ML17058A853

Discusses Flaw Evaluation & Possible Repair of HPCS Nozzle at Plant.Nrc Reviewed Revised Fracture Mechanics Analysis & Determined That Analysis Used Acceptable Residual Stress Distribution for Small Diameter Pipe

ML17058A853
Person / Time
Site:	Nine Mile Point
Issue date:	07/16/1991
From:	Brinkman D Office of Nuclear Reactor Regulation
To:	Sylvia B NIAGARA MOHAWK POWER CORP.
References
TAC-80557, NUDOCS 9107230378
Download: ML17058A853 (10)

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+p*y4 Docket No. 50-410 UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 July 16, 1991 Hr. B. Ralph Sylvia Executive Vice President, Nuclear Niagara tlohawk Power Corporation 301 Plainfield Road

Syracuse, New York 13211

SUBJECT:

FLA'kI EVALUATION AND POSSIBLE REPAIR OF HPCS NOZZLE AT NINE NILE POINT NUCLEAR STATION, UNIT 2 (TAC NO. 80557)

By letter dated December 28, 1990, Niagara IIohawk Power Corporation (NNPC) submitted for NRC staff review and approval a fracture mechanics evaluation of a flaw indication that had been detected in the weld (KC-32) joining the high pressure core spray (HPCS) nozzle safe end to the safe end extension.

In its safety evaluation dated January 11, 1991, the NRC staff concluded that weld KC-32 should be ultrasonically reexamined during the mid-cycle inspection and the fracture analysis required revision to include an assessment of the residual weld stresses and flaw sizing uncertainties.

In a letter dated June 10,

1991, NMPC proposed a contingent repair plan and a weld overlay design for repairing the flaw.

Subsequently, on June 19, 1991, NIIPC met with the NRC staff to discuss the revised analysis.

By letter dated June 28, 1991, NIIPC submitted the revised fracture analysis and a proposed acceptance criterion for flaw repair.

The NRC staff has reviewed the revised fracture mechanics analysis and has determined that the analysis used an acceptable residual stress distribution which is for small diameter pipe (less than 12-inches).

Nh1PC stated that the uncertainty associated with the ultrasonic test (UT) performed on weld KC-32 was 5X.

The NRC staff concludes that the revised fracture mechanics analysis is acceptable because the staff's concerns identified in its January 11, 1991, safety evaluation have been answered satisfactorily.

NhIPC proposed to use an increase of no greater than 10% in the length or depth of the flaw as an acceptance criterion for restart after the mid-cycle inspection.

The 10% criterion is a combination of 5X on UT uncertainty and 5%

on postulated crack propagation.

The NRC staff has concluded that the 10%

criterion is acceptable.

If the mid-cycle inspection shows that the flaw has grown more than 10% of the existing length or depth, NIIPC must repair the HPCS nozzle safe end weld before restart.

Otherwise, the repair is not necessary and the plant may resume and continue operation to the end of the fuel cycle.

However, if the weld is not repaired, Nt<PC must reexamine the flaw during the refueling outage at the end of Cycle 2 and perform further evaluation or repair.

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Mr. B. Ralph Sylvia July 16, 1991 The NRC staff has also reviewed the proposed contingency repair plan and the weld overlay design basis for repairing weld KC-32.

NMPC proposed to apply a

full structural Inconel 82 weld overlay if growth of the existing flaw in the weld exceeds the proposed acceptance criteria (10% of the existing flaw size) during the mid-cycle examination.

The designed overlay will completely cover the flawed weld (Inconel 182) and a portion of the safe end (SB-166) and safe end extension (SA 508 Class 1).

The NRC staff has concluded that, with certain modifications, the proposed repair plan and the weld overlay design basis is acceptable provided the following items are incorporated into NMPC's proposed contingent repair plan:

1.

NMPC is requested to document its bases for concluding that post-weld-heat treatment (PWHT) is not required for the components to be welded.

This documentation is to be included in the written report requested below and should include a discussion of any required weld pre-heat and 'interpass temperature requirements.

NMPC is also requested to provide a copy of the proposed welding procedure and procedure qualification record to the NRC Resident Inspector at least seven days prior to initiation of welding.

2.

The minimum required weld overlay thickness was calculated to be 0.255 inches in Table 1 - Weld Overlay Thickness Calculation Summary of NMPC's presentation at the meeting held on June 19, 1991.

'However, the calculated minimum thickness does not qualify for a full structural overlay because it does not meet the maximum allowable flaw depth of 75% of through wall thickness in ASMf Code,Section XI, Article IWB-3640.

The maximum Code allowable flaw depth should be maintained to provide additional margin in preventing leakage and in accommodating the uncertainties regarding the propagation mechanism for deep cracks.

Therefore, NMPC should ensure that the minimum thickness of the weld overlay in the flaw region is 0.3 inches.

3.

Other BWR owners have reported that the cumulated shrinkages resulting from weld overlay 'repairs had affected the normal settings required for the piping supports and pipe whip restraints.

Therefore, NMPC should assess the effect of overlay shrinkages in the piping system and its supports and pipe whip restraints.

NMPC should also assess the effect of increased deadweight and stiffness due to overlay repairs in the piping system.

Within 30 days subsequent to the completion of the mid-cycle inspection, NMPC is requested to inform the NRC, in writing, of the results of the inspection of weld KC-32 as well as the resolution of the above three contingencies if repairs are required.

Hr.. B. Ralph Sylvia July 16, 1991 This requirement for information affects one respondent; therefore, is not subject to Office of t1anagement and Budget review under P.L.96-511.

Sincerely, cc:

See next page Donald S. Brinkman, Senior Project 11anager Project Directorate I-1 Division of Reactor Projects - I/II Office of Nuclear Reactor Regulation

,Mv. B. Ralph Sylvia Niagara Mohawk Power Corporation Nine Mile Point Nuclear Station Unit 2 CC:

Hr. Mark J. Wetterhahn, Esquire Winston 5 Strawn 1400 L Street, NW.

Washington, D.C. 20005-3502 Mr. Richard Goldsmith Syracuse University, College of Law E. I. White Hall Campus

Syracuse, New York 12223 Resident Inspector Nine Hile Point Nuclear Power Station P. 0.

Box 126

Lycoming, New York 13093 Mr. Gary D. Wilson, Esquire Niagara Mohawk Power Corporation 300 Erie Boulevard West

Syracuse, flew York 13202 Hr. David K. Greene Manager Licensing Niagara Mohawk Power Corporation 301 Plainfield Road

Syracuse, New York 13212 Ms. Donna Ross Ncw York State Energy Office 2 Empire State Plaza 16th Floor

Albany, New York 12223 Supervisor Town of Scriba R. D. 84

Oswego, New York 13126 Regional Administrator, Region I U.S. Nuclear Regulatory Commission 475 Allendale Road King of Prussia, Pennsylvania 19406 Charlie Donaldson, Esquire Assistant Attorney General New York Department of Law 120 Broadway New York, New York 10271 Hr. Richard M. Kessel Chair and Executive Director State Consumer Protection Board 99 Washington Avenue

Albany, New York 12210 Mr. Hartin J. McCormick Jr.

Plant Manager, Unit 2 Nine Nile Point Nuclear Station Niagara Mohawk Power Corporation P. 0.

Box 32

Lycoming, NY 13093 Mr'. Joseph F. Firlit Vice President

- Nuclear Generation Nine Mile Point Nuclear Station Niagara Mohawk Corporation P. 0.

Box 32

Lycoming, New York 13093

n gr: B. Ralph Sylvia July 16, 1991 This requirement for information affects one respondent; therefore, is not subject to Office of Management and Budget review under P.L.96-511.

Sincerely, ORIGINAL'IGHED bY) cc:

See next page Donald S. Brinkman, Senior Project Manager Project Directorate I-1 Division of Reactor Projects - I/II Office of Nuclear Reactor Regulation Distribution:

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