ML25016A288

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Regulatory Guide (RG) 1.7, Revision 0, Control of Combustible Gas Concentrations in Containment Following a Loss-of-Coolant Accident
ML25016A288
Person / Time
Issue date: 03/31/1971
From:
Office of Nuclear Regulatory Research
To:
References
RG-1.007, Rev. 0
Download: ML25016A288 (1)
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Text

3 ' lll/il SAFETY GUIDE 7 CONTROL OF COMBUSTIBLE GAS CONCENTRATIONS IN CONTAINMENT FOLLOWING A LOSS OF COOLANT ACCIDENT A. Introduction General Desi~n Criteri1,n 'J 1*equires that systems t*, t11ntrol hy<irog,m, ff\\-ygcn, and other subst~nccs which may be rel('asecl into the reac-tor containment be prr,virled as necessary to control thei1* concentrations followmR" postu-lated aC'cidents to assure that containment in-tegrity is maintained. Thi;; guide describes an accept.able method of implementing this cri-terion.

B. Discu~on Following a lo~s of coolant accident, hydrogen gas may accumulate within the containment as a result of:

1. Metal-water reaction inrnh-ing the zirconium fuel cladding and the reactor coolant.
2. Radiolytir decompo!lition of the post-accident emergency cooling solutions (oxygen will also e,*olve in this proc-ess).
3. Corrosion of metal!:! by solutions used for emergency coolin!,! or containment spray.

If a sufficient amount of hydrogen is gen-erated, it m:iy react with the oxygen present in the containment atmosphere or, in the case of inetted containments, with the oxygen gener-ated following the accident. The reaction would take place at rntes rapid enough to lead to high temperatures and sismific-ant overpr,,s~urization of the containment, which could reqult in a loAs of integrity. Damage to systems and compon-ents essential to the continued coTJtrol of the post loss of coolant accident conditions could also occur.

The extent of metal-water reaction and asso-ciated h~*drogen production depend11 strongly on the course of events assumed for the accident and on the r.ffectiveness of emergency cooling 7.1 Ry:-;tem11. The rate of produdion <'f J!ll!'i**!I from radi,)l)*sis of c*1,olant solutions dept*ndi: on ( 1) the amount *ind q 1iahtr of racfo.tion encrJ.,ry ab-sorbed in the specific coolin~ solution~ employed and (2) the net yield of gases generated from the solutionR due to the absorbed radiation en-erll)*. Factors such as coola 1t flow rates and turbulence, chemical additives in the coolant, impurities, ancl coolant temperature can all ex-ert an influence on the gas yiPlds from radiolr-sis. The hydrogen production rate from cor.

rosion of materiah, within the containment, such as aluminum. depends on the corrMion rate which in turn depend!! on such factor:. as the coolant chemistry, the coolant pH, the metal and cooh,nt temperatures, and th<> surface arPa exposed to attack by the coolant...\\ccurate

,*aluec; d th1;- *n parameters are difficult to estab-lish with certainty for the conditions exr,eeted to pre-.*ail followin,R' a loss of cor,Jant accident.

The regulatory staff has revit*,,*ed the av:,il-able information concerning these pnrameters, including the results of cakulatwm1 and cXf>eri-ments. Table l defines values and other as-sumptions which the stnff belic,*es to b0 ren~on.

ably comien-ative that may be m;erl for purpo. e.

of "V'lluating the production of combustlblt!

raAe~ 1oi1owing a los of coolant acl'idcnt.

If these a~sumr,tions are used to calrulnte the concencration of hydrogt*n (1111d o ygen) within the containment structure. of r('actor plant14 of current dMig:1s following :1 lo"~ of coolant 11ctident, the* hyilroiren concent rat iun is cult*ulatPd to renc-h th,! flammnblt* limit within pc,riodH of less thnn a day uft<*r the an*ident for the 11malleMt ('Ontainmcntl:! and up to more than a month for the largP~t one~. Th1.: hyrlroi*en concentration could be mmntair.ed helow it lower fhtmmnblr limit by pur,1,inv 1hl' rnnfain-ment atmrn,pherc to the l'Il\\'iron-, at JI ('Olltrollc*tJ rate after the loss of coolant acddcnt; howevn,

radio ctive mat ri I in th cC1n* inment al.to be rele~ ed. If purging becnme n shortly after th ccid nt. qu ntiti of m ter1 l ~ *ould b, rcl ed.

In mall cont inm n the runo mt of m t 1-v.. t r re dion po tul ted in 'T ble ult in hyrlrogen concentrat' a

nbl limi The

  • n from the m tnl-t u

th n that from eith Operation of sm"ll rt (oxygen defkient) ufficicnt tim f u

ble gas control terns to ttduce th tr. tion of h:rdr f

of' accident before the rn d b oiJ;~is ~ul* in fi..

res in the con-t inm nt.

It 1s therefore ad ~ bl to pro\\;d r

rrunng, mpting nd I

ulH tio of essarily invol to th en,;

pro\\;de th m nt of ra teri co p

~n at pie.

n of

d.
1.

ter..cooled po er r cto.r f cili-ti hould ha,;

the capability for measuring the hydro n concentration and for mixing the tmosphere in the con inment following a lo of coolant ccident, nd for contro11ing combuAi-b e concentratiQm without reliance on purging of the containment atmc...

phere.

The continuous presence of 7.2 combu tihlc gns contr >I c11uipment the 11itc may not bt> nC<'

ry pr,vuied it

  • nvnllnble on un npproprintc time ralc; how *v1 r, :~~11roprint d htn nn,1-pro durd pro,*1 10n11 ~hould l>

mad for its u.r,

2. Combu tlblt>

1trol 8YII rm!\\ rand th ixini?, me.1suring, h

cl Aign,

  • , ent'rRl' r qmr*-
  • f tu, oulrl m,t Intro 1 t mn
  • ff t
3.

()

l r

i t-i\\

Ion P

l T

in

,1 s

I-r n g !I ro11-cc1 nd t*v lu-ti ntrol nnd to evolv d in of coolnnt ucrid *nt.

,

  • be l'hnnged on th ion I expcrimmtnl <'\\'l*-

ily. s.

5.

Is within the contninmcnt thnt ield hydro en gn clue to corro-from the emergency <'l olin or cont inm nt spray olution thould he idC'1 tifl d and thPir u* *.~houlu be lim*

it('(} as. much as practical.

TABLE 1

l.

raetion or fll!lllon prod-uct radiation encr :-y al>*

orbed by the coolant'

{a) flrta

( 1) Bt.'t II from fis~ion product in tht fu I roJ : 0 (2) Betas from fission produt't lntimat- -

ly mix1:d with cool-ant: 1.0 (b) Gamma

( l) Gamm,, from fis-sion pr-oducta in the fuel rods, coolant in (.;Ore region: 0.1'

TABLE 1-(cont.)

2. G(H,)'

(2) Gammas from fii.-

sion producb inti-mately mixed with coolant, ull coolant:

1.0 9.5 molecules/l0Oev

3. G(O,)'

0.25 molecu1es/100ev

4. Extent of metal-wa~r re-action (percentage of fuel cladding th:it reacts with water) 5
5. Aluminum corrosion rate for allll'ninum exposed to alkaline solutions. (This value should be adjusteJ upwan! for higher tem-peratures early in the ac-cident ~equence)
6. Fission product distrihu-tion model 200 mils/yr (a) 50,;t,-

of the h.alo-gens and l "', of the solids present In the core are intimately mixed with the coolant water.

7.3 TABLE 1-(eont.)

(b) All noble,zasl' nre releas,,d ttl the roJ".

tainment.

(c) All other fis~ion products remain in fuel rods.

7. (a) Hydrogen concentra-4 volume percent tion limit (Thi& limit

£hould not be excet-d-ed if more than 5 vol-ume :percent oxygen is present.)

(b) Oxygen concentration 5 volume percent limit (This limit should not be exceed-ed if more than 4 vol-ume J)ettl'nt hydrogen is present.)

l For water, borat,d water, and borated alkaline solu-tions; for other solution!', data should hfo presented.

  • This fraction is thought to be conservative: furthrr anal)'sis may show that it should be revised.

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