ML18040A260

Forwards SE Re Reinsp of Core Shroud Stabilizer Lower Wedge Retaining Clip & Evaluation of Shroud Vertical Weld Cracking

ML18040A260
Person / Time
Site:	Nine Mile Point
Issue date:	05/08/1997
From:	Hood D NRC (Affiliation Not Assigned)
To:	Sylvia B NIAGARA MOHAWK POWER CORP.
Shared Package
ML17059B543	List: ML17059B542 ML18040A260
References
GL-94-03, GL-94-3, TAC-M98170, NUDOCS 9705160106
Download: ML18040A260 (14)

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uNrraa salas UCl.EAR REGULATORYCOMMi~dlON WASHlNOTON) 0 C 305560M Hay 8, 1997 I

I gg F20 Hr. B. Ralph Sylvia Executive Vice President, Generation Business

Group, and Chief Nuclear Officer Niagara Hohawk Power Corporation Nuclear Learning Center

'450 Lake Road

Oswego, NY 13126 SUNECT MODIFICATIONS TO CORE SHROUD STABILIZER LOWER MEDGE RETAINING CLIP AND EVALUATIONQF SHROUD VERTICAL MELD CRACKING, NINE HILE POINT NUCLEAR STATION, UNIT NO.

1 (TAC NO. H98170)

Dear Mr. Sylvia:

During the 1995 refueling outage for Nine Hile Point Nuclear Station, Unit No.

1 (NHPl), Niagara Hohawk Power Corporation (NHPC) installed four core shroud stabilizer assemblies consisting of tie rods, brackets,

springs, wedges, and other parts.

This repair Ieasure was implemented to ensure the structural integrity of the core shroud with respect to the function of the circumferential welds that experienced cracks in somq boiling-water reactors (BWRs) as discussed in NRC Generic Letter 94-03, 'Intergranular Stress Corrosion Cracking of Core Shrouds in Boiling Mater Reactors,"

and other communications.

The 1995 shroud repair'was designed as an alternative to the requirements of the American Society of. Hechanical Engineers Boiler and Pressure Vessel Code (ASHE Code) pursuant to 10 CFR 50,55a(a)(3)(i) and was approved by the NRC staff by letter dated Harch 31, '1995.

During the 1997 refueling outage, NHPC inspected core shroud vertical welds in accordance with the BWR Vessel and Interna'ls Program (BWRVIP) document BWRYIP-07, 'Guidelines for Reinspection of BWR Core Shrouds'," dated February

1996, and observed cracks in excess of the screening criteria.

NHPC inspected the four shroud stabilizer assemblies and found that the tie rod nuts had lost some preload and that the. lower wedge retainer clips on three of the stabilizer assemblies had experienced damage.

NHPC informed the NRC staff of the inspection findings by telephone calls on Harch 20 and April 2, 1997.

By letter dated April 8, 1997, NHPC described the inspection findings, provided analyses of the vertical weld cracking, and proposed a plan to restore the stabiTizer assemblies to function as intended by the original design.

In the April 8 letter, NHPC discussed root cause and corrective

actions, provided design documentation and evaluations to demonstrate the acceptability of the as-found vertical weld cracking for, at least 10,600 hours0.00694 days <br />0.167 hours <br />9.920635e-4 weeks <br />2.283e-4 months <br /> of hot.(above 200 'F) operation, proposed a veld re-inspection

schedule, described actions taken to restore the stabilizer assemblies to the as-designed condition,, and proposed a lodification to the lower wedge retainer clip design.

NHPC requested the NRC staff's approval of the modified lower wedge retainer clips as an alternate repair under the ASHE Code Section XI definition of repair or replacement pursuant to 10 CFR 50.55a(a)(3)(i) for the proposed operating cycle of 10,600 hours0.00694 days <br />0.167 hours <br />9.920635e-4 weeks <br />2.283e-4 months <br />.

To support the design assumptions for the repair (i.e., that the horizontal welds were completely cracked for 9705160i06 970508 PDR ADQCK 05000220 9

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8. Sylvia 360'),

NMPC included a flaw-analysis for the vertical welds demonstrating that

~ ASIDE Code,Section XI margins would be maintained for'he operating period.

To support the request for approval, NNPC provided additional information by letters dated April 11, 23, 25 (two letters),

26, 27 (two letters),

30, and Hay 7, l997.

. As discussed in the enclosed safety evaluation (SE), the HRC staff has reviewed the proposed modification to the lower wedge retainer clip design and finds that it adequately restores the stabilizer assemblies to the intended function previously approved by the NRC staff.

The proposed modification is, therefore, acceptable.

The NRC staff has also reviewed the vertical welds and finds them acceptable for 10,600 hours0.00694 days <br />0.167 hours <br />9.920635e-4 weeks <br />2.283e-4 months <br /> of hot operation as proposed.

The NHPI core shroud cracks and stabilizer assembly repairs have been of considerable interest to members of the public, local officials, and various organizations.

The NRC staff received several questions and statements of concern during meetings in Fulton, New York, with the public on April l4,

1997, and in related correspondence.

The enclosed SE also addresses co@vents on the shroud and stabilizer assemblies received at this meeting and in related correspondence.

The NRC recognizes that your Nuclear Division Directive on Chemistry and Chemistry Department monitoring procedures have incorporated applicable values and action levels issued by the Electric Power Research 'Institute in "BWR Mater Chemistry Guidelines l996 Revision" and that you will continue to follow these 'guidelines throughout the upcoming operating cycle.

Me further recognize your intent to complete evaluati'on of the metallurgical ("boat")

samples of.the shroud cracks and provide a report to the NRC in September 1997.

Me request that you keep us'informed of any changes to this schedule.

Me acknowledge, based on your letter dated April 30, 1997, that you will provide us with copies of your reinspection plans for the shroud and stabilizer assemblies 3 months before the end of the 10,600-hour operating cycle.

This NRC approval under 10 CFR 50.55a(a)(3)(i) is contingent upon (I) maintaining reactor coolant chemistry within the guidelines set forth in Electric Power Research Institute technical report TR-)03515,

'BWR Mater Chemistry Guidelines-1996 Revision,'n accordance with the commitment in your letter dated April 30, 1997; and (2) satisfying the commitment of Hay 7, l997, to submit, within 60 days, an application for a license amendment that addresses the di,fference between the current TS conductivity limits for reactor coolant chemistry and the analysis assumptions for core shroud crack

'rowth rates. 'ailure to satisfy either of these conditions will render this approval, null and void.

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B. Sylvia This completes the NRC staff's efforts under TAC No. M98170.

If you have questions, please contact me by phone at (301) 415-3049 or by electronic mail

'at dshenrc.gov.

Sincerely, Docket No. 50-220

Enclosure:

Safety Evaluation cc w/encl:

See next page, DISTRIBUTION:

See next page 4

Darl Hood, Senior Project Manager Project Directorate I-l Division of Reactor Projects - I/II

, Office'f Nuclear Reactor Regulation St DOCUMENT NAME:

G: iNMPliNM198170. LTR

• See Pre 'urrence To receive a copy of this document, indicate in t

" = Copy without attachment enclosure "E" = Co with attachme t closure "N" = No co OFFICE HAHE DATE OFFICE NAME DATE PM:PDI-1 DHood/rs 05/

/97 NRR:DE:EMCB*

JStrosnider 05/06/97 E

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JLyons 05/05/97 OGC 05/

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B. Sylvia

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This completes the NRC staff's efforts under TAC No. M98170. If you have questions, please contact me by phone at (301) 415-3049 or by electronic mail

. at dsh8nr'c.gov.

Sincerely, Docket No. 50-220

Enclosure:

Safety Evaluation cc v/encl:

See next page Darl Hood, Senior Project Manager Project Directorate I-l Division of Reactor Projects - I/II Office of Nuclear Reactor Regulation

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B. Ralph Sylvia Niagara Hohawk Power Corporation CC ~

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Hr. Richard B. Abbott Vice President and General Hanager-Kuclear Niagara Hohawk Power Corporation Nine Hile Point Nuclear Station P.O.

Box 63

Lycoming, NY 13093 Hr. Hartin J. HcCormick, Jr.

Vice President Nuclear Safety Assessment and Support Niagara Hohawk Power Corporation Nine Hile Point Nuclear Station P.O.

Box 63

Lycoming, NY 13093 Hs, Denise J. Molniak Hanager - Licensing Niagara Hohawk Power Corporation Nine Hile Point Nuclear Station P.O.

Box 63

Lycoming, NY 13093 Hr. Kim A. Dahlberg General Hanager - Projects Niagara Hohawk Power Corporation Nine Hile Point Nuclear Station P.O.

Box 63

Lycoming, NY 13093 Hr. Norman L. Rademacher Plant Hanager, Unit 1-Kine Hile Point Kuclear Station P.O.

Box 63

Lycoming, NY l3093 Regional Administrator, Region I U.S. Nuclear Regulatory Commission 475 Allendale Road King of Prussia, PA 19406 Resident Inspector U.S. Nuclear Regulatory Commission P.O.

Box 126

Lycoming, NY 13093

. ~

Nine Hile Point Nuclear Station Unit No.

1 Charles Donaldson, Esquire Assistant'Attorney General New York Department of Law 120 Broadway New York, NY 1027)

Hr. Paul D. Eddy State of New York Department of Public Service Power Division, System Operations 3 Empire State Plaza

Albany, NY 12223 Hr. F. Milliam Valentino, President New York State

Energy, Research, and Development Authority Corporate Plaza Mest 286 Mashington Avenue Extension

Albany, NY 12203-6399 Hark J. Metterhahn, Esquire Minston SStrawn 1400 L Street, NW Mashington, DC 20005-3502 Cary D. Milson, Esquire Niagara Hohawk Power Corporation 300 Erie Boulevard Mest

Syracuse, NY 13202 Supervisor Town of Scriba Route 8, Box 382

Oswego, NY 13)26

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DISTRIBUTION:

"Docket File PUBLIC PDI-I Reading SVarga JZwolinski SBajwa SLittle DHood THarris (E-Hail TLH3)

OGC ACRS CCowgill, RI JRajan KNanoly RWessman JLyons JStrosnider RHermann KWichman MBanic WKoo KKavanagh DScrenci LDoerflein

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EXECUTIVE SUHHARY This safety evaluation.assesses the 1997 reinspections and analyses by Niagara Hohawk Power Corporation (NHPC and the licensee) for its core shroud at Nine Nile Point Nuclear Station, Unit 1 (NHPl) 4o determine whether the shroud meets the structural integrity requirements of the American Society of Hechanical Engineers Boiler and Pressure Vessel Code (ASHE Code),Section XI.

During the current spring 1997 refueling outage, NHPC inspected vertical welds in the core shroud in accordance with the Boiling Mater Reactor Vessel and Internals Project-07 "Guidelines for Reinspection of BWR Core Shrouds (BWRVIP-07)."

NHPC found vertical weld cracking that exceeded the screening criteria of BWRVIP-07.

Additionally, NHPC's inspections of four tie rod assemblies, installed as a pre-emptive repair during the last outage in 1995, showed that the tie rod nuts had lost some preload and that the lower wedge retainer 'clips on three tie rods were damaged.

NHPC found that the degraded repair was operational during the past cycle.

Through its structural

analyses, NHPC has concluded that continued operation at NHPl is justified for at least an additional.10,600 hours0.00694 days <br />0.167 hours <br />9.920635e-4 weeks <br />2.283e-4 months <br /> (about 14-1/2 months).

The allowable hours of operation until the next inspection ensure that the required ASHE Code margins will continue to be maintained.

NHPC implemented design changes to"the tie rod assemblies to correct the problems that were found during the inspection.

The NRC staff has concluded, based on the inspection and analyses performed and the modifications made to the tie rpd assemblies, that the NHPl core shroud is acceptable for an additional 10;600 hours0.00694 days <br />0.167 hours <br />9.920635e-4 weeks <br />2.283e-4 months <br /> of operation.

This is the NRC's approval under 10 CFR 50.55a(a)(3}(i} which is contingent upon NHPC (1) maintaining reactor coolant chemistry within the guidelines set forth in Electric Power Research Institute technical report TR-103515, "BWR Mater Chemistry Guidelines-1996 Revision," in accordance with its commitment by letter dated April 30,

1997, and (2) submitting, within 60 days, an application for a license amendment that addresses this matter in accordance with its commitment by letter dated Hay 7, 1997.

Failure to satisfy either of these conditions will render this approval null and void.

NHPC will submit to the NRC an inspection plan for the next outage at least 3

months before the outage is scheduled to begin.

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