ML053320210
| ML053320210 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 11/23/2005 |
| From: | Scherer A Southern California Edison Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| GL-04-001 | |
| Download: ML053320210 (8) | |
Text
ESOUTERN CALIFORNIA An EDISON INTURN ATIONVALt Comnpany A. Edward Schercr Manager of Nuclear Regulatory Affairs November 23, 2005 U. S. Nuclear Regulatory Commission Document Control Desk Washington, D. C. 20555
Subject:
Docket Nos. 50-361 and 50-362 NRC Generic Letter 2004-01 Requirements for Steam Generator Tube Inspections, Additional Information San Onofre Nuclear Generating Station, Units 2 and 3
Reference:
Letter from A. E. Scherer (SCE) to Document Control Desk dated October 26, 2004,
Subject:
Docket Nos. 50-361 and 50-362, NRC Generic Letter 2004-01 Requirements for Steam Generator Tube Inspections, San Onofre Nuclear Generating Station, Units 2 and 3
Dear Sir or Madam:
By the referenced letter, Southern California Edison (SCE) submitted a required response to NRC Generic Letter GL-2004-01. Subsequently, NRC staff requested additional information. The requested information is provided in the two attachments.
If you have any questions, or would like additional information concerning this subject, please contact Mr. Jack Rainsberry at (949) 368-7420.
Sincerely, Attachments cc:
B. S. Mallett, Regional Administrator, NRC Region IV J. N. Donohew, NRC Project Manager, San Onofre Units 2 and 3 C. C. Osterholtz, NRC Senior Resident Inspector, San Onofre Units 2 and 3 P.O. Box 128 San Clemente. CA 92672 949-368-7501 Fax 949-368-7575 NRC Requests for Additional Information and SCE Responses By letter dated October 26, 2004, (ML043070391) Southern California Edison, the licensee for Units 2 and 3, submitted a response to Generic Letter (GL) 2004-01, "Requirements For Steam Generator Tube Inspection." The staff has reviewed this letter and has determined that additional Information is needed in order for the staff to complete a review. Responses to the following questions are requested:
- 1.
Your response to Generic Letter 2004 - 01 indicated that the steam generator tube inspection practices at San Onofre Units 2 and 3 are not consistent with the NRC's position with respect to inspections within the tubesheet. You also stated a license amendment would be submitted for San Onofre Units 2 and 3 as part of your corrective actions. Please provide a schedule for submitting this license amendment request.
SCE Response:
The license amendment request was submitted November 3, 2005 (Reference 1).
- 2.
Steam generator tubes have been repaired at San Onofre Unit 2 using Combustion Engineering Alloy 690 tungsten inert gas (TIG) welded sleeves.
Alloy 690 TIG welded sleeves with a tubesheet rolled joint have a nickel band on the outside diameter of the lower portion of the sleeve in an attempt to improve the integrity of the sleeve/tube rolled joint.
Accordingly, the pressure boundary in the area of the joint includes the parent tube behind (i.e., adjacent to) the nickel band. After sleeve installation, inspections are performed to detect flaws in the pressure boundary region of the sleeveltube assembly. It is noted in your response to Generic Letter (GL) 2004 - 01 that the +Point* coil was used to inspect the full length of the sleeves during the most recent inspection.
2A.
For the portion of parent tube behind the sleeve's nickel band, discuss whether the +Point* probe was capable of detecting flaws of any type that may potentially-be present in the parent tube behind the nickel band, consistent with the requirements of the technical specifications (TS) in conjunction with Criteria IX, Xi, and XVI of 10 CFR Part 50, Appendix B.
If you conclude that your inspection technique was capable of reliably detecting flaws in the tube behind the nickel band, provide the technical basis that supports your conclusion.
Page 1 of 6 SCE Response:
The sleeve/tube lower roll joint has two regions. In the lower half, the sleeve has a nickel band. In the upper half the sleeve has a microlok band. Thus, inspection capabilities for both halves affect overall inspection capabilities for this roll joint.
The parent tube can be adequately inspected adjacent to the microlok band; however, inspection adjacent to the nickel band is limited.
The status of the ongoing evaluation and technical basis development follows.
Preliminary Results Westinghouse has assessed rotating plus point coil eddy current technique capabilities in a calibration standard with axially oriented Electric Discharge Machining (EDM) notches on the inside diameter (ID) of the parent tubing behind a sleeve's nickel and microlok bands. These notches were 50%, 70% and 100% throughwall (1W). Results are summarized below:
Parent tube behind the microlok band (previously reported in Reference 3): The three notches were readily detectable.
Parent tube behind the nickel band (Reference 4 updates previous reporting in Reference 3): The 70% and 100% TW notches are readily detectable. The 50% TW notch is observable, however the signal characteristics show distortion of the signal not present in the response of the 70% and 100% TW notches. Comparison of the EDM notch signal amplitudes, adjusted consistent with previous evaluations that have examined EDM notch and true Stress Corrosion Crack (SCC) responses, suggests that 70% axial SCC
_degradation within the parent tube adjacent to the nickel band is
- expected to be readily detectable, while detection of 50%
degradation depths are possible but at a lesser likelihood. A similar result is expected for circumferential degradation.
Plan for Completion SCE forecasts completion of the ongoing evaluation and technical basis development within the next year. This is being tracked within the SCE Corrective Action Program, as discussed in the response to request 2B below.
Page 2 of 6 2B.
If you conclude that full compliance with the TS in conjunction with Criteria IX, XI and XVI of 10 CFR Part 60, Appendix B, requires corrective actions, discuss your proposed corrective actions as requested by GL 2004-01, Requested Information #2. In addition, if the inspections are not being performed consistent with the NRC position on the requirements, submit a safety assessment as requested in GL 2004-01, Requested Information #3.
SCE response:
Three activities were discussed by SCE, Westinghouse (the sleeve supplier), and NRC in Reference 2. SCE provided a requested status report to the NRC in Reference 3. SCE entered these activities into its Corrective Action Program as follows:
- 1.
Investigate whether a technique can be qualified for detecting defects behind the nickel and microlok bands.
- 2.
Investigate the need to revise the topical report to address inspection of the region where the lower joint would be established.
- 3.
Address the implications of having flaws behind the nickel and microlok bands.
The corrective action status is summarized below.
Corrective Action 1 Status: Status was summarized in the above response to Request 2A. This remains open in the SCE corrective action program.
Corrective Action 2 Status: There is no need to revise the currently approved sleeve topical report (CEN-633-P, Rev. 02) to address inspection of the region where the lower joint would be established. Reference 4 (last paragraph on page 4 and first full paragraph on page 10) discusses that this has become a normal practice. Further, inspection of this region has become inherent in SCE's inspection for tube cracking in unsleeved tubes within the tubesheet. A license amendment request has been submitted to the NRC (Reference 1) that reflects this practice. SCE has closed this SCE Corrective Action Program item.
Corrective Action 3 Status: Reference 4 (a Westinghouse Owners Group Engineering Position Paper revised July 19, 2005) addresses the implications of postulated flaws behind the nickel band. Reference 4 explains why inservice inspection capabilities, within the parent tube due to the presence of the nickel band, are not required to ensure structural and leakage integrity of the tube/sleeve hardroll joint. Corrective Action 3 has been closed in the SCE corrective action program, since Corrective Action I remains open to address implications of NDE capabilities.
Page 3 of 6 A license change is not necessary for start up or for continued operation. provides a safety assessment that addresses any differences between the San Onofre Unit 2 sleeve inspection practices and those called for by the NRC's position. Reference 4 is the technical basis for the safety assessment (a Westinghouse Owners Group Engineering Position Paper). This assessment concludes that steam generator operability is maintained because the plant is in compliance with the program elements of Nuclear Energy Institute document number NEI 97-06, titled "Steam Generator Program Guidelines.'
Item 2B of this Request for Additional Information and item 3 of the Generic Letter also requests SCE to consider if the inspection practices rely on an acceptance standard which is different from the Technical Specification acceptance standards (i.e., the tube plugging limits or repair criteria). SCE response to item 2A of this Request for Additional Information describes ongoing evaluation of the capabilities of NDE techniques. This ongoing evaluation should increase understanding of technique capabilities relative to the existing Technical Specification tube plugging limit or repair criterion (44% TW in the parent tube).
Item 2B of this Request for Additional Information and item 3 of the Generic Letter also requests SCE to consider whether the safety assessment, performed for those conditions where sleeve inspections are not being performed consistent with the NRC's position, constitutes a change to the "method of evaluation" (as defined in 10CFR50.59) for establishing the structural and leakage integrity of the parent tube and/or the sleeve lower-most joint associated with it. In addressing this question, the GL inquires as to whether the safety assessment is redefining the ASME Section III pressure boundary and is using a different method of evaluation to demonstrate the structural and leakage integrity of the revised pressure boundary. SCE has reviewed GL 2004-01 and has concluded that the analysis approach does not redefine the ASME pressure boundary and is not a change in the method of evaluation per 1 OCFR50.59 based on the following:
- 1.
SCE does not consider the assessment approach, or the described inspection in the area of the sleeve nickel band, as redefining the ASME Section III pressure boundary. The extent of inspection does not, by itself, define the limits of the ASME pressure boundary. For example, the subject Generic Letter indicates that current technical specifications include language that excludes sections of cold leg tubing from inspection extent.
Page 4 of 6
- 2.
The NRC endorsed guidance for 10CFR 50.59 evaluations (NEI 96-07) defines "method of evaluation" and the associated 1 0CFR50.59 screening protocol. Section 4.3.8 of NEI 96-07 states that methods of evaluation that are not described, outlined or summarized in the UFSAR are excluded from departure consideration. The tube integrity assessments employed by SCE consider the entire length of pressure boundary tubing.
Undetected flaws and their impact on tube integrity are addressed. The assessments are consistent with industry standards. The analyses and analysis parameters are not described, outlined or summarized in ASME Section III, ASME Section Xl or in the UFSAR, and therefore would not constitute a change/departure in the method of evaluation per 10CFR 50.59.
- 3.
The safety assessment was performed in accordance with the provisions of the EPRI Steam Generator Integrity Assessment Guidelines and the structural and accident leakage integrity performance criteria specified in NEI 97-06. This ensures margins of safety consistent with the ASME Section III Code and draft Regulatory Guide 1.121 and that any potential accident leakage is within safety analysis limits.
Page 5 of 6
References:
- 1.
Letter from B. Katz (SCE) to the NRC Document Control Desk dated November 3, 2005;
Subject:
San Onofre Nuclear Generating Station, Units 2 and 3, Docket Nos. 50-361 and 50-362, Proposed Change Number NPF-10115-565, License Amendment Request, "Proposed Technical Specification Change, Define the Extent of the Required Tube Inspections and Repair Criteria Within the Tubesheet Region of the Steam Generators"
- 2.
Telephone Conference Call between NRC Staff, SCE and Westinghouse on March 17, 2004
- 3.
Letter from A. E. Scherer (SCE) to the Document Control Desk (NRC) dated September 23, 2004;
Subject:
Docket No. 50-361, Report of Inservice Inspection of Steam Generator Tubes, Cycle 13 Additional Information, San Onofre Nuclear Generating Station, Unit 2 (This is ADAMS Accession Number ML042710277)
- 4.
Final Engineering Position Paper on NDE Issues Related to TIG and Alloy 800 Sleeves with Regard to Sleeve Nickel Band NRC Discussion, Revisionl, dated July 19, 2005. This is Westinghouse Owners Group (WOG) document number WOG-05-388. This is not included with this submittal because it was previously provided to the NRC as Enclosure 1 of Reference 5 (ADAMS Accession Number ML052220335)
- 5.
Letter from M. Blevins (TXU Power, Comanche Peak Steam Electric Station) to the Document Control Desk (NRC) dated August 4, 2005;
Subject:
Comanche Peak Steam Electric Station (CPSES) Unit 1, Docket No. 50-445, Response to Request for Additional Information, RE: CPSES Response to Generic Letter 2004-01 Page 6 of 6 Safety Assessment The parent tube adjacent to the sleeve hardroll must be present in order for the sleeve hardroll joint to perform as designed. Thus, the parent tube in this region should be inspected so that parent tube conditions that could challenge structural and leakage integrity of the sleeve are detected. However, for a postulated condition of degradation in the parent tube radially adjacent to the sleeve's nickel band, the remaining tube/sleeve hardroll joint length above the nickel band will provide anchorage consistent with the design requirement. Therefore, in-service inspection capabilities within the parent tube due to the presence of the sleeve nickel band are not required to ensure structural or leakage integrity of the tube/sleeve hardroll joint. The technical basis for this position is a Westinghouse Owners Group Engineering (WOG) Position Paper, which is Reference 4 in Attachment 1.
The following table is a summary of NEI 97-06 performance criteria and the Sections of the WOG Position Paper that most directly address how the sleeve design addresses them.
NEI 97-06 Performance Criteria WOG Position Paper Section(s)
Structural Integrity Performance Load Bearing Capability of... sleeve joint for Criterion limited effective joint lengths Consistency of... sleeve joint design and performance with existing HEJ test data Accident Induced Leakage Leakage Integrity Performance Criterion Operational Leakage Leakage Integrity Performance Criterion In conclusion, steam generator operability is maintained because the plant is in compliance with the steam generator program elements of NEI 97-06.
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