NUREG-0409, Discusses NUREG-0409 Iodine Behavior in PWR Cooling Sys Following Postulated Steam Generator Tube Rupture Accident
| ML18004B979 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 02/22/1978 |
| From: | Vollmer R Office of Nuclear Reactor Regulation |
| To: | Vassallo D Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML18004B980 | List: |
| References | |
| NUDOCS 7904200331 | |
| Download: ML18004B979 (4) | |
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llOTE TO:
Dolllollic B. Vas"allo, Assistant Director for Light Hater ReacLor's, DPil
'FROh:
Richard II. Vollirer, Assistarrt Director for Site Analysis, DSE
- UBJECT:
COtlSULTA!!T REPORT REGARDIilG HO'l-CO!ISERYATISN Irl STAFF ViODEL As a resul t ol a tnclr>>ic:r1.issistancc contract viith a staff consultant, a tech!rical r epnr l (llll",EG-0~F09) on "Iodine Behavior in a PHR Cooling System Followirrg a f'ostulated St am Generator Tube Rupture Accident,".
by A.
V,. Postrra a>>d P.
S.
1'am, v;as published in January 1978.
1 Tire report is a tl coretical study of the.iodine behavior in the primary and secondary coolarrt systems of a PlR following a postulated steam generator tube rupture.
The report concludes
- that, as a result of such a rupture, priroar.y coolarrL water containing iodine v(ovid be atomized by hydrodynairic for'ces as it flashed through tlute leal: path into the steam system.
The rerioval ol iodine by tlie secondary vlater was predicted to be highly deperrderit upon the primary-to-secon<<ary pressure difference and upon the r'at r'epth.
Calc;rlations 'mode in the report, and which the report eral!!rasizcd wer
. designed to yield conservative predictions, indicated ttrat irr L'he ear ly pirt of the accident less than 50.. of the iodine might t!e rc!.:oved by thu secor.dary via".or, vrlrereas in the. later phases of thc accident, about 9:.'"'f the iodine would be removed.
Although the rc!!or't attempted to assess the iodine removal by steam separ.ators it did not examirr:. oossiblc iodine rer,:oval due to the prox-imity of neiglrbor irrg Lube". and other submerged structures in the steam generator.
The present staff model, as outlined in St.;r dard Review Plan 15.6.3, assumes that a corrstant v,".lur. of rO"'f tire iodine transferred to the secondary water is reroved arrrl retained in it.
Therefore, hUR G-0409
'mplies tirat the pr.serrt s~:al l'.;odel n:ay be non-cnnservative in the early plrases of th.. accidcrrt, but rray be overly conservative in the later phrases.
The overall degree ol'our;er":itisr. or non-conservatism of the staff's present;:ode1 cannot easi1v i. assessed witnorjt a much more detailed examination.
llovIever, sci:e per"pective regarding the implications may 0
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be gained hy observing that Llie present staff model predicts the radio-logical co>>sc((((enc(s of a stram generator tube rupture coincident with a large iodiiie sinai(:
to be about 75 revi to:he thyroid for a typical PMR at a site wi Lli (.on>
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1 w 10 3 sec/m3) meteorology.
He can conclude froi;: tnis thaL <.veii i( the staff's model was less conservative throui(hout the a".ci;Ie>>t by is iivch as a factor of four, that our con-clusions regarding the accep(:ability of this event would not likely change.
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The sLaff.is currently taI:i>>g action in this matter in two ways.
- First, the staff is
(>~ e(iaririg and evalu(sting a more detailed model to be incor-porated in its i'iseii SLa>>dard Review Plan in t>>is area which will allow
'or a time-dcpe>>:I;.>>t iodine r tention fraction in the secondary water.
'econd, ti)e stll'f i" I)lan>>in; Lo have experimc>>ts performed, as suggested by t(UI!EG-040".-, tlia(: will conl'irra or refute tne values indicated by the report.
" lie believe, in vie(i of the possibility of a non-conservative staff model in this regard, that the licrnsing boards currently in progress for all Pl(R plants should be <luly informed.
Richard H. Yollmer, Assistant Director for Site Analysis Division of Site Safety and Environr((ental Ana lysi s F
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