ML20058C146

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Safety Evaluation Supporting Amends 85 & 78 to Licenses NPF-2 & NPF-8,respectively
ML20058C146
Person / Time
Site: Farley  
Issue date: 10/22/1990
From:
Office of Nuclear Reactor Regulation
To:
Shared Package
ML20058C145 List:
References
NUDOCS 9011010011
Download: ML20058C146 (6)
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO. 85 TO FACILITY OPERATING LICENSE N0. NPF-2 AND AMENDFENT NO. 78 TO FACILITY OPERATING LICENSE G. NPF-8 ALABAMA POWER COMPANY 1

JOSEPH M. FARLEY NUCLEAR PLANT. UNITS 1 AND 2 DOCKET NOS. 50-348 AND 50-36_4

1.0 INTRODUCTION

By letter dated August 16, 1990, the Alabama Power Company submitted a reouest for changes to the Joseph M. Farley Plant (Farley) Units 1 and 2, t

Technical Specifications to allow steam generator tube sleeving using a laser welding methodology developed by Westinghouse. The amendment requests are applicable to both Units 1 and 2.

The technical justifica-tion supporting the proposed changes was provided as WCAP-12672, " Steam Generator Sleeving Report, Laser Welded Sleeves, J. M. Farley Units 1 i

and 2," (Proprietary), and WCAP-12673, " Steam Generator Sleeving Report, Laser Wolded Sleeves, J. M. Farley Units 1 and 2 " (Non-proprietary).

2.0 BACKGROUND

The proposed amendments would modify a portion of the Technical Specifications to specify the requirements for the repair of steam generator tubes by installation of sleeves with laser welded joints..

I Currently, the Farley, Units 1 and 2. Technical Specifications include requirements for repair using sleeves with mechanical joints for those steam generator tubes with eddy current indications showing greater than 40% through wall degradation. The proposed Technical Specification changes would specify the requirements for repairing degraded or defective tubes utilizing sleeves with laser welded l

joints. The proposed amendments also include criteria for allowable wall degradation in.the sleeve and in the tube in the region of the sleeve to tube joint.

3.0 DISCUSSION The supporting technical and safety evaluations for the subject amendments (WCAP-12672), show that the repair of degraded tubes using sleeves will result in tube bundle integrity consistent with the. original design basis.

The sleeving report addresses three distinct types of sleeves - a full length tubesheet sleeve, an elevated.tubesheet-sleeve, and a support i

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I plate sleeve. The full length tubesheet sleeve is us ed for degradation at the top of the tubesheet, since the lower joint h formed at the bottom of the tubesheet. The elevated tubesheet sleeve is used at Farley, Unit 2, because Farley, Unit 2} previously accepted by the NRC.

has full depth rolled tubes and an alternate plugging criterion (F*

The alternate plugging criterion allows tube degradation below a predetermined distance from the tubesheet secondary face to remain in service due to the support the tubesheet provides in the area of the defect.

For the elevated tubesheet sleeves, the sleeve's lower joint is formed at an elevation above the primary face of the tubesheet, which means the tube is the pressure boundary for some portion within the tubesheet. The support plate sleeve may be installed to bridge degradation located at tube support plate locations or in the free tube span.-

Laser velding sleeving technology has been previously applied at Doel 3 in Belgium in July 1988. Fif ty-five sleeves were installed and inspected i

in a demonstration program. Two tubes with laser welded sleeves were removed after one year of operation and metallographically examined. The' results of this inspection verified that both process parameters and inprocess inspection were accurate barometers of the as produced laser weld.

The Farley laser weld system produces a weld equivalent to the system applied at Doel 3.

The major differences are that the previous system used a gaseous CO2 laser while the current system uses a solid state Nd:

YAG laser and the CO2 system was mounted to the steam generator manway and directed by mirrors while the Nd:YAG system is delivered from outside the containment building by fiberoptic cable.

3.0,E1ALUATION The staff evaluation of the amendments proposed by Alabama Power Company and the WCAP-12672 report prepared by Westinghouse is based upon the following considerations. Steam generator tube sleeving is a repair technique that is an alternative to removing defective or degrading tubes from service by plugging. Sleeves are designed to span a defective or degraded region of a steam generator tube and to maintain the steam generator tubing primary-to-secondary pressure boundary under normal and accident conditions. A successful sleeving system must provide a corrosion resistant sleeve material with structural integrity and leak l

tightness of the sleeved tube. The sleeving process must not have a detrimental effect on the serviceability of the existing tube.

The sleeve configuration has been designed and analyzed in accordance with the rules of the ASME Boiler and Pressure Vessel Code.

Fatigue and

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stress' analyses of the sleeved tube assemblies produced acceptable i

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3-results. Mechanical testing has shown that the structural t ength of the sleeves under normal, faulted and upset conditions is wi ain acceptable limits.

Leak rate testing has demonstrated that he leak rates of the joints between the sleeve and the existing tube ander normal, faulted and upset conditions are below acceptable rates.

The existing Technical Specification's leakage rate requirements and accident analysis assumptions remain unchanged in the event leakage from the sleeve would occur. Any leakage through the sleeved region of the tube due to localized tube degradation.is bounded by the existing steam generator tube rupture analysis. The proposed Technical Specification changes to support i

the installation of laser welded joint sleeves does not adversely impact any other previously evaluated design basis ~ accident or the results of LOCA and non-LOCA accident analyses.

The results of the qualification testing, analyses, and plant operating experience demonstrate that the sleeve assembly is an acceptable means of maintaining tubes in service.

Furthermore, in accordance with Regulatory Guide 1.83 reconnendations, the sleeved tube can be monitored through periodic inspections with present eddy current techniques.

Plugging limit criteria are established in the technical specifications for the tube in the region of the sleeve.

The sleeve repair of degraded steam generator tubes, as identified in the sleeving report, has been demonstrated to restore the integrity of the tube bundle under normal and postulated accident conditions.

The safety factors used in the design of sleeves for the repair of degraded tubes are the safety factors given in the ASME Boiler and Pressure Vessel Code used in steam generator design, ib plugging limit criteria for the 1

sleeve has been established using the methodology contained in Regulatory 1'

Guide 1.121, and includes an additional margin (20%) as required by the staff. The design of the sleeve joints has been verified by testing to preclude significant leakage during normal and postulated accident conditions. Use of the ASME Code and Regulatory Guide 1.121 criteria and methods assures that the margin to safety with respect to structural i

integrity is the same for the sleeves as for the original steam generator tubes.

The staff concurs that the use of Inconel 690 TT sleeves is an improvement over the Inconel 600 material used in the original steam generator tubing.

Corrosion tests conducted under the Electric Power Research Institute (EPRI) sponsorship confirm WCAP-12672 test results regarding the improved 1

corrosion resistance of Inconel 690 TT over that of Inconel 600.

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Accelerated stress corrosion tests in caustic and chloride aqueous solutions have also indicated that Inconel 690 TT resists general corrosion in aggressive environments.

Isothermal tests in high purit water have shown that, at normal stress levels, Inconel 690 TT has hi h resistance to intergranular stress corrosion cracking under extended igh temperature exposure. EPRI concluded as a result of these laboratory corrosion tests that Inconel 690 TT material could be used.for PWR steam generator tubing with all volatile treatment of secondary water systems, i

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In addition to the Doel 3 demonstration program experience, extensive testing of laser welded joints shows that the laser welds meet dimensional and general weld quality requirements.

Weld process qualifications verify that the process is capable of reproducing sound welds. Laser welded joints, not within the tube sheet, will be given a post-weld heat treatment (PWHT) that relieves the residual stresses in the tube.

Residual stresses in areas adjacent to welds develop due to weld metal shrinkage upon solidification of the weld metal.

In mill annealed Alloy 600 tubing that is susceptible to primary water stress corrosion cracking (PWSCC), the post-weld residual stresses could contribute to the induction of PWSCC. Tests of as-welded joints in susceptible mill annealed Alloy 600 tubes indicate that the residual stresses adjacent to the laser weld do not lead to the degree of PWSCC as that experienced by roll transitions. Nevertheless, the process includes a PWHT that provides further enhancement in PWSCC resistance of the tubing, k

Thenon-destructiveexamination(NDE)ofthelaserweldedsleeves i

utilizes two techniques.

First a method to confirm that the laser welds meet critical proces,s dimensions and acceptable weld quality. Secondly, tests have shown that the sleeve / tube assembly is capable of being evaluated through subsequent routine in-service inspection. Ultrasonic inspection techniques are used during sleeve installation to confirm weld acceptance and eddy current inspection technology is used to establish baseline inspection and perform subsequent in-service inspections.

Conventional eddy current techniques have been modified to incorporate the most recent technology in the inspection of the sleeve / tube assembly.

Inspection of the sleeve / tube assembly involves the use of a cross-wound coil for the straight regions of the sleeve / tube assembly and for the transition regions.

The inspection of sleeves will necessitate the use of an eddy current probe than can pass through the sleeve's-internal diameter.

For the tube span between sleeves, this will result in a smaller fill factor than is optimum.

The possibility for tube degradation in free span lengths is I

less, as plant data have shown that this. area is less susceptible than other locations.

In the event that an indication is detected, the 3

licensee has made the commitment that any tube indication in this region that has not been previously identified on the prior sleeved tube baseline inspection, will require further inspection by alternate techriques prior to acceptance of that indication.

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SUMMARY

Based on the preceding analysis, it is concluded that operation of Farle Units 1 and 2, in accordance with the proposed amendment is acceptable. y, The staff further finds that the use of the eddy current equipment and techniques as described in WCAP-12672 or their equivalent to be currently ac:eptable. However, the licensee has comitted to utilize advanced state-of-the-art techniques as they are developed and verified after a 10 CFR 50.59 review.

5.0 ENVIRONMENTAL CONSIDERATION

These amendments change a requirement with respect to installation or use of a facility component located within the restricted areas as defined i

in 10 CFR Part 20 and change the surveillance requirements.

l The staff has determined that these amendments involve no significant increase in the amounts, and no significant change in the types of any effluents that may be released off site, and that there is no significant increase in individual or cumulative occupational radiation exposure.

The Comission has previously issued a proposed finding that these amendments involve no significant hazards consideration, and there has been no public

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conenent on such finding.

Accordingly, these amendments meet the eli orical exclusion set forth in 10 CFR 51.22(gi-c)(9).

bility criteria for categ(b), no environmental impact statement or environ Pursuant to 10 CFR 51.22 i

mental assessment need be prepared in connection with the issuance of these amendments.

6.0 CONCLUSION

The Comission made a proposed determination that this. amendment involves no significant hazards consideration which was published in the Federal Reairter (55 FR 38598) on September 19, 1990, and consulted with sne state of A'abamh. No public comments or requests for hearing were received, and the State of Alabama did not have any comments.

i The staff has concluded, based on the considerations discussed above, that:

(1) there is reasonable assurance that the health and safet p(ublic will not be endangered by operation in the proposed manner,y of the

2) such activities will be conducted in compliance with the Comission's regulations, and (3) the issuance of these amendments will not be inimical to the conrnon defense and security or to the health and safety of the public.

Dated: October 22, 1990 princiDal Contributor:

H.

Conrad i

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AMENDMENT NO. 85 TO FACILITY OPERATING LICENSE NO NPR FARLEY, UNIT 1 AMENDMENT NO. 78 TO FACILITY OPERATING LICENSE NO. NPF FARLEY, UNIT 2 Decket*ffTe NRC PDR Local PDR PDII-1 Reading)

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