ML20207S238

Comments on Draft Reg Guide Atmospheric Dispersion Models for Potential Accident Consequence Assessments at Nuclear Power Plants & Value Impact Assessment.Value Impact Assessment Does Not Suuport Guide in Present Form

ML20207S238
Person / Time
Issue date:	06/23/1978
From:	Hulman L Office of Nuclear Reactor Regulation
To:	Harold Denton Office of Nuclear Reactor Regulation
Shared Package
ML20207S219	List: ML20207S218 ML20207S220 ML20207S225 ML20207S235 ML20207S238 ML20207S240 ML20207S566
References
NUDOCS 8703190173
Download: ML20207S238 (3)

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JUN 2 31978

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-s't, MD(ORANDUM POR: 'Barold R. Denton, Director

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Division of Site Safety and Environmental Analysis 4

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Richard P. Denise, Assistant Director for @

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SUBJECr: ~."." ~ HHB COMMENTS AND POSITIONS ON JUN 12, 1978 DRAFT

~ ~~ T POTENTIAL ACCIDENT CONSEQUENCE ASSESSMENTS AT NUCLEAR 1.

... POWER PLANTS AND VALUE-DIPACT STATEMENT"..

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.We have reviewed the draf t regulatory guide.and value impact assessment.,4.;.

transmitted to the ACRS on June 12, 1978. Extensive' comments soneerning ~" C

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. I organization of the material, and clarification of the 'soncepts and

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i procedures presented in the guide will be supplied to OSD within the next week. The value-impact assessment does not support the guide in its present form. We will supply suggestions for improvement along

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with our comments on the guide.

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I We have two areas of substantive staff disagreement with"the~gside,. 7 ~

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as written:

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The rationale for selection of sector prob. ability levels;. e

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t.h. e rationale._fo.r.;..inelusion of..s. a.".ov.e.r_a.l.l..e.,f t_e".X

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As a result of the May 2,1978 meeting of the RRac, E.'O. Case approved

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• * '"an interim branch position that permitted limited ese of the Sep'lgebir 12."*"-

t 6.1977 draf t of the regulatory guide for licensing actions..This drtit e ci.-

of tEs ' guide specified a Trobability level of aboat'0.3% (equivalent to "*V.

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^" ~"~ 27 hours3.125e-4 days <br />0.0075 hours <br />4.464286e-5 weeks <br />1.02735e-5 months <br /> / year) in the critical sector for 'selectime"of the I/Q value.~".7.M.'IT '

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. /;'., this sector probability level, and our understand 1ag la that. the staff.cg.;.,..

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was directed to perform an additional parametric study to provide

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irmxI as the basis for a Commission paper on the model. " The June 12, 1978 rr M s

..~ 7* ~ version of the guide specifies a probability level of 0.61 in the 7 '_% 7 @ " Y

".u.. critical sector with the rationale that this would ". produce I/q. values * * * * *,

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. u.;.w. procedures (described la SRP S,ection,.,2.3.4), i.w,luding

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variable site boundary distances". In our presentation to RRRC on

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level was in the range of 0.4 to 4.6%.

We disagree with the stated bases j

for selection of the 0.6% probability level as presented in the June 12, 1978 version of the guide. The most significant innovation in concept of the new model is consideration of directional variability of atmos-

'pheric dispersion conditions and the subsequent calculation of.I/Q --49-7W.-

values at specifie locations. We believe that the most appropriate -' m basis for linking the direction-dependent Boncept with the~ direction ~~

independent approach should be a determination of what the direction-independent approach meant with respect to frequency of occurrence of

....- -.the "5% X/Q" at specific locations around a variable exclusion area m, e~

boundary. Using this rationale with the information~ presented la~ the enclosed graph summarizing the results of the parametric study of 18 sites, we conclude that a probability level of 0.5% for critical sectors

-f-seems most appropriate. We view this probability level as a reasonable

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' interpretation in view of the scatter of the data 'and the precision..of M... M..'

the statistics. We note that use of the 0.6y, value produces sa

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average reduction in the X/Q values over those produced by the old *-'"F'-".

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model that is roughly equivalent to the average reduction due to the o--

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consideration of plume meander alone.

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The June 12, 1978 version of the guide also includes a proceidure for a determining a direction-independent "overall-site" 5% I/Q as a limit _"g-te;____.

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.... :. to the direction-dependent model evaluation. ',,The 'rationhle for the ~'~"*'"

l :. ci.Hdetermination of this "overall site" I/Q is not presented isthe~guideN.E~l-

--' "- We do not believe that the "overall site" concept is necessary because G i M *;

the link to the old approach.would be accomplished. through, select on of 72

i 7...T.p."the probability level for the eritical sector.a.In addicion thingM.q.37,.%

~; * ~ J," concept has no physical meaning to an individual l.o,e.m..d. at a,n.y Y.o_i.n.t..~..-.r.

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on the esclusion area boundary or LPf..

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.In conclusion, we recommend thht the new model be used at.a articial..... A L sector probability level of 0.5% with the bases (rationale) as described er

--above, and that the procedures for determining as "overall site"_3/Q

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-- ---- - be deleted from this guide. Furthermore, this probabilistic selection, fi_

procedure should only be considered as an interim step in the intended, gang.

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.t development of an explicit siting policy which incorporates the.

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