittlement trends described above will be thoroughly evaluated from a micromechanical perspective, in the light of a high resolution microstructural investigation.
Effects of Radiation on Materials: 17th International Symposium
Charpy-size tensile specimens have been reconstituted starting from broken Charpy specimens. Prec... more Charpy-size tensile specimens have been reconstituted starting from broken Charpy specimens. Precautions have been taken to prevent fracture in the weld regions of the reconstituted specimens. Careful qualification of the tensile properties of the reconstituted tensile bars has been established and is in agreement with test results on ASTM/E8-size tensile specimens. The tensile properties of the unirradiated weld material of the Belgian PWR Doel 2 and of the unirradiated base metal of the German BWR Philippsburg 1 have been determined using this methodology. Both the resulting yield and maximum loads are in agreement with the actual expectations. Qualification to apply the technique on irradiated specimens is in preparation.
This study aims at assessing the applicability of the Master Curve procedure to the measurement o... more This study aims at assessing the applicability of the Master Curve procedure to the measurement of the reference temperature for three well-characterised reactor pressure vessel steels (22NiMoCr37, JSPS, JRQ). The following aspects of the methodology were investigated, using statistical tools such as the Generalised Maximum Likelihood (GML) and Monte Carlo methods: independence of To from test temperature and specimen type (configuration/dimensions); formula given in ASTM E1921 for evaluating the standard deviation of the reference temperature, and possibile expressions for estimating the standard deviation of the other Weibull parameters (m and Kmin); proposed relationships for estimating the median toughness and standard deviation for To(aTo) in the case of mulfi-temperature Master Curve analysis. In reference to the three Reactor Pressure Vessel Steels (RPVS) investigated, the independence of To was assessed from the test temperature (within the range prescribed by the following revision of the ASTM standard, To 9 50 ~ and, as far as C(T) specimens are concerned, from the sample dimensions; the well-known 10-15 ~ difference was however found between PCCv and C(T) geometries. Furthermore, using the Monte Carlo method, we assessed the relationship proposed by the ASTM standard for estimating the standard deviation of the reference temperature, which results fairly conservative; an alternative analytical function has been proposed. Clear trends have also been identified for the standard deviation of m (with respect to the number of valid data r) and Kmin (with respect to the median toughness). Finally, the proposed relationships for estimating Kjc,med and CrTo for the multi-temperature analysis have been validated by comparison with the results of the Monte Carlo method: an excellent agreement was found in terms of ~rTo (better than 0.2 ~
Fracture of Nano and Engineering Materials and Structures, 2006
In this paper it is described the work performed on the steel coming from a Spanish BWR Nuclear P... more In this paper it is described the work performed on the steel coming from a Spanish BWR Nuclear Power Plant (NPP) vessel currently operating in order to analyse its structural integrity assessment from different procedures. The classical procedures for the characterization of the cuasistatic fracture behaviour in the ductile to brittle transition region [1] are based on conservative correlations obtained from Charpy impact tests. In this work, on the contrary, direct measurements of cuasistatic KJC fracture toughness were performed. The results were analysed according to the recent Master Curve methodology [2] in order to obtain the Reference Temperature, T0, describing fairly the response of the material in such a region.
Mössbauer spectra (MS) at room temperature have been collected for non-irradiated Eastern- and We... more Mössbauer spectra (MS) at room temperature have been collected for non-irradiated Eastern- and Western-type nuclear reactor pressure vessel (RPV) steels. All samples showed a typical Mössbauer spectrum for steels with a low alloy-element concentration. Analysis with distributed hyperfine parameters revealed that the spectra consist of two magnetically split subspectra and that only for the Western-type RPV steels a small doublet
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1996
An advanced positron lifetime setup is described, particularly suited to perform measurements on ... more An advanced positron lifetime setup is described, particularly suited to perform measurements on irradiated nuclear reactor pressure vessel steel. The equipment exists of three BaF,-detectors operated in triple coincidence mode to avoid the very disturbing 60Co-contribution in the lifetime spectra. The use of BaF, scintillators gives rise to an acceptable efficiency and a time resolution well below 300~s.
The RESQUE project aims at optimising and normalising reconstitution techniques and is now in its... more The RESQUE project aims at optimising and normalising reconstitution techniques and is now in its final phase. The project belongs to the AGE-cluster, that also involves the REFEREE project being used as an input to RESQUE. At FISA '97 the reference data on non-reconstituted specimens were presented together with a set of recommendations on temperature measurements (WP1, WP2). Now, the
In the nuclear field, the importance of direct fracture toughness measurements on RPV materials h... more In the nuclear field, the importance of direct fracture toughness measurements on RPV materials has been nowadays widely recognized, as opposed to Charpy-based estimations. However, sample dimensions have to be kept small in order to optimize the use of available material (often in the form of previously broken Charpy specimens) or, in the case of new irradiations, make effective use of the limited space available inside irradiation facilities. One of the most appealing geometries for fracture toughness measurements is the miniature Compact Tension specimen, MC(T), which has the following dimensions: B = 4.15 mm, W = 8.3 mm, cross section 10 × 10 mm². Four MC(T) specimens can be machined out of a broken half Charpy, and in the case of irradiation ten MC(T) samples occupy approximately the same volume as a full-size Charpy specimen. The MC(T) geometry was already successfully applied and qualified for fracture toughness assessments in the ductile-to-brittle transition regime, using the Master Curve method (ASTM E1921-03). A further, comprehensive investigation is presented in this report, aimed at assessing the applicability of MC(T) specimens to measure fracture toughness in fully ductile (upper shelf) conditions. In this study, 18 1TC(T) and 20 MC(T) specimens have been tested at different temperatures from three RPV steels and one low-alloy C-Mn steel. The results obtained clearly show that MC(T) samples exhibit lower fracture toughness properties, both in terms of initiation of ductile tearing (according to various test standards) and resistance to ductile crack propagation (J-R curve). The reduction of tearing resistance might be attributed to work hardening prevailing over loss of constraint in the uncracked ligament in a side-grooved specimen, or to the inadequacy of J-integral to represent ductile crack extension in very small specimens. Both arguments will have to be verified with further investigations.
The Charpy test plays a fundamental role in the nuclear field for evaluating the neutron embrittl... more The Charpy test plays a fundamental role in the nuclear field for evaluating the neutron embrittlement of the reactor pressure vessel, specifically in the framework of the so-called Enhanced Surveillance Approach, developed at SCK·CEN and aimed at extracting as much information as possible from Charpy impact tests performed with an instrumented striker. Careful analysis of the instrumented force/deflection traces allows defining important parameters which can help investigate material characteristics such as flow properties, microcleavage fracture stress, crack arrest behavior and alternative characteristic (index) temperatures. For this advanced approach to be successfully applied, confidence in the quality of instrumented force values must be high; as a consequence, extensive research has been performed in order to establish an optimal procedure for the verification of instrumented Charpy strikers. Various approaches will be described in this paper and their applicability and effectiveness discussed. A procedure based on the comparison between yield stresses measured from tensile tests and calculated from instrumented Charpy curves has recently been adopted at SCK·CEN as the recommended in-house procedure for verifying instrumented strikers. This method has shown that for all strikers investigated, the so-called “dynamic” calibration (based on the equalization of dial and calculated energies) yields the most accurate results.
Broken Charpy specimens from the surveillance program of a Belgian nuclear power plant are used t... more Broken Charpy specimens from the surveillance program of a Belgian nuclear power plant are used to obtain the fracture toughness in the transition regime using the master curve concept. Two approaches are used. The first one is based on the reconstitution of Charpy specimens that are subsequently precracked and tested in three-point bending. The second approach is an innovative one that makes use of miniature Compact Tension specimens, which are machined from the broken pieces of the original Charpy specimens. Both approaches lead to consistent results. The recently developed miniature Compact Tension design has the advantage to use less material and is less costly in terms of machining operation. For the material investigated in this research, the current regulation, based on a semi-empirical approach to obtain the lower bound fracture toughness, is demonstrated to be conservative as compared to the direct fracture toughness determination.
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Papers by E. Van Walle