ML20134K814
| ML20134K814 | |
| Person / Time | |
|---|---|
| Site: | Byron, Braidwood  |
| Issue date: | 02/12/1997 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20134K801 | List: |
| References | |
| NUDOCS 9702140243 | |
| Download: ML20134K814 (4) | |
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4 UNITED STATES s
j NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20066-0001
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. as TO FACILITY OPERATING LICENSE NO. NPF-37, AMENDMENT NO. as TO FACILITY OPERATING LICENSE NO. NPF-66, AMENDMENT NO. 77 TO FACILITY OPERATING LICENSE NO. NPF-72, AND AMENDMENT NO. 77 TO FACILITY OPERATING LICENSE NO. NPF-77 COMONWEALTH EDISON COMPANY BYRON STATION. UNIT NOS. 1 AND 2 BRAIDWOOD STATION. UNIT NOS. 1 AND 2 DOCKET NOS. STN 50-454. STN 50-455. STN 50-456 AND STN 50-457
1.0 INTRODUCTION
By letter dated August 2,1996, Commonwealth Edison Company (Comed, the licensee), submitted a request to amend the Facility Operating Licenses at Byron, Units 1 and 2, and Braidwood Stations, Units 1 and 2.
The proposed amendment would eliminate a license condition which requires the licensee to conduct additional corrosion testing of sleeved steam generator tubes.
Specifically, the amendments would eliminate License Condition 2.C.(16) from Facility Operating License NPF-37; License Condition 2.C.(5) from Facility Operating License NPF-66; License Condition 2.C.(6) from Facility Operating License NPF-72 and License Condition 2.C.(5) from Facility Operating License NPF-77.
Presently, the license conditions require additional corrosion testing to be conducted to establish the design life of laser welded sleeves in the presence of a crevice. The purpose of the testing is to determine the effects that 1
material microstructure, chemistry, and joint crevices will have on primary water stress corrosion cracking (PWSCC) initiation and growth. The testing is to bound the material condition that exists in Byron and Braidwood steam generators, and include the associated stress intensity values. The testing results are to be reviewed and accepted by the NRC prior to the beginning of Byron Unit 1 Cycle 9, Byron Unit 2 Cycle 8 and Braidwood Cycle 7 for Units 1 and 2.
Until this testing is satisfactorily completed, the licensee also committed to performing an augmented inspection (increased sample size) of the installed sleeves of each unit. This requirement would also be deleted following corrosion testing. However, this requirement was subsequently revised in Amendment Nos. 83 (Byron) and 76 (Braidwood) which approved sleeving by the ABB/CE Tungsten Inert Gas (TIG) welded sleeving process. The current 9702140243 970212 PDR ADOCK 05000454 P
Technical Specifications (TS) (e.g. TS 4.4.5.2. (for Byron and Braidwood))
require the licensee to perform an inservice inspection of a random sample of a minimum of 20 percent of the installed sleeves, regardless of type. This sampling plan is in accordance with present industry guidelines and will be continued regardless of the deletion of the license condition on corrosion testing.
2.0 EVALUATION On March 4, 1994, the staff issued license amendments 58 (Byron) and 46 (Braidwood) which revised the technical specifications to permit sleeving of steam generator tubes using either Westinghouse laser-welded or B&W kinetically welded sleeves.
In the accompanying Safety Evaluation, the staff restated certain commitments made by the licensee that when implemented, would provide assurance that performance of the sleeves would be carefully i
monitored.
The commitments were: (1) amend the licenses to reflect a primary-to-secondary leakage limit of 150 gallons per day; (2) amend the licenses to reflect a more conservative plugging limit in the inservice inspection program; and (3) add a condition to the licenses to conduct additional corrosion testing.
On June 3, 1994, the licensee requested i
amendments to the licenses to incorporate the three commitments; they were approved on January 6, 1995, in amendments 67 and 57 for Byron and Braidwood, respectively.
In requiring that accelerated corrosion testing be done, the staff believed that the service life prediction would apply to those components susceptible to stress corrosion cracking (SCC).
The service life would be predicted as a result of accelerated corrosion tests.
These tests
- +tamoted to define a correlation between vendor proprietary laboratory tests of
" components and in-plant service life (time to cracking in comp,s.vien aceptible to SCC).
The resulting deterministic service life predictions, would then be used to establish service lifetimes and reinspection intervals for sleeved tubes or other components.
As more information has become available, the staff has concluded that the information obtained from the accelerated corrosion testing is inconclusive in establishing a reliable prediction of steam generator sleeve service life.
Consequently, the staff has since rejected this approach and continues to 1
mandate periodic reinspections.
The staff now finds the industry developed sampling plan (EPRI NP-6201, "PWR Steam Generator Tube Examination Guidelines," Appendix H, " Performance Demonstration for Eddy Current Examinations") acceptable.
The reasons for discontinuing the life prediction approach included unresolved issues such as data scatter and poor predictive results when the method was applied to a certain type of tube plugs.
In previous evaluations of accelerated corrosion test based service life algorithms, the stated staff finding (and current staff conclusion) has been that:
..... accelerated corrosion tests provide a good qualitative assessment of relative service life for various sleeving processes. However, 4
quantitative estimates of service life do not have a high degree of
reliability.
For this reason, the staff does not accept deterministic life prediction calculations for tube materials.
Periodic inspection (as required by the Technical Specifications) and primary-to-secondary leakage monitoring will identify any premature degradation that may occur in the sleeved joints."
This, or wording similar thereto, may be found in TS amendment Safety Evaluations for welded sleeve installations at several plants including:
Waterford Steam Electric Station, Unit 3, Byron and Braidwood Stations (amendments 83 and 76, respectively), and others.
Furthermore, in other welded tube sleeve safety evaluations, the staff has noted previously that over 10 yr s of operating experience with welded sleeves (both laser welded and 11G welded) has shown the technology to be highly reliable. No operationally induced degradation or leakage has occurred in any welded sleeve, with over 25,000 installed to date.
Three or four instances of installation defects have occurred that resulted in inconsequential leaks. All were removed from service.
3.0
SUMMARY
The staff finds that the subject license conditions for the respective units comprising the Byron and Braidwood Stations are no longer applicable and may be deleted from the licensee's licenses as requested.
No additional corrosion testing of welded tube sleeves as specified under the terms of the subject license conditions is required or warranted.
4.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Illinois State official was notified of the proposed issuance of the amendments. The State official had no comments.
5.0 ENVIRONMENTAL CONSIDERATION
The amendments change a requirement with respect to the installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20. The NRC staff has determined that the amendments involve no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure.
The Commission has previously issued a proposed finding that the amendments involve no significant hazards consideration, and there has been no public comment on such finding (61 FR 50340). Accordingly, the amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).
Pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendments.
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6.0 CONCLUSION
The Commission has concluded, based on the considerations discussed above, that:
(1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with 'the Commission's regulations, and (3) the issuance of the amendments will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor: G. Hornseth Date:
February 12, 1997 4
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