ML20205N059

Forwards RAI Re Which Describes Proposed Core Shroud Repair for Core Shroud Vertical Welds at Plant,Unit 1.Response Requested by 990414

ML20205N059
Person / Time
Site:	Nine Mile Point
Issue date:	04/12/1999
From:	Hood D NRC (Affiliation Not Assigned)
To:	Mueller J NIAGARA MOHAWK POWER CORP.
References
TAC-MA4701, NUDOCS 9904160136
Download: ML20205N059 (5)

Text

Mr. John H. Mueller i Chief NuclearOfficer April 12,1009

, Niag:ra Mohawk Power Corporation

. Nine Mile Point Nuclear Station Operations Building, Second Floor P.O. Box 63 Lycoming, NY 13093

SUBJECT:

REQUEST FOR ADDITIONAL INFORMATION REGARDING CONTINGENCY REPAIR PLANS FOR THE CORE SHROUD VERTICAL WELDS, NINE MILE i POINT NUCLEAR STATION, UNIT NO.1 (TAC NO. MA4701)

Dear Mr. Mueller:

I The NRC staff is reviewing your letter of February 3,1999, describing a proposed core shroud repair for the core shroud vertical welds at Nine Mile Point Nuclear Station, Unit 1 (NMP1). Our review is in anticipation that the inspection results during the upcoming refueling outage may reveal the need for such repair. To continue our review, we find that additional information, identified in the enclosure, is needed.

The schedule for responding to this letter was discussed with Mr. S. Leonard in your organization. Based upon that discussion, a mutually agreeable response date is April 14, 1999.

If you have questions regarding this letter or are unable to meet this response schedule, i please contact me by phone on (301) 415-3049 or by electronic mail at dsh@nrc. gov.

Sincerely, ORIGINAL SIGNED BY:

Darl S. Hood, Sr. Project Manager, Section 1 Project Directorate 1  ;

j Division of Licensing Project Management j Office of Nuclear Reactor Regulation Docket No. 50-220

Enclosure:

Request for Additional \

Information cc w/ encl: See next page 1 Oi 4 DISTRIBUTION:

E Docket File SLittle S. Barber, RI J. Rajan OGC PUBLIC D. Hood A. Blough, Rl K. Manofy ACRS PDI-1 R/F R. Caruso S. Bajwa K. Kavanagh JZwolinski/SBlack DOCUMENT NAME: G:\NMP1\RAIA4701.WPD To receive a copy of this document, indicate in the box: "C" = Copy without attachment / enclosure "E" = Copy with rttachment/ enclosure "N" = No copy ,

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\..,,,/ April 12,1099 Mr. John H. Mueller Chief NuclearOfficer' Niagara Mohawk Power Corporation Nine Mile Point Nuclear Station Operations Building, Second Floor P.O. Box 63 Lycoming, NY 13093

SUBJECT:

REQUEST FOR ADDITIONAL INFORMATION REGARDING CONTINGENCY REPAIR PLANS FOR THE CORE SHROUD VERTICAL WELDS, NINE MILE POINT NUCLEAR STATION, UNIT NO.1 (TAC NO. MA4701)

Dear Mr. Mueller:

The NRC siaff is reviewing your letter of February 3,1999, describing a preposed core shroud repair for the core shroud vertical welds at Nine Mile Point Nuclear Station, Unit 1 (NMP1). Our review is in anticipation that the inspection results during the upcoming refueling outage may reveal the need for such repair. To continue our review, we find that additional information, identified in the enclosure, is needed.

The schedule for responding to this letter was discussed with Mr. S. Leonard in your organization. Based upon that discussion, a mutually agreeable response date is April 14, 1999.

If you have questions regarding this letter or are unable to meet this response schedule, please contact me by phone on (301) 415-3049 or by electronic mail at dsh@nrc. gov.

Sincerely, Dad a ,

Darl S. Hood, Sr. Project Manager, Section 1 Project Directorate i Division of Licensing Project Management Office of Nuclear Reactor Regulation Docket No. 50-220

Enclosure:

Request for Additional Information cc w/enci: See next page I

John H. Mueller Nine Mile Point Nuclear Station Niagara Mohawk Power Corporation Unit No.1 cc:

Regional Administrator, Region I  !

I U.S. Nuclear Regulatory Commission 475 Allendale Road King of Prussia, PA 19406 l

Resident inspector U.S. Nuclear Regulatory Commission P.O. Box 126 Lycoming, NY 13093 Charles Donaldson, Esquire {

Assistant Attomey General j New York Department of Law J 120 Broadway New York, NY 10271 Mr. Paul D. Eddy State of New York ,

Department of Public Service Power Division, System Operations 3 Empire State Plaza Albany, NY 12223 Mr. F. William Valentino, President New York State Energy, Research, and Development Authority Corporate Plaza West 286 Washington Avenue Extension Albany, NY 12203-6399 Mark J. Wetterhahn, Esquire Winston & Strawn 1400 L Street, NW Washington, DC 20005-3502 Gary D. Wilson, Esquire Niagara Mohawk Power Corporation 300 Erie Boulevard West Syracuse, NY 13202 Supervisor Town of Scriba Route 8, Box 382 Oswego, NY 13126

F 4

REQUEST FOR ADDITIONAL INFORMATION REGARDING CORE SHROUD VERTICAL WELD REPAIR NIAGARA MOHAWK POWER CORPORATION (NMPC)

NINE MILE POINT NUCLEAR STATION. UNIT NO.1 (NMP1) -

DOCKET NO. 50-220 Provide the following additional information regarding your letter of February 3,1999, discussing contingency repair plans for the NMP1 core shroud vertical welds:

1. Page 11 of Calculation 2499702-302, "Effect of Repair Clamp Assembly on Downcomer ,

Flow Characteristics," states that the total core pressure drop is approximately 20 psi per l Reference 6 Appendix A. Reference 6 is MPR Specification 249014-001, " Design Specification for Nine Mile Point Nuclear Station Uniti (NMP-1) Core Shroud Vertical Weld Repair," Rev.1. Revision 2 (not Revision 1) of Reference 6 was provided with your letter of February 3,1999. Please identify any differences between Revision 1 and Revision 2 that cou;d affect the calculation of the differential pressure, or provide a copy of Revision 1.

Reference 6 Appendix A states that the total differential pressure above the core plate is 5.9 psi, whereas the total differential pressure below the core plate is 21.2 psi. Since the area of the downcomer that is being analyzed in this calculation is above the core plate it would seem that the total pressure drop of 5.9 psi should be used instead of the 20 psi.

Please clarify your selection in this regard.

2. Provide the basis for the leakage acceptance criteria, i.e., that the combined bypass leakage through welds V9 and V10 and their respective repair clamps shall be less than 0.25% of the total core flow for normal differential pressure and 0.08% of the recirculation flow for V4. Explain why you find this acceptance criteria to be acceptable.

3. In Design Specification 249014-001 for NMP1, Section 6.2 states that "For upset conditions there are no specific leakage acceptance criteria. However, the leakage shall be calculated and documented in the Desigre ilepert." It appears that this analysis was provided in Appendix A of Calculation 2499702 301. However, there is no justification as to why the calculated leakage is acceptable. Please discuss why the calculated leakage in the upset condition will not preclude acceptable performance of the emergency core cooling system.

4. The repair clamp is expected to fit snugly on the seating surfaces of the shroud and remain snug throughout operation. However, a gap could exist if the " drilled" holes are out-of round orif the holes are positioned slightly different from those intended by the design configuration. The inside surface of the shroud is of particular concern as a Enclosure

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mating surface since it may become brittle. The inside surface is also susceptible to impact damage from a loose clamp assembly, both during normal operation and during accident conditions. These factors could eventually result in the pin backing off from the '

hole in the shroud, rendering the clamp ineffective.-

Please address the potential of the above concems. Include an assessment of the wear damage at critical bearing locations of a loosely fitting clamp.

5. Page 6 of Design Calculation No. 24799702-204, Table 1, shows that the limiting stresses in the clamp assembly would be very close to the allowable values for steam line break conditions. It appears that the bearing surfaces could change significantly, even if there is a minor deviation from the precise configuration assumed in the design calculation, thereby eroding the small calculated design margin. How do you propose to verify the actual bearing surfaces at installation? How will you verify periodically that adequate bearing surfaces are being maintained after operation?

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