ML072780381

September 2007 Evidentiary Hearing - Applicant Exhibit 37, NRC Safety Evaluation: Drywell Structural Integrity, Oyster Creek Nuclear Generating Station

ML072780381
Person / Time
Site:	Oyster Creek
Issue date:	04/24/1992
From:	Dromerick A Office of Nuclear Reactor Regulation
To:	J. J. Barton GPU Nuclear Corp
SECY RAS
References
50-219-LR, AmerGen-Applicant-37, RAS 14248, TAC M79166
Download: ML072780381 (14)

Text

..,._APLICANT'S EXHIBIT 37 April 24, 1992 K..

DoEket Ho.50--....

0. 2i9 1, s-

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Docketcfl e.1 CS(0 NRC & Local PDRs

CWHehl, RI Mr. John J. Barton PD 1-4 Plant

-;L-.'Vice President and Director SVarga DOCKETED GPU Nuclear Corporation JCalvo USNRC O-,yster Creek Nuclear Generating Station

. SNorris Post Office Box 388.

ADromerick October 1, 2007 (1 0:45am)

Forked River, New Jersey. 08731 :">,..

OGC CPTan OFFICE OF SECRETARY

. Dea r. Barton:

RULEMAKINGS AND ADJUDICATIONS STAFF

SUBJECT:

EVALUATION REPORT O4 STRUCTURAL INTEGRITY OF THE OYSTER CREEK DRYWELL (TAC NO. H79166).-.;

The staff has completed the review and evaluation of the stress analyses and stability analyses reports of the corroded drywell with and without the sand bed..Our-evaluation report is contained in the enclosure.* GPUN.used the analyses to Justify the removal,-ofthe-sand.from the sand bed-region.

Even

--;ithough the staff-with.the assistance of consultants.from Brookhaven National L."

a bLaboratory (BNL)

c'oncurred with GPUN' s.conclusion'that the drywell meets the

• ASME-.ection IlI:Subsectlon.NE'requirenentsi-*;.lt is essential that-GPUN continue T "*UT.m. thi ckne s s' me as'urements -at"-' r.efuel I ng.., out ages" and atl outage's'.. fopportunity

'- for: 'the life 'of the-4plant. -.The.'measurements should cover not only. areas-..

.previouslylnspected but.also accessible areas which have never, been inspected so'as..to confirm that the thickness. of the corroded areas are as projected and

'the lorroded areas are 'localized......,

thty**'t a

u rsp6hd.with n 30 days of receipt of this letter indicating your intent to comply.with the.above requirements as discussed in

.: t he Safety Evaluation ;..-.-

"reuemets" ofathis letter affect fewer.than 10 respondents, and

5

• ,.- ;' therefore, are not subject to Office of Management and Budget -review under P L.-96-511..

Sincerely,

/*;*

s/

t.

3 Alexander W Dromerick, Sr. Project Manager

'O' Project Directorate 1-4 C., *.92O430007B 920424 f.'.

300'0eDCK 05000219:

Division of Reactor Projects -

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PDR..-.

,Of fice of Nuclear.Reactor Regulation 5 c d/"cl s r"

`EnclosUre=.

.it*" !,'Se e*next page."'

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` RECORD CO0,P Y.:

Document Name: M79166 FC::DI-4

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-Barton Oyster Creek"Nuclear

. PU Nuclear Corporation.

<. Generating Station- -.-

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-,*.Ernest L. Blake, Jr., Esquire Resident Inspector Shaw, Pittman, Potts & Trowbridge :

/o. U.S. Nuclear Regulatory Commission 2300 N Street, NW.-'

Post Office Box 445:

Washington,.DC20037..

Forked River, New Jersey 08731:--.-: --

+.

Regional Administrator,.. Region I

.Kent.Tosch, Chief U.S..Nuclear.Regulatory Commission--..:

. New'Jersey Department of 475 Allendale Road..

Environmental Protection

'of Prussia,.Penns Ivaina 19406 Bureau'of. Nuclear Engineering

.-.BWR Licensing Hanager.

Trenton, New Jersey 08625

- -- Nuclear Corporation n-

- Upper. Pond Road Parspany, few Jersey 07054 :..

o iLacey.Township.-..

West*Lacey'Road

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Forked River,- flew Jelrsey 08731 E e h's ng Ma n ag e r,ý

• Oyster..Creek Nuclear Generating Station.

lSto0:,.Site Emergency.Bldg.

y:* P0St1 0f f iCe Box.388

• -,;-F* orked..Rive-r -New Jersey. 08731 :.:2;-....

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"UNITED STATES 0 ;NUCLEAR REGULATORY COMMISSION

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L WASHINGTON. 0. C. 205B55" SAFETY EVALUATIO4 BY THE OFFICE OF NUCLEAR REACTOR REGULATION

• DRYWEL1 STRUCTURAL INTEGRITY i.-

Vi OYSTER CREEK NUCLEAR GENERATING STATION CPU NUCLEAR CORPORATION.

DOCKET NO.' 50-219 I HI

" I" RODUC i,

1986 the steel dryelI at Oyst reek Nuclear.Generating Station (OCNGS) found to be-tensivlyiccrroded in the. area of the shell which is in cntact"itht he ts ah~d ushi on-around 'the bottom of-the.drywell -- Since then :.-...-.-

,GPU Hucleary Corporation-;y (GPUN,% the-.* icensee o-f-OCtfGS),-:hittiit d- -n

': program of periodic:Inspection-of the drywell shell sand cushion area through

ultrasonic testing.(UT) thickness measurements...'he inspection has been Sxtended.to.other.areas.'of the-drywell.and some areas above the sand cushion Qhave been.found to be corroded -al so;.From. the UT thickness measurements,- one conclude that

- corrosion. of the drywel Yi shell in the-:sand cushion-area. is Mcontinutng.*;:n an attemptto eliminate::-corrosion.or. reduce. the corrosion eate,!`'-;,the ;1 enseetried.cithodici-protectoion and found-.it;.to.be 'of no -avail.

% n examination*of theresults,of consecutive UTimeasurements, anfirmed :that" kjthe corroslonios, continuing.7Fhereis.':concern.that the structural integrity 0Of the"drywell.cannot be' assured.",,Since the root cause of. the corrosion in

-1the sand..cushon -area-:isL-the-:presence*of. water in-the..sand--the-1 icensee.-has-..

" considered sand.removalto.bean.importafitelement In

.tsprogram to eliminate

":the corrosion threat itothedrywell.tintegrity;*-.,-.:.:. t

-in.the eprogram, the Ilcenseefhlstfestabished the sis :criteria and.then graKlai!sfl:

y, erfomed -the analyses of,',.thb'drywellbfor-.1ts.structural.adequacy..with and without:the.presence.of:'th~sand*.Th*11censee perforned dstress analyses and tability analyses-for both-iwith and wtthoutAhe:.sand cases and concluded the i V dryell :with ortithoiut.the's'and to be incompliincewith the criteria:'

ts'establ shed.,forthe -reealu at on.I t i s to be noted that',theortiginal purpose i;of..the sand cushlon is to provide a smooth transition of-.stresses from the

,-fixed portion:to th*efree-standing portion of the steel drywell.

....-~...;..-

9';...

ON.,/

F

~-The staff. wilth2the"s t

of consultants from Brookhaven Hational 4AeQLaboratory.(BNL) has reviewed and evaluated the information (Refs 1,2,3,4,5) yOrovided by the license.

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~Re-Analysis Cit'

• ia.

The drywell was originallyldesigned and constructed to the requirements of ASME Section VIII code and applicable code cases, with a contract date of July 1, 1964.

The Section Vill Code -.riquirtbents -for nuclear containment vessels at that time were less detailed than at any. subsequent date.

The evolution of the ASME Section III Code for metal-containments-and -its relation with ASME Section VIII Code were reviewed and evaluated by Teledyne Engineering Services (TES).

The evaluation criteria used are based on ASME Section III Subsection NE Code through the 1977 summer addenda.

The reason for the use of the Code of this vintage is that it was used in'the'KHark I

..... containment program to evaluate the steel torus for hydrodynamic loads and

.. that the current ASME Section III Subsection NE Code is closely related to that version.

The following are TES's findings relevant to Oyster Creek application:

a)

The steel material for ttle drywell is A-212, grade B, Firebox

'Quality (Section VIl), but-it is redesignated as SA-Si6 grade in Section 111.

a e

""b)-

_The-el t betwe tiih-alI b:whble.stre.-)AriSetidnV.IV-hd-the stress intensity (Smc) in Section III for s

. IS - Smc.

6c) Categorization of stresses into general primary membrane, general bending and local primary membrane stresses-and membrane plus bending stresses is adopted as in Subsection NE.

d).. The effect of a locally itressed region on the containment shell is considered in accordance]with.NE-3213.10.

In addition to ASME Section III Subsection NE Code,. the licensee has also invoked ASME Section XI IWE.-Co-de-týo-d-m-ristrt-th-e-ade- *ýa-

_f-t-e-5 '.Creek drywell.:.i-IWE-3519.3 and IWE-3122.4 state that it is acceptable if ether..the thickness of the base metal is reduced by no more.than 10% of the Mal plate thickness or.tho reducedthickness canibe shown. byanalysis to

-satisfy the requirements of.the design specification.

-The staff has reviewed the-licensee's adoption of ASME Section III Subsection

., NE and Section XI Subsection IWE in its evaluation of the-structural adequacy of the corroded Oyster Creekdrywell, and has found it to be generally m,

. reasonable and acceptable.

1, Byadopting the Subsection NE criteria, the licensee has treated the corroded

" areas as discontinuities per NE-3213.10, which was originally meant for change

• ,in.thicknesses,::supports, and penetrations.:..These discontinulties are highly D-loCaltzed and should be designed sothat their-presence-will have no:effect-on.

' the overall behavior' of thetontainment shellV NE-321310 defines 0-eailSi"he-d-_.

I,.>.,.;

l evel of stress i nte'ns ity a nid the extent o f the discontinuity to be considered

, localized. A stress intensitylimit o 1 of the region'within which "the membrane stress can' be higher than 1.1 'Smc.

The region whereFthe sttress-intensity vari es from -1.

1 Smc to :1 ASmc is-not -

defined in the Code-because of the'fact thaitvis thh7ldng

- In

~view of this, the Ilicensee rationalized that the 1.1 Smc canibe applied beyond tAhe region defined by HE-3213.10 for. localized discontinuity without any retrctonthroughout the -drywell. The-staff disagreed with~the licensee's interpre tat ion of the Code *z..The.staff--pointed ou~t that for Oyster Creek

--drwll srsses due' to inteirnai press'ure'should be used as.the criterion to

,establish such a region.

1tJe interpretation of Section XI Subsections IWE-a~~59.3 and.IWE-3122.4 can be made only in the'same context.;.-t is staff's

~--oition that the primary membrane stress'-limit of 1.1 Smc not. be used iniscriminately throughout-Ahe drywell j"'S

.--- :. * ! 5.

..* -'C -

~

InordeWto'"use HE-3213.16 to 'consider" the corroded area as alocalized

,,.discontinuity, the extent of the'reduction in thickniess due to corrosion

~t shoud be-reasonably-known -UT-hkns nasrm s.;are -highly---lpcal ized;.

y s er.Cr e..

drywell, one canthave a gentral idea of the overall corroded condition of the

- drywell shell and itris possible to Judiciously apply-the established re-SL-:::

a!onalysis criteria nbe S....

7 R

e.

a n

g

-IThe re-aonalyse were made

.byGes-lnteral l'ctric Company. for the licensee, one V.`-reafialysis considered thedsind presentand the,othericonsidered.the drywell-M1 V14.-,.

ithout-e M o ths, nd.thei Each ree ranalysis comprihssthe s

sr analysisbeand b

stabili

-axsymeticand another.'a 36 pi s Islice' -model:"wr ý ue..frA *.stess-hlsis.- T'ANSYS camp uter-. program.w as.

& t

.'.s r

on d

efined tl sEperifo.rm he0nly se'.feliaisyimmetrized model wasoused tou dtermine

'th

i.

stresses fourthoutseismi, c dthe-heermal gradient: loads.

The pie slice i;~~:node.

Was, -used.for."dead.:we fght -and -pressure'Aoads-:ý he iesice mdel7Z.

j 1-

,e

p,"'*:-ar id as al 6

~'-s-" inlu'des,the' Ven ipe and-the'renforcing,.r ng; andwsao used for.'-.

~tW.~rbukl I n4 Inalysii~~Tesm noes-w'ere used-for, the caises' With,and withoutý sand e*xept...nthat1petn

.f the Cfod er"-the:stiffne--ptn of' tandtin cryitact with.the 41.-'

W*.

"1" as-conidered 'sThe shellthicknesin the sandregion was dassumed td.bete sd anotn n

psd tobe usd0s736 forthe Without.

-'-The 70-w's,'.ascl aimed by"t lcensee, usedfs

• and--c es abls suc reOo..f

he, inepea io ofSetin.X SbsionservaE-s--

gr;6vidzz~and.he O.736l-%s'the,"projected'thickn ssat the start of fecce1R h

- same ti cknesses

-12theashell above theosaind region were uIed.for both cases.

Fo-"'-""

ot o n theawitth-sand case;*

brana s thes rwll With the original. nominal 4

th'icknessesnwas madenntocyheck hthe

.shel: stresses with the allowable..

values-e'stabl ishedfp6r: the xilan~alyses~-'

N.-

'ýTh~ icne sdIi*ýmec comb nations as specified In',Oyster Creek's Z~tu il~ design'safety analysis report (FDSAR) for the re-an'alyses. The i censee-ak'-;

comparison of the rloadcombinations and correspondi ngallowable stress

.'S.;

/hol b~ra~nby~n*

• ~t~knssmasreets.ar~hg~ylca-zd*v-

,*-':*-..i*:";:"

!dy~el, oe cn~hve genralide ofthe verll orroed ondtlo" fl~e

"':::'-)::.Yrf;,

"*ri*:

• dr~llhl An~t.i osbet.Jdcosypllh salse e

S IS r lt r a.:l*:..

Ui

. li cmits a

uigte S tand ard Re view Plan (SRP) sectio n

.3.8.2 and concluded they are. comp.,.ble

.=-.

Th Aeuts oft re-analyses indicated that the governing thicknesse's are in

,the upper. sphere' and the cylinder where the calculated primary membran'e stessaerespectively. 20,360. si -and 19,850 psi.-vs. the all6wable srs value of 19,300. sil,ýThere -is basically 'no difference,' in the calculated streses tth se i

-eesbtwe~

with and without sand cases. This should be.x,l-:'.--el se stutre the local effect'or the edge effect is damped in a very~short di'stance. ;The stresses calculated exceed the allow~ble.by 3%: to 6%, and such exceedance is actually limited to the corroded arez-a "sobtained from UT measurements. However, in order to

-~perform the axisymmietric. analysis and analysi oftepeslc oe, uniform-thicknesses; were 1assumed for each section of the drywell. Therefore, the cacltdover-srsea rersent only stresses at the corýroded areas-and-thestresses-f--areas-beyndthc.rroded 'areas 'are-l

-.likely be withl n the allowable as i n diatd2 an yonludred ter nominal thicab ses.-- The diagram in Ref. 6 indicated such a conditio

..ti to be noted that ithe" stresses for,the corroded areas~were obtained by Te rultiplying the stresses for nominal thicknesses-by the ratios between the corroded -and nominal -thicknesses,:

.. : *W1inghe uke spgranalyses'of heydyell were per fm ed in accordance with ASME

,Code. Case N s-284.,c The analyses weredone on-the 360: pie slice model for both

,-.with sand %and.

wi thout-s.and hecases...asExcept in the sand cushion area where a i i.

shell thickness leef:0.7b..efof.the.with-sand case and a shell thickness of 0.736 for the witcnoded are as wee sedrnominal shell-thicknesses were cnnsideredet f 6Fof~iit' rWS h~16i Ib

-t'i &ri h ch tharecri t~i ta'to-bu-ckl ibh'9e-r7 identified -as..thosse Involving -refueling and post-accident conditions. B applyingprfactor" of safety of 2.and 1.67 for the load combinations urvolving refueling.-and the, post-a cl dent*oecondh tions respectively, the licensee established for both cases the llowable buckling stresses which are:'

and

• -after being inodi ied by capacity and plasticity-reduction factors.

It is foundthat. the w-hout-s and,--cas for. the post-accident condition is most

.nmitlna hcný"terms of.buckling with ae.argin ofd14%;..-the staff and its S'rookhaven National-:Laboratory: (BN)

'consul tants :cohcur,.with-the licensee's

• conclusion that the' OysterCreek. drywel. has adequate margin against buckling

~ ith no sanid supoort for an assumed sandbed region seltikeso

.3 pof6Ovluatiyn.

he stressesvalunation reporthi s attached to this safety

• 'corroded and no..

..s;:*

ith sta ie of" consul tant: from BINL

e. -staff has reviewed and evauated

.the reiponses to the staff's concerns and the detailed re-analyses the drywell for.the with-sand and without-sand cases.

The reanaly es by the1licensee indicated that the corroded drywell meets the requirements for

-o r.ern.n t

eo "tIeab ihe f

r -both cae h

-alwal -uk

-n -srse -hc r:otie

j

£.

C6~ntainment vessels as contained in ASHE Section III Subsection NE through umer 1977 addenda' This Code wasadopted inthe Mark I containment program...

~~~he staff agrees-with the'.lI censee's.-Justi f icati on of using the above

~~-~~Lentioned Code requirements 'with one~exception, the use of1.-l.Smc throughout z he drywell shlAn.the'triteriajorti anlss f'

ste tf'

~ osition that the pr~imary. membrane stress limit of 1.1 Smc -not be used ndiscriminately throughout the drywell.-The staff accepted the licensee's

• reanalyses on the.assumption that the corroded areas are highly 'localized as

.A indicated byethe 'license'Is UTnmedinsremehts The' stressSu obtained for the of+ rsw e

duced7 addendhsscode be-inter peted to represent those inthe hcorroded' areas and theiradjacent.regionsof thedrywell shell. In view of

,'ethedse observationsutes' essential. that;the licensee f

peform UT thickness

.at shell..n.heotagesrt a

dat.outages-of.opportunity for the life

-- ofs the pltant..,The pmeasurymebnt e

s rhould cvers not only areasmnprevi ouslyd

,-,,ý.inspected but also 'accessibleareas which have never beeninspected so-as to con fire y that the:

ckes~supt ofha -the

'corroded areas are ai4roJected and the

.,ondJ cmtate y.theý t1 Jcken'sees*,s UT mesuee nt a;**Tesrse~bandfrte J.

• '*case~~~~~~~~

ao~eue nhcns~a~l benepetdt ere-sen thoses of the

i. :'corroded areas a-ire lIocalzed Both of these assumptionsrethe bases oft "reaunalyses and the staff 'acceptance

-. ofd-theoreanal ys is results.

! efterenc`-;e Jy An AS Se'tibn VIo 1; Evaluation of the Oyster Creek Drywell Part 1,

'Ji......Stress Analysis.

t GE s

'eport No.f9-1 DRF.00664 Novembers1990, prepared for GPU W

wtn h

aa) s a' nd

-V

~ Jstification foerlise' of Section' III,' Subsection -NE,"-.Guidance in

a.

-~"

Evlating the.Oyster Creek Drywell', TR-7377-1, Teledyne Engineering ReServices, **November-.

90 (Appendik.o-*.eference.)...

ki3l

• An AS'E.Sect i" VI*I Evaluation-of.the Oyster Creek Drywell Part2,

.'..Stressiy Analysis'. GE Report Ho,.9-1 DRF 100664, ReVbe 9, & Rev.-- I-

5..l'a&uattng Sethoe.

I vluto fOyster Creek Dryew,.R777]

eledn fogner ng

~, '2~~

at SabliyAnalysis tm E Rpor No. 9 -4,DF#064Rvi,

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ATTACHMENT I,

8 '.

BROOKHAVEN NATIONAL LABORATORY

'...."......TECHNICAL EVALUATION REPORT ON 1

.. - "I " ".

• . O N STRUCTURAL ANALYSESO oTHE"CoR*bED OYSTER CREEKSTEEL DRYWELL-1 -.

Introduction

• A

'inspection of the'steel drywellatheOseCrk uer

,".Generating' Station: in llovetbier' 1986 revedaled that some-degradation

.ue to

.corrosionhad occ.irred-in_

the..Sandbed-region-.of -the shell.

Subsequent inspections also identified thickness: -degra'dations i he.. upper spherical and eit ywell.'The

'nalysesn to. demonstra the integrity:- f the drywell!for ected

]$k c6orroded -conditions'.:that myex. atý-

testart,6f.:-the futet

-2i,,':refueling Sutage (14 N Theirs. outage hs expecte degsartin j.)e.....r-etoer.1992.r nan att o

p-torto :-arrest the corrosion` the licensee,:.

7,.plan*h "to.premovreiai and.fy indricab os etions onsethe.

h tly, -.-

• .T*.*ana5 cy

e.

ao.emn trat o-th ntgrty?.th.drywel 6

t-hrSeced:..-

'and without sand for drywellwall'thicknesses projected to exist at.'

hstart of 14R outage.

S

.ýe' a

.A' a

2'*

'Summaryý of Licen

' Anlses

• -*+~~~~~~~~~~~~~~~~~~~~~~.

+"-.........

"-.*.- --"+...-...... *-"?!...':.:.

,..The. analyses perfored" the iceýnsee utilized the drywell

.athicknesses summarized in.Table" 1.

S=.

Table'.!J Dryxell Wall Thicknesses As-Dedigned Confidence

!..fv

.'."Thicknesses

-4R r,5.

_-~

r w l Re io...

I....

.22,,,,L..,.

$,Cylindrical-Region '...640

• 0.619

~' KnUckle:C-?

'*2.5625*

2.5625*:

UprSpheirlcal :ýReigion Upper.

0.72. 2:,`.

0. 677

• .Midde Spherical. Region 0'.2770 0,73

• 'Lower:::Spherical Region -

154 1.154

,ý21,ýEcet-Sn Bed. Area

_.Sand.Bed. Region.

1..

154.,.

0.

736

%-47.

=, ".

+"-

--*NOE:

ncle

.of both References 1 and 3 indicates that.the :

.<F.*-O.. knuckle'..thickness"*{is: is.2. 625".-. This appears-to be a

-a

,'itak-s~fiW-- ftince. theTknfiufck1e-.th ickii*s-s is shown" to be'". 2-..,

."::Y

/l*U.

iriF gure.:. :-l-.of-t e"

m "reporto...:.,.:..

/.i."

. =.

.'5

• ..' v *..

. s' fp-T-r."..'-.-

J"-

21o'

' i:

=..- T

• :+* ".

, :...: ;..+. ',-

,.S.'.,..I

-...+.

i:..,

The stress analysis for the'"with sand" case is described in Reference 1.

For this analysis the licensee utilized the as-'

designed thicknesses, except for the sandbed region wher6 !a thickness of 0.70".-was used. The-stress results were obtained from...

a finite element analysis which utilized. axisymmetric solid elements and the ANS~!S computer program. Later, the stress results were scaled to address the local thinning in areas other than the sandbed region (thed projected 95% confidence 14R thicknesses in Table 1).

The loads and load combinations considered in the analysis are based -on.the:FSAR Primary-Containment Design Report and the 1964 Technical Specification for~the Containment.- Appendix E of Reference 1 compares the load combinations considered in the analysis with thsfgiven in section 3.8.2 of the NRC Standard Review Plan, Rev. 1,ý July 1981.

The stress analysis for the "without sand" case is described in Reference 3. For this analysis the licensee-also utilized thea as-designed thicknesses, except for the sandbed region. where 4a thickness of O.736". was used. hIn 'this case, twoe foinite relem.ent

• .;.*". eemetsand the ASY S

omuerr 7n-:30progra.-

' 'oder 1the sre--ssresults' 7iiisym~ii tii6tir

-6delI -is

-sta Reference 1;d however, the elements representing thee-sand stiffness were removed.

This' model was used to determine the seismic and thermal stresses.

The pie slice model was used to determine thýe dead weight and pressure stresses, as. well as the stresses for load

'combinations. The pie slice model included the effects of the vent

."pipes and the reinfiacing ring in the drywell shell inmthe vicinity of each vent pipe. The drywell and vent shell were modeled using 3-dimensional elastic,-plastic quadrilateral shell elements.

Atla distance of 76 inch~s from the drywell shell, beam elements wer'e used to model the rbmaindern of the ventline. -The loads and load

---combinations -are -thA --same-as those cons idered-inRef erence-l--e-------

The code of record for the Oyster Creek drywell is the 1962 Edition of the ASME bode,Section VIII with Addenda to Winteir 196j,

and Code* Ca*sesne 1270N-

1.27Nh and h1272N-5tcThen a licensee utilized th

-these criteria in eValuating the.stresses in the-drywell,.but also 0

'!i-.-..-..

utilizdes guidance.efromthe eRC Standard R'evsandbed with rerd to

`f-_ allowable stress~es f or.,-.service level-c and

~the post-accidenit jc ohicktnes 0The licensee'-also used guidance from Subsection NE of

'Section IIIsofmthe

-aSME Code.- in.-order to wJustify-the use of a limit the Ree inc

evaluating the general membrane stresses in areas of te w drywell where reduced thicknesses are specified. -

Based 6n these criteria the licensee hasmconcluded that the stresses in the

- dryweall shell are swthinrcodeallowable limits for both the owith

'tWsand" and "1withou cases.%ý-,

..Theblicaensee alsi-performed stabiluty analyses of the drywell fpor both the "with anfdo case (Reference 2) andithe "without sand" case (Re nt 4).For Thed"with sand" case thelieree uting LY.-

the as-designed thicknesses shown in Table 1 except in the sAandbed egion where a thicness of 0.700 inch wa's used.' For the "without 34i.;i-'C-:-co bi at on-ar-t

-m

+-a h s

-:.+

cons i------------------

V...

sand" case the s me thicknesses were used, except in the sandbed region where a kh ickness of 0.736.inch was -used.

The. buckling capability of.the drywell for both the.'.with sand" and "without sand" cases was.evaluated-by using the 36 -pie slice finite element model discussed above.

For the "with sand" -case spring elemnents i*. "

were used in the'sandbed-region to model the sand support.---For--the--....-

"without sand".Case -these spring elements were removed.

The'! most limiting-load co-binations which result in the highest compressive-stresses in the)sandbed region were considered for the buckling analysis.

These are the refueling condition (Dead Weight +:: Live Load + Refueling Water Weight + External. Pressure -+ Seismic.) and the post-acciden't condition -(Dead-Weight---+ -Live -Load-+ Hydrostatic--

Pressure for Flooded Drywell + -External Pressure + Seismic).

The buckling evaluations performed by the licensee follow the methodology described in ASME Code Case N-284, "Metal Containment shell Buckling Design Methods,Section III, Class MC",

App~roved August 25, 1980.

The -theoretical elastic buckling stress is calculated by an"alyzing the three dimensional finite element nodel discussed above.A. Then the theoretical buckling stress is modified by

-aloqkable"

--compressive-stress'..is.obtained-by. divi-ding-the.-calcu-lated-buckl-inz_,;

stress by a factor of safety.

In accordance with Code Case !/H-284 the licensee us.ed a factor-of safety of 2.0 for the refuteling condition and l.'67 for the post-accident condition.

The capacity reduction factors were also modified to take into account the effects of hoopi stress.

Originally the licensee based thel hoop stress modification on data related to the axial compressive strength of cylinders (References 2 and 4).

Later the licensee revised the approach based on a review of spherical shell buckling data and recalculated the drywell buckling capacities for both the with sand" and 4"without sand" cases (Reference-.8).

For the,"with.

.- ýsand"-.case,--_thq--licensee-reports.-a--margin--above--.the.--all'ý'able compressive stress of 47% !for the refueling condition and 40%- for the post-accideht condition."' For the "without-sand" case% the-licensee reports margins of'.24.5% for the. refueling conditi6n and

3. 4% for the post-accident condition.

3.

Evaluation of L censee's'"Amproach 1." -:

The analyses -performed by the licensee as summarized in Section 2 and discussed more fully in References 1 through 4.have been reviewed and found to provide an acceptable approach for demonstrating tte structural integrity of the corroded Oyster:iCreek drywell.

The finite element analyses performed for both the stress and stability eValuations are consistent with industry practice.

Except for the &se of a. limit of 1. 1S,3 in evaluating the general membrane--stressin'areas of reduced drywell-thickness, the --loads;--:

71 load combinations and, acceptance criteria used by the licensee are.--

consistent with! the guidance given in Section 3.8.2 of the NRC Standard Review-1Plan,. Rev. 1,-July 1981. To-further supportimtheir-.

position, the lcensee has provided two appendices to Reference 1.

• 4 4

A Z

[.

r""~-

o,

• :-~..........................................

Appendix A provides a-detailed justification for the use of Section' III, Subsection NE as-guidance in evaluating the Oyster Creek'

'".drywell.

Appendix E lcompares.-the load combinations given in the,.

4..-: "Final Design Safety%_ Analysis.Report. (FDSAR)

. with the load-.

combinations given in SRP.3.8.2 and demonstrates that the load' combinations used in the.analysis-envelop.those given..in the SRP.

In the areas of the drywell where reduced thicknesses are:.

specified, the licenjee has used a limit of to evaluate the general membrane sties-es.

In support of ths, position the.

licensee has cited tNprovisions-of N E-3213.

of the ASME Code-..

"c concerning local primary membrane stresses.

In

effect, the, i'lcensee's criteria would treat -corroded or degraded areas as;.

discontinuities.

For,.such -considerations the code places no limit' S.

a-on the extent of the region in which the membrane stress exceeds"

..~."*.0

-OS but is less than 1.1S,*.

In support of this position the'.

'licensee has providedthe opinion of Dr. W.E. cooper, a well known.

expert on the development of the ASME Code.

Dr. Cooper concluded

'..that."given a desiqn which satisfies the._general. Code intent, as:,;

.:..'".&..:;the Oyster._Creek..drywel*l-does-as-or inally.

.a Vilia~i6 of Subsectaon NE reilreentsfor the membrane stress:`

to be between 1.

OSOC and 1,1S., over significant distances".

The licensee has also cited the provisions of IWE-3519.3 which accepts' up to a 10% reductionlin the thickness of the original base metal..'

e.. -!."The licensee's position has merit, but great caution must be'j

'.exercised

' to assure that ý..such' a

position.is not applied.!

`_.....indiscriminately.

-In the case.'of 'the Oyster Creek drywell the..

licensee has concluded that "there are very few locations where theI..

,-<:*:-calculated stress ini.ensities for.design basis. conditions, wouldi'".-

exceed 1. O'S, and in these cases only sli.ghtly". (Reference 7).

The; 1 censd-dhas -- pr6-id- -7dddit'i-6-l:.iififm6rit~i6iffih-T6fi:Ene 6c:

support this conclusion.:... Based on the information provided by the!

licensee which demons-trates that the use of the 1.1Sac criteria is

.limited to localized

,areas, it is concluded that the Oyster Creek.

Jdrywell meets the int nt of the ASME Code.

As discussed in Section 2 the capacity reduction factors usedit I',-

in:.

the 'buckling analnsis.are.modif ied to take 'into account thek'

,.beneficial' effects oý -tensile:-hoop stress..

'A's a result -of a.'

i quest onraised

---during.the review regarding 'this matter, the".

esubmitted addcitional information in Reference 5 to support:.

j,4--the approach.-..'This infornation:included a report"prepared by.C.D.4.1 Z

Ki'Miller entitled "Effects of Internal Pressure on Axial Compression""

"i.Strength of. Cylindersý".,,(CB1 Technical Report No.,022891,' February'-.4:'*

bou.

hnd reportopreented a design.'equation.. whlchwasthe_-ower:

frT;bound of the test data included in the report. It. also demonstraed that the-equ-ation uled.in References 2 'and 4 'was conservative1 7.' relative to the propoped design equation.

The report presented- -

I'.-.

further arguments that. the-rules-determlned.for axiallycompressedi

'1

.'..cylinders subjected to internal pressure can be applied to spheres Subsequently the licensee has submitted Reference 8,

which;

-,'- -I'-

-**,W' 4

L..

M.2:.*..

1*

. i indicates that the original approach was not conservative with

" ::.-- regard to its application.to spherical shapes and recommends a new equation.

However,-the documentation supporting the use of this equation is not included in Reference 8,

but apparently is contained ina ref~nced-report prepared by C;. -Mi-ller entitled

-. "Evaluation of StabilityAnalysis Methods Used for the Oyster Creek Drywell" (CBI Technical,~ Report Prepared for " GPU"'-Nuclea-

"- Corporation, September 1991).'.. This report was-ubsequently submitted and reviewed by the NRC staff.

As discussed in Section 2,

the use of the revised equation still results in calculated capacities in compliance with the ASME Code provisions; however; the margins beyond those capacities are reduced from those reported..'

by References.2 and '4.

It is noted that the licensee may have "double-counted" the effects of hoop tension, since the theoretical elastic instabilit stress was calculated from the finite element model using the ANSYS Code.

The elastic instability stress calculated by the ANSYS Code; may have already taken into account the effects of hoop tensile stress.

However, by comparing the theoretical elastic instabilit~y stress and.-the'--corresponding --c rcum ereitia --stressdipred-.6-

• [*i!j.;:.::,.*.. th h i* cihns~e-.f 6--t h fibre

- lih -a'f..-p* t=acc*id e-n

.---as e s,.* it -appe ar*s :*,..

that the effect of hbop tension in the ANSYS calculations is smal.l

".:.'.. and there is suffici~nt margin in the results to.compensate for the:%

potential "double-counting".

Furthermore, it is judged that ther e'

.i:.-.

1"s sufficient capacity in the drywell to preclude a significant buckling failure under the postulated loading conditions since the licensee's calculations: (a) incorporate factors of safety of 1.67 to 2.0, depending upon the load condition, and.(b) utilize la conservative assumption by considering the shell wallthickness to be severely reduced -for the full. circumference of..the drywll throughout the sandl~ed region.

a"*c -_-..

=-

-:* L-.- *_1...

=-

a *"During the coure of the review of the licensee's sumittals a number of other issues were raisedriegarding the approach. 'These included:

(a) the basis and method of calculating the projected drywell thicknesses,, (b).the scaling of the calculated stresses -for..

r-- the nominal -thickness case by the thickness ratio, (c) the effeci VV.

"stress concentrations.:due:-to. the" change..of thickness, (d) imonitoring of the.. drywel temperature, -(e) sensitivity 'of stresses

'.'due to variations in, the sand spring stiffness,-'.(f) sensitivity ofi.

the plasticity reduction factor-in the buckling'*analysis, (g) us

-of. the 2 psi design. basis; external pressure-".in the buckling ':

• .C

analysis, (h) effect of the. large displacement' method, (i) thie

.... treatment of the large concentrated loads considered in thle analysis, and (J) the method of applying the seismic loads to the

-.pie slice model.

These issues were adequately addressed by tle additional in formatilon -provided -by-the-licensee-in-References and----""-

-4.-.;*

.r 6..

°,

-I

"/

5...'

-a4

'- ".-N.d

..:a-;r

4.

conclusions iThe licensee--s demonstrated that the calulated stresses in the Oyster Creek-rwell (both-with and without the sandbed),

asia result of the postulated_.loading conditions, meet.the intent of the ASME Code for projected.corroded conditions that may exist at the start o

the fueli

However, if the-ctu*'l thickness in the sandbed region at 14R is close to the projected thickness of 0.736",

there may-not be adequate margin left for further corrosion " through continued operation unless it is demonstrated that removal of sand will completely stop further thickness reductions.

The licensee has also demonstrated that there is sufficfen teargin -in th dr-ywel esign (both-with ed esandbed) to preclude a buckling failure under tle postulated loading *conditions..

1-,

It should be recognized that the conclusions reached by the licensee have beenaccepted for this particular application with due regard to.all the assumptions made in the-analysis and the available margins. of The use.ofthe l. 1S, criteria for evaluating general membrane stress in corroded or degraded areas-should 'be

'":..inv~estigated.

fu t erb.t hekNRC.s aff-_n-d_-1i-AS E-_-C-de-.6C iii tj

-and 't6pri~t-bu-5 esadtblish' d'Thff~r

=It-"is

-pt'd general use.

The, licensee's: buckling criteria regarding the modification of capacity reduction factors. for tensile hoop stress T

and the determination of plasticity reduction factors should alio be investigated inla similar manner.

5.

5 References

1.

GE Report lndex No. 9-1, "An ASME Section VIII-Evaluation,6f the Oyster Creek Drywell -. Part 1 - Stress Analysis", November 1990.

2.

GE Report Index No. 9-2, "An ASME Section VIII Evaluation *of the Oyster Creek Drywell Part 2 Stability Analysisj,"

November 1990..

3a GE Report lhddkc.lo. 9-31, "An ASME Section VIII Evaluation;1of S-the.Oyster Cr~ek Drywell* for Without Sand Case

-Part 1

.Stress Analys i§, P..' February 1991.

4.

GE Report IndexýNo. 9-4, "An ASME Section VIII Evaluation iof the Oyster Cr;eek Drywell for Without Sand Case Part 2 Stability Analysis,."

February 1991.

5.

CPU Nuclear letter dated March 20, 1991, "Oyster Creek Drywoue

. Containment, Ar

6.

CPU Nuclear letter dated June 20, 1991, "Oyster Creek Drywg 1 Containment".

0.1 q

I6 a

Co ta nm nt i

-.. 4-,#

I

2.

t "t

i7..:'- CPU "Iluclear 'letter dated October-9, *1991, "Oyster Creek

'Drywell Containment" I'

8.

GPU *Nuclear. letter dated January 16,

1992, "Oyster Creek '"7*;'

it-t L.. -'Drywell.Containmentll."CJ dat.'

Jaur 17,-

9o CPU Nula etrdtdJnay1,_k1992, "Oyte Creek Drywell Co.tai-ment"..

14'.

W X. J 4 4S da 7:

A'A'.

4 tt.t 37w.;

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