- Email: [email protected]
Extended analysis of VVER-1000 surveillance data
International Journal of Pressure Vessels and Piping 79 (2002) 661–664 www.elsevier.com/locate/ijpvp
Extended analysis of VVER-1000 surveillance data A. Kryukova,*,1, D. Eraka, L. Debarberisb, F. Sevinib, B. Acostab b
a RRC-KI, Moscow, Russian Federation Joint Research Centre (JRC) of the European Commission, Institute for Advance Materials, JRC-IAM, Petten JRC, P.O. Box 2, Petten, The Netherlands
Abstract Up to now 20 surveillance specimen sets of 14 VVER-1000 Reactor Pressure Vessel (RPV) have been evaluated in Russia, Ukraine and Bulgaria by different testing organisations: † Kurchatov Institute, Russia (10 RPVs); † Institute for Nuclear Research, Ukraine (two RPVs); † Institute of Metal Science, Bulgaria (two RPVs). The extended analysis presented here is based on the results of 17 surveillance sets testing results of surveillance programmes. The materials involved contain very low and homogeneous levels of phosphorus and copper and a significant variation of nickel and other elements like manganese, etc. The observed temperature transition shifts are showing consistent behaviour: † The steels with low nickel content are embrittling at a much lower rate than the one predicted by the Guide (chemistry factor ¼ 20). † The Guide looks to be conservative also for the higher nickel steels if the content of manganese is lower than 0.8 wt%. † The steels embrittling at much higher rates are those with high nickel and high manganese contents at the same time. The threshold for nickel is evaluated to be at Ni . 1.5 wt% and for manganese at Mn . 0.8 wt%. Manganese, together with nickel, seems to play a key role in low Cu and P steels embrittlement [1,2]. Correlation analysis which considers Ni and Mn and fluence dependence to 1/3 power are showing predictive capabilities within 20 8C scatter band in most cases. Other elements, like, for example, carbon and sulphur could also explain the residual scatter in the data [3]. q 2002 Published by Elsevier Science Ltd. Keywords: VVER-1000 surveillance data; Steel embrittlement; Correlation analysis
1. Materials The materials involved in this analysis are given in Table 1 together with their nominal compositions. Actual specific NPP material composition differs significantly from the nominal and it is used for this extended analysis. The contents of P and Cu are very low; so low that the two elements are not playing significant role in neutron embrittlement. A high level of nickel is characterising both the base metal and particularly the welds material.
* Corresponding author. E-mail address: [email protected] (A. Kryukov). 1 Visiting scientist at JRC. 0308-0161/02/$ - see front matter q 2002 Published by Elsevier Science Ltd. PII: S 0 3 0 8 - 0 1 6 1 ( 0 2 ) 0 0 0 6 9 - 8
Based on the reported chemistry factor provided by the Russian Guide PNAE, CFmax, see Table 1, it is evident that the critical materials are: † Welds 10ChGNMAA and † Base metal 15Ch2NMFA which need to be more carefully investigated.
2. Extended analysis of surveillance results on 10CHGNMAA weld irradiation embrittlement The observed temperature shifts for all considered surveillance sets have been analysed as a function of fluence.
662
A. Kryukov et al. / International Journal of Pressure Vessels and Piping 79 (2002) 661–664
Table 1 VVER-1000 materials Material
Nimax (%)
Pmax (%)
Cumax (%)
CFmax
Remarks
15Ch2NMF(AA) 15Ch2NMF(A) 08ChGNMTA 10ChGNMAA
1.4 1.4 1.3 1.9
0.010 0.010 0.014 0.014
0.07 0.17 0.08 0.08
23 29 20 20a
All RPVs except 3 3 RPVs ,20% RPV welds ,80% RPV welds
a
According to actual analysis this value could be up to 34. Fig. 2. Observed DBTT shifts for Ni ¼ 1:7 wt% and medium Mn content.
As expected, for such a low level in P and Cu contents, P ¼ 0:005 – 0:010 wt%; Cu ¼ 0:03 – 0:08 wt%; no significant role of P and Cu is observed. All results together are shown in Fig. 1. On the same figure, a trend curve according to the Russian Guide with Af ¼ 20 is also drawn. Data have been subdivided into three groups in order to put in evidence the following. As it can be seen, all steels with low nickel content are embrittling at a much lower rate than predicted by the Russian Guide. The Russian Guide is in this case very conservative [4]. The Russian Guide is conservative also for the higher nickel steels provided that the content of manganese is low. The steels embrittling at much higher rates are those with high nickel and high manganese contents. The threshold for nickel is Ni . 1.5 wt%. The threshold for manganese is Mn level . 0.8 wt%. Other elements could play a role in combination with Ni and Mn; including C, Si, S, etc. The earlier mentioned observations are in agreement with recent findings. Mn and Ni are the elements to become non-randomly distributed and co-segregated in welds with high Ni and low Cu. 2.1. Examples of the detailed data analysis In Figs. 2 – 4, the results for specific NPP steels containing Ni ¼ 1:7; 1.88 and 1.76 wt% are given, respectively. The data shown in Fig. 2 are for steel containing low levels of manganese, Mn , 0:8 wt%; while the data in Figs. 3 and 4 are for higher Mn contents.
Fig. 1. Observed temperature transition shifts as a function of fluence. All analysed data sets.
Independently of some uncertainties on the data, it is very clear that the data for each individual material composition are quite consistent. Most of the data for the same material still follow a 1/3 power function of the fluence in spite of some uncertainty in fluence determination itself. The differences in nickel and manganese content can explain the large difference in sensitivity to embrittlement. The content of other elements, like residual S, C, Si, etc. could even explain some minor deviations from the general trend. A correlation analysis is presented in Section 3.
3. Correlation analysis The data sets have been studied by using statistical correlation analysed taking Ni and Mn as variables and a 1/3 dependence with neutron fluence in the form of: Shift ¼ ðaNi þ bMn þ cÞ £ F1=3 The results are shown in Fig. 5. All data sets are nicely aligned to the diagonal of the plot, and most of them are laying within a scatter band of just 20 8C. The result is impressive considering the various uncertainties; scatter in fluence values, data treatment between different laboratories, and in particular the different content of S and C and other elements. Such parameters, when properly known, can be considered for more advanced predictive correlations. Just as example, the content of the residual S has been considered and the results for a subset of data with narrow S
Fig. 3. Observed DBTT shifts for Ni ¼ 1:88 wt% and high Mn content.
A. Kryukov et al. / International Journal of Pressure Vessels and Piping 79 (2002) 661–664
663
Fig. 4. Observed DBTT shifts for Ni ¼ 1:76 wt% and high Mn content.
content variation are shown in Fig. 6. The scatter band is already reduced when compared with the previous regression; most of the points are laying within a 15 8C scatter band now. The observed average chemistry factor CF for steels with high nickel content has also been calculated and is given in Fig. 7 as a function of Mn. Clearly values of CF higher than 20, up to 30 and more, are observed for Mn contents higher than , 0.8 wt%.
4. Conclusions The results are based on the results of 17 of surveillance programmes of 14 VVER-1000 Reactor Pressure Vessel (RPV) tested in Russia, Ukraine and Bulgaria by different testing organisations: Kurchatov Institute, Russia, Institute for Nuclear Research, Ukraine, Institute of Metal Science, Bulgaria. Based on the earlier mentioned results, a key to understand VVER-1000 steel embrittlement is found in spite of the uncertainties in the surveillance data set. Manganese and possibly other elements, in combination with the nickel content, are playing a significant role in the embrittlement of low Cu and P steels.
Fig. 5. Transition temperature shifts; measured versus calculated. For all NPPs.
Fig. 6. Transition temperature shifts; measured versus calculated. For a subset of data.
The materials involved are very low phosphorus and copper steels; with significant variation of nickel and other elements like manganese. The observed temperature transition shifts are showing consistent behaviour: † the steels with low nickel content are embrittling at a much lower rate than predicted by the Russian Guide ðAf ¼ 20Þ: † The Russian Guide is conservative also for the higher nickel steels if the content of manganese is medium. † The steels embrittling at much higher rates are those with high nickel and high manganese contents at the same time. The threshold for nickel is evaluated to be at Ni . 1:5 wt% and for manganese at Mn . 0:8 wt%. Manganese, with nickel, seems to play a key role in low Cu and P steels embrittlement. Correlation analysis which considers Ni and Mn and fluence dependence to 1/3 power is showing predictive capabilities within 20 8C scatter band in most cases. Other elements, like, for example, carbon and sulphur could also explain the residual scatter in the data.
Fig. 7. Average CF versus manganese content.
664
A. Kryukov et al. / International Journal of Pressure Vessels and Piping 79 (2002) 661–664
Further study need to be done in order to build more precise predictive correlations and update the Russian Guide.
5. Recommendation for future activities A more precise analysis in order to reduce the uncertainties can be done in co-operation with the VVER1000 Surveillance Testing Laboratories. Such a precise analysis for VVER-1000 surveillance data must be performed as soon as possible in order to allow for improved: † RPV integrity assessment; † Plant life prediction; † Mitigation methods/plant life management. The following steps need to be undertaken: 1. Harmonisation of the method for transition temperature determination for involved testing laboratories (common database, training, Round-robin and/or Benchmarking exercise). 2. More precise assessment of Ukrainian and Bulgarian testing results, e.g. Individual fluence value for each specimen; verification of actual fluence rates, etc. 3. Decrease of data scatter by using re-constitution of broken Charpy specimens (based on the experience
acquired in TACIS 96 projects and AMES projects like RESQUE, etc.). 4. Direct measurement of the irradiation temperature of surveillance specimens. 5. Launch AMES projects and studies on the subjects [5]. 6. Possible update of the Russian Guide.
References [1] Debarberis L. The effect of nickel, phosphorus and copper in irradiation embrittlement of RPV steel model alloys. NATO International Workshop on RP Vessel Embrittlement, Varna, Bulgaria; September 2000. [2] Debarberis L, To¨rro¨nen K, Sevini F, Acosta B, Kryukov A, Nikolaev Y, Valo M. Experimental studies of copper, phosphorus and nickel effect on RPV Model alloys at two different fluences. Sixth International Conference on Materials Issues in Design, Manufacturing and Operation of NPP Equipment, VTT, St Petersburg, Russia; 19 –23 June 2000. [3] To¨rro¨nen K, Crutzen S, Debarberis L, von Estorff U, Stamm H, Markgraf J, Sordon G. RPV steel embrittlement experimental and modelling studies at the Institute for Advanced Materials, IAM, KTG Germany. [4] Kryukov A, Debarberis L. Achievements, open issues and developments on VVER RPV irradiation embrittlement assessment and AMES European Network Strategy. IAEA Specialist Meeting on Irradiation Embrittlement, Madrid; 1999, PLIM þ PLEX. [5] Sevini F, Debarberis L, Davies M. The European Network AMES. Sixth International Conference on Materials Issues in Design, Manufacturing and Operation of NPP Equipment, St Petersburg, Russia; 19–23 June 2000.
Extended analysis of VVER-1000 surveillance data A. Kryukova,*,1, D. Eraka, L. Debarberisb, F. Sevinib, B. Acostab b
a RRC-KI, Moscow, Russian Federation Joint Research Centre (JRC) of the European Commission, Institute for Advance Materials, JRC-IAM, Petten JRC, P.O. Box 2, Petten, The Netherlands
Abstract Up to now 20 surveillance specimen sets of 14 VVER-1000 Reactor Pressure Vessel (RPV) have been evaluated in Russia, Ukraine and Bulgaria by different testing organisations: † Kurchatov Institute, Russia (10 RPVs); † Institute for Nuclear Research, Ukraine (two RPVs); † Institute of Metal Science, Bulgaria (two RPVs). The extended analysis presented here is based on the results of 17 surveillance sets testing results of surveillance programmes. The materials involved contain very low and homogeneous levels of phosphorus and copper and a significant variation of nickel and other elements like manganese, etc. The observed temperature transition shifts are showing consistent behaviour: † The steels with low nickel content are embrittling at a much lower rate than the one predicted by the Guide (chemistry factor ¼ 20). † The Guide looks to be conservative also for the higher nickel steels if the content of manganese is lower than 0.8 wt%. † The steels embrittling at much higher rates are those with high nickel and high manganese contents at the same time. The threshold for nickel is evaluated to be at Ni . 1.5 wt% and for manganese at Mn . 0.8 wt%. Manganese, together with nickel, seems to play a key role in low Cu and P steels embrittlement [1,2]. Correlation analysis which considers Ni and Mn and fluence dependence to 1/3 power are showing predictive capabilities within 20 8C scatter band in most cases. Other elements, like, for example, carbon and sulphur could also explain the residual scatter in the data [3]. q 2002 Published by Elsevier Science Ltd. Keywords: VVER-1000 surveillance data; Steel embrittlement; Correlation analysis
1. Materials The materials involved in this analysis are given in Table 1 together with their nominal compositions. Actual specific NPP material composition differs significantly from the nominal and it is used for this extended analysis. The contents of P and Cu are very low; so low that the two elements are not playing significant role in neutron embrittlement. A high level of nickel is characterising both the base metal and particularly the welds material.
* Corresponding author. E-mail address: [email protected] (A. Kryukov). 1 Visiting scientist at JRC. 0308-0161/02/$ - see front matter q 2002 Published by Elsevier Science Ltd. PII: S 0 3 0 8 - 0 1 6 1 ( 0 2 ) 0 0 0 6 9 - 8
Based on the reported chemistry factor provided by the Russian Guide PNAE, CFmax, see Table 1, it is evident that the critical materials are: † Welds 10ChGNMAA and † Base metal 15Ch2NMFA which need to be more carefully investigated.
2. Extended analysis of surveillance results on 10CHGNMAA weld irradiation embrittlement The observed temperature shifts for all considered surveillance sets have been analysed as a function of fluence.
662
A. Kryukov et al. / International Journal of Pressure Vessels and Piping 79 (2002) 661–664
Table 1 VVER-1000 materials Material
Nimax (%)
Pmax (%)
Cumax (%)
CFmax
Remarks
15Ch2NMF(AA) 15Ch2NMF(A) 08ChGNMTA 10ChGNMAA
1.4 1.4 1.3 1.9
0.010 0.010 0.014 0.014
0.07 0.17 0.08 0.08
23 29 20 20a
All RPVs except 3 3 RPVs ,20% RPV welds ,80% RPV welds
a
According to actual analysis this value could be up to 34. Fig. 2. Observed DBTT shifts for Ni ¼ 1:7 wt% and medium Mn content.
As expected, for such a low level in P and Cu contents, P ¼ 0:005 – 0:010 wt%; Cu ¼ 0:03 – 0:08 wt%; no significant role of P and Cu is observed. All results together are shown in Fig. 1. On the same figure, a trend curve according to the Russian Guide with Af ¼ 20 is also drawn. Data have been subdivided into three groups in order to put in evidence the following. As it can be seen, all steels with low nickel content are embrittling at a much lower rate than predicted by the Russian Guide. The Russian Guide is in this case very conservative [4]. The Russian Guide is conservative also for the higher nickel steels provided that the content of manganese is low. The steels embrittling at much higher rates are those with high nickel and high manganese contents. The threshold for nickel is Ni . 1.5 wt%. The threshold for manganese is Mn level . 0.8 wt%. Other elements could play a role in combination with Ni and Mn; including C, Si, S, etc. The earlier mentioned observations are in agreement with recent findings. Mn and Ni are the elements to become non-randomly distributed and co-segregated in welds with high Ni and low Cu. 2.1. Examples of the detailed data analysis In Figs. 2 – 4, the results for specific NPP steels containing Ni ¼ 1:7; 1.88 and 1.76 wt% are given, respectively. The data shown in Fig. 2 are for steel containing low levels of manganese, Mn , 0:8 wt%; while the data in Figs. 3 and 4 are for higher Mn contents.
Fig. 1. Observed temperature transition shifts as a function of fluence. All analysed data sets.
Independently of some uncertainties on the data, it is very clear that the data for each individual material composition are quite consistent. Most of the data for the same material still follow a 1/3 power function of the fluence in spite of some uncertainty in fluence determination itself. The differences in nickel and manganese content can explain the large difference in sensitivity to embrittlement. The content of other elements, like residual S, C, Si, etc. could even explain some minor deviations from the general trend. A correlation analysis is presented in Section 3.
3. Correlation analysis The data sets have been studied by using statistical correlation analysed taking Ni and Mn as variables and a 1/3 dependence with neutron fluence in the form of: Shift ¼ ðaNi þ bMn þ cÞ £ F1=3 The results are shown in Fig. 5. All data sets are nicely aligned to the diagonal of the plot, and most of them are laying within a scatter band of just 20 8C. The result is impressive considering the various uncertainties; scatter in fluence values, data treatment between different laboratories, and in particular the different content of S and C and other elements. Such parameters, when properly known, can be considered for more advanced predictive correlations. Just as example, the content of the residual S has been considered and the results for a subset of data with narrow S
Fig. 3. Observed DBTT shifts for Ni ¼ 1:88 wt% and high Mn content.
A. Kryukov et al. / International Journal of Pressure Vessels and Piping 79 (2002) 661–664
663
Fig. 4. Observed DBTT shifts for Ni ¼ 1:76 wt% and high Mn content.
content variation are shown in Fig. 6. The scatter band is already reduced when compared with the previous regression; most of the points are laying within a 15 8C scatter band now. The observed average chemistry factor CF for steels with high nickel content has also been calculated and is given in Fig. 7 as a function of Mn. Clearly values of CF higher than 20, up to 30 and more, are observed for Mn contents higher than , 0.8 wt%.
4. Conclusions The results are based on the results of 17 of surveillance programmes of 14 VVER-1000 Reactor Pressure Vessel (RPV) tested in Russia, Ukraine and Bulgaria by different testing organisations: Kurchatov Institute, Russia, Institute for Nuclear Research, Ukraine, Institute of Metal Science, Bulgaria. Based on the earlier mentioned results, a key to understand VVER-1000 steel embrittlement is found in spite of the uncertainties in the surveillance data set. Manganese and possibly other elements, in combination with the nickel content, are playing a significant role in the embrittlement of low Cu and P steels.
Fig. 5. Transition temperature shifts; measured versus calculated. For all NPPs.
Fig. 6. Transition temperature shifts; measured versus calculated. For a subset of data.
The materials involved are very low phosphorus and copper steels; with significant variation of nickel and other elements like manganese. The observed temperature transition shifts are showing consistent behaviour: † the steels with low nickel content are embrittling at a much lower rate than predicted by the Russian Guide ðAf ¼ 20Þ: † The Russian Guide is conservative also for the higher nickel steels if the content of manganese is medium. † The steels embrittling at much higher rates are those with high nickel and high manganese contents at the same time. The threshold for nickel is evaluated to be at Ni . 1:5 wt% and for manganese at Mn . 0:8 wt%. Manganese, with nickel, seems to play a key role in low Cu and P steels embrittlement. Correlation analysis which considers Ni and Mn and fluence dependence to 1/3 power is showing predictive capabilities within 20 8C scatter band in most cases. Other elements, like, for example, carbon and sulphur could also explain the residual scatter in the data.
Fig. 7. Average CF versus manganese content.
664
A. Kryukov et al. / International Journal of Pressure Vessels and Piping 79 (2002) 661–664
Further study need to be done in order to build more precise predictive correlations and update the Russian Guide.
5. Recommendation for future activities A more precise analysis in order to reduce the uncertainties can be done in co-operation with the VVER1000 Surveillance Testing Laboratories. Such a precise analysis for VVER-1000 surveillance data must be performed as soon as possible in order to allow for improved: † RPV integrity assessment; † Plant life prediction; † Mitigation methods/plant life management. The following steps need to be undertaken: 1. Harmonisation of the method for transition temperature determination for involved testing laboratories (common database, training, Round-robin and/or Benchmarking exercise). 2. More precise assessment of Ukrainian and Bulgarian testing results, e.g. Individual fluence value for each specimen; verification of actual fluence rates, etc. 3. Decrease of data scatter by using re-constitution of broken Charpy specimens (based on the experience
acquired in TACIS 96 projects and AMES projects like RESQUE, etc.). 4. Direct measurement of the irradiation temperature of surveillance specimens. 5. Launch AMES projects and studies on the subjects [5]. 6. Possible update of the Russian Guide.
References [1] Debarberis L. The effect of nickel, phosphorus and copper in irradiation embrittlement of RPV steel model alloys. NATO International Workshop on RP Vessel Embrittlement, Varna, Bulgaria; September 2000. [2] Debarberis L, To¨rro¨nen K, Sevini F, Acosta B, Kryukov A, Nikolaev Y, Valo M. Experimental studies of copper, phosphorus and nickel effect on RPV Model alloys at two different fluences. Sixth International Conference on Materials Issues in Design, Manufacturing and Operation of NPP Equipment, VTT, St Petersburg, Russia; 19 –23 June 2000. [3] To¨rro¨nen K, Crutzen S, Debarberis L, von Estorff U, Stamm H, Markgraf J, Sordon G. RPV steel embrittlement experimental and modelling studies at the Institute for Advanced Materials, IAM, KTG Germany. [4] Kryukov A, Debarberis L. Achievements, open issues and developments on VVER RPV irradiation embrittlement assessment and AMES European Network Strategy. IAEA Specialist Meeting on Irradiation Embrittlement, Madrid; 1999, PLIM þ PLEX. [5] Sevini F, Debarberis L, Davies M. The European Network AMES. Sixth International Conference on Materials Issues in Design, Manufacturing and Operation of NPP Equipment, St Petersburg, Russia; 19–23 June 2000.