ML20217L797

Submits Results of Review of 990521 & 0709 Ltrs Which Provided Core Shroud Insp Results & Tie Rod Stabilizer Assemblies

ML20217L797
Person / Time
Site:	Nine Mile Point
Issue date:	10/20/1999
From:	Hood D NRC (Affiliation Not Assigned)
To:	Mueller J NIAGARA MOHAWK POWER CORP.
References
TAC-MA6073, NUDOCS 9910270074
Download: ML20217L797 (6)

Text

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sp rag g 'a UNITED STATES y, y. j NUCLEAR REGULATORY COMMISSION o ' WASHINGTON, D.C. 20066 4 00*

% ,,/g Other 20,1999 Mr. John H. Mueller Chief Nuc'sar Officer Niagara Mohawk Power Corporation Nine Mile Point Nuclear Station Operations Building, Second Floor Lycoming, NY 13093 '

SUBJECT:

. REVIEW OF 1999 CORE SHROUD REINSPECTION RESULTS, NINE MILE POINT NUCLEAR STATION, UNIT NO.1 (TAC NO. MA6073)

Dear Mr. Mueller:

During the last refueling outage (RFO-15) at Nine Mile Point Nuclear Station, Unit 1 (NMP1),

Niagara Moh.awk Power Corporation (NMPC). reinspected the core shroud and its tie rod stabilizer assemblies. By letters dated May 21 and July 9,1999, NMPC provided the core shroud inspection results to the NRC. This letter presents the results of our review of those submittals.

The scope of NMPC's inspections is briefly described as follows:

(1) NMPC inspected all accessible areas of the ring segment welds (V1, V2, VS, V6, V13 and V14) using the ultresonic testing (UT) method.

(2) . NMPC performed UT inspection of all accessible areas of the vertical welds (V3, V4, V7, V8, V9, V10, V11, V12, V15 and V16). Enhanced visual testing (EVT-1) was performed on the inside diameter (ID) surface for a longth of about 6 inches at weld V4.' NMPC also UT inspected the base metal adjacent to vertical welds V9 and V10.

The inspected base metal consisted of areas about 12 to 18 inches parallel to both sides of V9 and V10 welds. During inspection of other vertical welds, the weld l coverage was expanded to include several inches of base metal para:!el to both sides of the welds.

(3) .NMPC performed UT inspection at horizontal welds H1, H2, H4, H5 and H6b. The inspected areas were limited to the areas adjacent to the intersections with the vertical welds. The length of each inspected area varied from 37 inches to 96 inches.

(4) NMPC inspected shroud support welds H8 and H9 from the annulus region using the {

EVT-1 method, 1 O

(5) NMPC performed visual examinations with a combination of VT-3 and EVT-1 at each of the four tie rod stabilizer assemblies. The tightness inspection was also performed to demonstrate the presence of adequate preload. 9(D The ; rep,orted inspection results and repair activities are summarized below:

1. NMPC found no indications in the ring segment welds; shroud support weld H9; vertical welds V15, V16 and V11; and horizontal weld H6b. .

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2. For vertical welds V9 and V10, NMPC re-inspected all the crack irdications (main cracking and secondary cracking) found during RFO-14, The secondary cracking located outside the~ heat-affected zones did not show any significant change in depth or length. The secondary cracking was believed to be initinted by local surface cold work conditions 'resulting from the original core shroud Iabrication and installation.

These surface cold work conditions were observed in the boat samples taken from vertical welds V9 and V10. The main cracking in tne heat-affected zones did not show significant change in length. NMPC did observe Mme crack growth in the main cracks in the depth direction. NMPC reported the average crack growth rate in the depth direction to be approximately 4.12E-06 inch / hour and 1.54E-05 inch / hour in

- vertical welds V9 and V10, respectively.

3.- Due to expanded weld coverage during inspection, minor cracking outside the heat-affected zones was found in vertical welds V3 and V12. NMPC attributed this cracking to local sur' ace cold work conditions or conditions associated with attachment welds.

4. For the inspection of the horizontal welds, the re-inspected cracks did not show significant changes in thv crack depth since RFO-14,

5. For shroud support weld H8, the length of the crack Indications did not show ar'y measurable changes since RFO-14 based upon EVT-1 sizing methods.

6. During the tightness inspection of the tie rod stabilization assemblies, NMPC found a 3/8-inch cap screw, made of Alloy X-750 material, to be broken. The broken piece had dislodged from the upper spring assembly. NMPC modified the upper spring assembly for each of the four tie rods. The modification replaced the design function of the failed cap screw and other cap screws that have the potential for future failure.

The NRC staff approved the design of the modification in h letter dated June 7,1999.

7. NMPC performed a pre-emptive repair of vertical weLis V9 and V10 using a repair design that the NRC staff had approved by letter dated April 30,1999.

On the basis of its review of NMPC's submittal, the NRC staff finds that the core shroud re-inspection performed at NMP1.during RFO-15 meets the guidelines in BWRVIP-07,"BWR Vessel and Internals Project Guidelines for Reinspection of BWR Core Shrouds," and exceeds the scope of the re inspection plan to which NMPC committed in its letter dated December 30, l

1998, as approved by the NRC staff in a letter dated March 24,1999. The re-inspection j performed during RFO-15 included the additional inspection of the cbre shroud base metal adjacent to vertical welds V9 and V10 and the selected areas at horizontal welds H1, H2, H4, H5 and H6b adjacent to the intersections of the vertical welds. NMPC did not perform any

additional detailed vertical weld finw evaluation to ensure the structural integrity of the core shroud.' The NRC staff finds that this is acceptable because vertical welds V9 and V10 were pre-emptively repaired during the outage, and the minor latergranular stress corrosion cracking (IGSCC) obse ved at other vertical welds did not show significant changes in size. The potential crack growth of these welds in the current fusi cycle is bounded by the previous flaw evaluations per10 med for welds V9 and V10.

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l Accordingly, the NRC staff concludes that the structuralintegrity of the core shroud will be '

maintained during the current operating cycle in its present configuration.

The NRC staff acknowledges that the core shroud will be reinspected during the next refueling outage (RFO-16). The criteria for reinspection are those contained in BWRVIP-07. The scope of.that re-inspection will be defined and provided to the NRC staff for information at least 3 months before the start of RFO-16.

This completes the NRC staff's review efforts under TAC No. MA6073.

I If you have any questions regarding this matter, please contact me by phone .a (301) 415-3049 or by electronic mail at dsh@nrc. gov.

Sincerely, DJM 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 cc: See next page I

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Nine Mile Po:nt Nuclear Station -

Unit No.1 Regional Administrator, Region I Warren Bilanin, EPRI Task Manager

~ U.S. Nuclear Regulatory Commission 3412 Hillview Ave.

' 475 Allendale Road. Palo Alto, CA 94303 King of Prussia, PA 19406 Robin Dyle Technical Chairman Resident inspector .

BWRVIP Assessment Task U.S. Nuclear. Regulatory Commission Southern Nuclear Operating Company P.O. Box 126 Post Office Box 236

' Lycoming, NY 13093 40 Inverness Center Parkway .

Birmingham, AL 35201 Charles Donaldson, Esquire Assistant Attorney. General  ;

New York Department of Law '

120 Broadway .

New York, NY 10271 Mr. Paul D. Eddy State of New York Department of Public Service Power Division, System Operations s 3 Empire State Plaza .

3

. 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 f.4rk 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

l...

Octcber 20,1999 B , 4 J. Mueller Accordingly, the NRC staff concludes that the structural integrity of the core shroud will be i maintained dudng the current operating cycle in its present configuration.

The NRC staff acknowledges that the core shroud will be reinspected during the next refueling outage (RFO-16). The criteria for reinspection are those contained in BWRVIP-07 The scope of that re-inspection will be defined and provided to the NRC staff for information'at least 3 months before the start of RFO 16.

This completas the NRC staff's review efforts under TAC No. MA6073.

If you have any quesdons regarding this matter, please contact me by phone on (301) 415-3049 or by electronic mail at dsho nrc. gov.

Sincerely, Original signed by: l Darl S. Hood, Sr. Project Manager, Section 1 1 Project Directorate I l Division of Licensing Project Management Office of Nuclear Reactor Regulation Docket No. 50-220 -

cc: See next page 1

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EDocket Filed D. Hood M. Oprendek, RGN-1 FUBLIC S. Peterson W. Bateman PDl-1 Reading W. Koo ACRS OGC R. Hermann S. Little DOCUMENT NAME: G:\PDI-1\NMP1\LTRA6073.WPD To receive a copy of this document, Indicate in the box: "C" = Copy without enclosures "E" = Copy with enclosures '"N" = No copy

! OFFICE PM:PDI LA:PDI no l SC:PG-ec (dcA l l

l NAME DHood:lecbJ// SLittleP SPetels8n M ' /o f DATE 10/2,999 10/40/99 10/20/99 "V#r OFFICIAL RECORD COPY

E 0:tober 20,1999

'J. Mueller According!y, the NRC staff concludes that the structuralintegrity of the core shroud will be maintained during the cLnreat operating cycle in its present configuration.

The NRC staff acknowledges that the core shroud will be reinspected during the next refueling outage (RFO-16). The criterla for reinspection are those contained in BWRVIP-07. The scope of that re-inspection wit: be defined and provided to the NRC staff for information at least 3 months before the start of RFO-16.

This completes the NRC staff's review efforts under TAC No. MA6073.

If you have any questions regarding this matter, 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. P oject Manager, Section 1 Project Directorate n Division of Licensing Project Management Office of Nuclear Reactor Regulation Docket No. 50-220 cc: See next page DISTRIBUTION:

Docket File D. Hood M. Oprendek, RGN 1 PUBLIC S. Peterson W. Bateman PDI-1 Reading W. Koo ACRS OGC R. Hermann S. Little DOCUMENT NAME: G:\PDI-1\NMP1\LTRA6073.WPD To receive a copy of this document, indicate in the box: "C" = Copy without enclosures "E" = Copy with cnclosures "N" = No copy OFFICE PM:PDI _' LA:PDI no SC:PQhro (dea l NAME DHood:lecDJ// Slittle7 SPeters8ii O C ' po f l

_DATE 10/2 8/99 10/40/99 10/20/99 "V-#r l OFFICIAL RECORD COPY