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UNITED STATESNUCLEAR REGULATORY COMMISSION

WASHINGTON, D.C. 20555-0001

October 29, 1996

LICENSEE: American Electric Power Service Corporation (AEP)(Indiana Michigan Power)

FACILITY: D.C.'Cook, Unit 1

SUBJECT: FORMER BOLTS INSPECTION AND REPAIR PLANS FOR THE 1997 REFUELINGOUTAGE

A meeting was held at NRC Headquarters on October 22, 1996, with the AEP andWestinghouse representatives, to discuss the licensee's plans for theinspection and replacement of the D.C. Cook Unit 1 core barrel former bolts,during the plant's upcoming refueling outage.

During the 1994 Unit 1 refueling outage, a bolt and associated locking barwere found on the reactor vessel internal's lower core plate. The bolt wasidentified as the type used to secure the core baffle former plates to thecore barrel. During a subsequent refueling outage in 1995, the reactor corewas defueled and the core barrel was removed from the vessel. An inspectionof all the core barrel former bolts was performed. A bolt missing from thetop former plate was identified. Further testing disclosed that two formerbolts located on either side of the missing bolt were loose.

On September 26, 1995, the licensee met with NRR to review the root cause andsafety evaluation conclusions based on the inspection results and analysesperformed with support from Westinghouse (internals supplier). Based on thesafety evaluation at that time, the licensee concluded that the plant couldsafely operate during the upcoming cycle without replacing the three formerbolts or making any other repairs. The licensee had committed to (1)reinspect the former bolts at the next refueling outage, (2) develop andprepare repair procedures, methods and equipment, (3) monitor and analyzeneutron noise and loose parts data throughout the operating cycle, and(4) keep the NRC informed of any new developments.

During this meeting, in the discussion and responses to NRR questions, thelicensee and Westinghouse representatives provided an update on the root causeevaluation and analyses and presented a description of the procedures,techniques, equipment and redesign of replacement former bolts that had been

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developed. The licensee outlined its plans for a reinspection of the corebarrel former bolts and implementation of the repair and replacement of thethree bolts, during the next refueling outage. The next refueling outage isscheduled for February 1997.

Docket Nos: 50-315

John B. Hickman, Project ManagerProject Directorate III-1Division of Reactor Projects - III/IVOffice of Nuclear Reactor Regulation

Enclosures: 1. List of attendees2. Slides

cc w/encls: See next page

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developed. The licensee outlined its plans for a reinspection of the corebarrel former bolts and implementation of the repair and replacement of thethree bolts, during the next refueli'ng outage. The next refueling outage isscheduled for February 1997.

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Docket Nos: 50-315

Original signed by:

John B. Hickman, Project ManagerProject Directorate III-1Division of Reactor Projects — III/IVOffice of Nuclear Reactor Regulation

Enclosures: 1. List of attendees2. Slides

cc w/encls: See next page

DISTRIBUTION w~enclsDocket Fil ePUBLICPD3-3 R/FACRSOGC

e-mailFHiragliaRZimmermanJRoeEAdensamEJordan (JKR)GMarcusBMcCabeJCaldwell, RIIIFGrubelichWBurton

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Indiana Michigan Power Company

CC:

Regional Administrator, Region IIIU.S. Nuclear Regulatory Commission801 Warrenville RoadLisle, Illinois 60532-4351

Attorney GeneralDepartment of Attorney General525 West Ottawa StreetLansing, Hichigan 48913

Township SupervisorLake Township HallP.O. Box 818Bridgman, Michigan 49106

Al Blind, Site Vice PresidentDonald C. Cook Nuclear Plant1 Cook PlaceBridgman, Michigan 49106

U.S. Nuclear Regulatory CommissionResident Inspector's Office7700 Red Arrow HighwayStevensville, Michigan 49127

Gerald Charnoff, EsquireShaw, Pittman, Potts and Trowbridge2300 N Street, N. W.

Washington, DC 20037

Mayor, City of BridgmanPost Office Box 366Bridgman, Michigan 49106

Special Assistant to the GovernorRoom 1 — State CapitolLansing, Michigan 48909

Drinking Water and RadiologicalProtection Division

Hichigan Department ofEnvironmental guality

3423 N. Hartin Luther King Jr BlvdP. 0. Box 30630 CPH HailroomLansing, Michigan 48909-8130

Donald C. Cook Nuclear Plant

Mr. Steve J. BrewerIndiana Hichigan PowerNuclear Generation Group500 Circle DriveBuchanan, Hichigan 49107

Hr. E.E. Fitzpatrick, Vice PresidentIndiana Hichigan PowerNuclear Generation Group500 Circle DriveBuchanan, HI 49107

MEETING ATTENDEES

FOR OCTOBER 22, 1996

D.C. COOK UNIT 1 FORMER BOLTS INSPECTION AND REPAIR PLANS MEETING

NAME

John B. HickmanFrank GrubelichSteve BrewerFrank R. PisarskyJohn C. MatarazzoDavid A. HowellMelita P. Osborne

AFFILIATION

NRC, Project Directorate 111-3NRC, Mechanical Engineering BranchAEP, Regulatory AffairsAEP, Production EngineeringWestinghouse, EngineeringWestinghouse, NSD

Westinghouse, NSD

ENCLOSURE 1

~ UNIT 1 BARREL-FORMER BOLTDISCUSSION

~ INTRODUCTION AND BACKGROUNDSTEVE BREWER, AEP

~ ROOT CAUSE EVALUATIONUPDATEMELITAOSBORNE,WESTINGHOUSE

~ BOLT REPAIR PROCEDUREDAVE HOWELL, WESTINGHOUSE

~ 1997 U1 REFUELING OUTAGEPLANS — FRANK PISARSKY, AEP

UPPER CORE

BARREL

~ ~ ~ ~ ~

THERMAL SHIELD ~ ~ ~ ~

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BAFFLE

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THERMAL SHIELD

PLAN VIEW, BARREL — FORMER — BAFFLE — BOLTING

o UNIT 1 1994 REFUELING OUTAGE» LOOSE BOLT FOUND ON LOWER CORE

PLATE

» BOLT IDENTIFIEDAS BARREL FORMERBOLT

» WESTINGHOUSE PERFORMED SAFETYEVALUATION

» DECISION TO PERFORM VISUALINSPECTION NEXT REFUELINGOUTAGE

~ UNIT 1 1995 REFUELING OUTAGE» FOUND MISSING BOLT LOCATION (A5)» FOUND TWO LOOSE ADJACENT BOLTS

(A4 AND A6)

PLANT OPERATION ACCEPTABLEFOR NEXT FUEL CYCLE

~ CONSIDERED:» LOOSE PARTS

» EFFECTS OF NEXT CYCLE OFOPERATION ON REMAINING BARRELFORMER BOLTS

» FUEL ASSEMBLY GRID CRUSH

~ CONSIDERED:» BYPASS FLOW CHANGES

» FLOW-INDUCED VIBRATION

» CONTROL ROD INSERTION CAPABILITY

~ INSPECTION OF BARREL FORMER.BOLTS NEXT OUTAGECOMMUNICATESCOPE AND

TECHNOLOGY TO NRC

~ CONTINUE TO REFINE ROOT CAUSEANALYSIS

~ DEVELOPMENT OF APPROPRIATEREPAIR APPROACH, TECHNIQUES

ROOT CAUSE ASSESSMENTFROM 1995

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Causes Eliminated~ Stress corrosion: NOT seen in examined bolts~ Manufacturing/Assembly: NOT supported by

Westinghouse records or examination of bolts

Postulated Root Cause:

~ Acceptable loads were exceeded locallythermal shield support blocks

~ A4-A6 locations~ Mechanisms result from thermal transients

and flow induced vibration

ROOT CAUSE ASSESSMENT 1996 (Cont)

Flow Induced Vibration (FIV) Analyses~ Purpose is to determine local variations in

loads for as-built configuration~ FIV loads caused by flow of water through the

internals

(e.g., horizontal flow from nozzle changesdirections as hit barrel)

~ Investigate as-built thermal shield supportblock configuration

~ 360'-D model of barrel, baffle and thermalshield, A-H formers

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ROOT CAUSE ASSESSMENT 1996 (cont)

Flow induced Vibration (FIV) AnalysesPreliminary Results,

~ Bolts located under thermal shield supportblocks have highest loads

~ Bolts located under 4 of the 8 locations havehigher loads magnitude for these fourlocations essentially the same A4-6 are underone of these four thermal shield supportblocks

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ROOT CAUSE ASSESSMENT 1996 (cont),.gf

~ As-built configuration {dowel pins) hasnegligible effect on loads

~ Highest overall loads on A former level~ Predicted frequencies of vibration correlate

with measured neutron noise data

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ROOT CAUSE ASSESSMENT 1996 (cont)

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Steady State Thermal Analysis~ Purpose is to determine relative thermal

growth between baffle plates, former plates,and core barrel

~ Determine steady state thermal loads onformer bolts

~ Thermal loads cause bending loads in bolts~ May cause loss of preload, allow bolt to vibrate

ROOT CAUSE ASSESSMENT 1996 (cont)

~ Same model as FIV analysis; as-builtconfigurations

~ Plant specific thermal loads {heat generationrates, T,„, T,„,)

~ Analysis still in progress

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D. C. COOK BARREL TO FORMERBOLTS COMPARISON

ORIGINALBOLT

REPLACEMENTBOLT

ThreadEffective Lengthof EngagementMaterial Spec

Material

Yield StrengthUltimate Strength

3/4 - 101.18 in.

W PDS70041KB

347 SS

30-55 KSI75 KSI

1"-8

0.805 in.

SA 479

316 SS StrainHardened

65 KSI85 KSI

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D. C. COOK BARREL TO FORMERBOLTS COMPARISON

OLD BOLT NEW BOLT

DIMENSIONS DIMENSIONS

Length Overall:

Bolt Head Height:

Shank Length:

Shank Diameter:

Bolt Head Diameter:

3.500 3.920

0.750 0.962

2.750 2.775

0.620 0.620

1.125 1.440

D. C. COOK BARREL TO FORMERBOLTS COMPARISON

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D. C. COOK BARREL TO FORMER BOLTLOCKING DEVICES

DeviceOriginal LockBarNew Crimp

Torque to Undo48 F.t-Lb

150 Ft-Lb

BARREL-FORMER NEW BOLTDESIGN TESTING

Purpose: Confirm the performance of the newly-designed bolt with respect to the original boltto support new bolt design

Load-Deflection Measure strain in each bolt design at

different loading levels when applied in a

direction perpendicular to bolt longitudinalaxis

Comparative

Fatigue

Tests:

Determine bolt preload for each bolt

design; monitor preload degradation

throughout test Fatigue

Testing willbe completed at the Westinghouse Science and

Technology Center (STC)

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REPAIR EQUIPMENT

~ Elevator delivery device is used for positioning

~ End effector with EDM probe used to machine a3.0" through hole in the thermal shield

~ EDM is qualified to remove the old bolt

~ Vacuum system used to clean up debris

~ EDM used to machine larger hole for bolt andnotches for locking device

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REPAIR EQUIPMENT

~ Tapping end effector used to machine new 1"-8threads

~ Torquing tool installs new bolt

~ Crimping tool locks bolt in place

~ Hole in thermal shield acceptable without repair

BARREL - FORMER BOLTINSTALLATIONDEMONSTRATION

a Mockup will be a simulated section ot the DCCook reactor vessel lower internals

~ Mockup and tools will be submerged underwater

~ The demonstration willshow the followingoperations

~ Positioning of the tool on the thermal shield

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BARREL - FORMER BOLTINSTALLATIONDEMONSTRATION

~ EDM of the new 1" bolt hole"~ Tapping of the 1" bolt hole~ Installation and torque of bolt~ Crimping of the bolt~ Removal of the tool from the thermal shield

* EDM of the 3" access hole through the thermalshield was previsouly demonstrated

Frank Pisarsky

Engineering Manager of MechanicalComponents

D.C. Cook Nuclear Plant

ore arre ns ections

~ Section XI visual inspection of core supportstructures

~ Visual inspection of all 640 former bolt locations

~ Mechanical agitation of A Level former bolts, B Levelin proximity of discrepant bolts, 56 random bolts, andH Level bolts P3, 4, 5, 6, 7, 8 8

~ Detailed visual inspections of key areas formovement/stress

~ UT measurements of gap between barrel wall and ALevel former plate

e Fiberscope inspection of discrepant bolt holes

arre — ormer o tc e u e ns ections

~ Visual inspection and mechanical agitation ofall A (Top) Level former bolts

~ Visual inspection and mechanical agitation ofB Level bolts (B1 through BB) in proximity ofmissing bolt holes (A4, A5 8 A6)

~ Minimum of 86 bolts inspected

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e Install 1" Bolts in holes A4, A5, A6

~ Return Core Barrel to originalconfiguration (A4, A5, A6 3i4" to 1" bolts)

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