ML070290668
| ML070290668 | |
| Person / Time | |
|---|---|
| Site: | Oyster Creek |
| Issue date: | 04/24/1992 |
| From: | Dromerick A W Office of Nuclear Reactor Regulation |
| To: | Barton J J GPU Nuclear Corp |
| Ashley D J, NRR/DLR/RLRA, 415-3191 | |
| References | |
| TAC M79166, TAC MC7624 NUDOCS 9204300078 | |
| Download: ML070290668 (14) | |
Text
.-- .... .April 24, 1 Doc'ket No. 50-219 N~.:>; rJohn J. Barton~ ~icePresident and Director S GPU Nuclear Corporation
.Oyster Creek Nuclear Genertn Stto-..Post Office Box 388 ../'Forked River, New Jersey 08731 Der Mr. Barton: *992 I..j i~)istribution:)ocket-File16 IRC & Local PDRs'D 1-4 Plant Varga ICalvo Norris flromeri ck)GC:PTan ACRS (10)CWHeh1, RI..,:,SU.BJECT:
EVALUATION REPORT CHI STRUCTURAL INTEGRITY OF THE OYST"ER CREEK DRWEL(TAC NO. M79166)-'ý The staff has completed the review arnd evaluation of the stress analyses and stability analyses reports of the corroded 'drywell with and without the sand-S-,bed. ,-Our, evaluation reportiAs contained in the enclosure.
-GP.UN used the.!.analyses to Justify the removal--of~he -sand ýfrom the sand bed -region. Even:~though the staff ,:with-the
'assistance 6f cons'ultants':from Brookhaven National* Laboratory
-(BNL),"concurred-With GPUN's.concluslon'that the drywell meets the-'.ESection III:-Subsection.
NE requirements-i1t is es~sential that GPUN continue..-.;.-UT.,thickn'ess."m'ea'surements at refuellng:.outages rand at outag~s'.6f opportunity
- for.-the' life -of' th ln;'T easurements~should cover not. only areas.previously inspeicted but.,also' accessible areas which have never, been inspected.. ..:so-as-to confirm that th6 thickness.
of the corroded areas are as projected and.-.the: corroded areas are' local ized..,.:.,"~W.Irqet that you respond -withfn 30' days of receipt of this letter indcatngyour -intent -to .comply with the.-above requirements as discussed in.-,the 'Safety Evaluation,"...-,*".7-,'The requirements of this letter 'affect fewer than 10 respondents, and-"therefore,-
are not subject to Office of Management and Budget review under Sincerely,-. I ..Alexander W. Dromerick, Sr. Project Manager.24007 ......4 Project Directorate' 1-4 P24dR v 9DC 2o4O24' Division of Reactor Projects -1/11 PDR Office of Nuclear Reactor Regulation t-.'gIAs*
stated ccwecosure:
..IUBLL bLAIIR COPY See *next page ..~~OFICIAL RECORD' Document Name: 1479166 OFC !LA:PDI-4.PMI:P
-4 z-:D: PDI-4 : L&-----------------------------------
...-:ý.. q-.. I"01 4.*S A.W.7 Mr* John -Barton "Oyster Creek-Nuclear
'PUNuclear Corporation-GeeaigStation Ernest 1. Bl'ake, Jr., Esquire -Residýent inspector ,,Shaw, Pittman, Potts & TrowbrIdge d/o, U.S. Nuclear Regulatory Commiission
_*2300 N Street, NW- ..Post' Office Box 445*.,r..-_
Washin6gton, DC. 20037 Forked River, New Jersey 08731--..ýRegional Administrator,.'Region L. Ient -Tosch, Chief.,-;U.S. Nuclear. Regulatory Conmisslo'n".:
.New'Jersey Department'of
"'-475 Allendale -Road i*Enromnta Potection..igoPrsiPennsylvania 19406' .Bure au of. Nuci ear Enginern--~~~CN 415 .ern*~Wk. cnsig Manager T.renton,;
New Je'rsey 08625 GP`"ýU-Nuclear
'Corporatio6n
-'ý1I: Upper. Pod Road R~a~ippay, ew'Jersey 07054 i._Mayor~>,.-
'~Lacey.-
owship.818.West Lace Rad vFjorked -RiVer, NIew Jelrsey 08731 6 ielhs ng ag y R 0Ysteriýrerek:
Nucl ear Genierating'Station-J~a~;Stp:..iteEmergenc'y'Bd
"-Poit t OfficeBo38
- Yorkied :Rive'r, Ne Jere- 83.'4 4 4 UNITED STATES;3; NUCLEAR REGULATORY COMMISSION-WASHINGTON, 0. C. 20555 SAFETY EVALUATIO.4 BY-THE OFFICE OF NUCLEAR REACTOR REGULATION-V.-.- ... DRYWELI. STRUCTURAL TNTEGR17Y-OYSTER CREEK NUCLEAR GENERATING STATIOR.,GPU-NUCLEAR CORPORATION 7DOCKET NO' 50-219'I INTRODUCT-ION
.,: *****. ..In 1986-the s'te'el driyw*ellI at Oysiter" Creek Nu'clear..Generating Station (OCNGS).~ WSfound to b -exte'1.ns~ival) cc 8 sr~oded in-the area of the shell which is in-~j}j~<conactli tr,. hesid _cushi on-. around tebtoof-the dryw'ell;-
Since -then.---1* -GPU Iluclear-.Corp-6ration,; (GPUN te-. icensee O fG)F'nttitd
- ~ rogam f periodic:
inspection-of the drywell shell sand.cs; n rathog"O..S1-. ul tra son ic testing .(UT) thickness..measurements.
'The inspection has been Sext ended. to.te.aes*f the~drywell..and some 'areas above the sa'nd cushion^,!.have been.-found to' be corroded al so.'-'iýFrom the UT thickness ineasurernetson
Caconclude "that'V-corrosion.
of ýthe~dryweli"shell,-in the'sand cushion-area is~~ an atternpt'to' e~liminate-corrosion
- or.re. c tecroin~~~2~at i~enseel tried da-thodic.:poetoadfudt;obo oaal~tesan cuh io --,a's-th- proesenc-ioh'-water in-the isan,: 6 he-'ofense-has-
--A xm sndt ren'ovath""rl to.,beo an-mortnsct el'T'easent In ihts programt'o ei'min tate*1' 'k, thecoro i sn threat i u;to .",."4 te ryel A I cnc rn.i t-testrutua ntegrity..
~ nthe program, theo llea-nsee.-.-:prstesencebofisherj -the .analsscrtran h--zr. ~wi toutthe --snc~fthe-1d~zh licensee -hared~tes nl sesad.Vii nstaidrty sanalysesoal tf o .bet~wt animp wtorta'th leent'san cas~pganico elimedathe h~'dyellcorrosio:.thouat.t the,$sadry to b,;incogityplincewith-the criteri J ýe:establ gshed -fothe- reheCauto.f I isf is to bhedte the'anatssýtheoriainal prpoen-'Zg hout-te -san cs ons tof-th poinde smoothl1 transiti' ronmd ofstresss fs o thlyes'n~~~~fied porti on~to the free-standing portion of the steel drywell.'XAILUATI.IQI iN~ ~~i~e saf wih te ssistance of consultants from Brookhaven -National-
--V ab~aot'.(BNL) has reviewed and evaluated the "information (Refs. 1,2,3,4,5)
.. -`.'provided by the licensed*.,..
9204300097'920424 f 4., S 4.PD~ADOCI"I 05000219)S 4 '443T ý 4, 1. Re-Analysis CROWWa -The drywell was originally-de'signed and constructed to the requirements of* ASZ4E Section VIII code and applicable code cases, with a contract date of July 1, 1964. The Section VIII -Code --riqurements
~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 HE Code through the 1971 summer addenda. The reason*for the use -of the Code of this vintage is that it~was -used -in 'the:M'a'rk.I
ý'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 t~le drywell is A-212, grade B, Firebox Quality (Section VIII), but-it is redesignated as SA-516 grade in Section III. .--the stress intensity (Smc-) in"Section III fo m~etal containment is 1LIS -Smc.c) 'Categorization of strss itgeneral primary membrane, general bending and local primary membrane stressesand 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.
I In 'addition to0 ASME Sectio'n III..Subsection HE Code,,the licensee has al' s I...-..,,,nvoked ASME Section Xl-I IWE-Code-todio-rsr-te-he--~-4a f~.Ceek drywelliIW-3519.3 and IWE-3122.4 state-that it isacceptable if eIther. the thickness of the base metal is reduced by no more-than 10% of the* formal plate thickness or thO reduced, thickness.
can,--be shown. by. analys~is to.7..._,7
'saisf the requirements of-the design,.s.pecification.-Thestaf ha reiew' th "-a o~ t io nof ASME Section III Subsection NE and Section XI Subsection.
IWE in its evaluation of the structural adequacy of the corroded Oyster Creek drywell, and has found it to be generally' re rasonabl e and acceptable..
By adopting the Subsection N.E criteriag' the licensee has treated the corroded'areas as discontinuities per NE-3213.10,, which was originally meant for change ,ý..;,4. .."ý,ý.in thicknesses,::
supports, and penetrations.. -These discontinuities are highly~ ocalized and. should be designed so that their prsnewl aen fecton T'~ the 'overal I behavior of the jconitainment -she'll'.
NE-3A1 10 defines cl early`--i the11I 1 I1:..:-evel of stress inte'nsity anid the extent of the discontinuity to be considered local ized. A stress intensity limit--of 1 A-Smc--s-specified at- -the -boundary ofthe region within whi'ch 'the* membrane stressý can be higher than 1.1 Smc';-The region whereFthe--stress-intensity varies from-1.1 Smc to1;0-OSmc is-not defined i the Codebecaus e of the fact that-i ~~swthh odn.vewof this, the licensee rationalized that the 1.1 Smc canibe applied beyond~the region defined by NE-3213.1O for. localized discontinuity without any.rsrcti on throughout the -drywel I.-hestaf f di sagreed wi th~the l icensee's r~~interpretation of the Code.--ý,..The .staff-.pointed'out that for ýOyster Creek<drywell,-.stres'ses due'to An-trinal pres'sure'sholuld be used asthe criterion to'esablshsuch a region.M,T'1fe interpretation of Section XI Subsections IWE-Th3519.3 and. IWE-3122.4
- can' be made only in the same conte'xt.-.,It is staff's.,3p 0sition that the primary' membrane stress Llimit of 1.1 Smc not be used.~ idiscimintelythroughout-thedrwl
..In ordert use E23.40 to o ns'`' o:c' ider' th'e:-c'orroded area as 'a localized4
.'dsotiutthe extent 'of. the'reduct ion in thickn~ess due to corrosion.i.tshould be- reason ably -known.- ---1T-th icknes s-:me asurement
- s. .are- h ighl y---iocal ized 'Z 0 r--oihfrb hthb 7 ,umerous!
mefiasuremtents -so- far'mad t-on ,th e7iyster_-Cree k.z-:--.,----
drywell, one can have a general idea of the overall corroded condition of the drywell. shell and it:.is possible'.to Judiciously apply~the established re-nalysis criteri a..:~ Re-analyses.
re m.. .. ... .... .Th eaay es were made. by GeneralElectric.
Company. for the llcensee,.one.
2 F~eaalysis considered thd'sand present and-the ,other considered .the drywell Iýý%'ýWhu.
h ah-ý'nls compriises.41-streissanalysis and stabilityA
.ýVWt4 Ean alysis 3Two:, f16iite ýel ement. model i*%ý,one"`axi symmnetric"and another.a
- 36. pie "r.MN,ý nslice* model:;wer'e used -for.-the--.stress-a'nalsi s;.-,*T:he'ANSYS c m -.poga -s--~U iM sdt eform the Analyss he-a'x`i'symmetri&
6model was.used to' determine....
th srsssfor t.he seisIW*ri the-thermal*.gradienti loads.---T.he-pie slice--.ýmodel: was- -used: for.. dead 'weight~and -pressure'-oads'<Thý ejlice model' .3-1nclu'des':the',Ventý'pipe'.
a-nd thdf'reinforcipg-rlgan was: als iused for .: I&ucl Ing analysis hesmeodel s-.were~used or.-the case s""W'ith -and without.~ sad,~excpt.tha1 t~fomerthiesti ffnes U'osand In con'tact with.the..
..;g~~te l sellwas:.cotislderid4 Th helhckesin hthsandj-egion was!-M -`assuife6d td be .00.7OO"'forjth6wi th-ýs and,,cate. -and .tobe&'0.
736!.'.for
- thi wi thout-~ adcs~Te0.70" wa's%`as--cl aimed. b.bythe".llcen~see,u-sedý;6or' onservatism
~ te0.736 ..is the p*'rojected .thickness'iat the start of fuel'cycle 14R.' The~~4~'sme thicknesses of 'the shelab e Ithsad region were us'ed for both cases.X, R tFor..the'with-sand case an anal ys is of. 3 the..drywell 1With the original.
nominal-al-.hicknesseswa made tocheck th~selsrse with the allowableý vlesetblished,-fb'r-the ý.re-an~alyses:'.ý-.+ý~?.
-...... , -....-*The license'e-useid the i'same load co1mbinations a's specie in" Oyster -Creek's~fina1. design safety analysis report (FDSAR) for the -re-analyses.
The i censee comparison..of the load combinations -and corresponding*
allowable stress Qj~..I
-e-4-4 limits using the 'Standard.Review Plan (SRP) section 3.8.2 and concluded they are comparab~le. .Ii .*.-.. .... .....-..-*The result of the re-anailyses
'indicated that the governing thicknesse's are in the upper sphere',;and~the cylinder where the calculated primary membran'e stresses are respectively.
20,360. psi an 985 s.vs. the allowal*srs
-value of 19,300 p 4siThere -is basically'no difference,~
i n the acltd .-:stresses
- at-these'.levels, between~the'with and without sand cases. Vhis should be' expecte~d'because.-in, asteel shell structure the local effect or the edeeffect is damped in a very'short di~stance. .The stresses calculated-exceed the allowaible.by 3%.:to 6%, -and such exceedance is actually limited to-the corroded arez) as~obtained from UT measurements.
However, in order to p....erform the~axisynimetric.
analysis and analysis of the pie slice model,' uniform thicknesses were lassumed for each section of the drywell. Therefore, ,the calculated.oers~tresses may reprks-9ie l s a the corýroded areas. and-th sreseIo-aea-byodthe'-cor roded 'areas .-areiles -`a~d7 NiW6d ino!st.....likely be within the'allowable asidctd rsuit of thniaysesifor-
,",nominal thicknesses-.;.~-,-The
ýdiagram in Ref. 6 indicated such a condition~.
It is"At be-noted that ~the stresses for,.the corroded areas~were obtained by~ ultiplying the stresses for nominal thicknesses by the ratios between the y orroded -and nominal ,-thicknesses.
býWTije-:analyses'of
'the dryeli were performed in accordance with ASME'-iode Case.N-284.%.-.ýThe
- analyses were done on-the 360-. pie slice model for both s~ ith-s and~and. without-s and-.cases...Except in the 'sand cushion area where a 7, shell thIckness cof:0.7!..-
fof,.the..with-sand case and'a shell thickness of 0.736"*-for the -withoutAiahd~cas'e'were -used,: nominal shell,!-thicknesses were cdnsidered
..-identi f ied -as.thoss Ivolving'.refueling and post-'accident conditions.
!, By p, aplying a~factoi; of safety of 2. and 1.67 for the load combinations involving~j~ refuel ing and. the post-accident*
conditions respec~tively,, the licensee-established for -both cases the~allowable buckling ýstresses which are obtained#'--' ater~being modi fled by capacity and plasticity reduction'factors.
It is~*Wfound that the..wlthout-s and,**case6for.the post-accident condition is.rnost imi.roting in'termIs of. buckling -with a'iargi nof'4 The staff and its".BrokhvehNational Laborator
-'(BNL)-consul tants. ~concur,.with the licensee's w-,~conclusion that the' Oyster. Creek -drywel 1. has adequate margin against buckling~V~kk~wth o snd upprt or n asumed sandbed region shell thickness of 0.736 Inch. 'c"$I5 opy of BNL's technical, evaluation report is attached to this safety....... evaluation..
I.- I CNCUS.ithe rw o 1-the with-sand and wihu-adcss h reanlalyses by uatedli thesre pinsiaes-toa the staf'sroned rnse andt the detaidre-analseso c cont a inme nt vessels as contained in ASME Section III Subsection NE through su~er 1977 addenda' This Code was~adopted in the Mark I containment program,.The staff agrees-with the'licensee's...Justification of using the above mentioned Code requirements with one.exception, the use of;. ..Smc throughout
~'&he drywell shell.lin.
the'criteria~for.V~inlss-I-l th staff'--position that the' primary membrane stress limit of 1. Smc .not be used i ndiscriminately.
throughout the drywell;..
The staff accepted the licensee's Sreanalyses on -the, assumption`
that -the cor'roded areas are highly'local ized as ,indicated bythe licensee"'s UT me urtiemehts.,ý'...The'stresses'6.`obtained for the~-~cseof.reduced thickness "car '-nly be i nterprýeted to represent thos'e in'the S~cro d'areas a'nd..their:
aidjacent regions~of the'd rywel l,'s hellI..In view of these observations'..
i -:ii' essential.-that--.the'licensee, perform UT thicknessT
.:. ,measurement atrfuel inig."out ages -.6fd -at :ýoutages-of-. opportunity for the life-o t eplant. .The 'me asur~ements should cover'-not_*ohly areas .previously i E:h.2...npce but also "accessible';ar'eas which have never been iAnspected so-as to'-".~conf irm that the -.th Ickne s'se s o'f the'"corroded are as' are as prjected 'and the yt-crr e arasare l ocal ized-." 'Both of these .assumptions' are the bases of-the.....reanalyses.
and.*the staff 'acceptance of thereanalysis.*results..
~-.2.12.:"nASME..Section V111 Evauato o-the Oyster Creek Drywell Part 1 SSrsAnlsis" GE Report No.-9-i DRF #00664 November.1990, prepared for ~G P UN ( w ith sa n d). *!2~Just If cati for'Use' of Section'II,'.Subsection NE,:Wudance in Yr-k7 *Evaluating the Oyster Creek Drywell'"-TR-7377-1, Teledyne Engine~ering
.~~Services, -November, 19?9O (Appendix:Atto Reference
- 1) <n'.~ 3 -A~ ASM Sec'ti'n',-1 VIIe~a ~nof Abe Oyster. Creek Dr~ywell, Part 2,'-`:?---:Stability Analysis'..
GE Report: No-:'9-`2 DRF 1006649 Rev;ý.O-~O
& Rev. I : Novemiber,,1990
- preo'ifedfjorGPUN
- (w ith. s and). -*:.._,;:'4 A,~ hA A S E Se&6ti ohIV I I E luatiovf.Oy s t erCr e'ek 'D ryweI f o r-_ W.6i-* ~th-out"'iand case';-Part;:,L`
stressanialysis!,GE.
Repor o. 9-3 DRF 1006.64,' Rey~ 0,. february, 199 i-.',PriPared .for'-GPUN!`!^?;--':--
'. ,--. .*i.F'An ASHE S v AecttionVII Evlain, of -Oyster. Creek Drywell, for withbout sand.',.-:
-at2 Stability Analysis" GE Report No. 9-4, DRF #00664 Rev. 0, SRev.,.I.
November 1990il. prepared ~for GPUN..~ .--igram attached to dletter from 3.i C. Devine Jr. of GPUN to NRCdae:.-i-Jnay.17ý.,1992 (C321.-.92-20209.
5000-92-2094).
.ýH'i~ncipal Con P .Ti a n ,BNL-.Technic'al Evaluation
'R ..' Ali i~ I Iinuimiuin hEEl E EEl HElM IIIPEIiEEiIliiIfliiiiil lUll I BROOKHAVEN N'ATIONAL LABORATORY TECHNILCAL EVALUATION REPORT'.I ON STRUCTURAL ANALYSES.
OF -THE -CORRODED OYSTER CREE1X STEEL DRYWELL-14 ý.Introduction An 'inspection of the' steel drywell at the Oyster..Creek Nuclear jt"G Generating'Station~in November-1986 revealed that-some -degradation due to'corrosion had occfirred-in the s'andbed.
region,.'f the shell-Subsequent inspections
--also identified thickneiss:
d egradations in.-'the a'upper. spherical and c6ylindric'al
..sections :of the -dryel 11Th*GPU Nulm- ýAopoain,..:has-.
perfo-mid":stuctura 1:-:-analyses -to. dem~onstrate.
the integrity.!of6i, the .drywell--ýo"r"'projectedI
~~orroded
.conditions, :that;.may:?exist*
- at..te -start:,bf.:.tthe f ourteenth"rfuin ote(4R.jThsotage S ý:.expl t to' start in<>i,...0ctber192.>n-an at'mtt arrstthe'corroson the* licensee-2 thy ubh :ei al~y~s'es o 'the. o1 bbwith~ adwithout sand for dryiwell, wall *thicknesses pro~jected to exist at te.start of 14R outage, ~.~.*.2 Summar-of Licensee'sAaye7 r ................
f'~.'.~The.-analyses performed by he lieseutilized the drywell 'r_M. -A'al-'thicknesses summariz'ed in .Table-I,-.
DrywJell Wall Thicknesses
___ -_.... : .., .Proected 95%~ ~~k~' 1As-mDesignhed Confidence
,.,ThicknesseS.
14R'Thicknesses p rvwell-Reioh*
_________IT_
- -,"-Cylindrical-.
Region* 0~ 06 40 -"~.. .0,619~ nule -' 2.5625i 2 2.5 62 5 v¶:Upr)6.er~s~
icil':Reigioni 0* 0.2 ~.067 7/"gPMiddle
--Spherical.
Region 0 07 7 0 0.723 e4':;Lower;::SphericalI Region- 1154 1.154 111','E-xcept -Sand "Bed Area ..** ~ ' .3~.imNT~v Tal -fbthRfrn i and 3 indicates' that',the'*,.
$~ k, knuckle" thickniess".
i 265".This appears"t Qa:'~misak siceCth kucke hikhes~d is shown" to- be"2-9/16"in Fgure 1 o thesame report.~Figure. 1-1* of .'h~:: 1q r.u I ..
The stress analysis for the'"with sand" case is described in Reference
- 1. For this analysis the licensee utilized the as--designed thicknesse~s, except for the sandbed region wher6 )a thickness of 0-.70"1. wa~s used.- The -stress results were obtained from.a finite element analysis which utilized axisymmetric soli'd elements and the ANSIFS computer program. Later, the stress results were scaled to address the local thinning in areas other than the Y 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 Repor~t and the 1964 TechnicAl specification for*.the Containment.--
Appendix E of Reference 1 compares the load combinations considered in the analsiswit thsejgiven in section 3.8.2 or the NRC Standar 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 the as-designed thicknesss exept f or the sandbed region. where ~j..thickness
--'0.3-1 was used.,- In'this case, to f inite 'ele-ment modelsr-, 7an--axisymmetric
.-and-a- 360-pi .-sl-ie model i-:were- usedi-j-=The
: a isiii c 6Ti~ d'ilT is -esseftialyf---the-- -same ---as- --that -7isin .Reference 1; however, the elements representing the-sand stiffness were removed. This model was. used to determine the seismic and thermal stresses.
The pieslice model was used to determine tI~e 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 reinforcing ring in the drywell shell in'the vicinity-.of each vent pipe. The drywell and vent shell were modeled using-'3-dimensional e last ic-ýplastic quadrilateral shell elements.
Atla* K-i.~.'.distance of 76 inch~s trom'the drywell shell, beam elements were, 4k *used to model the rbmainder.
of. the ventline.
- The loads and load i.
- ' combinations-are -th4 -same-:as those considered-in Reeec f ~ The code of recor fr the Oyster Creek drywell is the 1962 Edition of the ASME bode,Section VIII with Addenda to Winter 196j, g, and Code*Cases%1270N-5, :'1271N and 1272N-5'.--The' licensee utilized-~~ thse riteria in, evaluating the~stresses in the ýdrywell, but also'utilized guidance.fr'om~the NRC Standard Review. Plan with regard to*allowable stressesfr~srie-lvl and 'the post-accidenit condition.,.
The licensee'-also used guidance from Subsection UE of.,Section Ill'of the ASME Code.in*order to 'justifythe use of a limit of 1.1S*in evaluat~ing the general membrane stresses in areas of the drywell where reduced .thicknesses are specified.
.Based on ,K ý .-- these criteria the licensee has. concluded that the stresses in the~~~-'.'-dryellshell are wi.thin code allowable limits for both the "with -sand"t and "without~
an'. cases.-T e-nd -iyaaye ftedy She licensee also'performed stabilit alyeofterwell Sfor both the "with sand" case (Ref erence 2) and .the "without sand'case (Reference
- 4) .For.the ."with sand" case the licensee utilized th e as-designed thicknesses shown in Table 1, except in the sandbed region where a thicljness of 0.700 inch wa's used.' For the "withou't----. ........-Z.
j sand" case the spme thicknesses were used ,except in the saridbed region where a ihickness of 0.736 inch was-used.
The, buckling-.capability of..th~edrywell for..both the -with. sand" and ."without sand" cases was -evaluated--by using the 360 -pie slice f inite el~ement model discussed iabove. For the "with sand" -case spring- 61e~nents were used in the'sandbed.".reg ion -to model the sand support.---.For:-the---"without sand" Cdase -these spring elements were removed. -Thel most limiting-load com~binations which result in the highest compressive stresses in thelsandbed 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-accident.
condition
-(Dead. Weight--+- -Live Load-+ Hydrostatic
--Pressure for -Flooded Drywell + -External -Pressure
+ -Seismic).
The bucklin~g evaluations performed by the licensee follow the methodology described in ASME Code Case N-284, "Metal Containment Shell Buckling Design Methods, section 111, Class MC"', Approved-August 25, 1980. The -theoretical elastic buckling stress is calculated by anr'alyzing the three dimensional finite element model discussed abovea...
Then the theoretical buckling stress is modified, by -- c .apaLcit i4n-ýýgs~~--36~itoi,;icos
.--- :--:-compre~ss~ive-stregs-.~i~s-.obtained.-by--divi-ding.-the,.ca-lcxlato-d*.buckl-ing~--.-
stress by a factor of safety. In accordance with Code Case '1"-284 the.licnse usd a factor -of safety of 2..0 for the refu'ling condition and 1.;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 the, hoop stress modifica~tion on data related to the* axial compredssive strength of cylinders (R~eferences 2 and 4). Later the licensee revised the approach based on a review of spherical shell buckling data and recalcu'lated the dry~well buckling capacities for both the"1with. sand" and '"without sand" cases (Ref erence-B ). For the `-'with-compessve"-stdssof 47% -for the refueling condition and 4q0%- for teps-accident condition., For the "without-sand" case", the-licensee reports
argins 'of .2'4. 5% for the. refueling conditi6'n and 14% f or the post-accident.
condition.
---3. Evaluation of Licens-eeis
'Approach The analyses'-
performed-by the licensee as summariz~d in Section 2 and discussed more fully in References 1 through 4 .have been reviewed and f ound to provide an acceptable approach f or demonstrating t;ý structural integrity of the corroded Oysterý!Creek
- drywell. The finite element analyses performed for both the stress and stability eValuations are consistent with industry practice.--Except for the 6ise of a limit of 1.1S., in evaluating the general membrane- -stress~ in'areas of reduced drywell1.
thickness, the--1oads,---
-load combinatio~is and, acceptance criteria used by the licens'e'e are--consistent with! the guidance given- in Section. 3.8.2 of tije -NRC*Standard ReviewlPlan, Rev. 1,. July 1981. To further support,ý'their-position, the licensee has provided two appendices to Refere~nce 1..33. 3 A.,I J,.,"..~--Appendix A provides adetailed J- stif ication for the use of Section'III, Subsection NE e's.giac in evaluating .the oyster Creek'drywell. Appendix E :*compares .the load combinations given in the Final DO-sign Safetyt. nls i s -Report, -.(FDSAR) .with the load,.combinations given in SRP ~.308.2' and demonstrates that the load'combinations used in the analysis en'velop.those given..in the* SRP.In the areas of the drywell where reduced thicknesses are: specified, the licenqee has used a limit of 1.lS* to evaluate the gneral 'membrane .t.~e. n spotof.-tis:.posi#ion the licensee has cited tfiie poiin of NE-3213.1 of the ASME Code: 'concerning local primary membrane stresses.
'In effect,, the`licensee's criteria would treat -corroded or degraded areas as;'Idiscontinuities.
For~, such -considerations the code places no limit" on the extent of the .1 region in which the membrane stress exceeds'*1 ~ 1 M.. .S~ but is less th~an 1. IS~ In support of this position the" licene hspovided" the opionion of Dr. W.E. Cooper, a well kseha rnown;:-expert on the development of the ASME Code. Dr. Cooper concluded:*
that #qvefl a des ign which satisfies the:-general.Cod.int__
..-.the Oyster--Creek
.'dr lzdssLrigialycristructed,..itj.
i-not`)!:-A-' to be between 1.OS* a~nd isiS,, over significant distances".
The..Ilicensee has also cited the provisions of IWE-3519.3 which acceptsJ up to a 10% reduction~in the thickness of the original base metal..I I.the licensee's position has merit, but great caution must be' 4-.indiscriminately..
-.In the case .'of the Oyster Creek drywell the'.'licensee has conclude4~
that "there are very few locations where the~i1"~calculated stress. intlensities for..design basis..conditions, wouldl'exceed 1.0S 3 0.-and in these cases only slightly" (Reference 7). The't "--~ '*' li-cen se--h as -ProVidd 'dddit tibal .if 6riWat'ibi' 96fce9t support this conclusion..
..'Based on the information provided .by the., 1 icensee which demonstrates that the use of the 1 ISa criteria is.;lmited to localized
ý6reas, iti ocue~ht teOyster Cr'eek.."'drywell meets the intent of the ASME Code..'As discussed .in'Section 2, the capacity reduction factors usedj*~j -in."the buckling anlssaemodified to take 'into account the'-42. ,..beneficial'.effects
'oý :tens ilel::ýhoop stress. 'A's a result -of a'.question-raised -'during *..the :reiview regarding
'this matter, the'11 .lc e ns ee-s ubmitted additional information in Reference 5 to support:-;,:the approach....
'This information.
included a report "prepared by. C.D..iK~ erentitled "Effebts of Internal Pressure on Axial Compression"'
Srngth of. Cylinders!'
,-.(CBI Technical Report No.:%022891,,FebruarY
~ 199) .e report .p~pt..a'design~equation hcwas .the..owr býoundo h test' daa included in..the report. -It also demonstrated..
.~.that 'th eqution u 'in References
'2 'and 4 'was 'cons ervat ive', 4:-I'J';Kelative to the proposed design equation.
The report presented:-,'
.J~~;.'N'f urther arguments that*. the-rules-..determin6d -for axial ly'compressed
'Jý'~',Cylinders' subjected to-internal pressure can be applied to spheres.1, i~~iSubsequently the licensee has submitted Reference 8, wh i ch I. Ra~-ý ;y' ii:. ,' .,J, indicates that the original approach was not conservative with regard to its application to spherical shapes and recommends a new equation.
However, ~the. docutmentation supporting the use of this -equation is not .included in Reference I8 u paetyi contained in-a: rd'f irlenced-repo~rt prepared by C;D. -M-i-iler entitled-4. "Evaluation of Stability'Analysis Methods Used for the Oyster Creek Drywall" (CBI. Technical Report Prepared for" GPU--Nucleair
- Corporation, September 1991). This" 1port-was subsequently, submitted and reviewed by the NRC staff. As dis~cussed in Section* 2, the u~se of the revised equation still results in calculated caaiisin compliance with the ASME Code provisions; however,ýthe argis beond. tho'se capacities are -reduced from those reporte -by References
.2 and *.It is noted that the licensee may have "double-counted" the ef fects of hoop tension, since the theoretical elastic instabilitý
%stress was calculated from the finite element model using the ANSYS Code. The elastic instability stress calculated by the ANSYS Code; .I, may have already taken into account the effects of hoop tensil~e stes.However, bycomparing the theoretical elastic instabilitly stress- and.:-thle.'-corresponding
- -cirumerential
--..rs-pre.'c,~d-b'-'
that the effect of h-bop tension in the ANSYS calculations is smal-I and there is suf fici~nt margin in the results to compensate for th;_p ..potential "double;-counting".
Furthermore, it is judged that therie is sufficient capacity in the dry'well to preclude a signif icant buckling failure under the postulated loading conditions since the...'licensee-*s calculatio6ns: (a) incorporate factors of safety of 1.67 .* o2.0, depending bpon' the load condition, and .(b) utilize ~a conservative assumpt'ýion by considering the shell wall thickness'to
,:.' f be severely reduced -for the full. circumference "of. the drywall throughout the sand1~ed region. *~* ~.4. -A Durng he ourrse of the' review oifthe licene' s ~imita~3~f~- anumber* of othe tissues were raised' rgdigtearoc.Tese
, I.'.included: (a) the basis and method of calculating' the projectea drywall thicknesses,,, (b). the scaling of the calculated stresses -for: r 2-1Zthe nominal -thickness case by the thickness ratio, (c) the effect~~1.ý0 ."stress concenitrationsde-otecag f thickness, (d), montorngof the..drywell'.temperature, .'(e)" sensiti'vity of stresses Sdue to variationsln.
the. sand spring stiff ness,._(f) sensitivity of~1~the* plasticity redudtion factor- in the buckling analysis, (g) US6 .'"of .the 2 psi .desi~n. basis external pressure7 in 'the bucklin K SanalysisI (h) ef fect of the'. large displacementý method, (i) the'~..~~- treatment
'of the large concentrated loads considered in t!~e.;.t~~:analysis, and (J) tie method of applying the seismic loads to the W!pe lc mdl These issues were adequately'addressed by tl~e :......aditinal nfomatifon-provided by.the-licensee-in-Ref erences a'd-~A. .6V.'N'-; 4ý A Conclusions The licerns-eeh-f~id~e'monitrated that the calculated
ýtreisses in-theOyser ree dr 11l (both witan without the sandbed), asia reslt f he osu~ _eloading.
onditions, meet -the intent of the ASME Code for projected.
corroded -conditions that may exist at thie*. start of the f 6urt~ein~th riefuel1in'g
'outage.*e Howeverf, if th'e -ctu'a 1... thickness in the. sandbed region_ at 14R is close to the projected thickness of 0.736",1.
there may- not'be adequate margin left for furhe coroion ý through continued operation unless it i......demonstrated that removal of sand will completely stop furth'e'r thickness reductions.
The licensee 'has also demonstrated that there is suffic"~~~niited I~ein(~~ with nd"" without the sandbed) to -preclude a buckling failure under thie postulated loading Lconditions.
It should be recognized that the conclusions reached by the licensee have been aiccepted for this particular application with due regard to~all the assumptions made in the-analysis and the'* ~ available margins. The use, of the 1.1 S., criteria for evaluating g=-=erl mmbrnestress in corroded -rdegraded areas. shoud be and 'Atfpi~e cu ed~bish abf ist es --t~ e~ ~general us. The licensee's:
buckling criteria regardn h~~'~. modification of capacity reduction factors for tensile hoop stress and the determination of plasticity reduction factors-should also~ .be investigated in '~a similar manner.5. References A 1 GERepot Id~x o. -1, "An ASME Section VIII Evaluation b the Oyster Creek Drywe'll -Part 1 -Stress Analysis", Novembýýr 1990. -~ -_F 2. GE Report Index No., 9-21 "An ASME Section VIII Evaluation of the Oyster Creek Drywell -Part 2 -Stability AayiA* ~November_1990..------
34 GE Report Inddk.No.
9-31 "An ASME Section VIII Evaluation
'Of the Oysteir Cr6e6k Drywell' for Without Sand Case -Part V, S Stress Analysib,"!..
February 1991.4.."* GE Report Index No. 9-4, "An ASME Section VIII Evaluation'to f the Oyster Creek Drywell for Without Sand Case- Part 2~i-ýýV "'Nstability Analysis," February 1991.Y. ý ý5. GPU Nuclear letter dated March 20,. 1991, "Oyster Creek Drywq'l_Containment."11----*
1-6 GPU Nuclear letter dated June 20, 1991, "Oyster Creek Drywei,1l~ ' -Containme~nt".
6.07-
- 7. cpu fulea -date Ocober -9, 1991, "OysterCre Drywell containment" !8. GPT Nula etter date January 16, 1992, "Oyster Creek U ~ Nucea --de Drywell Conltainmentll".
- 9. GPU Nu1ilclear lettr dated' January 17,,. 19,"yster Cr'eek.4 Drywell 'Corita~irment".., -... .-----,-.V7.;.44."r4 ...4 .....