ML20053C424

Order Authorizing Issuance of Full Power,Full Term License to Dpc,Conforming to Terms of 810609 Draft License.Related Info Encl

ML20053C424
Person / Time
Site:	McGuire, Mcguire
Issue date:	06/29/1981
From:	Chilk S NRC OFFICE OF THE SECRETARY (SECY)
To:	Bradford P, Gilinsky V, Hendrie J NRC COMMISSION (OCM)
Shared Package
ML20049A255	List: ML20053C419 ML20053C424
References
FOIA-81-516 NUDOCS 8206020106
Download: ML20053C424 (13)

Text

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C:to as 14 NRC 1 (1981)

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NUCLEAR REGULATORY COMM:SSION JFM

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3[,3 if COMMISSIONERS:

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Joseph M. Hendrie, Cha,rman f y} g 3 L W g

Victor Gilinsky

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In the Mattee of Docket Nos. 50-369 i.,% /

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DUKE POWER COMPANY (Wil!!arn 5. McGuire i

Nuclear Station Unita 1 and 2)

June 29,1981 Following the iuuance of a Lnensir g Board's decuson (LBP-81-13) i l's authorinng the Director of Nuclear Reactor Regulation to issue a full-power, full-term bcense for the operatmn of Units 1 and 2 of the McGuire facility, and upon the completion of its "efTectneness review" of that decision as it relates to full powc operation of Urut I, the Comnussion authorizes the Director to inue the full power, full-term bcense for the operation of Unit 1. The Commnsion, takes this action without prejudice to its "efTectiseneu review" for Unit 2, the normal appellate renew of the Ucensing Board's decision (as it pertains to both Uruts I and 2) by the Appeal Board and by the Comrrusuon. and the motion to stay the efTectiveness of the Licensing Board's decnmn now before the Appeal Board.

ORDER

.c In its supplemental initial decision dated May 26. 1981, the Atorruc gN

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Safety and Licensing Board resobed the remairung inues m this proceeding P

g' and authorized the Director of Nuucar Reactor Regu:ation, after makmg

,.N the requisite findings, to issue full term twenses to Duke Powa Company

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suthonnng full power operation of McGuire Nuclear Station. Unns I and 2.

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Intervenor, Caruhna Environm< ntal Study Gruup (CESG), has request-

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,kh ed the Atomic Safety and Licensit.g Appeal Board pursuant to 10 C.F.R.

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,%8 2.788 to stay the effectneness of the decision. However, qui:e apart from

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5 this stay request, the Licensing Board's iruttal decision does not become an q

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effective authonzation untii the C4 mniuien has taken the actic s outhned

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in its Order, dated May 28, 1931 These actions entail analysis of the g

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Ucensing Board's decision to deterunne whether it should bec.ime efTective.

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G The Comminion completed a panial efTect:veneu review and on June s

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ful 11, 1981, authoriied the Omc4 of Nuclear Reactor Regulauon to issue a

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licenu to Duke Power Company to eperate McGuae Nuclear Station, Urat g

I at steady state reactor core power lesels not in excess of 5% of rated g

MM y*gfgf power. He Conuniuion has now completed its effecuveness review as it,

g,".de relates to full power operations of Unit I and has decided that the Ucensing

%rp A$ggf@[M hahP1 Board's May 26,1981 supplemental initial decision may become eft-ctive g

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?v insofar as full power operauon of Unit I is concerned. nts efTecuverass

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d decision is without prejudice to Comminion efTectiveness review for Unit 2, W;.

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the normal appellate review of the Ixensing Board's decision by the Mg

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Appeal Board and by the Comnussion, and the Intervenor's stay motion

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7N filed June 8,1981, which is now before the Appeal Board.'

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an excess of the design hmits m 10 C.F.R. 50 44, and the efTectneneu of

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The hkelihood of an accident that would lead to generauon of hydrogen j

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measures to mitigate the consequences of such hydrogen generation, were

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critical issues in the Commission's debberations on efTectiveness. He

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~ Jp j shik.f hQ Iicenwe has agreed to install and use an igniter hydrogen nutigation sptem.

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and has speed to license conditions which provide that (1) for operauon

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beyond January 31,1982 the Commission must confirm that an adequa'e

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hydrogen control system for the plant n mstalled and nll perform its

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.ed ;-s=mmhng 9 h .a L dated May A 1981. CF.SO's anot.on is an ingwrmetde r&rt to c*aasa n=4=wusy gb { V[* d e*r==-a renew of a txessing fkerd swUrr and in. therches. beums 10 CJ IL 2 ?sl and a '. Q. gg 2.7BA Qgg &y"e% ' g:; e 'r 4 2 s. NY.. gw be, i.

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h;. Accadingly, the Director, Omce of Nuclear Reactor Regu!.ation is 'Jfsyd)r34p>$qd authorized to issue a full power full term license to Duke Power Con pany ,4 iw$gSM.yM j.4 which shall conform substantially to the terms of the June 9,1981 dran (.f. %,pf# .,3 licene Wk

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ld SAMUEL J. ClllLK D;4-7?ti . Mi[W[9C M Secretary of the Commission 5 [^~

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Oiaarman IIendrie's Additional Views, the Separate Views ci h $ 0N Commissioners Gilinsky and Bradford, the Separate Opinion of y ' W. Commeoner Bradford,and Commissioner Ahearne's Additional -J ~ p. ,3 V:cws are attached. Dated at Washington, D.C. '!?{ the 29th day of June,1981. f. x,, ,o. 4 ! - {.A . 7 ?@-

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>Y J'- 1.' 6, 6 CilAIRMAN llENDRIE'S ADDITION AL VIEWS .,jp t e 1 support m full the Commiumn order authorumg the Director of Nuclear 1 r. 1 0 :fQ.n-;M U

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%g Reactor Regulation to inue. full term. full power h(ense fer McGuire Unit 'jd* -

1. I add thew comments in order to speak to some of the additional news of i

trS,lMfkg _,N] Ojs7 Commiwioner Gihnsky. ' ^M5f;Q

& &gj]t I do not agree with my solleague that the i nenung Board's decision in this y[

Y b pg y jyg%gq p - {p case is "wnously defectne " I find the Board to hase interpreted correctly ? "l,# +1 the proper boundanes of its conederatior, of the hydrogen question as set i' M 6. P hk 9 forth m the Commisuoni regulations and m its orders on that question in the Bree Mde Idand t'mt I restart proseedmg. CLl4ttl6.11 NRC 674

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i ~"; # t (1980)and Commiwion Order dated September A 1%0. 94; { My colleague's complamt. it seems to me. n really with the Commissmn's . J' .J standing directions on this matter rather than wvh the Board's actions and j.NJ. ~ decision. Ilis uews here are sertainly conmtent with his news on the -f i 4A Comrmssioni deciuons on hydrogen m the 1 Ml-l proceedmp, but those G ~ decisions went apamst him and stand now.n the operatn e ducctions to the h [ID 4 Board. He ham for those decnions n pelled out m the Commission's w. D orders and in Commnuoneri additional ucws m she 1 MI.I case and need not be repeated here v h e >9n V. GM m e 'g. I W j 9 ( 4 r ~. f, l,'.. [ 7, { . ? M

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,s v a s .,7 ... y a I b P., g.C s r A ' <Wu yi @ @tg A... % Jr} [y - ]Q,;'. Q g c 4 $ $a% Q*o y SEPARATE VIEWS OF jog n 0r d COMMISSIONERS GILINSKY AND llR ADFORD ' W 'l.A L~ 6.emh.e. .Y f' g q t p j *h ' *,,sa g 'g,[. n

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q We approse full power operation for McGuire Umt I in spite of the g. ~wbW c4 LicensmE Ibard's senousi) defectise deciuon. Smcc the Board avoided i" hr M A; WWQQ. making findmgs on the nsks posed by the Feneration of hydrogen in the M $~. s "h J@;hjp reactor during an accident or on the adequacy of the glow plug igniter Mty-g $, hE jWn' system designed to cope with such risks, the Commission reviewed the t., .Kn n f record, was bntfed by the parties, drew its own conclusions, and decided, M..W grgy ? as it had previously in the Sequoyah case to make the installation of a ._. g;y, P J m. e y i W'.'6% i hydrogen control system a condition of the operating hcense. his is the '[ " M basis for our approval of a full-power operat F Kense for McGuire Umt 1. F I o,%s 2 Em ap -

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.S [V ? v N nsa.:q ne inue of immediate concern is the adequaev of reactor protection d.k ti against burns or cuplosions of bydrogen gas s hah r'nay be generated dunng g. [' %g Q[ an accident. Ilydrogen would be generated in the rentor's core if the -6A "s. m - zircaloy fuel cladding. the thin metal tuhmg contaming the uramum oxide j M .h. fuel pellets, reached escewisely high temperaturev This claddmg scacts i with steam at high temperatures to form nrcomum eude and hydrogen. If a ~. '. [Q.${g c Q7 substantial fraction of the claddmg reacts with steam, the resultant d l{kM9 &Jl. concen. ration of hydrogen in the reactor contaament (an exceed combusti-y M 'V tle hmits. ..," " 4 fk h skY 3rb if 7 9 ( dW

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Ilydrogen Burn at D112 t n ,4 J. M M-His: happened during the nree Mile Island acedent. As mmh u 50 d,..f r' MN {M y *,,y percent of the cladding in the core -- wme ten tons of metal - n thought V> c,c

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by the accident's irnestigators to have react:d chemaalls with ucam.' Part ,pjj~[M of the several hundred kilograms of hydrogen prmhaed by the reacth:r: y found its way out of the reactor's coohnF system into the u.rroundmg containment where it was set off, presumably by a spark trom elettncal ~ equipment,about ten hours after the start of the accident NRC regulations, promulgated in a more innocent time. required protectam apsmst an amount of hydroEen only about (.ne-tenth as larfc 3 nas stcndard was believed to provide a substantial safety margin because the (. mm:nion's ..3J1,. a g regulations on emergency core coohng systems contemplated that no more ';,, :, y f'llj_i . (* [ ?;, than about one percent of the cbddmg would react with steam. d' h {s,*M' j[y ~. t

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%;l 'Three Mile faland. A Report to the Commm. mm and to the Pu%. MC Sprual Ingen jh %g. NT Group Vol. 2. Pan 2. January 19tc. p $35 l f p., g/ML, 35madards for Combustkle Gas Cemtrol Systern in lyhi % am lestM Po=ct Reutors,4) 93g . - ~, , (J l'~ ?QJ A p '~ FR 50163, October 27,1978 (tierei.uner 10 C I R. % 44) t gI/ ^ 't= k: - /* !?? l V y. A h +,- e -,en lr 3 g

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V+. h 7 .: m ..kh@g l h .;I 2 i'.[S i h% ' 'h'! Hg' j The hydrogen nre that swept through the TMI-2 reactor cor.trinment had L .hp Wag;4 two important effects. First, while the nie apparently did not cause vital Qgd,&g e W g,gp*/ safety equipment to fail, it charred winng and melted telephones. T1us . M.') fy !(. l mg,CRsQky;. shows that safety egwpment inside a containment should be qu.ahned to - @ gin'4 yg y'. g er 3 3b[iW W[;\\ 9 w,thstand the efTects of burns. Second, e,d more importantly, the hydroEen pN ;, k' Nb.- burn raised the pressure inside the TMI-2 containment, a lasge steel.hned = a. y

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remforced concrete shell with an internal volume of about two milbon 94 F[ d w h' @.' cubic feet, by about 28 pounds per square inch (roughly two atmospheres). j Mjj5 Fortuna:ely TMI.2's large containment has a " design pressure" - the p '*M;Tyi internal pressure the containment is designed to w,thstand with an ampic'(ppn[!-n*4, ft y y' .h. u (l margin of s.afety - of about 60 pounds per square mch, wc!) abose the 28 s e,u.-:4.x, psi expenenced. c. g Nh&T n.. Jgy 3 + ff[ Impilcarkins foe Sma!!cr Containments ~ Qf *, lj{ r y V :W jffM d if the same quantity of hydrogen had burned in a smaller contamment, d] ?:Q:]M o' a ; howeser, the internal pressure nse would have been proportionately greater. .y ~y For esample, had the burn taen place m a contamment with half the ~ .,y j. volume of the one at TMI 2, which is roughly the case for an ice coadenwr g g. 1g containment such as McGuire, the pressure would hase been approssmaie-i. 3 -? ly twice as great Moreover, the design pressure of the ice condenser ig A.. $s containments is about one-third of the design pressure of other large g - [,,. pressurized water reactors containments: about 15 psi as compared w,th . WW @ a >]?pipf'- the typical PWR containment design pressure or about 50 psi.8 %@Myi .h The abihty of a containment to resist a hydrogen burn is proportional to PV, the containment design pressure (P) times the c<mtamment volume (V). y q u On this basis, the ice condenser contamments ase about sta tunes less p at ,j{ capable of withstandmg hydrogen fires than the ordmary large PWR P 'n p containment. e 4 Odgla of Smallee Containments The smaller cheaper containments were made acceptable for larte tc by the Atomic Energy Commission's retreat, wme fifteen years ago. . ors J' its regulatory philosophy of " defense-in4!epth' Until that time. contam. 'n, . om ,s h ments of the smaller reactors were genera!!) expected to mamtam their A tntegnty even m the event of a core melt. In the mid-sixties, howeser when the first of the near-one thousand megawatt plants were being reviewed,itf.- L Y .F became evident to the regulators that the 1.rge plants' contamments would WM lh m-u 'nm m a was or 10 km oo den = contamm,nu um m c.un,.. unau w,uuun,on. S q *' rj,L wH "n f. In additwo thm m t9 General E3er'nc MaA til h=Imit =aus reactor c etammenu t=sth M y < ? : ?' - - D design p essures orsbout 15 pm) under wrwuuctwut ,e* ,%,n ,? ? ,? b 2

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)h h5 t & ~t n Qffl ~y.,,u:,%y;.y@.v;k & M yy e g(,..~y ;: M,y,QQq.,n-gygy(g& f' y r. .m,.s .Qn. g z -:& i M. Mm a, n<;,J.V v ) n tA. _e J I ,. A . y. u.W. . M'" h,D h j *Hi .Qf ~ .f % ;'; hkely..at be able to withstand a core melt. As the power of reactors .M% d.;hgh{g# [K%g -puQg increased the amount of " decay heat" in the wre grew so large that the E *jA,.,,% Q+.% containment could no longer be expened to remam mtact if all coohng . &q w% '. , W,.y$ W k,y a. .c p systems failed to work.* y k dh g N:/ J.r .y ,y j fp ~ 'My nis r:atuation came at a time of rapidly mcreasing utility comrmtment to g$ 'j n M [4 pdm nuclear plants. Despite some hesitation on the part of the Adnsory - ${ i M jd Committee on Reactor Safeguards' the AEC chose not to rethink its I Q&p'Qid commitment to custing deugns and decided simply to drop the contain- !,F .I. WF ment as an mdependent barner m tbc scheme of " defense-in-depth". De ~ 7hk

1. p.; k AEC decided, instead, to concentrate on improving the emergency core

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~ g% n g r ,Np Mg, [ Simultaneously, the Commission decided that accidents involving the %y' "%g T failure of the emergency core wohng systems would not be comidered in ] %y Y ,y the safety review and hearing process. TE. in efTect. ruled out substantial %9 b'dh L{ hydrogen Eeneration and meant that the centa.nment structure had only to i Q te designed to withstand the steam preuure ar d temperature that would ]7 'i result from a loss of coolant accident. Iluilders were thus face to house large ee e .+ "y reactors in smaller and weaker " pressure suppression" centamments which 1 ( y i used water or ice to condense steam and thus hmit pressure increases.' i b jh lociting to Present flydrogen Burn %e .,y > q f,' 'y yy Even so, hydrogen generation remair.ed a concern for the scry small g ' f py. y *= a containments such as the General Electnc Mark I's The obvious way to 4 - e.t +- protect against large hydrogen fires or esplosions in the reactor contain. Q a ment is to " inert" the contamment, that is to keep it idled with inert gas ^j. (nitrogen), during reactor operation liefore the TMI accident, the NRC stafT required the small General Electnc Mark I contamments to be inerted .' P on the basis of Safety Guide 7. ' All but two of these contamments are now s._. inerted. L '"Enwrracy Core Cooling' Repet d the Advu.wy Task nece on Pe=cr Reacer y Emergency Coolmg, U1 Alonuc Energy Cemmannen Report 11th24226. Deutntwr 4.19e7 p - $,6 p 6. Partacutarty interesung is the follomnt uwnn.ent. "Thus, the contamment =sth respct g%'&; *% 4Q to its checuve and relation to other safegwsde simu1J not be viewed as an andependent s. l p;, %g, ' bamer, tut it stdl reyementa a substannat safeg.ard system

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? ,4,o. 'As talenstag account of tbs pnad, mth sourte darumer ts. is penested m Devid Oa1ent s

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~ A "On the History of the Evolubon of 12ght Water Reactor Saferv m the Uruted Sta:es. n-y@Q g i ? ',. Undatad report completed in 1979, Mr. Okrent is a memher of the ACR5 4 .g #

• For lasse cuotaanments, bydsgen generanoe was v.c.ed ordy as a potucident potery,

[ ; y$. reauttmg frorn radiolyns and vanous chernical mimetens. but n mas th'*6 t that it maJd h pg fg] take about a month to generate a womsome anwunt of hydrogen Tbs allowed p6cary d ume ('. g + g%tQQ (d4 to kaa up smaD bydrogen "recomt=ners". GQ p'# P' A Contret of CornbushtJe Gas Concentratens m Centamment Folk =seg a less of Castant ' ? W W.g. f Accident".U1 Atomic Energy Comnusuon Safety Gwde 7. March 10.1971. PQj> pr g D 7 d ff ,b k e Ju Ni j r tr3 r 3 l e

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? a q;)hf$$ In 1978, a new rule (10 C.F.R. 3044) was pubbshed, pernuttmg reactor L. ,dQEd@[r$n operators to seek an exemption Irom the menmg requirement if they could % y# i yW*,M demonstrate, on the basis of calculations which anumed that the ECCS

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,,J$$%{N mteraction m the esent of an accident. Jus: before ihrce Mile Island. 'DC + QE$@hgg General Ejectnc and the utthties ownmg its reactors were m the proccu of f( ' p{A N:p'. h[ J serbng such an emeraptmn. ney were expectcd to succeed m all but a j [Q* g[.p$1r; couple of cases. But after the nree Mile Island accident, and the . G: 4-.p expenence of the hydrogen burn, the NRC stafT proposed and the hg Commission pubbshed for comment an mienm hydroyen control rule '. ;Q ~ t; 'G'd $g W which would require incrung of all GE Mark I and 11 piants ne qucsuon '.

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of how to deal with GE Mark lli contamn.cnts and Westmghouse ice gg condenser containments was left for future rulerralmg3 L' g Q M YC ne inening solution is a relatnely easy one m the case of Mark I and il , g;., , J}f,.g/Q 5; y plants; almost twenty plants hase operated on this basis for some years. It f ge - .gN n more dimcult, however, in the case of the ne condenser and M.srk Ill .j ' "g plants because a good deal of wtal eqwpment m these plants is mside the '? L r,: containment, necessitating frequent containment entry dunng eperatmn. ,? [l;y! Entry into a mtrogen-filled contamment requires special breathmg appara- .,g p d b(.y.h tus. His Unuts the abihty of a reactor worLer to do hnjob, especially m the O j '@g;f/' ice condenser plants where access to pans of the crowded wntamment n ( 4,: dimcult. Moreover, frequent entry into inerted contamments mas rnk the v.% s M[$$[ .d h hves of plant operators especially where mertmg and demerting t.ILn place Q.k * ' I, often. Finally, it is said that there e a substanual emnomic penalty for - D {% Gl q i-frequently changsng the contamment atmosphere m ice mndenser contam-L t $7 ments because this will lead to more rapid rueltmg of ice and the need to Ei N replenish it more often than would otherwne be esonormc. .j g. K.a M f Commialon Dil-1 Order on flydrugen Rule [ The Commission first confronted hydrogen mnu.it af ter the I MI accident in the TMI-I restan case. The TMI Licensmg h.iard certified two questmm y(,, to the Commission: (1) Whether the provmons of the hydroyen contro! '? rule' (which requires protection agamst a reaction of, at most. $ percent of a the claddmg with steam) should be maned m ue of the generation at f:m ,f TMI-2 of an amount of hydrogen corrnponding to an mieraction of about ?F M 4,4 50 percent of the fuel claddmg with sicam. and t2; whethei pi%t amdent h h g?:(D Wg hydrogen control should be an mue m the proceedmg. At stake was Qh y ,r* l e 4 gh. ' Domestic L4cennang of Product =>n and t ?ulaat=>n I aula.es intenen F rysacme ts Relata$ ie f - h u arna. c-ra sa carw. o.paa c-c_.w.an.m em

)~

1 sne% J r L-k,' O h' Mip.: 7 { Cktoter 2.1990 s -d 'l0 CF.It. 30 44 vf. q O. 8 kw b.* q y >< 3 q J' <* Ph , d s $@ W@- . wor ,w >i; _.w. w 7s - b, k? 4 ja m $p w ,;m.4,y.jh h hfp h h w,,.e[v w n+w a p ya v wn w = 4 p.<d wm0 mr.ej.gg& % 4. - 2 a g.pf I{E 7 k_ [ 1 h L'[ jN MW -yL. Il& ^. '. hi Q f J; y - : ~ r' +,% ~ h q 7'g60 % @ Ml g W y $s,,;., ;hk' hk /U yjpf,%$.$i , ;,jgY h b , s QM.b.$ g; y ndl % p'g, g y g,.M y'% 5"%"h &p (. g, ~ q1'

GMMy

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9. y l. - M *ig

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v o . - 3 y w!Qs : y.Cl n f U.s-.yQ y4g } p% g-9.vw &e. s;t.f;dlfv.. &a;n -3..[p- % ;~Qf M gg 7 9;

r. w,- ;w

~ a wh %.4MZ,:q.67sp/Q% ? p.%&M ' hh NIhhf[ whether intersenors could htigate the adequacy of the reactor protectwn p 74GyQDW%cd 'h agairtst amounts of hydrogen greater than contemplated by the rule. ~'

M g %, h [r.y s -

.Ys; Y$hh In spite of the experierne at the adjoining reactor, ti.e Commission by a 3 to "D a M;y%gyhp 2 sote would not waise 10 C.F.R. 50.44." The Comnunitm permitted the . 'dET2M%'M MQ p h broader nsue of hydrogen wntrol to be litigated under 10 C.F.R.100("Part 'h 100"), the Comminion's sitmg regulation. De Commission's opimon noted .h:vd S[M$.s gyNd2'57Y,hQp N that "I'nder Part 100, hydrogen control measures beyond those required by

1) & M A w iR M /m M D[R; 10 C.F.R. 50.44 would be required ifit is determined that there is a oedible

.N s', $$ M 3 loss-of-c olant accident uenano entailmg hydrogen generaten hydrogen Q f fgi Qh.,7,.- " Wgf y; s combustion, cuntainment bicach or leakmg. and ofNtc radiation doses in ,,ggj g )M Q body dose. He Commiuion ungled out operator interference w,th EOCS excess of Part 100 guidehne ulues "" that is, m excess of a 25 rem wbole r5's sh 'g.g jp operation as "the root cause of the hydrogen pencration problem at Dree Ag$e{g.,m gs mMQ Mile Island 2",u and stated that the hkehhood of such mierferente in the @M)?i($h. [h[. future would be a cntical inue m any htigatmn of hydrogen wntrol. In g, I Septemkr 1980, the Commiuion, now reduced to four members, demed by g a vote of 2 to 2 a motmn for reconuderatmn filed by the Umon of C Concerned Sacntnts." Wy 6 b' QT ' f,rp$}NTM .; c.

VH y

Rus, esen after experiente has amply cemenstrated the madequacy of the

• by safety regulations on protectmn aF2mst hydrogen burns further hydroden 4M3MtCW

,1 control measures are only required if it a demenstrated that a.speofic 79d.47' i " credible" accident sequence leads to contamment failure and pubhc iY F radiation exposures in cuew of those perrmited by Part if0 Rn amounts to saying that there is no need to protect agamst an acadent that car. riot be f ~ [ anticipated in detail, even when a closely related accide st has already .,,jd. occurred. g ~ W;g, w '? Part 100 as a Sutatitute for 10 C.F.R. 50.44 m J Cunously, Part 100 itself uses the word " credible" to desenbe accidents involvmg substantial meltdown of the core " he rule which was put out in ~ 1%2 as intenm guidance for utmp m adsance of more specific rules on the +.. q separate aspects of plant deugn. reqtares apphcants to am me large releases 3 ~q, ip of fission products in order to test whether (crtain p..pu!.itmn dose hmits th W 9b@ ;, t U "la the Manar d Meuchtan Id.m.n Cm r n. ahrw sCe 1.:ar.d urar 5 au.m. t'n.t i No. IL th.ket No %239 tRestam. ( t l M it 11 NRC M4 Ma, 16, 1%n. p 2. ' Ng ] (r%..- m Bradfied and Calmh dawi.tany ) "fb d. p.1 . ' gW _ y:S W b., "In the Maiter d Metu@taa 14m.n rep.n, abn MJe 1.: y hi,ar stata t.;nat "Tb.d. p. 4. \\ h )hp No. Ik thlet No 2289, Septemkr 26. IV9 S'J " Reactor site Cntena. 27 FR 3s09. Agn! 12.1H.2 b3 9 F > =_,= 4 - rum - @ & G }l Q gj$g. & -lh & yy^fy ]e f Vj). ;f T[ fy)sR~' & h, .;n.7, ~sgm

\\

.,x y -I n gej e w-n -a bN k kkk M %[ m g"a % hd8 MrsM%; y bb M ik b hd bb ^ c.3 g.;] ~.T. '8 ~ . f w A f;;.

a s wz

casg 1-

? ? Mg%%y&%y.;.:<', q; ~ $';'. w g? g: e gl h 2Q r '. AM '%fhK<fDN b n , N. d p,fEf% would be cacceded. He AEC was not swa c of the hydroge.i generation ~ tA&y$g%Q 9 b. l ihg h j problem at the time. It seems hkely that had the framers of Part 100 been f 7 aware that hydrogen mentably accompames large retcases of fhsion ' 6. - g r A y-w products they would have snecihcally included it in the Part 100 accident 3 Q[M4hp ' ;g'O%Jp, W yq awumption As it is the only conustent way to apply Part 100 n. in fact, to M*, = ogk m dgiMkm? assume the prewnce of hydrogen rn along with the Part 100 fiuion N,dl f product insentury. Here is no need. m applying the test of Part 100, to F

1. "'*~

, ];~7MQ 6 [gg ,5;cquoyah Ikendng g m r_ mM, ,x rs. T (', 'k,D De Cornmauon u>nfronted the e pyhiems again m the caw of the s, - d (' Sequoyah I operatir,g licenw. De staff and the ACRS had not required or s y, M:a recommended any steps to prntect the plant's ese c4mdenser contamment from hydrogen burn beyund fuder stud 4cs of the prob!ctrt floweser, the -p - Tennence Valley Authonty agteed to mstall a hydrogen control system,' j 1 %.4 -) (.M gg2pp based on a i s ' hod TVA was examinmp. His msolved installation of y M_ C'4,4 (YN l.. %f -Ud, sescral don...ontrolled igmtion po nts. in practice diesel gluw plugs, f throughout the containment. In the event of an atodent. :hese would be turned on and would be expected to burn oli the hydrofen present at a g 4, controlled rate. This could reasonably be espesied to modente pressures , t.44 n f/ within the containment for many types of senous acadents, though a Eood deal of research stdl remains to be done to naluate the concept. In ( p { Ak yn,,,h, licensing the Sequoyah I plant for full power opcrr.tmn. 7.fier catensive dncusuon, the Commswion required." as a condation of the hcenw the 4W g, [# 4.5 N (& installation of such an agniter system the continuation of the research ,7 program, and a Commnuun review %T Uf adequacy. m 1982 of the system to check its

q yy -

M'. McCulre Dahloo c !Q~ ? ' 3.p g, pf y-Dis bnnyt us to the senous questmns m this phase ut the MWmre p proceedmg: whether the WGune containment un withuand an accident in which subst.sntial quantities of hydroern.tre generated and,ifit ,y cannot. what remedial measures are nesewan i nrortunatch. the hoard's 3-decision does not answer these questions M.. [ Y3h. 7,; M, De best that can be said for thn deouon n that the lioard w.n for(ed to , /p(h jf;. work m htmders Sy the Comnnw.on's i MI I Onter hi A tric lioard read its ~ s g,p unfortunate mandate t m the narrowest p..wi N e way

g * "p esaluated the "credibihty" of an atodent smular to that atar.d labonously

~ I MI-2. Ihe a m, W. *, .* 'R%j Torrunstmorberg Ahearne, firau*rofd. arbd Osihrah v s i U c rnap.ni, )th e >q a A l "tdr 10 + .t, ,79 o h gyh,ur. s' x +q.gma m Myw ym, bb _d gwg Qma Mk, d$ hN h s m m.. w wum . my n s , NMP pg =r,p r_ sv 4R w =c z nr m iGgL Mk 1 m,m ~-n - - - ~ - ~ ~ - - -

~,--'~ ' v ~~ ~ '~ mm:'N

.....n. .n r ? ': s = s [, l t.., J. - y. ,..sQ;:& n \\ r c :. ;. b k i 1 % n q M' N:6 . :W ' ~' '"" **.5 4j;r WQ?M 7 % d.N u ;< %c : d.. ; @t; m/Nhy 6.;W b.g@@%g:jdjQ# C %[h.ss m.ggw: - " b ' N;dM ~ W # ' " O h ' ~ n ,3 wr4.s .gy rp Q f,.?4M ~ Board 'oand that, in view of new instructions to reactor operators and other (* ~ ' ~ < M5,M DgN/), g<g/ jD< ' improvements, an event which actually occurred two years ago was no ( w m. u - .c

pgg a EN**y;,4 I nger "credib!

" and that, therefore, there was no need to pursue pouible

,,g j remedial steps. It is a findmg th1t couto only have been nude by a group g' * -aid.g - Q > hh schooled in the arcane subtleties oinuclear regulation. No ordinary person -f <m;yp,v f;, y m. w+

ga m

is capable of such foolishness. After the nil coerience, this review of the . As%, v r g "credibihty" of an accident involving hydrogen has been a waste of the gQ. ' Mpff . (M part.es', the Board's, and the Commission's time. P can ords contribute to N y A: e M, dh1d)f fsh public cynicism about nuclear regulation and the role of put'>lic hearings in h ^ dNN $J D!k"k the decissormaking process. E.9 . Mf4 OSk[pg ^, M' %^' hydrogen control issue, the Corraassion should oserturn the TMi-1 .? De McGmre cup.nence makes clea that to deal resp mubly with it.e , % j M*} Q kM precrdent, suspend 10 C.F.R. 50.44, and put m place a new rule on

f I-A

, j, h;. hydrogen protect on, ne Commission has decided, in both the Sequoyah

M t

f and McGuire cases, that adequate protection of public health and safety

3'

'f p;g m requires the installation of hydrogen control systems in ice condenser g . g[ % 9 .p .g containments. To continue to require the panies, includmg the stafT if a 31 Q licensee should choose to contnt the pomt, to prose the "credibihty" of q MN - ' .Q ha given accident sequences when the Comm.suon itself requires the 'f .%dNk $t 3; installabon of hydrogen control systerns without such proof, is an exercise [ J& i,.gTS f in futility. ne Ikurds and the parties should be allowed to focus their ~ k 1 ot b,, - mv. +e4, H 4 ? e,s attention on the real iwues. Beyond that, retaimng the optimistic assump-r p [Q g A. k ,4 j[hi 8 tion on r taumum hydrogen generation in the current rule is mdefensible j f A' when ten times that amount was apparently generated in the Dree Mile a ^i g m ;:- P 4 1 hiand accident. De Comnussion should adopt a new rule reqmnng b ' f 4[NM1 S' h: ~, hydrogen control systems m ice condenser and Mark III contamments. It ? ']g will necessanly be an mienm rule unce the problems of hydrogen control .gj, g g ~ g-are not yet fully understood. Iloweser, the fact that the problem affects

W some 30 plants, operatmg and under construction, means that we cannot 3

continue on an adhoe haus e.y .$~ % a. \\ U 4 f- >f ?$Q ;b,, ,l , w ; 3...e~ m ea, - y' 7 J - i 2M, C-iW' .s, N, f,d.4 et s s% ,i a c fj

• r 4,

us Q x I:Q ni Ke SI b 4 g "& q' g Y 0,1 5-i 0 *y... c. pa .a c.a..u t s., + * ' ' - y -m gjm s N PRi?.Cim m 6 M.,se;&- h 4 Mt d g< q_ mm

.f g, f( C

• E T C 1;'#3m9%pMM O 5y '};y

• (;[- ! Q,b

,p f, ;pT %& m: . $$, ff.urt w h,hf* '%_ ARR, g -..y;;4g-Q: J ,.fT m 9- # .-a @ k' 1 i_). g. F.' gd hQib5 b h Y 0 .,1 .n: [ %f ). . k'; C Y k k, w ' w w. a & w,,9. a k '. $ 5;N I ~

9.M mg;mww&

k gi m, ,y, me -,.m y y y%. M .,,n., y +6;,, b) e.q,. g. A M oAn.c;n4a)A, ;.) o.:. - .;9 w: .y ,a , >pu: r m 4 W .g ._;p W..,s w --- w e v n,.3-e. ,.g.,, p,- g.v y f..~g%,. l lM:.WQ.y' '* m %W,2;N' N*J t & Plf U t* $$ ;[ W Q hr' ' L.*i J,} g1'.i :.* ; ;f: %g.- -:s s, .m; k hY J x A.u ~ M 'g g? M Q: 8 ?gQ 4spp AN SEPARATE OPINION OF COMMISSIONER BRADFORD 'W l W -ll$$?Wd*. s -t3yg 9.a

p g ; M v., qg I am adding my own brief postscript to the joint statement of the view A

g ?gj ..C M.Q" '33?g that I share with Commissioner Gilinsky in order to note disagreement with cg d %Z the views of Chairman Hendrie. The most that the Commission can legs 11y ~;., ((g g[w:s have done in its earlier TMI orders on hydrogen control is to require. hat Mi dh; 1 u , y the matter be litigated in the content of Part 100. It cannot,in i decision in d . MgAg[g;j] an individual case, have modded Part 100 itself. < QM bg ;3 As Part 100 postulates them, accidents of a type that wuld inevitably .A@ y, Q.*c2[ '

• N W generate hydrogen r : to be considered credible. Futhernwe, the ignition g-

&f t or detonation of a TMI quantity of hydrogen at McGuire might sery stil 5 j%p*dh h,%hi. have given rise to greater Board concern even under the Commission's g ?- have breached that more fragile containment. These two facts alene should m }&*ig May,1980, TMI order. h-7 ,gggfg7 j The fact is that Part 100 is a duly promulgated and adopted regulation of Q ' p'/% - A the Commission, and cannot be modied in an individual adjudication 'iflgd .g such as TM11 or McGuire. Only a rulemakmg would su!Tice for that l purpose, and no such rulemaking hAs betn held.I ConsCgbeDtIy, accidents 'gg ~ releasing hydrogen are " credible" by NRC definition as well as historical ggg ' i gg g fact, and they must be considered in light of the ability of individual y h y.' ,} y containments to stand up to them. Contrary to the Chairman's view,it is Part 100 and its " credible" segaences that govern here, not the truncatica q J A Rg g a % 6.-hy;. v n that the Commission gsve it in May,1980, to say nothmg of the gloss that 9 two Commissioners--nolonger a majority-sought to put on that truncation f efglg (d 'g. g in a later denial of a motion for reconsideration.3 7p

3a.

'tadsed, the accluamo d the oc5raded csus rdinaking, d ebdi the Commuason made p

• f[p;. -

g 7', much in ci agmg to 10 CF.R. 50 44 on May l A 1980(11 NRC 674)is ec= fathee amey than at

g' was theaL f

rta a==entmg ce th.s denia:. the hard enoneously ammk4 to Curr== mes Oslanaky and ~ I the new that the c%==== na e der requared "a chanenger to ley out a sr*"& accident i-qu co. This quoiaion i. from cur de.m;wo a the ne-. a the r Cm=%merc a r denying rwh tm on September 29.19% nos the Communaue cproce d May 16. The WQ 3 ( J" 1 Heedns/Ahearne Sepwenber nr, aie not a Comnuname opi.uon and should not be read as 'q ; cae by any 1.acenaang or Agcal BoartL .Q y s' } Q_ < c ^,. & s 1,.h,; g% n. 12 .Nd ' OVM,6 ' ' M.

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5 a,e a **Q 'Q h CDMMISSIONER Al!EARNE'S ADDTTIONAL VIEWS 3 q f hr [ T P M;G, hll Q.J %. . 's. IW 3 , J. i g.,, MM ' I agree with granting a full power license for the McGuire Station. b ~ WM6 However, there are several elements of the decision and accompanying e z 'gNQ3Md%@ views with which I degree because I believe they represent potentially v]' u.$3{ y4:.wp g v.;! S harmful methods of reaching conclusions. V t b.g[If . "y g ' First, I do not believe it appropnate under the Appendiz B review for the v.-, M 't

Q( >

. 7 the Commission conducted a full review. Herefore, I dmgree wi'h the ~' / Commmien to make judgmental comments on the Ucensing Board e ~ ,, @M 4 y-decision, since the Appeal Board has not yet conducted its review nor has .I r 7 %,Qa un!gW.h

w. - c &

.a MyN.h. M g y ' ^ M p's vi'** **Prened in the additional views of Comminioner Gilinsky.' Sced, 7 x; the adjudicatory approach is a poor process for resohing technical issues. ' pgh[.1 The Commission revision of the i niter procedures, while perhap correct, 6 gy" pg magnifies the weakneues of the adjudicatory process. Third, the Commis-(Qg g sion should move to publish the interim rule on hydrogen control. We have V^ l@f $q made it clear that ignitcrs are the acceptable interim solution for ice ' ( * -'T r g - g' condenser plants. Although questions remain about the exact evolution d ? p,.. ~p W bydrogen at TMI and the efficacy of igniters, the Comminion should y establish acceptable interim positions for plants in addition to ice

g* r ' ',

condenser plants. Using the limited interact 2on with staff that is possible in a plant specific adjudication is a poor way to establish such positions -y 7;;%f / is am - g my p-ex. part wi.=d may umrtaix=..hach eght be drm frun 4 ,f '..M.}i J , - x.'#* h A M h 4C9, AMB-M 18 NRC M W(IM) w w vgw% i e c>

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v,. sc,,+ . D c. POUCY SESSIO!fiiEM " "4 ItEPO W.Cs.FOR: The Comissioners O' VHRU: W. Dircks, Acting Executive Director for Operatior.s /' j,j FROMi H. Denton, Director, Of fice of Nuclear Reactor Regulation SUBJ ECT : PROPOSED INTERIM HYDROGEN CONTROL REQUIREMENTS FOR SMALL CONTAINMENT 5 Furpose: To establish the technical basis for interim hydrogen control requirements for small containm nts Di_sc u s si on: The accident at Three Mile Island, Unit 2 (TMI-2) involved a large amount of metal-water reaction in the core with re-sulting hydrogen generation well in excess of the amounts specified in 10 CFR 50.44 of the Cormiission's regulations. A rulemaking proceeding on the subject of degraded cores and hydrogen management is under consideration by the Con-I mission. This proceeding was suggested in Item II.B.8 of the "NRC Action Plans Developed as a Result of the TMI-2 Accident," Draf t 2, NUREG-0660, January 23, 1980. l Based on our review of the THI-2 experience, we have found that certain interim hydrogen control require.ents for small containments are needed. This interim action would require the inerting of all Mark I and Mark 11 containments for boil-ing water reactor plants. The enclosed technical discussion provides the bases for:

1) the proposed interim action; and 2) continued operation and licensing of nuclear pcwer plants pending the rulemaking p roceedi ng.

The proposed interim rule requiring inerting of the Mark I and Mart 11 containments, and including other measures to protect against degraded core conditions that need to / te irmlemnted in the near erm, is in preparation and will be sent to the Comissicn soon. E....s c t : V. R. :iutler. NRR (X2778F ~ h I I I i The Cora.1 ssioners q l Ccordination: The Of fices of Standards Development and Inspection and En-k forcecent concur in the proposed action. The Office of the l Executive Legal Director has no legal objection. j Sunshine Act: Recorrend consideration at an open reeting. j Scheduling: For early consideration. r /. - h a 9 0-t.L 5 W Harol R. Dent n, Dire ctor hth h Office of Nuc ear Rea(. tor Regulation j

Enclosures:

(

Technical Discussion y

J

)

D85TolBUTION' 555hissioners 1

Comission Staff offices Exec Dir for. Operations

/

ACRS Secretariat j

r:

j Er L

b i;

I t

r TECHNICAL DISCUS $10N l'

i

1. C-pilk000CTION t

The > resent design basis for post-accident hydrogen management, as e. bod-led in 10 CFR 750.44 and Regulatory Guide 1.7, " Control of Combustible j

Gas Concentrations in Containment following a loss-of-Coolant Accident,"

is the provision of systens to deal with the hydrogen that would be re-leased as a result of metal-water reaction amounting to betwee.n one and five percent of the fuel cladding in the reactor core.

The TMI-2 accident involved metal-water reaction in the range of 30 to 50 pert.ent. Thus, the need for reexamining the NRC's requirements re-l garding post-accident hydrogen management is clearly indicated by the TMI-2 experience.

Consequently, the staff has proposed that rulemaking l

proceedings be held to develop revised criteria for hydrogen management l

and other aspects of a degraded core which take into account the THI-2 3

experience. Pending the completion of these proceedings,10 CFR 650.44 S

should be revised to require inerting of all Mark I and Mark 11 contain-ments.

The objective of this paper is to provide the technical bases for the p

1 t

staff's conclusion that: 1) all Mark I and Mark II contairrnents should be required to be inerted; and 2) continued operation and licensing of l

other nuclear plants can be permitted pending completion of the rulemak-l l

ing proceeding.

t L,

In Section 2.0 of this discussion, the concentration of hydrsgen inside a containment, as a function of the anount of retal-water reaction, is s

, s s

ENCLOSURE 1 N

/

Yl

s

-2 providad for each class of containtent designs.

The regions where hydrogen cocbustion and detonation can occur are identified.

In Section 3.0, the contain:ent pressure response as a function of the amount of catal-water reaction is addressed for each class of contain-ment.

Both the partial pressure from the resultant hydrogen concentra-tions and the catal-water reaction energy are considered in this dis-cussion.

In Section 4.0, containment failure pressure is discussed in terms of the design pressure.

The various citigation measures are addressed in Section 5.0.

These reasures include:

1) containment inerting to prevent hydrogen combus-tion and detonation; 2) use of halon systems; 3) use of a filtered-vent system; 4) hydroger. combustion systems; and 5) other cethods.

i l

In Section 6.0, the technical bases for continued operation and Itcens-ing of nuclear plants are addressed.

\\'

The. views of the ACRS are given in Section 7.0 and the staf f's conclu-sions in Section 8.0.

I L

2.0 liYOROGEN CONCENTRATIONS Following a loss-of-coolant accident, hydrogen gas can be generated by netal-water reactions, radiolysis of coolant, corrosion of zinc-based paints and radiation damage to organic paint.

The TM!-2 experience indicates that our licensing requirenents dealing with hydrogen gas f rom catal-water reactions r.eed to be reexamined.

s nave calculated the concentraticn of hydrogen insict-e cont 6tnn:.

each class of containNnts, as a function of tae arcant of c.etal-

'sr water reaction.

The results are shown in figure 1.

To co: ply with the provisions of Regulatory Guide 1.7, the total hydrogen concentration in the containrent ust be less than four percent when metal-water reactions of less than five percent are postulated.

The corbustion and detonation characteristics for hydrogen are depicted i n Fi gu re 2.

Note that hydrogen in steam-free air can be expected to burn at concentrations of from four to eighteen percent and detonate above eighteen percent.

It is evident from Figures 1 and 2 that a THI-2 type of eve"nt involving a 30 to 50 percent e.etal-water reaction will definitely lead to a com-bustible raixture and possibly even to a detonable mixture of hydrogen in the non-inerted Mark I and Mark 11 containraents.

This situation is primarily the result of the very small (300,000 cubic feet) net free volume inside these containmnts and the f act that boiling water reac-tors (BkRs) typically have twice the amount of zirconium cladding that pressurized water reactors (Ph75) have.

A cocparison of typical contain-ment volu:res and. design pressures for each class of containments is shown in Figure 3.

l r or a given f raction 'of metal-water reaction The corresponding hydrogen concentrations in a Mark 111 containant, in an ice condenser containa nt, and in a subatnospheric contain.ent are substantially less than those for the Mark I and Mart 11 contain ents.

Nevertheless, they are well within the range of hydrogen comustion for cetai-water reactions in the 30 - 50

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p.-r cent range.

It should be noted that: 1) the first domstic Mark 11!

contain.ent plant is not scheduled for fuel loading until abaut August 1981; 2) fuel loading for the first dorrestic Mart 11 plant is scheduled for July 1980 and; 3) there are two operating ice condenser plants and four operating plants with subatrosph2ric contain=2nts.

As will be dis-cussed later, the non-inerted ice condenser and Mark III containtents can tolerate between 20 and 25 percent r:2tal-water reaction without ex-ceeding the estituted failure pressure of the containment.

The design pressure of subatraspheric containm2nts is more than "three tirnes that of ice condenser containmerits and therefore can tolerate a greater anount of metal-water reaction.

The dry containmnts have unt.ormly distributed hydrogen concentra-1 tions below 10 percent for the situation described above; i.e., 30 to 50 percent metal-water reaction. Moreover, their design pressures are usually in the range of 45 to 60 psig.

Therefore, even if the hydro-gen were to burn, the resulting pressure inside containtnent is not likely to fail the containmnt.

This was the experience at THI-2 on March 28, 1979.

t t

3.0 CONTAIK4ENT PRESSURE RESPONSE i

If substantial amunts of retal-water reaction were to occur following onset of a loss-of-coolant accident (LOCA) there would be substantial l

increases in the containment pressure response.

The principal contri-I butors to this pressure increase are:

1) the addition of substantial amounts of hydrogen (non-condensible) gas to the containmnt; 2) the increased energy release to the containrent due to the exothernic reac-action (oxidation) of Zircaloy with water; and 3) as appropriate, the 0

ene r gy release associated with the co-bustion of the hydrogen gas,

(C.; t' at this latter condition need not be considered f or ir.u1.ed contcirrents.

f t

(

llc have completed a preliminary analysis of each class of contair.:.ents to estimate the peak pressures that might be expected from an event in-volving up to 100 percent mtal-water reaction followed by a. postulated successful reflood of the core.

The matters that need to be considered in this analysis are:

1) the rate of catal-water reaction; 2) the en-crgy storage and removal rates; and 3) the resultant accident pressures vs. design pressures.

3.1 Rate of Metal-Water Reaction The rate and extent of matal-water reaction and associated hydro 2en production depends strongly upon the course of events assumed for the accident and upon the effectiveness of the ecergency core cooling sys-tems(ECCS).

For this analysis we assumed a temporary but total fail-ure of ECCS 1rnedtately after blowdown.

This timing assumption is con-

?fi servative because the fission product heat rate will be at its maximum level. Although we have assumed the total though temporary failure of L

the ECCS, we have allowed for an unlimited amount of steam in the core in order to obtain the maximum zirconium-steam reaction rate.

k The maximum rate of metal-water reaction is needed so that assessments L<

can be made of the effectiveness of pressure mitigating systems such as the containment heat removal system and the filtered-vent system.

L k

Once the core has been uncovered, the fuel clad will heat up rapidly.

'j Figure 4 shows a plot of fuel clad temperature versus time as calcu-L.

lated with the staff's T00DEE2 computer code.

This plot is for the b;<

hot spot of the average fuel pin.

It is assum d in this analysis that a

suf fici@ng core coelinfL@atsquR91162 meaarh AflRw RM meeme b'

FIGURE 4 FUEL CLAD TEMPERATURE RESPONSE w.

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,r '

CLAD HEATUP RATE FOR THE HOT SPOT OF THE AVERAGE FUEL PIN f

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. This corresponds to the termination of accurulator water delivery folic -

ing bloadawn of the primary system.

At decay heat rates associated with full poser operation, the water rer.aining in the core would be rapidly boiled of f or entrained out of the core during the blowdown.

At this time, it is assum.ed that all of the stored energy in the fuel is removed and adiabatic heatup begins.

Figure 4 show the cladding hestup rate for the hot spot of the average fuel pin.

It also shows the percent of cladding in the entire fuel pin (not the hot spot) that has reacted with steam.

Approximately 80 percent of the fuel pin's cladding has reacted within 15 minutes of the accident.

Not shown on Figure 4 is the percentage of clad at the hot spot that has re-acted with steam.

The cladding hot spot reaches its melting point of 3400 F at 370 seconds.

At this time, approximately 15 percent of the cladding at the hot spot has reacted.

It takes an additional ten seconds for the clad-ding to melt at this spot.

When the malting is corplete, about 20 percent of the hot spot cladding has reacted. Af ter an additional 36 seconds, the hot spot cladding has reached 6500 F and has completely reacted, it should be noted that this calculation assumes that the structural integ-rity of the core and fuel pin has been natntained.

Sluoping of the clad has not been assur.ned.

it is, however, expected that slumping of the clad would not reduce the reaction rate, unless the clad slumped into a pool of Hater thus quend ing the reaction.

Another assumption was that suf ficient steam would be available to prorote the reaction.

At higher temperatures, steam availability would tend to limit the rate of reaction.

It is esti-meted that the times discussed above would be at least doubled if steam.

__Julattaura_nteren_raaRRGtea4L________ ______________ ________ ___

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1

- i i

The exothernic oxidation heat of reaction is 2800 BTU /lbm of zirconium.

A typical PWR has 50,000 lba of zirconium, end the typical BWR has 90,000 lba of zirconium. If these annunts of zirconium were to react 6

with steas or water, the resulting heat addition would be of 140x10 BTU 6

and 250x10 BTU, respectively.

The capacities of the active heat re-moval systems are discussed in the next section.

Therefore, mitigating systems must be able to accommodate the non-condensible hydrogen gas along with the associated reaction energy i

assuming their generation to be complete in about ten minutes.

3.2 Energy Storage and Removal Rates Each of the five contain=ent types has its own characteristic active and passive heat recoval systems.

By, passive heat sinks, we maan the massive

~

amount of water in the suppression pool of the BWR containment and the 2.5 million pounds of ice in the ice condenser containment. The active heat recaval systems include the f an coolers and containment spray systems in PWRs and the RHR systees in BWRs.

The passive heat sinks accomnodate the short term (one hour) energy release in the event of a LOCA.

The active heat removal sy stens are sized to acccommodate the fission product decay heat rates in the longer term; i.e., 3 bout an hour foll& ding onset of the LOCA.

In the event of a LOCA, the short term energy release from the prinary re-actor systen amounts to about 400 million BTU.

The subsequent fission pro-duct heat generation rate amounts to a maximum of about 200 million BTU per I

hour and f alls of f at a sled rate with time.

(

i

D )

The exothernic reaction energies associated with 100 percent metal--ater d

reaction are 140 million BTU and 250 million BTU in a PWR and a BWR.

.I

)

respectively.

If the associated amounts of hydrogen were to burn, the i

corresponding energy releases are 117 million BTU ad 205 million BTU, I

respectively.

f e

In Section 3.1 of this discussion we find that oxidation of the Zircaloy I

cladding can be corplete in periods of from five to ten minutes. Moreover, l

1 the cortustion process can be corplete in cuch shorter periods of time.

1 It is evident, therefore, that only the design curgins in the passive heat sinks would be available to mitigate the pressure increases caused by the hydrogen nuss, the exothermic reaction energy and the hydrogen cor:bustion l

energy resulting fro:a metal-water reactions; that is, the amount of energy that can be removed by the containment's active heat removal sys-6 tem in periods as short as ten minutes is en the order of 30x10 BTU.

Tnts is not significant relative to the amounts of energy associated l

s l

with either hydrogen generation or corbustion.

j l

Hcwever, the containcant's active heat removal systems can contribute sig-i l

.i nificantly for that set of degraded LOCA scenarios where excessive core 1

heat-up occurs long af ter onset of the LOCA; i.e., about 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br /> later.

In these situations the energy storage capacity in the passive heat sinks will have been restored.

Our analyses in the next section take no credit l

for availability of the slow acting active heat removal systems, though credit is taken for the effect of the energy transfer capability for such syste::ts as the containrent spray system, which transfers containrent at-b h

cosphere energy to the water in the contair. rent su :p.

2

l s

i l

t I Tr.re are also substantial cargins between the contain ent c.esign pres-

• ure and the contain.ent f ailure pressure.

This matter is adJres',ec in Section 4.0 of this discussion.

In ou r vi ew, it is appropriate to take a

credit for these substantial margins during the period between noe and the ti:y

',he ruleraking proceeding.

3.3 Degraded-Accident Pressures vs. Design Pressures The current designs of containments for light water reactors are based on the assumption of successful operation of the engineered safety features in the event of a LOCA.

In this section, we consider the con-quences of a rajor degradation of the ECCS resulting in substantial metal-water reaction in the reactor core.

The ac.cident sequence is as-sumed to be turned around by a successful reflood of the core, and thus j[

F.

avoiding any need for considering core-melt scenarios.

In our analysis model, we assumed that the core was uncovered inmedi-ately af ter blowdown and remained uncovered until the entire core ap-proached 3400 F, the melting point for Zircaloy.

We have examined

• (

i the containment pressure response to various metal-water reaction percentages up to 100 percent of the Zircaloy cladding for each class i

of containments.

Both the design pressure and estimated f ailure pres-sure are used in our assessment of containment capability.

~,

3.3.1

" ark 1 Containment

.]

kY

(*h, If 100 percent of the cladding in a BkR/ Mart I containnent system g

E[*

-ue to oxidize (retsi-water reaction). tne non-condensibles in the k.

. dssinating pressure determining feature and severely limits the pres-sure mitigsting capability of the containnent heat removal systems.

Solution of the energy balance equations indicates that the post-LOCA peak pressure will be 88 psig.

This peak pressure includes the effect of:

1) the non-condensible hydrogen gas from a 100 percent metal-water reaction; 2) the energy produced in oxidizing this amount of cladding and 3) the mass and energy release associated with the postulated de-sign basis LOCA.

It does not include any energy contribution from the burning or detonation of hydrogen.

e The above result means that the peak pressure in an inerted Mark I con-tainment, which experiences a degraded LOCA involving as much as 100 percent r.etal-water reaction, would be no more than 88/62 or 1.42 tir.es the design pressure.

In Section 4.0, we discuss the basis for our view that failure pressures for these containments is expected to be more than twice the design pressure.

We have performed another calculation to detensine the amount of metal-water reaction that can be tolerated in a non-inerted Mark I containment assuming that the resulting hydrogen is burned, without having the re-sulting peak pressure exceed twice the design pressure.

The resulting amount of metal-water reaction is about nine percent of the Zircaloy cladding.

)

_ 11 Exanination of the hydrogen concentration curve for Mark I contain-cents in Figure I shows that a detonable mixture can be expected for

r. tal-water reaction amounts that exceed 10 percent.

Since the con-i sequences of detonations can be rather severe and are not readily prc-dictzble, we conclude that situations that can lead to the creation of detonable mixtures should be avoided.

We concluda that substantial improvement in hydrogen management capa-bility in the Mark I contaircant system can and should be achieved by requiring the inerting of the contaircants.

3.3.2 Mark II containment The design parameters of the Mark II contairment with respect to hydro-gen management capability are essentially the sane as those for the P

Mark I contairnent. The only substantive difference is that the de-sign pressure is typicsily 45 psig compared with the 62 psig for Mark I containments.

Considering the peak pressure identified in the previous section, the ratio of peak pressure to design pressure in the Mark 11 contairnent will be 88/45 or 1.96.

We find that our conclusions for the Mark I contatrnent also apply to the Mark II containment.

i 3.3.3 Ice Condenser Containment In an ice condenser contairnent, the maximum amount of metal-water reaction that can occur without exceeding the containrent failure pressure is 25 percent.

This assumes a failure pressure of 36 psig, (See related discussion in Section 4.0), cocbustion of the hydrogen gas and availability of only one of the two trains of containment

.ZT]

7 spray systems for a spray flow rate of 3400 gallons per minute.

A 15 percent metal-water reaction would lead to a peak containment pres-sure equal to the design pressure of 12 psig.

If the ice condenser containment were inerted so that hydrogen com-bustion need not be considered, ersentially all of the Zircaloy clad-ding could react without exceeding the estimated containment failure pressure of 36 psig.

Inerting the ice condenser would substantially increase the amount of metal-water reaction that can be tolerated with-out exceeding the containment's estimated failure pressure. Howeve'., an l

inerted ice condenser containment will lead to restrictions on access to the containment for performing important maintenance functions.

There-l fore in view of the feasibility question discussed in Section 5.1 of this i

discussion and the fact that about 25 percent metal-water reaction can l

be tolerated even with burning, we conclude that, pending the rulemaking l

proceeding, additional mitigation systems are not required for ice con-l denser containments.

3.3.4 Mark III Containment The design pressure of the Mark III containment is 15 psig.

The non-inerted Mark III containment can accommodate the burning of the hydrogen produced by between 16 and 19 percent metal-water reaction without ex-ceeding its design pressure.

This amount will increase to between 22 and 25 percent if we considered the containment failure pressure to be twice its design value or 30 psig.

Therefore, since the first domestic

i

. Mcrk til containment plant will not be operational until ::cui la 1981 and since as much as 22 to 25 percent netal-water reaction can te tolcrated without centainment failure, we conclude that, pending the rult -

caking proceeding, additional mitigation systems are not required for the Hark III cor.tainments.

3.3.5 Subatmospheric Containment The design pressure of the subatmospheric containment is 45 psig.

For the non-inerted case, between 51 and 64 percent metal-water reaction can occur without exceeding the design pressure.

Moreover, at twice the design pressure, essentially all of the Zircaloy cladding can be allowed to react.

The addition of non-condensibles to the containment will make it more difficult for the containment heat removal systems to return the con-tainment to subatmospheric conditions. Assuming 100 percent metal-water reaction, about 400,000 standard cubic feet (SCF) of hydrogen gas will be added to the contalmnent, which before the accident contained about 1,250,000 SCF of air.

Since the containment volume is 1,850,000 cubic feet, we can expect the containment pressure to eventually reachieve subatmospheric conditions.

It should be noted that much of the hydro-gen gas will combine with oxygen to form water and thus mitigate this concern.

Analysis of this effect and of the associated dose conse-quences will be performed in conjunction with item II.B.8 of the Task Action Flan.

. 3.3.6 Dry Containment The dor containment is the least impacted by these considerations.

It has the largest volume and matches the highest design pressure of all the containnent designs.

For the non-inerted case, about 70 percent catal-water reaction can occur without exceeding the design pressure of 60 psig. Complete reac-tion of all the Zircaloy cladding will result in a containment pressure that is well within our estimated failure pressure of twice the design p ressu re.

3.4 Hixing of the Containment Atmosphere The analyses performed to estimate the effects of hydrogen burning in containment buildings were performed with the assumption that the con-tainment atmosphere consisted of a homogeneous mixture of air, hydrogen and steam.

Burning or detonation of local pockets of higher than aver-age hydrogen concentration was not considered.

We assumed that cdequate mixing would be assured in the large, open dry containnent building (including the subatmospheric containment) by the operation of redundant Emergency Safety Features (ESF)(1.e., containment spray systems and con-tainment f an cooler systems), which would promote vigorous mixing of the abnosphere in the containrent building.

In addition, depending upon the s2 verity of the accident (i.e., its ef fect upon containment atmosphere temperature and pressure), non-ESF ventilation systems cuy also be used to aid in the mixing of the containment atrosphere, as was the case at I M!- 2.

. ~ _

! i In the ice condenser contairmant design, there is a high degree of cos-partrentalization within the contairnent.

Because of the compartmental-ized contairnent, the ice condenser contairr ent design includes redundant ESF systems to procote post-accident mixing of the contairraent atmosphere.

These systems (the Return Air Fan system and the Hydrogen Skimer systeo) have been designed to expressly provide a capability to assure post-acci-dent mixing of the contaircent atcosphere and to prevent any

• pocketing" of d

hydrogen in contaircent subcocpartments.

With both trains of the redundant system operating, the entire contairment atmosphere will be circulated through the fans approximately every 15 minutes. With only one train oper-q ating, this " cycle time" is increased to about 30 minutes.

305 Temperature Effects of Hydrogen Burning a

In performing the calculations to estimate the effects of hydrogen l

burning in contairraant buildings, we assumed that all the heat of com-

[d bustion went directly to heating the contaircent atmosphere.

In reality, E

3 cuch of the energy would be lost directly to the aussive structures i

(walls, supports, etc.) by radiant heat transfer. Our very conserva-tive analyses yielded contairnent atmosphere temperatures up to about N

2500 F for the burning of large amounts of hydro g a.

This energy would be remved from the atmosphere by containment spray and fan cooler sys-ja i

tems. Rough calculations indicate that the thermal transient caused by q

7 hydrogen burning would be terminated by sprays and fan coolers in a few

](

. [1 minutes (on the order of 5 minutes).

Thus, the characteristics of the

' '/

s 5

--~_ -

[

1 i

. crpected transient would be a rise to a peak temperature in a fe.< sec-t onds and a subsequent return to normal temperature in a few minutes.

Ccaponents located in the contairr..ent whose continuing function is essen-

~

tial to safety would be subjected to this themal transient.

Examples are, instrument sensors and transciitters, instruc.entation and power cab-ling, valves and their operators, electric motors for fans, pumps and valves.

During the thermal transient expected for hydrogen burning, heat transfer to these cmponents would be governed by natural convection and would, M

2 4'

therefore, be limited to the order of a few BTU /ft -hr-F with an average 4

driving temperature on the order of a few hundred degrees Farenheit. This s;.

, a.;

would result in an average heat flux to the components that is on the or-Q 2

se der of a 1000 BTU /f t -hr for the few minutes of duration for the transient.

a Y$$

In perfoming thermal analyses for the same type of components subjected gy;

.a to the environment of Hain Steam Line Break (MSLB) accidents, we find that G

. ci; these components are subjected to heat transfer that is dominated by con-j u

densation.

For these MSLB accident analyses, the average heat flux of

' {;,(

2 6-j the co,ponent is also on the order of 1000 BTU /ft -hr for a few minutes' Q3 duration.

In these analysrs, the themal capacity of the components is ff Judged to be high enough that for these short exposure times the equip-

fl l 59 ment temperatures are not expected to exceed the values used in equipocot gW qualification tests for the LOCA conditions.

Therefore, it appears rea-

'i sonable to assume that the same satisf actory results would be expected if the cceponents were analyzed for the themal transient conditions expected b!

for the assur,ed hydrogen burnirg in the containr.ent.

This was de onstrated g

W5

. [

b., tu centi.ved sJccessf ul operatian of e *.entially all s_.

-.; a rc cmponents of TMI-2 follcuing the contairr.ent hydrogen fire.

4.0 Contain ent Structural Response The nass and energy releases associated with large amounts of netal-water reaction are not considered ir. arriving at design pressures for contaircent buildings.

If considered, the resultant accident pressure N

will exceed the design pressure.

The object of this section is to de-

/_.

velop estimates of the safety margins between design pressure and fail-ure pressure so that judgments can be made as to the interim licensing requirements pending the rulemaking proceeding.

hc The contatrnent buildings are designed by use of load combination equa-T

.M tions v.hich involve conservative assumptions to ensure that the as-built

[

structure maintains an adequate margin of safety.

Upon completion of t7 construction and before plant operation, utilities are required to pres-surize the contairnent structure to 115% of design pressure to demon-p strate the structural integrity of the containment.

The leak testing f

requirements of Appendix J,10 CFR Part 50 provide that the containment f

shall be periodically pressurized to demonstrate leaktight integrity l

'?

l for periods up to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.

Therefore, it can be expected that the

/

primary contaircent building would withstand short tem pressure 2

transients that significantly exceed the contairnent design pressure.

,.I]

/"

ii The exact margin of safety that exists for a given containment is dif-l?

+

ficult to quantify.

An unspecified nargin of safety exists between the ccntaircent design pressure and the minimum specified yleid stress.

,...,s Significant amount of leakage are not expected until the stress in

,y$

V-the steel contairnent and in the liner plate of the reinforced concrete y

3.f 01

. containment reaches yield stress.

This leakage will tend to relieve the pressure untti equilibrium is reached, i.e., leakage will eventu-ally equal bloadeen in the containment.

Another unspecified margin of safety exists between the minimum speci-fled yield strength and tt.e ultimate strength of the steel used in containaants.

If the ~ ultimate strength of containrent is reached, ca-tastrophic failure may be postulated.

However, it is highly probable that leakage failure will begin to occur before the ultimate strength is reached.

Therefore, any failure can be postulated to occur in a gradual and ductile manner.

Considering the uncertainties discussed above, an examination of the best estimate yield stress was performed for two free standing steel containments, the Sequoyah plant in Hamilton County, Tennessee and the McGuire plant in Hecklenburg County, North Carolina.

The major assuup-l l

tions used in the cotputation for both types of containment was the l

l existence of a uniform static internal pressure loading.

Al though 1

other containments may have different factors, the difference is not expected to be substantial.

Therefore, some extrapolation of the re-sults to other plants may be appropriate.

The result of the best esticate yield stress for Sequoyah is 36 psig with an uncertainty range between 32 psig and 48 psig.

Since the de-sign pressure of Sequoyah is 12 psig, this approximates a nargin of 1

)

l saf ety of about three times design pressure for f ree standing stee',

containments.

The result of the best estimate yield strest. for McGuire is 47 psig with an uncertainty range of between 42 psig and 63 psig.

Since the l

design pressure of McGuire is 15 psig, a safety margin of about three times design pressure can also be assur.ed.

The ice condenser containments for the currently operating D. C. Cook, Units 1 and 2 are different from those for Sequoyah and McGuire in that i

they are steel-lined reinforced concrete structures.

Although we have not performed a structural analysis of these containments, it is our i

judgment that their failure pressures are at least as high as those i

l for the Sequoyah units.

We conclude, therefore, that significant amounts of leakage would not occur for internal containmeqt pressures of less than twice containment design and that any failure of containment will occur in a gradual and ductile msnner.

Conventional dry PWR containments and the BWR Mark I and II contain-ments typically have design pressures ranging from 40 to 60 psig.

l Therefore, these containments should be expected to withstand internal pressures ranging from 80 to 120 psig, respectively.

I f ?. ?'$ f 5 H N Q Q T; QO ] h $ k K k by'

& WtW $5(($?*$hTi.5. Y$ Y h SEY f

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'he ty:t ca' :esign pressure for the BWR " ort III containment is li psig,

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tnus allesing an expected margin cf safety of up to 30 psig.

Ice ccndenser can'ainments have the icwest design pressures of 12 to 15 psig.

Our best estimate analyses. indicate that these containments 1) r will not fail at peak containment pressures below 36 and 47 psig, re-

[

I spectively.

j c

5.0 MITIGATION MEASURES There are a number of mitigation measures which can permit the accom-3 medation of substantial amounts of hydrogen without a consequential H

E failure of containment integrity.

These measures include:

1) inert-ing of the containment; 2) use of halon suppression systems; 3) rie of filtered-vent systems; 4) use of hydrogen combustion systems; and 5) other methods such as the use of chenical catalysts and gas turbines.

k Each ef these measures is discussed below in tenus of its potential

?

Y for erfectively managing the consequences of substantial amounts of T

h metal-water reaction.

5.1 Inerting U

Boiling water reactors with Mark I containm.nts have been operating I

quite successfully with inerted containments.

Equipment maintenance l

and oceraticnal flexibility are hampered to some extent because acces-q sibiltty into the containment is reduced when the containments are in-

[l.-

t c ted.

For this reason, the Verment Yankee and Hatch 2 licensees pre-f-

c n ed, and 'ollowing a staff finding of ctcpliance with 10 CFR j50.44 1

F4 s.y

.ere sunseuuantly authorized, to operate their p! ants w thou: inerti,9 yq y

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. the containments.

An ALAB decision was involved with respect to this l

issue in the Vermont Yankee case, Vermont Yankee Nuclear Power Corp.,

Yerront Yankee Nuclear Power Station, 8 AEC 425 (1974).

If all Mark I containments were inerted, then the effects of combus-tion and detonation need not be considered.

Our analyses have shown that if 100 percent of the Zircaloy cladding were oxidized following a 1.0CA, the resultant hydrogen concentration and peak contairrtent pressure would be about 70 percent and 85 psig, respectively.

Although the design pressure for Mark I containnents.15 62 psig, failure pressure is esti-f i

mated to be about 124 psig.

We conclude, therefore, that inerting of Mark I containments leads to substantial improvement in their ability to accomnodate large amounts of metal-water reaction.

Accordingly, tha inerting of all Mark I con-tainments should be made a licensing requirescent.

The hydrogen concentrations and associated concainment pressure re-sponses in a Mark II containment are essentially the same as those for the Mark I containments.

However, the design pressure for the Mark !!

containments is lower than that for the Mark I contalment and is typi-Cally 45 psig.

Nevertheless, a failure pressure above two or three times the design pressure would be between 90 and 135 psig, which is well above the 85 psig pressure associated with 100 percent metal-water reaction without combustion.

It is, therefore, our view that all. Mark II containments, none of which are yet licensed to oper-ate should be inerted like the Mark I contain.ments.

. The uniformly distributed hydrogen concentrations in an ice condenser containnent f or 50t metal-water reaction will be about 15t.

The as-sociated pressure is well above the design pressure and is estimated to be about 90 psig.

Th's high pressure is caused by the assumed burning of the hydrogen gas when it exceeds the flammability limits.

Inerting of an ice condenser containmcqt would provide a capability to acconmo-date about 90 percent metal-water reaction.

Preliminary calculations predicted the associated taximum containment pressure to be equal to the r.atimum structural capability of 36 psig.

Hewever, the f requency of con-tainment entry for safety-related maintenance functions (especially for the ice chests) is such that inerting of the ice condenser containments cay be impractical.

Certain maintenance functions in the ice chests nay not be safe for the maintenance personnel unless the area is de-f rerted.

The air-changes associated with each inert /de-inert cycle would probably involve excessive ice-loss making inerting of the ice condenser impracti-cal.

If access to the containcent were restricted because of inerting, there would be come penalties in equipment reliability.

The above mat-ters warrant and will be given further consideration in conjunction with our Action Plan Item II.B.8.

I t i s ou r vi ew, therefore, that although some gain in safety might be achieved by inerting, opera 'onal and equipment reliability considera-tions argue against inerting.

Further studies are needed on the effective-ness question concerning high containnent pressures and on the practicality

Al

. issue.

Other mitigating measures such as the use of halon systens and filtered-vent systems may be found to be more appropriate.

These measures are discussed later.

The Mark III containments have higher concentrations of hydrogen than ice condenser containments for the same fraction of metal-water reac-tion.

This is caused by the larger inventory (about twice) of Zircaloy in the BWR core relative to the PWR core.

Inerting of the Mark III con-l l

tainment does not involve the severe practicality question relative to I

maintenance functions in the ice chests of ice condenser containments.

Nevertheless, much more equipment is located inside the Mark III con-l I

tainment than in the Mark I or Mart 11 containments.

Since the first i

domestic Mark III plant is not scheduled for fuel loading until about August 1981, sny decision on inerting of the Mart III containment can await the results of more detailed impact / benefit evaluations.

The hydrogen concentrations in subatmospheric containments are compar-able to those in ice condenser containments.

This results from the f act that, although the volume is larger, the mass of air inside contain-ment is about the same as that in an ice condenser containment, since the containment is operated at a lower pressure. Further analyses are needed to determine the amount of metal-water reaction that can take place with-out exceeding the estimated failure pressures for the subatmospheric con-t ai nrents.

These analyses will be perf ormed in conjunction with Action l

I l

1

• d f

Plan Item II.B.8.

It is our view that s nce the design pressure for :, ; b -

I 1

atr.ospheric containc:2nts is core than three times that for ice condenser c

s containments, no interim action is needed relative to inproved capability l

J l

for hydrogen cunagerent.

I The hydrogen concentration and associated pressure consequences in q

l large dry containm2nts are more favorable than those for the Mark 111 l

containments and ice condenser containments.

Wnile the hydrogen con-centrations can exceed the lower flamubility limit of four percent for l

ratal-water reactions above 40%, these containments can accccinodate a fair amount of hydrogen co::bustion as deconstrated by the THI-2 ex-perience.

It is our view, therefore, that mitigative measures such as inerting for these containcents can and should be deferred pending rulemaking proceedings on this subject.

5.2 Use of Halon Suppressants If Halon gas were mixed with the containment atrosphere, neither com-bustion nor detonation of the hydrogen gas can occur.

Halon is a cheatcal corpound in which a halogen (fluorine, chlorine, bromine and l

iodine) atom is added to a hydrocarbon molecule.

Chemical forculas i

for some Halon corpounds include CBrf and CBrt1F.

l 3

2 The required concentration of Halon in the contairunent atmosphere is i

about 20 percent.

Although the cocpound is chemically inert, it nay l;

be hazardous to humans for extended exposure at concentrations of j

about 20 percent. Moreover, if the cc: pounds are exposed to tempera-tures above 900 F they decocpose to form halogen acids and some amounts of carbonyl halides, which are extremely toxic.

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The costs e ncciated with use of these

<.y stems.. arir..rily in the

[

t ccst of tne corpounds themselves.

We estimate the e gense per plant to be in the range of two to five million dollars.

s Halen suppression systems would probably be useful as part of a hycro-gen rana.ccnt system in an ice condenser plant.

When a substantial

9. i lb core damage but no core malt situation (a degraded LOCA) is known to exist, the Halon system can be actuated before any major release of

.g

..:A hydrogen into the containment.

The large volume, return-air f ans will i

assure ef fective mixing of both the Halon and hydrogen gases with the

':5'1 atmosphere.

5Rp e

Although the Halon system can prevent corbustion and detonation of j:},i

'G hydrogen gas inside an ice condenser containment, it might not prevent

{

1. 1 overpressurization of the containrent due to the addition of substan-Q tial arcunts of non-condensible hydrogen gas and Halon.

The filtered-7 7,.

m vent system discussed in the next section may be appropriate for cont-ol-k Ew ling the associated pressure build-up.

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f. i,i L

I The Halon suppression system appears to be an excellent candidate for d

preventing the combustion and detonation of hydrogen gas in the event 4n of a degraded LOCA. McNever, its success in dealing with large amounts M$

of metal-water reaction requires the use of a corpanion filtered-vent rB{,

system.

Both systems have a fair number of potential problems that re-7, :

G quire thorough analyses, g

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- 26 5.3 filtered-Vent Systems filtered-vent systems have been studied in the recent pa,t in terms of their ability to prevent failure of the containment due to over-pressurization.

For severely degraded accident situations, the fil-tered-vent system would be effective in minimizing off-site darage by retaining most of the fission products inside the intact contain-cent and releasing to the environment only that amount of fission products that cannot be held up in its filter system.

Practically-sized filtered-vent systems cannot accocmodate the rapid pressurization associated with any major combustion or detonation of hydrogen gas inside a containment. However, if a Halon system were used to prevent the cocbustion or detonation of the hydrogen gas, the filtered-vent system need only accoccodate the pressurization rate as-sociated with the rate of generation of hydrogen gas. Our analysis of the oxidation rate across the thickness of the Zircaloy clad indicates l

that about ten minutes are required for complete oxidation.

These rates of hydrogen production can be readily accoerodated by a vent pipe that is no larger than 10 to 15 inches in diameter.

5.4 Ilydrogen Codaustion Systems Hydrogen combustion systems involve the intentional and slow burning of the hydrogen as it is released into the cor.tainment.

Such a sys-tem would:

1) burn small amounts of the hydrogen ga, at a time as it l

l 1s released into the containment so that detonable mixtures do not develop and so that the associated reaction energy can be effectively transferred to the water in the containrent sump and then to the

b i

ultteate heat sink; and 2) ccrbir.e non-condensible hydrogen and oxygen I

gases so as to reduce the pressurization of the containrent, i

)

Another potential application of the hydrogen co-bustion system is to prevent the development of detonable mixtures in stea: -air-hydrogen at-e.ospheres.

Steam from the blowdown process during a LOCA will serve as a diluent to reduce the concentration of any hydrogen gas and as a sup-l pressant raking the hydrogen gas less flarmble.

As the containrent spray system condenses the steam, the hydrogen con-centration and flant. ability will incrr.ase.

The corbustion system could prevent the developrxont of detonable mixtu.es by the timely burning of the hydrogen gas.

5.5 Other Methods Other cethods such as the use of chemical catalysts and gas turbines have been suggested as means for accormudating large releases of k

i ttydrogen in containments. Moreover, coraining the controlled combus-tion system with the filtered-vent system may also prove effective for

~

some contain=ent designs, i

A substantial amount of additional staff work and licensee and appli-cant work is needed to assess the merits of these other systems.

Their assessment will be made a part of our longer tem action (Action Plan Itea 11.B.8) on systems for teproving the capability for hydrogen canagecent.

4 1.l g

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1 l 5.0 EASES FOR CONTINUED OPERATION AND LICEN51HG The only interira action prepared by the staff with respect to the capa-bility for hydrogen onagecant is the inerting of the Mark I and Hart 11 contain.m. ants for BhRs.

It is our view that if this action is taken cor.tinued operation and licensing is justified pending corpletion of the ruler.3 king proceeding on degradad cores and hydrogen canagement. The bases for this view for each class of containe2nts are sues:3rized below.

I 6.1 Mark I and Mark II Containnents l

Metal-water reactions in the range of 30 to 507, can produce hydrogen

}

concentrations in flark I and Hut II containments that are well within b

l the range for rapid corbustion and detonation.

Inerting these contain-I.

l cents as proposed will eliminate the concern relative to cocbustion and i

detonation.

The peak contain=2nt pressures, considering the effect of the non-condensible hydrogen gas and the associated exothermic reaction energy, will approach twice the design pressure for the worst case as-(v sumption of an uncooled core inmediately following a reactor shutdown.

f In our jud nant, Mark I and Mark 11 containcents can withstand without 3

, 4 failure, a slowly applied press'ure that is as ruch as two or three ticies the design pressure.

Accordingly, pending the ruleraking proceeding on hydrogen Anagerent, we find that continued operation and licensing of Mart I and Mark II contain ent plants is justified if they are inerted.

6.2 Ice Condenser Containments i

r Metal-water reactions in the range of 30 to 507, in ice condenser con-tainrent plants can produce hydrogen concentrations in the range of

[.

9 to 151.

At these concentrations, detonation is not expected.

p k;

5 Morecver, corbustion will be inhibited for stea:s concentrations e

, operation of the contaircent spray system and/or the ef fects of pas-sive heat sin'r-91 condense the steam and produce mixtures that are cocbustible.

Assuming that there is cortustion of hydrogen gas and considering the effect of the non-condensible hydrogen gas and the energy associated with its formation, the estimated amount of metal-water reaction needed to achieve the containment design pressure and failure pressure are 15%

and 25%, respectively.

The design pressures for ice condenser plants are between 12 and 15 psig and the corresponding failure pressures are esti-mated to be between 36 and 47 psig.

The "Short Term Lessons Learned" from the TMI-2 accident have been imple-mented at all operating plants and will be implemented at all the other plants before issuance of the operating licenses.

This action will re-duce the likelihood of occurrence of accidents that could lead to sub-stantial amounts of metal-water reaction.

We have considered inerting as a mitigative measure for ice condensers.

We find that although it might improve the hydrogen managecent capability, I

certain important maintenance functions will be restricted.

Therefore, since the likelihood of degraded LOCAs have been made more remote by implementation of the "Short Term Lessons Learned" and since substantial amounts of metal-water reaction can be tolerated without jeopardizing containment integrity, we conclude on balance that, pending the rulemaking proceeding, continued operation and licensing of nuclear plants with ice condenser contairnents is justifbd.

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K_. r i_. l_i_l C o n t a i re.e nt W

r ti If 30 to 50 percent of the Zircaloy clodding were to oxidize in a l

Mark !!! containment system, the resultant uniform concentration of hydrogen gas would be between about 13 and 21 percent.

To avoid detona-tien and ccabustion for the non-inerted containment, the steam concen-trations would have to be greater than about 557. and 70%, respectively.

If it is assumed that the hydrogen gas does not burn, the resulting containnent pressure will be between 15 and 20 psig, respectively, for the assumed 30 and 50 percent metal-water fractions.

In arriving at 1

these containment pressures, the non-condensible hydrogen gas and its l

associated energy of fomation are assumed to enter the containment along with the cther 1.0CA mass and energy sources.

If it is assumed that the hydrogen gas does burn, the Mark II contain-ment can accommodate the burning of the hydrogen produced by about 17 percent metal-water reaction without exceeding its design pressure and about 23 percent metal-water reaction without exceding twice the. design J

l pressure. The design pressure for the Mark III containments is 15 psig.

1 l

While analyses have not been performed to determine their failure. pres-(

sures, we believe that it would be at least twice the design pressure (30 psig).

This view is based on the analysis that was performed for the ice condenser plant discussed in Section 6.2.

I The currently scheduled fuel load date for the first domestic plant using a Mark III contrinment, the Grand Gulf Nuclear P1 ant, Unit 1, J

l l

1s August 1981.

It is our view that, pending the rulenaking pro-l l

ceeding, additional mitigation systems are not needed for the M

l Mark II1 contairnent.

.. (

6.4 Subatnospheri'c Containments If as much as 50 to 65 percent of the Zircaloy cladding were to react with steam or water in a subatmospheric containment plant, the resulting containment pressure would be less than its design pressure. Essentially all of the cladding would have to be oxidized for the resulting contain-ment pressure to exceed its estimated failure pressure.

As indicated in the discussion for ice condenser plants in Section 6.3, 1

the "Short Term Lessons Learned

• frcxs the THI-2 accident have been implemented at all operating plants and will be implemented at all the other plants before issuance of the operating licenses.

This action will reduce the likelihood of occurrence of accidents that could lead to substantial amounts of metal-water reaction.

]

Therefore, since the likelihood of degraded LOCAs have been made more l

remote by implementation of the "Short Tern lessons Learned' and since substantial amounts of metal-water reaction can be tolerated witheut jeopardizing contatrt.ent integrity, we conclude that, pending the rulemaking proceeding, continued operation and licensing of nuclear k

plants with subatmospheric containments is justified.

l l

t j

6.5 Ory Containments The dry contairrents have about two million or more cubic feet of net i

f free volume. Assuming 30 to 50 percent metal-water reaction in the j

1 core, the resulting unifonaly mixed concentration of hydrogen in the g

containment will range frcn six to ten percent.

This is well below the concentrations for detonation and even below the limits for cuc-g S

bustion if there were more than 50 percent steam in the contattrent e

atnesphere.

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e > I I

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Ihc design pressures f or these large cc.taire.cnts range f ru.t 50 to f

60 psig.

Although analyses have not been perforced to cetermine their f ailure pressures, we believe that such analyses would sh>

l that the f ailure pressures would be at least twice the design pres-s u re s.

This view is based on the analysis performed for the ice condenser plants as discussed in Section 4.0.

A If the substantial amunt of metal-water reaction were to occur fol-lo.<ing onset of the large LOCA and while the containment is still near its peak pressure, the pressure increase caused by the non-condensible g,

La hydrogen ;s and its associated exothermic forrution energy will be

,.:e is

]

substantially less than the f ailure pressure.

If the metal-water re-action were to occur well af ter onset of the large LOCA, when the con-tg tainment heat removal systems have been able to condense most of the M

2d steam and also reduce contal". ment pressure, then a substantial margin e

exists for accomodating the hydrogen generated by the metal-water re-gL'1 action.

a As indicated in the discussion for ice condenser plants in Section 6.3,

( j b

the "Short-term Lessons Learned" from the THI-2 accident have been im-i;[?j iiS plemented at all operating plants and will be icplemented at all the gIN other plants before issuance of the operating licenses.

This action p

$3 will reduce the likelihood of occurrence of accidents that cot.ld lead to substantial amounts of metal-water reaction.

4 Hs tccordingly, pending the rulemaking proceeding on hydrogen generation, y:d we fidd that continued operation and licensing of nu-lear plants with f:].:s ac dry containments is accepteble.

C R %" M'

?Xv ' u M~-eres' t%

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s.r e 7.0 ACRS Views The ACRS views on this subject are described in Item 10, Design Fea-tures for Core-Damage and Core-Melt Accidents, of its " Report on l

TMI-2 Lessons Learned Task Force Final Report," dated December 13, 1979.

The ACRS stated that:

"The ACRS supports.this recommendation.

However, the Connittee be-lieves that the recommendation should be augmented to require concur-rent design studies by each licensee of possible hydrogen control and filtered venting systems which have the potential for mitigation of accidents involving large scale core damage or core melting, in-cluding an estimate of the cost, the possible schedule, and the pro-tential for reluction in risk.

"The ACRS agrees with the recommendation made by the Lessons Learned Task Force in NUREG-0578 that the Mark I and Mart II BWR containments should be inerted while further studies are made of other possible containment modifications in accordance with the general recommenda-tions in this category.

The ACRS also recommends that special atten-l tion be given to making a timely decision on possible interim measures for ice-condenser containoants."

We believe the course of action we plan is responsive to the recom-mendations of the ACRS.

=

O e

8.0 CONCLUSION

The 'Short-Term Lessons learned" from the THI-2 accident have been im-plemented at all operating reactors and will be itplemented at all plants under construction before operating licenses for them are issued.

This action cakes the. likelihood of accidents involving substantial amounts of metal-water reaction scaller than was the case before the THI-2 accident.

A ruleruking proceeding on design features to mitigate the consequences of degraded core and core melt accidents is under consideration.

Perd-ing this rulemaking proceeding, we conclude that:

1) all Mark I contain-ments that are not now inerted and all Mark 11 containments should be required to be inerted; 2) no interim requirements are required at this time for improvecent in hydrogen management capability at nuclear power plants with other types of containment designs; and 3) subject to imple-centation of Item 1, above, continued operation and licensing of nuclear power plants is justified.

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UNIT ED ST AT Es NUCLEAR REGULATORY CO?/.M!SSION

[__ril 22, 1[ Q W AsHINGT ON, D. C. 205ss SECY-C-107A lf

~

INFORMATIDFJ REPORT t '.

I k.

k FOR:

The Comissioners I'.

.E' FROM:

H. Denton, Director, Office of Nuclear Reactor Regulation

' 'i W. Dircks, Acting Executive Director for Operations N N-THRU:

i. '

SUBJ ECT:

ADDITIONAL INFORMATION RE:

PROPOSED INTERIM HYDROGEN

>r CONTROL REQUIREMENTS II

(:3 Purpes_c:

To provide the additional information requested by the e

Comission regarding the Proposed Interim Hydrogen Con-trol Requirecents for Small Containments (SECY-80-107).

,'A Discussion:

In SECY-80-107, Proposed Interim Hydrogen Control Require-ments for Small Containnents, dated February 22,1980, the

'f staff reported its recorrrendation for certain interim hy-J drogen control requirenents for small containments on the i

basis of a review of the TMI-2 experience.

Specifically,

[1 the staff recomended inerting of all Mark I and Mark II

.,P _

containments for boiling water reactors as an interim meas-ure pending a rulemaking proceeding on the subject of de-ch l

graded cores and hydrogen manage:ent.

Q As a result of the March 19, 1980 meeting in the Comis-ston's Conference Room to discuss SECY-80-107, a memoran-N.

i dum was sent from S. Chilk to W. Dircks requesting that W

ib;$

certain additional supporting information be provided to the Comission.

The documents identified below are hereby g1 proYided in response to the Comissioners' request:

(The numbering corresponds to that used in the Chilk memorandum.)

i. (

,[l 1.a The identity of the contractor who performed the i"

I$# /

calculations of containment capability to accomo-T3d

/

date hydrogen generation from.netal-water reaction g

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and a copy of the contractor's analysis.

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Enclosure I contains this information.

w Distribution:

( %q,

Ccntact:

V. Butler, CSS / DSS Comis sioners N

s

I e5 iU r

h G

1 I

t!

it:t Cunaissioners.

'd The analysis was performed by Dr. L. F. Greitrann

,1 of Ae.es Laboratory.

A copy of the contractor's

'i analysis is enclosed.

u It is to be noted that the enclosed analysis is a preliminary one in a program designed to refine the ultirate strength characteristics of the Sequoyah/

McGuire type of contain ent.

1.b A list of all plants whose containent types fell within the following categories:

Mart I, ?tari II, Ic~e Condenser, Mark III, Sebataospheric, and Dry Containraent. contains this information.

o l

1.c A cogarison of the experience with drywell en-tries for inerted Mark I plants with the inforra-l tion provided by representatives of the Ver ent Yankee Nuclear Station, which is a non-inerted Mark I plant.

i contains this infrrmation.

f 9

2.

The Comission also requested that the views of I

the General Electric Comany on the utility of

)

inerting, including any calculations which differ R

from those provided by the NRC staff, be provided in writing. is a copy of the April 8,1980 letter

[

from Richard P. Denise to A. Phillip Bray of General Electric.

This letter advises General Electric of the Ccmission's request and of the staff's planned respense.

It also acknowledges i

that General Electric is planning to submit its d

own letter to the Comission on this subject.

Enclosures 5 through 8 contain the following docu-N ments which the staff believes tu represent the General Electric views on the subject of inerting.

Encloture 5 contains copies of the vu-graphs used 3

in the General Electric presentation on October 12,

[d 1979 to Dr. Mattson on the subject of "THI Evalu-ation Effort-hview of BWR Hydrogen Accomctation F.

Capability;"

C c.1 N.

P

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C; r;:ssione r.

il contains copies of the vu-graphs used in

[

I the General Electric presentation to the Comisticn I

i on March 19, 1980 entitled, "The BG Perspective on Interim Hydrogen Cor. trol Measures;" is a copy of the General Electric letter of August 3,1979 f rom Mr. Sherwood to Mr. Denton, "Inerting Mark I and 11 Containrent;" and is a copy of the General Electric letter of March 7,1980 from Mr. Bray to Chairman Ahearne, "BWR Mart I and II Containnent Inerting."

The other itens requested by the Comission (Items 1.d and 1.e in the Chilk memoran'dum) are being prepared and will be provided in about two weeks.

Af Harold R. Denton, Director h Office of Nuclear Reactor Regulation

Enclosures:

4 As stated l

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