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St Lucie Pressurizer Examinations

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St Lucie Pressurizer Examinations

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    1. St Lucie Pressurizer Examinations Phil Ashwin EPRI 3rd International Workshop of In-service Inspection Qualification Bodies October 15-16, 2008 Vienna, Austria

    2. Recap from 2007 Recommendations Operational Experience (OE) Feedback is important and should be carefully analysed to see if and how it may influence the Qualification file. It is recommended the there is a loop in the Qualification process to allow for Operational Experience Feedback.

    3. October 10th 2007… How do the results of ISI get back to the qualification process? Summary Qualified procedures provide reliable examinations when performed in the qualified manner The component configuration must be appropriate We need to do a better job of characterizing the surface condition and dealing with it properly The search unit must be selected carefully Data must be acquired and analyzed carefully All available factors must be evaluated before reaching a conclusion Putting too much weight on the details of the earliest information disseminated to the industry can be harmful This often is not the plant’s official OE

    4. Relevance Presentation provides an example and the consequence of Putting too much weight on the details of the earliest information disseminated to the industry can be harmful

    5. Overview of the St Lucie Pressurizer Examinations Florida Power & Light removed the pressurizer from St Lucie Unit 1 and donated it to Nuclear Regulatory Commission (NRC) Office of Research In collaboration with NRC, EPRI Materials Reliability Program (MRP) and NDE examined the nozzle welds using manual UT 360° indications were reported “Either SCC or multiple fabrication defects” If SCC, the operating basis of eight PWRs was challenged NRC Office of Regulation prepared to shut down the eight PWRs for inspection (Friday, March 7) Intensive NDE data acquisition confirmed no major cracking was present (Friday, March 14) NRC cancelled the shutdown activity

    6. Topics Retirement of St Lucie pressurizer Initial NDE of safety nozzle welds NRC response to initial NDE Industry mobilization Enhanced NDE results NRC decision Destructive analysis Industry self-assessment Summary

    7. Topics Retirement of St Lucie pressurizer Initial NDE of safety nozzle welds NRC response to initial NDE Industry mobilization Enhanced NDE results NRC decision Destructive analysis Industry self-assessment Summary

    8. Retirement of St Lucie pressurizer Florida Power & Light (FPL) chose to replace its pressurizer Faced high inspection and mitigation costs Pressurizer design enabled removal FPL donated the pressurizer to USNRC Office of Regulatory Research (RES) Shipped to Studsvik hot storage facility in Memphis RES planned an NDE round-robin followed by destructive analysis (DE) First step: perform a UT survey of the nozzles, to learn whether there was any cracking to support the NDE research project

    9. Topics Retirement of St Lucie pressurizer Initial NDE of safety nozzle welds NRC response to initial NDE Industry mobilization Enhanced NDE results NRC decision Destructive analysis Industry self-assessment Summary

    10. Initial NDE of pressurizer nozzles NRC RES had no budget to examine the nozzles, and requested EPRI Materials Reliability Program (MRP) to collaborate MRP funded EPRI NDE Program to engage an NDE vendor to examine the dissimilar metal welds Structural Integrity Associates Manual phased array UT Dye penetrant (PT)

    11. Initial NDE of pressurizer nozzles PT results A few short, linear indications on the inside surface (ID) of the welds A few rounded indications on the outside surface (OD)

    12. Initial NDE of pressurizer nozzles UT results Reflectors were numerous, present 360° around circumference Depth about 80% Detected in A, B, and C safety nozzles

    13. Initial NDE of pressurizer nozzles Indication profile built from 19 measurement points

    14. Topics Retirement of St Lucie pressurizer Initial NDE of safety nozzle welds NRC response to initial NDE Industry mobilization Enhanced NDE results NRC decision Destructive analysis Industry self-assessment Summary

    15. NRC response to initial NDE The initial NDE was reported to NRC RES There was interest and discussion of follow up work RES communicated the data to NRC Office of Nuclear Reactor Regulation (NRR) On May 7, senior NRR management indicated an intention to require eight PWR units to shut down for immediate inspection or mitigation These eight units were operating until their next scheduled outage based on an EPRI MRP advanced finite element analysis (FEA) indicating that 360°, deep circumferential cracks cannot exist without leakage If the St Lucie indications were SCC, it would challenge the FEA

    16. Topics Retirement of St Lucie pressurizer Initial NDE of safety nozzle welds NRC response to initial NDE Industry mobilization Enhanced NDE results NRC decision Destructive analysis Industry self-assessment Summary

    17. Industry mobilization NRR’s intention was communicated to industry at about noon on Friday, March 7 EPRI MRP and NDE coordinated a rapid response effort to obtain more advanced NDE data, to be followed by DE DE required NRC RES permission (they own it) Vendors onsite at Studsvik in Memphis, beginning Saturday noon: LMT – encoded phased array UT WesDyne – encoded ET scanned on the ID IveyCooper – radiography Four EPRI staff provided oversight and coordination NRC RES staff member and consultant Utility representative from MRP

    18. Topics Retirement of St Lucie pressurizer Initial NDE of safety nozzle welds NRC response to initial NDE Industry mobilization Enhanced NDE results NRC decision Destructive analysis Industry self-assessment Summary

    19. Enhanced NDE results Encoded phased array UT Showed clear evidence that no significant SCC was present in any of the three safety nozzle welds Evidence of extensive fabrication defects Not surface-connected Encoded ET on the inside surface A few, short (~0.5” long) linear indications No evidence of extensive surface-connected cracking Radiography No indications of cracking Indications of fabrication defects

    20. UT rollout showing embedded defects St Lucie Safety Nozzle A

    21. Correlation of UT, PT, ET, RT

    22. Correlation of UT, PT, ET, RT

    23. Correlation of UT, PT, ET, RT

    24. Topics Retirement of St Lucie pressurizer Initial NDE of safety nozzle welds NRC response to initial NDE Industry mobilization Enhanced NDE results NRC decision Destructive analysis Industry self-assessment Summary

    25. NRC decision NRC RES and NRR were kept closely informed of all activities, from the beginning at Friday noon Informed NRC on Monday (maybe Tuesday) that there was no evidence of significant SCC By Wednesday night the picture was complete On Thursday there was a public meeting with senior NRR and RES management Senior utility representatives presented industry’s conclusion that there was no safety concern EPRI provided discussion of the NDE methods and results On Friday NRC notified the eight units that their operational basis was intact; no unscheduled shutdown would be required

    26. Topics Retirement of St Lucie pressurizer Initial NDE of safety nozzle welds NRC response to initial NDE Industry mobilization Enhanced NDE results NRC decision Destructive analysis Industry self-assessment Summary

    27. Destructive analysis With NRC RES permission, EPRI MRP has cut off one of the three safety nozzles and performed destructive examination The results have not been published yet The DE showed: No service-induced cracking Several fabrication defects in the body of the weld

    28. Topics Retirement of St Lucie pressurizer Initial NDE of safety nozzle welds NRC response to initial NDE Industry mobilization Enhanced NDE results NRC decision Destructive analysis Industry self-assessment Summary

    29. Industry self-assessment A self-assessment was performed to identify any lessons that could be learned from the St Lucie event, and applied to future emergent issues Several recommendations resulted from the assessment A key one: improvement and regularization of communications with NRC staff Another: keeping senior utility management aware of any research activities that could impact operating plants

    30. Topics Retirement of St Lucie pressurizer Initial NDE of safety nozzle welds NRC response to initial NDE Industry mobilization Enhanced NDE results NRC decision Destructive analysis Industry self-assessment Summary

    31. Summary The retired St Lucie pressurizer was found to contain no service-induced cracking Manual UT made a conservative interpretation, recognizing the possibility that the indications could be fabrication defects Encoded UT showed clearly that there was no significant cracking Destructive examination results will be published shortly

    32. October 10th 2007… How do the results of ISI get back to the qualification process? Summary Qualified procedures provide reliable examinations when performed in the qualified manner The component configuration must be appropriate We need to do a better job of characterizing the surface condition and dealing with it properly The search unit must be selected carefully Data must be acquired and analyzed carefully All available factors must be evaluated before reaching a conclusion Putting too much weight on the details of the earliest information disseminated to the industry can be harmful This often is not the plant’s official OE

    33. For discussion As qualification bodies, How can we be more effective at sharing Operational Experience? What are the IQB responsibilities following the qualification and application of the NDE system? Does being proactive challenge being independent?

    34. Questions

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