ML20034G409
| ML20034G409 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 03/04/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20034G410 | List: |
| References | |
| NUDOCS 9303090479 | |
| Download: ML20034G409 (2) | |
Text
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4 UNITED STATES i
E NUCl. EAR REGULATORY COMMISSION E'
f MSHINGTON. D.C. 23555-0001
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RE0 VEST FOR RELIEF FROM THE ASME CODE INSPECTION REOUIREMENTS FOR CONTAINMENT ELECTRICAL PENETRATION WELDS PACIFIC GAS AND ELECTRIC COMPANY i
DIABLO CANYON POWER PLANT. UNITS 1 AND 2 DOCKET NOS. 50-275 AND 50-323
1.0 INTRODUCTION
By letters dated July 14, 1992 and February 8, 1993, Pacific Gas and Electric (PG&E), the licensee, requested relief from the inspection requirements of ASME Code Section III, paragraph NE-5221.
In place of NE-5221, the licensee proposed substitution of Code case N-505. NE-5221 specifies that volumetric methods, either radiography (RT) or ultrtsonic (UT), be employed to inspect full penetration butt welds in containment penetrations. Code case N-505 provides for alternative use of liquid penetrant (PT) or magnetic particle (MT) examination of containment penetration welds. Code case N-505 has been adopted by the ASME Main Committee but its evaluation for incorporation by reference in the appropriate Regulatory Guide is pre-decisional, hence the need for NRC approval.
The proposed Code case application was for refueling outage work planned on four 12 inch diameter containment electrical penetrations at Diablo Canyon Power Plant Units 1 and 2.
Twc electrical penetrations on each unit were planned to be replaced during their respective refueling catages; unit 2 fifth refueling outage (2R5) and unit I sixth refueling outage (lR6). The final closure welds would be butt weld joints on the outside portion of containment electrical penetrations 10E and 6E (both units). The closure weld would be performed after the cables were reinstalled in the conduit.
The basis of the licensee's request was the impracticality of performing RT of a cable conduit with wires and cables inside. Their presence would interfere with the interpretation of a radiograph. The licensee has had unsatisfactory experiences with UT in previous similar applications.
In the past, UT has resulted in false indications of flaws. This resulted in an excessive amount of weld repair and delays that were found to be unnecessary.
2.0 DISCUSSION ASME Section Ill permits electrical penetration welds to be either lap joints with fillet welds er full penetration butt joints.
Fillet welds can only be examined by means of a surface examination (PT or MT).
Full penetration butt 9303090479 930304 PDR ADOCK 05000275 P
welds are required by the Code to be examined by volumetric means (RT or UT).
This is a more comprehensive, and thus more stringent, examination than the surface examination required of the fillet welds.
Code case N-505 permits surface examinations of the butt weld as it is being executed as an alternative to the volumetric examination requirement in Section III.
This is accomplished by requiring PT or MT of the butt weld root pass and the completed weld. Since a majority of weld defects are found in either the root or final passes, this examination of both passes provides a reasonable assurance that a structurally sound weld is produced.
For welds greater in thickness than 3/8 inch, an intermediate P) or MT examination is required after approximately half the weld thickness has been deposited.
A second requirement of the Code case is a reduction in the allowable stress for the weld joint. The allowable stress for the joint is reduced to 80% of that for a radiographed butt joint. This follows the practice of pressure vessel design wherein allowable joint strength is reduced by factors that are dependent upon the degree and type of weld examination. The staff finds this to be a reasonably conservative approach to structural design.
A prime function of the containment is leak isolation in the event of design basis events.
In order to perform this function, leak tightness must be maintained to the maximum extent practical.
This can be demonstrated by one of a variety of leak tests: pressure test with air, helium leak, or vacuum box.
In addition to the surface examinations specified in the Code case, the licensae is required to perform a leak tightness test on the associated containment electrical penetration welds in accordance with Diablo Canyon Post Modification Test-45.06, " Pressurized Test of Conax Penetrations 06E and 10E Welds." Thus, the proposed alternative will provide reasonable assurance that the subject butt welds would perform the intended functions and, thus, provide an acceptable level of quality and safety.
3.0 CONCLUSION
Pursuant to 10 CFR 50.55a(a)(3), the use of other Code cases may be authorized by the staff. The licensee must demonstrate that (i) the proposed alternatives would provide an acceptable level of quality and safety, or (ii) compliance with the specified requirements of this section would result in hardship or unusual difficulties without a compensating increase in the level of quality and safety. The staff finds that the proposed use of Code case N-505 will provide an acceptable level of quality and safety and, pursuant to 10 CFR 50.55a(a)(3)(i), is authorized for use during refueling outages 2R5 and 1R6 at Diablo Canyon Power Plant.
Principal Contributor: G. Hornseth Date:
March 4, 1993 l
l
t Docket Nos. 50-275 and 50-323
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Mr. Gregory M. Rueger
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7 Nuclear Power Generation, B14A f
Pacific Gas and Electric Company
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77 Beale Street, Room 1451
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P.O. Box 770000 San Francisco, California 94177 f
Dear Mr. Rueger:
SUBJECT:
REQUEST FOR RELIEF FROM THE ASME CODE INSPECTION REQ REMENTS FOR f
CONTAINMENT ELECTRICAL PENETRATIONS, DIA3LO CANYON 0 NITS 1 AND 2 f
(TAC NOS. M84115 AND M84116)
By letters dated July 14, 1992, as supplemented February 8, 1993, you l
requested relief from the ASME Code requirements for iffspection of containment electrical penetration welds. The relief request prp$osed substitution of the alternative requirements of Code case N-505, which as not been incorporated by reference in the appropriate Regulatory Guide. The staff concluded that i
the proposed alternative may be authorized pursu nt to 10 CFR 50.55a(a)(3).
This alternative will provide an acceptable
'el of quality and safety.
A copy of the related Safety E.aluation is inclosed.
This completes the staff effortonthisissueandclosesTACNos.Jis4115andM84116.
If you have any j
questions regarding this matter, pleaseA ontact Sheri Peterson at i
(301) 504-1325.
l Sincerely, Theodore R. Qauy, Director i
Project Directorate V
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Division of Reactor Projects III/IV/V l
Office of Nuclear Reactor Regulation
Enclosures:
Safety Evaluation
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cc w/ enclosure:
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