AUG 2H1? Serial No. 12-508 - NRC: Home Page · 2012. 9. 19. · Dominion Energy Kewaunee, Inc. 5000 Dominion Boulevard, Glen Allen, VA 23060 ATTN: Document Control Desk AUG 30 2H1?

Dominion Energy Kewaunee, Inc.5000 Dominion Boulevard, Glen Allen, VA 23060

ATTN: Document Control Desk AUG 30 2H1? Serial No. 12-508U. S. Nuclear Regulatory Commission LIC/JG/ROWashington, DC 20555-0001 Docket No.: 50-305

License No.: DPR-43

DOMINION ENERGY KEWAUNEE. INC.KEWAUNEE POWER STATIONREACTOR VESSEL INTERNALS INSPECTION PLAN REVIEW REQUESTSUPPLEMENT AND RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION

By application dated December 12, 2011 (Reference 1), Dominion Energy Kewaunee,Inc. (DEK), requested approval, pursuant to the provisions of Renewed OperatingLicense DPR-43, of the inspection plan for reactor vessel internal (RVI) components atKewaunee Power Station (KPS). This inspection plan submittal was to fulfill certainrequirements of Renewed Operating License DPR-43, Section 2.C(1 5)(b); specifically,Commitment Items 1 and 2 of Appendix A of NUREG-1958, "Safety Evaluation ReportRelated to the Kewaunee Power Station," dated January 2011. The inspection planwas supplemented on June 28, 2012 (Reference 2).

Subsequently, the Nuclear Regulatory Commission (NRC) transmitted a request foradditional information (RAI) regarding the inspection plan (Reference 3). The NRCquestions were discussed with NRC staff to obtain clarification, during a telephoneconference on July 23, 2012. The DEK response is provided in Attachment 1 to thisletter. Attachment 2 provides revised RVI components inspection plan tables.

If you have questions or require additional information, please feel free to contact Mr.Jack Gadzala at 920-388-8604.

Very truly yours,

J. AI rice

Vice President - Nuclear Engineering

Attachments:

1. Response to Request for Additional Information Reactor Vessel InternalsInspection Plan Review Request

2. Supplement to Reactor Vessel Internals Inspection Plan Review Request, Table 3(Revision 1)

/A07

Serial No. 12-508Page 2 of 2

References:

1. Letter from J. Alan Price (DEK) to Document Control Desk (NRC), "Reactor VesselInternals Inspection Plan Review Request," dated December 12, 2011.

2. Letter from J. Alan Price (DEK) to Document Control Desk (NRC), "Reactor VesselInternals Inspection Plan Review Request, Supplement and Response to Requestfor Additional Information," dated June 28, 2012.

3. Email from Karl D. Feintuch (NRC) to Jack Gadzala (DEK) et al, "ME7727 -Kewaunee - Request for Additional Information Re: RVI components InspectionPlan - Follow-up RAI to response provided for RAI item Cher-006," dated July 17,2012.

Commitments made by this letter: NONE

cc: Regional Administrator, Region IIIU. S. Nuclear Regulatory Commission2443 Warrenville RoadSuite 210Lisle, IL 60532-4352

Mr. Karl D. FeintuchProject ManagerU.S. Nuclear Regulatory CommissionOne White Flint North, Mail Stop 08-H4A11555 Rockville PikeRockville, MD 20852-2738

NRC Senior Resident InspectorKewaunee Power Station

Serial No. 12-508

ATTACHMENT 1

RESPONSE TO REQUEST FOR ADDITIONAL INFORMATIONREACTOR VESSEL INTERNALS INSPECTION PLAN REVIEW REQUEST

KEWAUNEE POWER STATIONDOMINION ENERGY KEWAUNEE, INC.

Serial No. 12-508Attachment 1

Page 1 of 6

RESPONSE TO REQUEST FOR ADDITIONAL INFORMATIONINSPECTION PLAN FOR THE AUGMENTED INSERVICE INSPECTION PROGRAM

FOR EXAMINATION OF REACTOR VESSEL INTERNALS

On July 17, 2012, the NRC transmitted to Dominion Energy Kewaunee, (DEK) a requestfor additional information (RAI) (Reference 1) concerning the inspection plan for reactorvessel internal (RVI) components at Kewaunee Power Station (KPS). This inspectionplan submittal was to fulfill certain requirements of Renewed Operating License DPR-43, Section 2.C(1 5)(b); specifically, Commitment Items 1 and 2 of Appendix A ofNUREG-1958, "Safety Evaluation Report Related to the Kewaunee Power Station,"dated January 2011. The inspection plan was supplemented on June 28, 2012(Reference 2).

The NRC staff reviewed DEK's June 28, 2012 supplement (Reference 2), specifically asit responds to NRC question ME7727-RAII-EVIB-CHER-006-2012-05-09, and has someconcerns regarding the aging degradation in Alloy X-750 clevis insert bolts.Consequently, the NRC staff developed a follow-up question (below) on the issue.

This question was discussed with NRC staff to obtain clarification during a telephoneconference on July 23, 2012. During the conference, NRC staff requested that DEKstate whether a VT-3 inspection is required by ASME Section XI (because the clevisinsert bolts are a reactor vessel internals structure). The staff also requested aqualitative analysis regarding the minimum number of clevis insert bolts (and the dowelpin) that must be functional.

The RAI question is provided below, followed by the DEK response.

NRC Question ME7727-RAII-EVIB-Cher-017-2012-07-17

According to Section A.1.4 in MRP-175, "Materials Reliability Program: PWR InternalAging Degradation Mechanism Screening Threshold Values," susceptibility to stresscorrosion cracking (SCC) in Nickel Base Alloy X-750 depends on the type of heattreatment that is performed on the alloy. The high temperature heat treatment (HTH)process that is used on Alloy X-750 offers better resistance to SCC than the other agehardened heat treatment processes.

Previous operating experience in a US PWR unit indicates that the Alloy X-750 clevisinsert bolts experienced cracking. In Table 4-9 of the MRP-227-A report, the MRPidentified only wear as an aging mechanism for the clevis insert bolts.

A - Based on the operating experience as stated above, the staff believes thatcracking should also be included as an active aging degradation in the clevis insertbolts. Therefore, the staff requests that the licensee confirm that Alloy X-750material in HTH condition was used for clevis insert bolts at KPS.


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B - If the Alloy X-750 material is not in HTH condition, the staff requests that thelicensee include verification of aging degradation due to cracking in its inspectionand evaluation guidelines for these bolts at KPS.

C -VT-3 examination of the bolts every 10 years would detect completely failed ormissing bolts but not partially cracked bolts. Therefore, the staff requests thelicensee to provide:

(1) Justification that VT-3 technique would be adequate for monitoring the crackingissue in the clevis insert bolts before it fails;

(2) Information on the number of clevis insert bolts that are necessary formaintaining their function during the extended period of operation; and,

(3) Information on the number of clevis insert bolts that are currently present atKPS.

Response:

The primary function of the core barrel is to support the core. Lateral support for thecore is provided at the upper and lower core plate locations and at intermediatepositions during a seismic and LOCA event. During a seismic and LOCA event, thecore may impact the baffle/former assembly that is supported by the core barrel(Reference 3).

The core rests directly on the lower core plate that is ultimately supported by the corebarrel. The lower core plate is attached at its periphery to the core barrel insidediameter and supported by lower support columns that are attached to the lowersupport forging. The lower support forging is welded at its edge to the bottom end ofthe core barrel.

Four alignment pins located at 900 intervals are welded to the core barrel and engagethe upper core plate. These pins restrain the lateral motion of the upper core plate.The baffle/former assembly is bolted to the core barrel and forms an outer envelope forthe core.

Four radial keys located at 900 intervals are attached to the core barrel at the lowersupport forging level. The radial keys restrain large transverse motions of the corebarrel, but at the same time allow unrestricted radial and axial thermal expansions.Each radial key fits into the keyway of its corresponding clevis, which is welded to thereactor vessel (Figure 1).

The lower core barrel is restrained laterally and torsionally by these uniformly spacedradial keys. The radial keys, along with the matching clevis inserts, are designed to limitthe tangential motion between the lower end of the core barrel and the vessel. At


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assembly, as the internals are lowered into the vessel, the keys engage the keyways ofthe inserts in the axial direction. With this design, the core barrel is provided with asupport at the farthest extremity and may be viewed as a beam fixed at the top andguided at the bottom. With the radial key and inserts, the radial and axial expansions ofthe core barrel are accommodated, but circumferential movement (i.e., rotation) of thecore barrel is restricted. The thickness of the clevis inserts is customized to have theoptimum gap sizes.

Each clevis is welded to the inside wall of the reactor vessel at 900 intervals to align withthe four radial keys. The clevis inserts are attached to the clevis with eight bolts andone dowel pin. Each bolt is restrained by a bolt-head locking bar that prevents it fromvibrating out of its threaded receptacle. The locking bar is attached with a tack weld oneach end. The clevis inserts are retained within the clevis by friction (interference fit).Therefore, the clevis bolting is a designed redundancy to the friction fit (Figure 2). Thefunction of the dowel pin is to offload any shear from the bolts for a case where a load isacting vertically upward on the clevis insert.

A loose parts evaluation of a clevis insert bolt that experienced cracking at anotherutility (performed by Westinghouse Electric Company) determined that the separatedheads will remain captured in the clevis insert counter-bores and will not impactoperation. No safety or operability concerns were identified during this evaluation(Reference 4).

The core barrel and its radial support keys are classified as core support structures.The clevis inserts are classified as reactor vessel internals structures and are also oneof the components that form the interface between core supports and internalsstructures.

CLM IS INSERT

Top view ofexpandedsection

Expandedview at right

FORGING

Figure 1

Serial No. 12-508Attachment I

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Locking Mechanism(tab across bolt head)

Clevis Insert Bolt Head 0

Dowel Pin

Clevis

Clevis Insert

Clevis Insert

(Section A-AFigure 1above)

View towardsreactor vesselinterior wall

Figure 2

Basis for VT-3 Examination of Clevis Bolts

Since the clevis insert bolts are a reactor vessel internals structure (and a componentthat forms the interface between core supports and internals structures), a VT-3inspection is required by ASME Code, Section XI. These inspections are covered underan existing ASME Xl program and not under MRP-227 (Existing Program Items, ItemB13.70 (formerly identified as Item B13.10), VT-3 examination of the clevis bolting).Based on the staff's concern, DEK has revised this item to include "loss of material(wear) and cracking" (in Table 3, Reactor Vessel Internals Inspection Plan (Reference5)).

The Alloy X-750 clevis insert bolts at KPS did not undergo the HTH treatment process.

Based upon time of manufacturing and shipping, Westinghouse Electric Companyindicates that the X-750 clevis insert bolts are supplied as Condition BH:

* Hot worked," Solution treatment at 980'C for 1 hour, air cooled, then," Aged at 704'C for 20 hours, air cooled; or,

7300C for 8 hours with a furnace cool followed by 6200C for 8 hours with an air cool.

The proposed inspection and evaluation guidelines for these components are adequateto ensure that degradation would be indentified prior to loss of the redundant restrainingfunction of the bolts. Because the bolts are restrained, the potential for loose parts from


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a bolt failure is not significant. Therefore, the planned VT-3 inspection of these boltsevery 10 years, as required by ASME Code, Section XI, is adequate for verification oftheir condition. Three previous VT-3 inspections have verified that the clevis bolts areinstalled and that the locking bar and tack welds are in place.

Degradation of the clevis insert bolts would not result in a loss of intended function dueto the nature of the design. A significant change in this support would be recognized bycomparing changes from baseline neutron noise data from the excore detectors, thusproviding a means for observing core barrel motion and the frequencies and modeshapes governing such motion. Moreover, to reach this stage, two additionalcomponents would have to fail. Therefore, the effects of primary water stress corrosioncracking (PWSCC) of the clevis insert bolts are not considered significant (Reference3).

As discussed above, each of the four clevis inserts is secured to its support via eightbolts and one dowel pin. Therefore, a total of 32 clevis insert bolts and four dowel pinsare in place to provide their restraining function. Since the clevis inserts are retained inplace by means of an interference fit and dowel pin, the bolting is a designedredundancy. The function could reasonably be expected to be maintained (and reactoroperation could safely continue) even with failure of multiple clevis bolts, since failedbolting would remain in place due the locking mechanism. Additionally, the close fit ofthe radial key (when the core barrel is in place) would prevent any bolt (and any dowelpin) from backing out of its housing. Even if a bolt completely cracked and itsassociated locking bar concurrently failed, the cracked bolt would not actually bereleased until the core barrel was subsequently removed. The primary consequence ofa clevis bolt failure (should it occur) would be potentially to increase local wear betweenthe radial keyways and clevis inserts. Failure of multiple bolts would likely lead to anincrease in that wear potential. The presence of the dowel pin will provide somesupport to shear loads, thereby limiting the potential wear.

In an extreme postulated case, if a loose clevis insert would be able to dislodge from theclevis (e.g., during a refueling outage when lifting the core barrel for the 10-year ISI),this could create a concern for loose parts and excessive motion of the lower internals.Multiple physical constraints exist to prevent this from occurring, even in the case offailed bolts. In the basic installation of the clevis insert, the insert is captured on eachside by the clevis, such that it cannot become dislodged by moving in the right or leftdirection. Due to the close proximity of the radial key, lower internals, and vessel, theclevis insert is unable to become dislodged in the radial direction. Additionally, theclevis insert has a flange on the top that rests on the top side of the clevis. This ledgewill prevent the clevis insert from becoming dislodged vertically downward. The onlypotential direction not constrained by significant lower internals and vessel structures isin the vertically upward direction (which is constrained by gravity). For the clevis insertto become dislodged upward, the bolts and dowel pins would all have to fail flush at thebolting surface between the clevis insert and vessel lug, which is unlikely. Based on thelock bar wear identified at another utility, it is more likely that the bolts would fail at the


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head to shank radius. If failure did occur at the head to shank radius, the remainingshank provides an additional defense against the clevis insert dislodging verticallyupward.

As such, no additional inspections to assure the function of the clevis insert bolts areneeded during the period of extended operation. As stated above, DEK has revised theKPS Reactor Vessel Internals Inspection Plan, Existing Program Items, Item B13.70,VT-3 examination of the clevis insert bolting, to include "loss of material (wear) andcracking". The revised Reactor Vessel Internals Inspection Plan Table 3 showing thischange is provided in Attachment 2 to the letter transmitting this response.

REFERENCES

1. Email from Karl D. Feintuch (NRC) to Jack Gadzala (DEK) et al, "ME7727 -Kewaunee - Request for Additional Information Re: RVI components Inspection Plan- Follow-up RAI to response provided for RAI item Cher-006," dated July 17, 2012.

2. Letter from J. Alan Price (DEK) to Document Control Desk (NRC), "Reactor VesselInternals Inspection Plan Review Request, Supplement and Response to Requestfor Additional Information," dated June 28, 2012.

3. Letter from Christopher I. Grimes (NRC) to Roger A. Newton (Westinghouse OwnersGroup), "Acceptance for Referencing of Generic License Renewal Program TopicalReport Entitled, 'License Renewal Evaluation: Aging Management for ReactorInternals', WCAP-14577, Revision 1, October 2000," dated February 10, 2001.

4. Westinghouse InfoGram IG-10-1, "Reactor Internals Lower Radial Support ClevisInsert Cap Screw Degradation," dated March 31, 2010.

5. Letter from J. Alan Price (DEK) to Document Control Desk (NRC), "Reactor VesselInternals Inspection Plan Review Request," dated December 12, 2011.

Serial No. 12-508

ATTACHMENT 2

SUPPLEMENT TOREACTOR VESSEL INTERNALS INSPECTION PLAN REVIEW REQUEST

TABLE 3 (REVISION 1)


Serial No. 12-508

Table 3 (Revision 1)

Reactor Vessel Internals Inspection Plan

MRP-227

Westinghouse Plants Existing Programs Components

(3 pages)


Serial No. 12-508

Reactor VesselInternals

B13,70 Core Barrel Assembly Attachment Reactor Vessel Y X x2 VT-3 examination. Loss ofCore Barrel Flange Figure 4 Core Barrel material (wear).

XK-67866

B13.70 Upper Internals Attachment Reactor Vessel Y X X X X VT-3 examination. CrackingAssembly Upper Figure 4 and Upper Internals (IASCC, Fatigue)

Support Ring or Skirt Figure 5 Assembly

XK-67866 Upper SupportRing or Skirt

B13.70 Lower Internals Attachment Reactor Vessel Y X X VT-3 examination of the lowerAssembly Lower Core Figure 4 and Lower Internals core plate to detect evidence of

Plate Figure 5 Assembly distortion and/or loss of bolt

XK-67866 Lower Core integrity. Cracking (IASCC,Plate Fatigue)

B13.70 Lower Internals Attachment Reactor Vessel Y X X VT-3 examination. Loss ofAssembly Lower Core Figure 4 and Lower Internals material (wear).

Plate Figure 5 Assembly

XK-67866 Lower CorePlate

B13.70 Alignment and Attachment Reactor Vessel Y X X X X VT-3 examination. Loss ofInterfacing Figure 2 Upper Internals material (wear).

Components Upper XK-67866 Upper CoreCore Plate Alignment Plate Alignment

Pins Pins

Category Notes:

1. End of Original License is December 21, 2013.

2. Examinations are performed when the core barrel is removed typically once per interval.

Table 3, Page 1 of 3

Serial No. 12-508


B13.70 Alignment and Attachment Reactor Vessel Y X VT-3 examination once per intervalInterfacing Figure 4 Internals when the lower internals are

Components Clevis removed. Loss of material (wear)Insert Bolts and cracking (Note 4). Eight bolts

per clevis; four clevis at 900I Iintervals.

Category Notes:


2. The clevis insert bolts are located on the reactor vessel below the lower internals.

3. Per B-N-3, the structure shall be removed from the reactor for examination.

4. Clevis insert bolts were screened in because of stress relaxation and associated potential for cracking; however, wear of the clevis/insert isthe primary reason for the inspection.


Serial No. 12-508


IEB 88-09 Reactor Vessel Flux Thimble Y X Eddy Current ExaminationBottom Mounted Tubes (36) of the Flux Thimble TubesInstrumentation Once Every Five Years

System FluxThimble Tubes

Category Notes:



Documents

AUG 2H1? Serial No. 12-508 - NRC: Home Page · 2012. 9. 19. · Dominion Energy Kewaunee, Inc. 5000 Dominion Boulevard, Glen Allen, VA 23060 ATTN: Document Control Desk AUG 30 2H1?