ML20203D858
| ML20203D858 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 02/23/1998 |
| From: | Rainsberry J SOUTHERN CALIFORNIA EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| TAC-M99641, TAC-M99642, NUDOCS 9802260171 | |
| Download: ML20203D858 (3) | |
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Manager riant 1.icensing An IDIAOV 671RMTlOVL%enwny February 23, 1998 U. S. Nucl:ar Regulatory Commission Attention: Document Control Desk Washington, D.C.
20555 Gentlemen:
Subject:
Docket Nos. 50-361 and 50-362 Amendment Application Nos. 170 and 156 Steam Generator Sleeving San Onofre Nuclear Generating Station Units 2 and 3 (TACNos.M99641andM99642)
References:
1.
January 21, 1998 letter from Mel Fields (NRC) to H7rold B. Ray (SCE),
Subject:
Request for Additional Information - Preposed Steam Generator Sleeving Technical Specification Amendment for San Onofre Nuclear Generating Station, Units 2 and 3 (TACNos.M99641andM99642) 2.
September 16, 1997 letter from Dwight E. Nunn (SCE) to Document Control Desk (NRC),
Subject:
D0cket Nos. 50-361 and 50-362, Amendment Application Nos. 170 and 156 Steam Generator Sleeving, San Onofre Nuclear Generating Station Units 2 and 3 This letter provides the information requested by the January 21, 1998 NRC letter (Reference 1) concerning the Steam Generator Sleeving Amendment Application Nos. 170 and 156 for San Onofre Units 2 and 3.
These amendment
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applications are Proposed Change Number 487 (Reference 2) which requested NRC approval to use ASEA Brown Boveri/ Combustion Engineering (ABB CE) leak-tight sleeving as an alternative steam generator tube repair to plugging.
The NRC questions from Reference 1 and Southern California Edison's (SCE's) responses are as follows:
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NRC Question No. 1 The proposed TS limit for the imperfection depth at or beyond which the steam generator tube shall be removed from service or repaired is equal to 44% of the nominal tube wall thickness.
This could be less conservative from the sleeve plugging limit discussed on page 8-9 of ABB/CE Topical Report CEN 630-P, once allowance for NDE uncertainty (typically 10%) and flaw growth San Onofre Nudear Generating Station.
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Document Control Desk (typically 10%)aretakenintoaccount.
Please justify the use of 44% in light of the information contained in Topical Report CEN 630-P.
Response-The percent (%): allowable degradation of a steam generator tube is 64%.
This value is derived in accordance with NRC draft Regulatory Guide 1.121 in ABB CE report CENC-1645, " San Onofre Steam Generator Revised LOCA Tube Analysis,"
July,.1984, which was reviewed and approved by the NRC in the Safety Evaluation for Amendment No. 26 to NPF 10 and Amendment No. 15 to NPF-15. The value was reaffirmed in ABB CE report CSE-97-211. " Evaluation of Maximum Tube Stresses During a LOCA for Southern California Edison SONGS Unit 3 Steam Generators wi+h Degraded Eggerates," dated August, 1997. These calculations, which consider uniform tube wall thinning, are typically associated with wear-type eddycurrent testing (ECT) indications.
Taking into account traditional non-destructivt. examination (NDE) uncertainty factors (10%) and flaw growth considerations (10%) for the 1600 steam generator tube material, a Technical Specification plugging / repair limit of 44% is established. With proper flaw sizing techniques, this allows a tube to remain in service for a period of time (from one refueling or inspection cycle to the next) af ter flaw detection.
Topical Report CEN 630-P uses sic.11ar analytical techniques to show that the percent allowable degradation of an ABB CE sleeve in an ABB CE steam generator tube is 48.7%. Once again, this value is derived in calculations whict:
consider uniform tube wall thinning.
ECT uncertainty factors are not a concern based on the success rate in detecting indications of 40% or greater, asstatedintheEPRIAppendixHqualification(EPRIReportNumber 9f-0SW-003-P). Wall thinning associated with wear is not considered a viable failure mechanism for sleeves. And since the 1690 sleeve material has demonstrated excellent corrosion resistance in primary and secondary environments, sleeve wall thinning from corrosion is considered unlikely.
As an additional conservatism, Section 5.5.2.11.f.1 f) of the proposed San Onofre Units 2 and 3 Technical Specifications state that " Sleeves shall be removed from service upon detection of service-induced degradation of the sleeve material or any portion of the sleeve-to-tube weld."
NRC Question No. 2 Tcpical Report CEN-630-P discussed a VT associated with the weld preparation pocess, but states that this VT is optional.
The statf believes that this
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' Document Control Desk inspection would confirm the adequacy of the brushing step to prevent weld failures due to oxide inclusions. Please clarify if this VT will be performed in accordance with_the_ topical report.
If a VT_wil' act be performed,. provide thetechnicaljustification(i.e.,providedetails at demonstrate the high degreeofcleanlinessacceptedinthefield).
Response
SCE and ABB CE agree that a VT confirming the adequacy of the brushing step is a required step in the sleeve installation process. This examination step has been included in all ABB CE sleeve installation procedures since January, 1996.
Some current sleeving campaign examples are Prairie Island i.
Unit #1 in October 1997, Calvert Cliffs Unit #1 for May 1998, and KRSK0 Unit #1 for June 1998. All sleeve installation procedures for San Onofre Units 2 and 3 will also include this VT step.
Including this VT step is stated in the attachment to the Reference 2 submittal in the Technical Considerations Section:
.. cleaning the inside diameter of the tube in the joint region, visual examination (VT) of the tube ID surfan in the weld region, installation of the sleeve..."
In addition, there is a second required VT step in the sleeve installation process involving the ID surface of the sleeve weld. Once again, all sleeve installation procehres for San Onofre Units 2 and 3 will include this second Vi step.
If you have any further questions or would like additional information on this subject, please let me know.
Sincerely,
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E. W. Merschoff, Regional Administrator, NRC Region IV K. E. Perkins, Jr., Director, Walnut Creek Field Office, NRC Region IV J. A. Sloan, NRC Senior Resident Inspector, San Onofre Units 2 & 3 M. B. Fields, NRC Project Manager, San Onofre Units 2 and 3