Update on Core Shroud Focus Group Activities
Update on Core Shroud Focus Group Activities Wayne Lunceford, P.E. Principal Technical Leader BWRVIP Integration Committee June 2016
© 2016 Electric Power Research Institute, Inc. All rights reserved.
Hatch Boat Sample Analysis - Status As of end of 2015, testing not yet completed included: – Helium concentration analyses – ATEM characterization of a crack tip from the primary crack
All testing now complete PNNL / SI currently documenting final results and adding these to the final report Draft final report complete in July Final report published in August
2
© 2016 Electric Power Research Institute, Inc. All rights reserved.
Hatch Boat Sample He Measurement Results As Measured He Concentration
Weldability Threshold for 304SS
50 Base Metal
He Concentration (appm)
40 Weld Metal 30
20
10
y = 37.14e-2.126x R² = 0.9926
0 0
0.5
1
1.5
Depth (inches) from Shroud ID (1.5 inch thick shroud)
Welding repair of shroud ID likely challenging, would require location specific qualification and use of laser beam welding processes Weld repair of shroud OD likely could be demonstrated by generic weldability assessment, likely possible with application of laser beam welding processes Results demonstrate that even “highly irradiated” BWR shroud locations potentially weldable by advanced welding process after > 40 years of operation 3
© 2016 Electric Power Research Institute, Inc. All rights reserved.
Hatch Boat Sample Analysis – ATEM Characterization After several attempts, PNNL successfully obtained one primary crack tip specimen by focused ion beam lift-out Primary crack tip characterization resulted in observations notably different than those from secondary crack tip characterization All results are preliminary – final reporting not completed
4
© 2016 Electric Power Research Institute, Inc. All rights reserved.
ATEM Characterization – Preliminary Summary of Results Similarities: – Ni enrichment ahead of crack tip – Cr enrichment in matrix behind crack – Both Ni and Cr enriched to levels beyond that induced by RIS in the matrix
Differences: – Primary crack specimen not entirely filled with oxides – Primary crack specimen contains indications of Cu and Zn; these elements not present in secondary crack specimens – APT data (not presented here) suggest Zn observed is from depleted Zn oxide injections not natural zinc oxide injections (depleted zinc oxide introduced at Hatch Unit 1 in mid-1990s)
5
© 2016 Electric Power Research Institute, Inc. All rights reserved.
Preliminary Results - Comparison of ATEM Results from Primary and Secondary Cracks Secondary Crack Specimen
6
Primary Crack Specimen
© 2016 Electric Power Research Institute, Inc. All rights reserved.
Preliminary Results - Primary Crack Tip ATEM Characterization
7
© 2016 Electric Power Research Institute, Inc. All rights reserved.
ATEM Characterization – Preliminary Observations Primary and secondary crack tip oxide characteristics are different – Lack of oxide-filled crack potentially indicates coolant access to crack tip region – Significance of observed Cu and Zn not clear
Not known whether these differences are indicative of a difference in status (active/dormant) of crack
8
© 2016 Electric Power Research Institute, Inc. All rights reserved.
Preliminary Evaluation of Brunswick Unit 1 Off-Axis UT Results As described in OE presentations, BNP 1 conducted examinations using “off-axis” UT to meet the requirements of the interim guidance Results presented are preliminary, more detailed evaluation planned
9
© 2016 Electric Power Research Institute, Inc. All rights reserved.
Brunswick Unit 1 Off-Axis UT Results 100% H4 - ID H4 - OD H4 - TW H5 - ID H5 - OD H5 - TW V6
Off-Axis Flaw Depth (% Thru-Wall)
90% 80% 70% 60% 50% 40% 30% 20%
Note: One > 12 inch off-axis flaw associated with V6 not shown.
10% 0% 0
1
2
3
4
5
6
Off-Axis Flaw Length (inches)
Significantly greater propensity for off-axis flaws to grow thru-wall if 1 inch in length or more – < 1” in length: 7% of flaws are thru-wall – 1 – 2” in length: 38% of flaws are thru-wall – > 2” in length: 82% of flaws are thru-wall 10
© 2016 Electric Power Research Institute, Inc. All rights reserved.
Comparison of New BNP 1 Data with Prior Data Data from BNP 1 2016
Data Presented in Interim Guidance
100% 90%
Cumulative Distribution
80% 70% 60% 50% 40% 30% 20% 10% 0% 0
1
10
Off-Axis Flaw Length (inches)
Note: A number of the data points on the right hand plot are from prior BNP 1 visual exams (integration of new data into existing database not yet performed) Distribution of flaw lengths confirmed. The addition of the BNP 1 data to the length distribution database will not substantially affect the distribution BNP 1 UT data provides further confirmation that “longer” off-axis flaws now are deep or thru-wall 11
© 2016 Electric Power Research Institute, Inc. All rights reserved.
Comparison with IGSCC data from BWRVIP-278 Clear difference in thru-wall growth probability between off-axis flaws and IGSCC oriented parallel to shroud welds 100%
Cumulative Distribution
90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 0%
20%
40%
60%
80%
100%
Depth (% Thru-Wall)
BNP Unit 1 Off-Axis Flaws
Circumferential Weld IGSCC (BWRVIP-278) Note Depth Scale Difference
12
© 2016 Electric Power Research Institute, Inc. All rights reserved.
Preliminary Observations Clearly confirms that off-axis flaws have a strong propensity for thru-wall growth – Consistent with and expands data from off-axis UT performed at Hatch 1 – Most off-axis flaws longer than about 2 inches are deep or thru-wall – Consistent with our current understanding of stress state near welds and the detrimental effects of fabrication practices on SCC occurrence
Flaw lengths are generally contained to less than 6 inches (except for one long > 12 inch long flaw associated with V6) – Suggests that the planned additional analytical work is valuable as a means to provide a rational technical basis for field observations – The BNP 1 off-axis UT results improve the capability to characterize the distribution of off-axis crack lengths
Preliminary data available did not include fluence information, further evaluation to assess correlations between fluence and offaxis cracking severity will be performed as data are available 13
© 2016 Electric Power Research Institute, Inc. All rights reserved.
General Observations Relative to Core Shroud Off-Axis Flaw Interim I&E Guidance (2016-030) The BNP 1 UT results continue to indicate that off-axis cracking has no impact on shroud structural integrity – Flaw lengths remain well below conservatively determined generic values provided in the interim guidance for core shroud off-axis cracking issued earlier this year
However, these results continue to indicate that leakage assumptions and associated impact on design basis limits are of concern – The interim guidance requires further evaluation to assess flaw depth & probability of leakage for flaws 4 inches and longer. That value appears not to be conservative based on available UT data. – However, the guidance also assumes continued crack growth – without any assumption of crack arrest. That assumption continues to be shown to be very conservative.
Hatch results suggest that some cracks could potentially experience additional growth over time 14
© 2016 Electric Power Research Institute, Inc. All rights reserved.
Planned Next Steps 1) Continued collection and evaluation of field data 2) Analytical evaluation of stress state near welds to provide a technical basis for the field performance observed 3) Consider potential revisions to interim guidance 2016-030 based on 1) and 2) above 4) Long-term action to determine what changes, if any, should be incorporated into BWRVIP-76 to address off-axis cracking
15
© 2016 Electric Power Research Institute, Inc. All rights reserved.
Together…Shaping the Future of Electricity
16
© 2016 Electric Power Research Institute, Inc. All rights reserved.
© 2016 Electric Power Research Institute, Inc. All rights reserved.
Hatch Boat Sample Analysis - Status As of end of 2015, testing not yet completed included: – Helium concentration analyses – ATEM characterization of a crack tip from the primary crack
All testing now complete PNNL / SI currently documenting final results and adding these to the final report Draft final report complete in July Final report published in August
2
© 2016 Electric Power Research Institute, Inc. All rights reserved.
Hatch Boat Sample He Measurement Results As Measured He Concentration
Weldability Threshold for 304SS
50 Base Metal
He Concentration (appm)
40 Weld Metal 30
20
10
y = 37.14e-2.126x R² = 0.9926
0 0
0.5
1
1.5
Depth (inches) from Shroud ID (1.5 inch thick shroud)
Welding repair of shroud ID likely challenging, would require location specific qualification and use of laser beam welding processes Weld repair of shroud OD likely could be demonstrated by generic weldability assessment, likely possible with application of laser beam welding processes Results demonstrate that even “highly irradiated” BWR shroud locations potentially weldable by advanced welding process after > 40 years of operation 3
© 2016 Electric Power Research Institute, Inc. All rights reserved.
Hatch Boat Sample Analysis – ATEM Characterization After several attempts, PNNL successfully obtained one primary crack tip specimen by focused ion beam lift-out Primary crack tip characterization resulted in observations notably different than those from secondary crack tip characterization All results are preliminary – final reporting not completed
4
© 2016 Electric Power Research Institute, Inc. All rights reserved.
ATEM Characterization – Preliminary Summary of Results Similarities: – Ni enrichment ahead of crack tip – Cr enrichment in matrix behind crack – Both Ni and Cr enriched to levels beyond that induced by RIS in the matrix
Differences: – Primary crack specimen not entirely filled with oxides – Primary crack specimen contains indications of Cu and Zn; these elements not present in secondary crack specimens – APT data (not presented here) suggest Zn observed is from depleted Zn oxide injections not natural zinc oxide injections (depleted zinc oxide introduced at Hatch Unit 1 in mid-1990s)
5
© 2016 Electric Power Research Institute, Inc. All rights reserved.
Preliminary Results - Comparison of ATEM Results from Primary and Secondary Cracks Secondary Crack Specimen
6
Primary Crack Specimen
© 2016 Electric Power Research Institute, Inc. All rights reserved.
Preliminary Results - Primary Crack Tip ATEM Characterization
7
© 2016 Electric Power Research Institute, Inc. All rights reserved.
ATEM Characterization – Preliminary Observations Primary and secondary crack tip oxide characteristics are different – Lack of oxide-filled crack potentially indicates coolant access to crack tip region – Significance of observed Cu and Zn not clear
Not known whether these differences are indicative of a difference in status (active/dormant) of crack
8
© 2016 Electric Power Research Institute, Inc. All rights reserved.
Preliminary Evaluation of Brunswick Unit 1 Off-Axis UT Results As described in OE presentations, BNP 1 conducted examinations using “off-axis” UT to meet the requirements of the interim guidance Results presented are preliminary, more detailed evaluation planned
9
© 2016 Electric Power Research Institute, Inc. All rights reserved.
Brunswick Unit 1 Off-Axis UT Results 100% H4 - ID H4 - OD H4 - TW H5 - ID H5 - OD H5 - TW V6
Off-Axis Flaw Depth (% Thru-Wall)
90% 80% 70% 60% 50% 40% 30% 20%
Note: One > 12 inch off-axis flaw associated with V6 not shown.
10% 0% 0
1
2
3
4
5
6
Off-Axis Flaw Length (inches)
Significantly greater propensity for off-axis flaws to grow thru-wall if 1 inch in length or more – < 1” in length: 7% of flaws are thru-wall – 1 – 2” in length: 38% of flaws are thru-wall – > 2” in length: 82% of flaws are thru-wall 10
© 2016 Electric Power Research Institute, Inc. All rights reserved.
Comparison of New BNP 1 Data with Prior Data Data from BNP 1 2016
Data Presented in Interim Guidance
100% 90%
Cumulative Distribution
80% 70% 60% 50% 40% 30% 20% 10% 0% 0
1
10
Off-Axis Flaw Length (inches)
Note: A number of the data points on the right hand plot are from prior BNP 1 visual exams (integration of new data into existing database not yet performed) Distribution of flaw lengths confirmed. The addition of the BNP 1 data to the length distribution database will not substantially affect the distribution BNP 1 UT data provides further confirmation that “longer” off-axis flaws now are deep or thru-wall 11
© 2016 Electric Power Research Institute, Inc. All rights reserved.
Comparison with IGSCC data from BWRVIP-278 Clear difference in thru-wall growth probability between off-axis flaws and IGSCC oriented parallel to shroud welds 100%
Cumulative Distribution
90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 0%
20%
40%
60%
80%
100%
Depth (% Thru-Wall)
BNP Unit 1 Off-Axis Flaws
Circumferential Weld IGSCC (BWRVIP-278) Note Depth Scale Difference
12
© 2016 Electric Power Research Institute, Inc. All rights reserved.
Preliminary Observations Clearly confirms that off-axis flaws have a strong propensity for thru-wall growth – Consistent with and expands data from off-axis UT performed at Hatch 1 – Most off-axis flaws longer than about 2 inches are deep or thru-wall – Consistent with our current understanding of stress state near welds and the detrimental effects of fabrication practices on SCC occurrence
Flaw lengths are generally contained to less than 6 inches (except for one long > 12 inch long flaw associated with V6) – Suggests that the planned additional analytical work is valuable as a means to provide a rational technical basis for field observations – The BNP 1 off-axis UT results improve the capability to characterize the distribution of off-axis crack lengths
Preliminary data available did not include fluence information, further evaluation to assess correlations between fluence and offaxis cracking severity will be performed as data are available 13
© 2016 Electric Power Research Institute, Inc. All rights reserved.
General Observations Relative to Core Shroud Off-Axis Flaw Interim I&E Guidance (2016-030) The BNP 1 UT results continue to indicate that off-axis cracking has no impact on shroud structural integrity – Flaw lengths remain well below conservatively determined generic values provided in the interim guidance for core shroud off-axis cracking issued earlier this year
However, these results continue to indicate that leakage assumptions and associated impact on design basis limits are of concern – The interim guidance requires further evaluation to assess flaw depth & probability of leakage for flaws 4 inches and longer. That value appears not to be conservative based on available UT data. – However, the guidance also assumes continued crack growth – without any assumption of crack arrest. That assumption continues to be shown to be very conservative.
Hatch results suggest that some cracks could potentially experience additional growth over time 14
© 2016 Electric Power Research Institute, Inc. All rights reserved.
Planned Next Steps 1) Continued collection and evaluation of field data 2) Analytical evaluation of stress state near welds to provide a technical basis for the field performance observed 3) Consider potential revisions to interim guidance 2016-030 based on 1) and 2) above 4) Long-term action to determine what changes, if any, should be incorporated into BWRVIP-76 to address off-axis cracking
15
© 2016 Electric Power Research Institute, Inc. All rights reserved.
Together…Shaping the Future of Electricity
16
© 2016 Electric Power Research Institute, Inc. All rights reserved.
