ML20128G764
| ML20128G764 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 06/17/1985 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20128G757 | List: |
| References | |
| TAC-57126, NUDOCS 8507090314 | |
| Download: ML20128G764 (5) | |
Text
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NUCLEAR REGULATORY COMMISSION WASHING TON. D. C. 20555
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ENCLOSURE SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION REQUESTS FOR RELIEF FROM ASME CODE SECTION XI EXAMINATION REQUIREMENTS FOR REACTOR COOLANT PUMP CASING WELDS A.'lD INTERNAL SURFACES SACR *,MENTO MUNICIPAL UTILITY DISTRICT RANCHO SECO NUCLEAR GENERATING STATION DOCKET NO. 50-312 I.
BACKGROUND Technical Specification 4.2.2 for the Rancho Seco Nuclear Generating
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Station states that inservica examination of ASME Code Class 1, 2, and 3 components shall be performed in accordance with the requirements of Section XI of the ASME Boiler and Pressure Vessel Code and applicable l
addenda as required by 10 CFR 50.55a(g) except where specific written relief has been granted by the Commission.
By letter dated January 28 I
1983, the NRC transmitted to the Sacramento Municipal Utility District (SMUD) a Safety Evaluation with an attached Technical Evaluation Report in which requests for relief from certain examination and testing require-ments of Section XI for Rancho Seco were evaluated and the requests either granted or denied.
The granting or denying of the requests was based on information submitted to the NRC by SMUD by letters dated July 18 and December 10, 1979, and April 19, 1982, in the inservice inspection program, revisions, or additional information related to requests for relief from the Code requirements for Ranch Seco.
ByletterdatedMarch5,1985,SMUDtransmittedtothe$RCarevisionto the request for relief from examination of the reactor coolant pumos at Rancho Seco.
This request had been denied in the Safety Evaluation / Technical pg7090314gD000312 50617 ADocM l
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Evaluation Report cited above.
The revised request and supporting infor-mation are evaluated and the necessary findings made to grant relief from i
the Section XI requirements.
The revised request, supporting information, and our evaluation and conclusions are given below.
II.
REQUEST, INFORMATION, EVALUATION, AND CONCLUSIONS RELIEF REQUEST Relief is requested from performing 100% of the' Code requirements for a reactor cpolant pump CODE REQUIREMENTS (1974 Edition, Summer 1975 Addenda) 6 (1)
Item B 5.6, Examination Category B-L-1:
I The pressure-retaining welds in the pump casing shall be volu-metrically examined during each inspection interval.
The examination shall. include 100% of the welds in at least one pump in each group of pumps performing similar functions in the system.
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areas examined shall include the weld metal and base metal for I
one wall thickness beyond the edge of the weld.
(2)
Item B 5.7, Examination Category B-L-2:
The internal pressure boundary surfaces of one pump in each group of pumps performing similar functions in the system shall be visually examined during each inspection interval.
The examination may be performed on the same pump selected for the Category B-L-1 examination.
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The B-L-1 and B-L-2 examinations may be performed at or near end of the inspection interval.
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3 LICENSEE'S BASES FOR RE0 VESTING RELIEF
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The Reactor Coolant Pumps were designed and manufactured by Bingham-Willamette Company before Section XI of the ASME Boiler and Pressure Vessel Code was developed.
The pump casing was designed in such a way that a large portion of the internal pressure boundary is inaccessible for visual inspection, and small areas at the outer edges of the volute are inaccessible for volumetric inspection using radio-graphy.
The area on the inside radius of the discharge nozzle is too thick (.14") to inspect witti any available technique.
The geometry of the pump casing and the internal volute also make it impractical to achieve the IT base metal coverage specified by Table IWB 2500 of the 1974 Section XI with Summer '75 Addenda.
The pump casing is composed of cast stainless steel.
Ultrasonic inspection is impractical due to the large grain size and high attentuation.
Therefore, the Code as it presently stands does not give adequate consideration to pumps that were designed in this manner.
These areas can be seen on the attached illustration.
A visual inspection of the areas above the internal volute would require cutting the pump casing open.
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PROPOSED ALTERNATE EXAMINATIONS
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The retraining portion of the casing can be visually and volumetrically inspected and the results of this portion of the inspection should be indicative of the conditions that may exist in the inaccessible areas.
The area covered by the volumetric inspection will be as shown in figure IWB-2500-16 of the 1980 Edition of ASME Section XI, except in the areas covered by the volute (estimated to be less than 7% of the area of interest) and the inside radius of the discharge nozzle (approximately 5% of the area of interest).
The visual inspection will cover those areas accessible through the four volute openings.
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STAFF EVALUATION AND CONCLUSIONS The Code requirements to perform (1) volumetric examination of 100% of j
the pressure-retaining pump casing weld, (2) visual examination of 100%
i of the internal pressure boundary surfaces, and (3) volumetric examination of the base metal for one wall thickness beyond the edge of.the weld are i
impractical to perfora on the reactor coolant pumps at Rancho Seco because of the pumps' design.
The internal volute prevents access for performing
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100% volumetric examination of the pump casing weld and 100% visual in-spection of the internal surfaces.
The base metal thickness of the pump casing (which can typically vary from 8 inches to 14 inches) makes the requirement to examine one wall thickness beyond the edge of the weld I
an impractical requirement.
We have reviewed the Code requirements as applicable to the Rancho Seco reactor coolant pump examinations. The licensee stated in the letter of March 5, 1985, that the area subject to examination but covered by the pump volute is less than 7% and that in the area of the discharge nozzle f
approximately 5%. The requirement to examine the base metal one wall thickness beyond the edge of the weld was changed in later editions of the, Code in recognition that the heat affected zone does not extend one wall thickness in relatively thick components. The requirement was changed to l
1/2-inch beyond the edge of the weld as shown in !WB-2500-16 of the 1980 l
Edition of Section XI and as proposed to be examined by the licensee.
We conclude that the licensee's proposed alternative examinations of the l
reactor coolant pumps at Rancho Seco will provide the necessary assurance of the pumps' structural integrity and that relief from the requirements, as I
requested, may be granted. We conclude, based on the considerations
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discussed above, that the granting of this relief is authorized by law and l
l will not endanger life or property or the comon defense and security and is I
otherwise in the public interest giving due consideration to the burden upon the licensee that could result if the requirements were imposed on the l
facility.
Dated:
Principal Contributor: G. Johnson i
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