ML20207K237
| ML20207K237 | |
| Person / Time | |
|---|---|
| Site: | Seabrook  |
| Issue date: | 03/09/1999 |
| From: | Feigenbaum T NORTH ATLANTIC ENERGY SERVICE CORP. (NAESCO) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| AR#98021732, GL-97-01, GL-97-1, NYN-99022, NUDOCS 9903170095 | |
| Download: ML20207K237 (8) | |
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North Atlantic Energy Service Corporation North P o n= 3*
Seabrook, Nil 03874 A i hl18I)llG (603) 474-9521 The Northeast Utilities System i
March 9,1999 Docket No. 50-443 NYN-99022 AR# 98021732 Ref.: GL 97-01 NYN-97043 NYN-97089
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United States Nuclear Regulatory Commission Attn.: Document Control Desk Washington, DC 20555-0001 Seabrook Station Response to the RAI on Previously Submitted Generic Letter 97-01 Responses in Relationship to Westinghouse Owners Group's Integrated Inspection Program and Westinuhouse Electric Corporation's Tonical Report WCAP-14901 This letter provides North Atlantic Energy Service Corporation's (North Atlantic) response to NRC's request for additional information (RAI), dated December 9,1998, on Generic Letter (GL) 97-01'. Specifically, the Staff requests additional information concerning North Atlantic's responses to GL 97-01 that were previously submitted as they relate to Westinghouse Owners Group's integrated industry inspection program, for assessing the potential for vessel head penetration nozzles to undergo primary water stress corrosion cracking or intergranular attack and, to the contents of Westinghouse Owners Group Topical Report No. WCAP-14901,
" Background and Methodology for Evaluation of Reactor Vessel Closure Head Penetration Integrity for the Westinghouse Owners Group."
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By letters dated May 1,1997 and July 30,1997, North Atlantic previously submitted a 30-day response' and a 120-day response' to GL 97-01. In the 120-day response, North Atlantic 1 GL 97-01," Degradation of Control Rod Drive Mechanism Nozzle and Other Vessel Closure Head Penetrations," dated April 1,1997 2 T. C. Feigenbaum, to U.S. Nuclear Regulatory Commission, Seabrook Station,30-day Response to Generic Letter 97-01, NYN-97043 dated May 1,1997.
3 T. C. Feigenbaum, to U.S. Nuclear Regulatory Commission, Seabrook Station,120-day Response to Generic s
Letter 97-01, NYN-97089 dated July 30,1997.
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prdvided the information requested by the GL on inspection activities of control rod drive mechanism and other closure head penetrations.
Additionally, in the 120-day response, North Atlantic noted that it is a participant in the Westinghouse Owners Group / Nuclear Energy Institute reactor pressure vessel penetration integrated inspection program to address NRC's Staff request in GL 97-01 and indicated that the information in WCAP-14901 is applicable with respect to the assessment of vessel head penetration nozzles for Seabrook Station. Accordingly, the Enclosure contains North Atlantic's response to the request for additional instruction on GL 97-01.
Should you have any questions regarding this response, please contact Mr. James M. Peschel, Regulatory Compliance Manager, at (603) 773-7194.
Very truly yours, NORTH ATLANTIC ENERGY SERVICE CORP.
bl&b Ww Ted C. Feigenbau[ ~
Executive Vice President and Chief Nuclear Officer cc:
IL J. Miller, NRC Regional Administrator J. T. Harrison, NRC Project Manager, Project Directorate 1-3 R. K. Lorson, NRC Senior Resident Inspector 1
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United St:tes Nuclear Regulatory Commission NYN-99022 / Page 3 k
STATE OF NEW HAMPSHIRE Rockingham, ss.
March 9,1999 Then personally appeared before me, the above-named Ted C. Feigenbaum, Executive Vice President and Chief Nuclear Officer, North Atlantic Energy Service Corporation that he is duly _
l authorized to execute and file the foregoing information in the name and on the behalf of North Atlantic Energy Service Corporation and that the statements therein are true to the best of his knowledge and belief.
mAnt e4 i
s Marilyn R. fullivan' Notary Public
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My Commission Expires: March 19,2002 i
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ENCL,OStiRE TO NYN-99022 4
Response to Generic Letter 97-01 Request for Additional Information Introduction By letters dated May 1,1997 and July 30, 1997, North Atlantic Energy Service Corporation (North Atlantic) provided a 30-day and a 120-day response to Generic Letter (GL) 97-01. In the 120-day response to the NRC, North Atlantic provided the information requested by the GL on inspection activities of control rod drive mechanism and other closure head penetrations.
Additionally, North Atlantic noted that it is a member of the Westinghouse Owners Group and a panicipant in the Westinghouse Owners Group (WOG)/ Nuclear Energy Institute (NEI) Reactor Pressure Vessel (RPV) penetration integrated inspection program to address the staff request in GL 97-01, and stated that the information in WCAP-14901 is applicable with respect to the assessment of vessel head penetration (VHP) nozzles for Seabrook Station.
The following is North Atlantic's response to the requested information. Nuclear Energy Institute's generic response to the NRC Requests for Additional Information (RAI) on GL 97-01 has been subn.itted on December 11,1998 under separcte cover to the NRC by the NEI. The NRC Staff have encouraged generic industry response to this issue.
NRC RAI Ouestion [.g Provide the susceptibility rankings compiled for the WOG member plants for which WCAP-14901 is applicable.
In regard to other WOG member plants to which WCAP-14901 is applicable, include the basis for establishing the ranking of your plant relative to the others.
North Atlantic Response to RAI Ouestion 1 a.
The susceptibility rankings for the Pressurizer Water Reactors (PWRs) RPV head penetration cracking assessments for PWRs, including WOG members, is shown in the histogram contained in of NEI's " Generic Responses to the NRC Requests for Additional Information on GL 97-01." The basis for these rankings is also provided within Enclosure 1 of NEI's responses to the RAI.
As indicated in NEI's Response to the RAI, the histogram groups plants into three categories based on the predicted time to reach the allowable flaw depth limit. The development of the histogram was based on a comparison to D.C. Cook Unit 2.
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I NRC RAI Ouestion 1.b.
Describe how the probabilistic failure model in WCAP-14901 for assessing postulated flaws in vessel head penetration nozzles was bench-marked, and provide a list and discussion of i
the standards the model was bench-marked against.
l North Atlantic Response to RAI Ouestion 1.lt The reply to Question 2 in Enclosure 2 of NEF s " Generic Responses to the NRC Requests for Additional Information on GL 97-01" explains how the model was benchmarked and the standards used in the model.
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As indicated in NEI's Response to the RAI, the Westinghouse probabilistic analysis model was developed using the structural reliability and risk assessment methodology. This methodology was extensively benchmarked against failure data and calculations as described in WCAP-14572, Revision 1. Supplement 1.
NRC RAI Ouestion 1.c.
l Provide additional information regarding how the probabilistic failure models in WCAP-14901 will be refined to allow the input of plant-specific inspection data into the model's analysis methodology.
North Atlantic Response to RAI Ouestion 1 c.
The reply to Question 3 in Enclosure 2 of NEI's " Generic Responses to the NRC Requests for Additional Information on GL 97-01" explains how plant specific data is incorporated into the analysis.
As indicated in NEl's Response to the RAI, two types of variations, ranrlom and mechanistic, are considered in the Westinghouse probabilistic model. Random type variations use a Bayesian updating process, to combine distribution on time to failure with observations from each penetration inspection, while mechanistic type variations are included directly in the Westinghouse probabilistic model. This model is revised when inspection observations differ sigt *antly from what was calculated.
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NRC RAI Ouestion 1.d.
Describe how the variability in product forms, material specifications, and heat treatments used to fabricate each CRDM penetration nozzle at the WOG member utilities are addressed in the probabilistic crack initiation and growth models described or refekenced in Topical Report No. WCAP-14901.
North Atlantic Response to RAI Ouestion 1.d.
The reply to Question 1 in Enclosure 2 of NEI's " Generic Responses to the NRC Requets for Additional Information on GL 97-01" addresses incorporation of variability in fabrication w the probabilistic analysis rrodels.
As indicated in NEI's Response to the RAI, Westinghouse probabilistic analysis models are mechanistically based models. Uncertainties are provided into the models, to directly account for fabrication related variables. These models also include the observed uncertainties on the coefficients used to calculate residual stress, initiation time, and crack growth rate.
i NRC RAI Ouestion 2 Table 1-2 in WCAP-14901 provides a summary of the key tasks in WEC's vessel head penetration nozzle assessment program.
The table indicates that the Tasks for (1)
Evaluation of PWSCC Mitigation Methods,(2) Crack Growth Data and Testing, and (3)
Crack Initiation Characterization Studies have not been completed and are still in progress. In light of the fact that the probabilistic susceptibility models appear to be dependent in part on PWSCC crack initiation and growth estimates, provide your best estimate of when these tasks will be completed by WEC, and describe how these activities i
relate to and will be used to update the probabilistic susceptibility assessment of VHP nozzles at your plant.
i North Atlantic Response to RAI Ouestion 2 The reply to Question 5 in Enclosure 2 of NEI's " Generic Responses to the NRC Requests for Additional Information on GL 97-01" provides the response to this question.
As indicated in NEl's Response to tile IMI, the programs on crack growth testing and crack initiation have been essentially completed. The program on mitigation is now underway and targeted for completion in mid-2000. These programs have thus far served to confirm the assumptions used in the original safety evaluations and models.
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NRC RAI Ouestion 3 In the NE1 letters of January 29,1998, and April 1,1998, NEI indicated that inspection plans have been developed for the VHP nozzles at the Farley Unit 2 plant in the year 2002, and at the Diablo Canyon Unit 2 plant in the year 2001, respectively. The staff has noted that although you have endorsed the prebabilistic susceptibility model described in WCAP 14901, Revidon 0, other WOG member licensees have endorsed a probabilistic susceptibility model developed by an alternate vendor of choice. The WOG's proposal to inspect the VHP nozzles at the Farley Unit 2 and Diablo Canyon Unit 2 plants appears to be based on a composite assessment of the VHP nozzles at all the WOG member plants.
Verify that such a composite ranking assessment has been applied to the evaluation of the VHP nozzles at your plant. If composite ranking of the VHP nozzles at WOG member plants have been obtained from the composite results of the two models, justify why application of the probabilistic susceptibility model described in WCAP-14901, Revision 0, would yield the same comparable relative rankings of the VHP nozzles for your plant as would application of the alternate probabilistic susceptibility model used by the WOG member plants not subscribing to WCAP-14901, Revision 0.
Comment on the susceptibility rankings of the VHP nozzles at your plant relative to the susceptibility rankings of the VHP nozzles at the Farley Unit 2 and Diablo Canyon Unit 2 plants.
Noah Atlantic Response to RAI Ouestion 3 The reply to Q1 in Section II, Resps_nJgs to RAI Ouestions Specific to WOG Member Plants, in of NEI's " Generic Responses to the NRC Requests for Additional Information on GL 97-01" provides an abbreviated response to this question. Enclosure 1 of the same document furnishes a more comprehensive discussion on how the results from the two different probabilistic models were used to determine comparative rankings for RPV head nozzle PWSCC susceptibility.
Seabrook Station is in the third grouping of plants depicted in the Enclosure 1 histogram.
Specifically, this grouping of plants have greater than fifteen Effective Full Power Years (EFPY) from January 1,1997 to reach a probability of having a crack at the allowable depth that matches the D.C. Cook probability of one 75% through wall crack at the time ofits 1994 inspection. This comparative susceptibility ranking placed Farley Unit 2 in the first grouping of plants, with less then 5 EFPY, and placed Diablo Canyon Unit 2 in the second grouping of 5-15 EFPY.
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