ML19323H335

Fr Notice Re Nuclear Plant Accident Considerations Under NEPA of 1969.Revises NRC Policy for Considering Class 9 Accidents from Environ Point of View.Supplementary Info Encl

ML19323H335
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Site:	La Crosse File:Dairyland Power Cooperative icon.png
Issue date:	06/09/1980
From:	Chilk S NRC OFFICE OF THE SECRETARY (SECY)
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ML19323H330	List: ML19323H329 ML19323H335
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/b90201 NUCLEAR REGULATORY COMMISSION (10 CFR PARTS 50 AND 51)

Nuclear Power Plant Accident Considerations Ur. der the National Environmental Policy Act of 1969 AGENCY:

U.S. Nucl ear Regulatory Comission ACTION:

Statement of Interim Policy

SUMMARY

The Nuclear Regulatory Commission (NRC) is revising its policy for considering the more severe kinds of very low probability accidents that are physically possible in environmental impact assessments required by the National Envirornt, ental Policy Act (NEPA).

Such accidents are commonly refer-red to as Class 9 accidents, folloking an accident classification scheme proposed by the Atomic Energy Comission (predecessor to NRC) in 1971 for purposes of i plementing NEPA.

The March 28, 1979 accident at Unit 2 of the Three.ile Island nuclear plant has emphasized the need for changes in u

NRC policies regarding the considerations to be given to serious accidents from an envf r:nnental as well as a safety point of view.

This statement of interim policy announces the withdrawal of the proposed Annex to Appendix D cf 10 CFR Part 50 and the suspension cf the rulemaking

r:ceedin; that began with the publication of that prcposed Annex on December 1, 1971.

is the Cc=ission's position that its Envir:nnental Impact State-cents shall include considerations of the site-spe:1fic environmental impacts attributable to accident secuences that lead to releases of radiation and/or radioactive etterials, including sequences that can result in inadequate cooling of reactor fuel and to melting of the reactor core.

In this regard, attention shall be given b:th to the probability of occurrence Of such releases and to I Prc;osed as an Anner to 10 CFR Part 50, Appendix D, 25 FD. 22851. The Cornis-sion's NEFA-icslenenting regulations were subsequently (July 18, 1974) revised and recast as 10 CFR Par El but at that ti e the Connission noted

ht: "T'.e Precesed Annex is still under considerati:n..."

39 FR 26279.

8006.1203q

I s)C1L)"\\).L the ere'r:- ental consecuences of such releases.

This stater.ent of interim clic is taken in coordination with other ongoing safety-related activities that are directly related to accident considerations in the areas of plant desi;n, c:eraticnal safety,, siting policy, and ecergency planning.

The Com-

-issi:n intends to continue the rulemaking on this matter when new siting requirements and other safety related requirements incorporating accident considerations are in place.

DATES:

Comment period expires September,'ll, 1980.

AC3F. ESSES: The Co= mission intends the interim policy guidance contained hereir. to be inmediately effective.

However, all interested persons who desire to submit written comments or suggestions for consideration in con-necticn with thi: statement should send them to the Secretary of the Commis-sien, U.S. "uclear Regulatory Commission, Washington, D.C.

20555, Attention:

Docketing and Service Branch.

FOR FJRTHEP. INFORMATION CONTACT:

R. Wayne Houston, Chief, Accident Evalua-tion iranch, Office of Nuclear Reactor Regulation, U.S. Nuclear Regulatory C:: issicn, kashington, D.C.

20555, Telephone:

(301) 492-7323.

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5:;:y_: TION:

1::':er: : side a icns in Pas NEPA ?.eviews e ; ::: sed Ar.r.ex to Appendix D cf 10 CFR Part 50 (hereafter the " Annex")

was :.:lis' ed #cr corrent.on Decenber i,1971 by the (forner) Atomic Energy C:n-issi:..

; reposed to specify a set of standardized accident assumptions t: be used ir. Environmental Reports'subnitted by applicants for construction,

er.i s er 0;erating licenses for nuclear power reactors.

It also included a systen fcr classifying accidents according to a graded scale of severity and obability cf occurrence. Nine classes of accidents were defined, ranging i

f :- trivial to very serious.

It directed that "for each class, except j

classes 1 and 9, the environmental consequences shall be evaluated as indicated."

i Class 1 events were not to be considered because of their trivial consequences, i.e eas in regard to Class 9 events, the Annex stated as follows:

'The c:currences in Class 9 involve sequences of postulated successive failures core severe than those postulated for the design basis for orotec;tve systems and engineered safety features. Their consequences

culd be severe. However, the probability of their occurrence is so srail that their environmental risk is extremely low.

Defense in de::h (ruitiple physical barriers), quality assurance for design, manu-fa ure, anc operation, continued surveillance and testing, and con-servative design are all applied to provide and naintain the required

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.igh de;ree of assurance that potential accidents in this class are, ar.d aill re.ain, sufficiently rerete in probability that the environ-er. a. risk is extremely low.

For these reasors, it is not necessary

dis::ss such events in applicants' Environmen al Reports ~."

A =:: r.3 e t: the Annex stated:

'11:h::;h this annex refers to ~applican 's Envir:nnental Reports, the

--er; ass :: ions and other orovisions therecf are applicable, except as -,e ::r. er.: :ay otherwise require, to AEC draft and final Detailed 5 a e er.:s. "

rir; cre

:blic comment period that followed publication of the Annex a r.. :er f criticisms of the Annex were received.

princical amon: these were l

e :11: ir;: '

/00U-U1 (1) The ;F.iloscphy of prescribing assumptions d:es r:: lead to objective a r. a'. ys i s.

(2)

It failed to treat the probabilities of accidents in any but the n:s general way.

(3)

Ne su;; rting analysis was given to show that Class 9 accidents are sufficiently' low in probability that their :onsecuences in ter.s cf environmental risks need not be discussed.

(4) No guidance was given as to how accident and normal releases of radioactive effluents during plant operation sh uld be factored into the ecst-benefit analysis.

(5) The accident assu=ptions are not generally applicable to gas cooled or liquid metal cooled reactors, (6) Safety and environmental risks are not essentially different considerations.

Neither the Atomic Energy Commission nor the NRC took any further actiori on this rule aking except in 1974 when 10 CFR Part 51 was pronulgated.

Over the intervening years the accident considerations discussed in Environmental Impact St tenents for proposed nuclear power plants reflected the guidance of the Annex with few exceptions. Typically, the discussions of accident consequences through Class 8 (design basis accidents) for each case have reflected specific site characteristics associated with meteorology (the discersion of releases of radica:tive naterial into the atmosphere), the ac: cal pcpulation within a 50-nile radius of the plant, and some differences te: ween boiling water i

reactors 'EWF.) a.d pressuri:ed water reactors (pWF.). Eey:r.d these few spec-ifics, :Pe discussicas have reiterated the guidance cf t e Annex and have

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relied u; n the Annex's conclusion that the. probability cf occurrence of a Class 9 event is oc low to warrant consideration, a con:lusion based upon j

generally stated safety considerations.

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-i-M t.e :.::t-icn cf the P.eactor Safety Study (WASH-lac 3), in draft form in ;.;;.;st 1971 and final forn in October 1975, the accident disecssions in Er.vi-:- ertal I :act Statements began to refer to this first detailed study cf

^.e risks assc:iated wi,th nuclear power plant accidents, particularly ever.ts which :an lead to the melting of the fuel inside a reactor.2 The references to this study were in keeping with the intent and spirit of NEPA "tc disclose" relevant information, but it is obvious that WASH-1400 did not S r, the tasis for the conclusion expressed in the Annex in 1971 that the probability of occurrence of Class 9 events was too low te warrant their (site-specific) consideration under NEPA.

The Cc rnissien's staff has, however, identified in certain cases unique circunstar.ces which it felt warranted more extensive and detailed considera-tion cf Class 9 events. One of these was the proposed Clinch River Breeder Reactor Plant (CRBRP), a liquid metal cooled fast breeder reactor very differ-ent fror. the cre conventional light water reactor plants for which the safety experience base is much broader.

In the Final Environmental Statement for 2

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the staff included a discussion of the consideration it had g'ven to ~iass 9 events.

i Ir the ea-ly site review for the Perryman site, the staff perferned an ir cr al assess >ent of the relative differences in Class 9 accident conse-

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e cuer.:es a cn; the alternative sites.

(SECY-78-137)

-he case cf the a: plication by Offshore Power Systems to nanufacture e :a-'r.g u: lear power plants, the staff jutiged that the environmental risks A - is cf ir.terest that the Reactor Safety Study never refers : nor uses t' e e - " Class 9 accident" although this ter-- is ccm:nly used as loosely ecuivaient to a core melt accident.

I N;;.Es.:129, February 1977.

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' s: e Class 9 events warranted special consideration.

The special circum-s a :es -ere the potentially serious consequences associated with water (licuic) sat.says leading to radiological exposures if a molten reactor core were :: fall ir.t: the watey body on which the plant floats.

Here the staff e thasized its f:cus on risk to the environment but did not find that the probability of a core melt event occurring in the first place was essentially,

ar.y different than for a land-based plant.

In its Memorandum and Order In the Matter of Offshore Power Systems, the Commission concurred in the staff's judgment. Thus, the Reactor Safety Study and NRC experience with these cases has served to refocus attention on the need to reemphasize thit environmental risk entails both probabilities and consequences, a point that was made in the 1

publication of the Annex, but was not given adequate emphasis.

In July 1977 the NRC commissioned a Risk Assessment Review Group "to clarify the a:hievenents and limitations of the Reactor Safety Study." One of the conclusiens of this study, published in September 1978, as NUREG/CR-0400,

" Risk Assess ent Review Group Report to the U.S. Nuclear Regulatory Commission,"

was that "The Review Group was unable to determine whether the absolute prob-I a:ili-ies cf accident sequences in WASH-1400 are high or low, but believes

".a : -he err:r b:unds on those estimates are in general, greatly understated."

1 T-is ar.d ther findings of the Review Group have alsc subsequently been refer,

rec o in Environmental Impact Statements, along with a reference to the C:mrissicn's policy statement on the Reactor Safety Study in light of the

f sk :.ssessmer.t Review Group Report, published on January 18, 1979.

The

--issi:n's statement accepted the findings of the Review Group, both as to

-he Reactor Safety Study's achievements and as to its limitations.

1. E :ke: No. STN 50-437, September 14, 1979.,

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A few :raf-E.'r:- +.tal State ents have been publis'id s.bst:uer.: to,the Three Mile :s'ar: a::ident. These were for conventional lar.d-based light water rea:::r :~ a.ts and centinued to reflect the past ;ra:tice' with respect to a: cider s at s.:

Tants, but noted that the ex;erience gained from the Three M.i".e :s'.ar.d accident was not factored into the discussion.

Our experien:s nith ;ast NEPA reviews of accidents and the TMI accident clearly leads us to believe that a change is needed.

Ac:orcingly, -he preposed Annex to Appendix D of 10 CFR Pa-50, published on December i,1571, is hereby withdrawi. and shall not hereafter be used by appli-cants nor by the staff. The reasons for the withdrawal are as follows:

1.

The Annex pr: scribes censideration of the kinds o' at:idents (Class 9) that, ac::rding to the Reactor Safety Study, decir. ate the accident risk.

2.

The definition of Class 9 accidents in the Annex is n:t sufficiently precise to warrant its further use in Commission policy, rules, and regulations, nor as a decision criterion in agency practice.

3.

The Annex's crescription of assumptions to be used in the analysis of the environ ental consecue,ces of accidents does.c: Ocntribute to cbjective censideration.

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~5e 'n ex d:es not give adequate consideration

the de tiled treatment f Easures taken to prevent and to mitigate -he consequences of acci-der.ts ir the safety review of each application.

-re classi'icati:n of accidents pro:osed in that Annex sha'.1 no lenger be used.

Ir e ts iace :' e fellowing interin guidance is given 'or : e treatm.ent of a c:i den: -isk ::nsideratiens in NEPA reviews.

1 A :' der.: :: s'de ati:ns in ~uture EPA ?.eviews

is -he ::st:i:n O' the Cennission that its Envircr ental :::act Statements, pursuan :: See:icn 102(c)(i) of the National Environ ental ?clicy Act of 1959, sha'.1 ' clude a -sas:ned censideration of the envi or en a' -isks (impacts) l a-ri:::atie :: a::idents at the particular facility :- ft:i'ities within the secse cf ea: su:P. statene nt.

In the analysis and dis:ussi:r of such risks, 7

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du 5::-:y' 1:s'.y ecuai attention shall be given to the protability of occurrence

' rEisases and to the probability of occurrence of the environ ental cor.se-quen:es Of -hose releases.

Releases refer to radiation and/or radioactive ateria's enterin; environ-ental exposure pathways, including air, water, and grounc water.

Ever.ts ;r accident secuences that lead to releases shall include but not be limited to those that can reasonably be expected to occur.

In-plant accident seq;er.ces that can lead to a spectrum of re' leases shall be discussed and shall include secuences that can result in inadequate cooline of reactor fuel and The extent to which events arising from te nelting of the reactor core.

causes external to the plant which are considered possible contributors to Detailed the risk associated with the particular plant shall also be discussed.

c.uanti ative considerations that form the basis of probabilistic estimates of releases need not be incorporated in the Environmental Inpact Statements but shall be referenced therein. Such references shall include, as applicable, re;crts en safety evaluations.

he en.ir:nmental consequences of releases whose probabili y :f occurrence Such

' as beer. esti.ated shall also be ciscussed in probabilistic terms.

secuen:es shall be characterized in terms of pcten-ial radiological expo-individuals, to po;ulation groups, and, where a;:licable, to biota.

22-es t:

l h ll 2es'. h and safety risks that may be associated with e:.;osures to pecp e s a state of knowledge

s discussed ir a ranner that fairly reflects the curren:

ri;artin; su:h risks.

Socioeconomic impacts that P.i;.: he associated with e er;ency measures during or following an accident sh:uld also be discussed.

e e vironrental risk of accidents should also be cc :ared to and co l

si-- -adicio;ical risks associated with normal and a ici:ated coerationa

-eleases..

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-:-f ;ati ; :-is interir guidance, the Co :-issicn is aware that there are a.: wCl *.ike'.y remain for some time to come rany uncertainties in the a::1':ttic7 :# risk assessment methods, and it ex;ects that its Environmental

m:a:: 5:1 e.Ents will identify najor uncertainties in its probabilistic es-i ates.

^r the cther hand the Ccanission believes that the state of the ar: is suffic'ently advanced that a beginning should now be made in the itse cf t ese re:h:dolsgies in the regulatory process, and that such use will re: resent a c:nst uctive and rational forward step in the discharge of its responsibilities.

It is the ir. tent of the Cor:: mission in issuing this Statement of Interim po' icy that the staff will initiate treatments of accident considerations, in accordance with the foregoing guidance, in its ongoing NEPA reviews, i.e.,

for ar.y proceeding at a licensing stage where a Final Environmental Impact State ent has no yet been issued.

These new treatments, which will take ir.to account significant site-and plant-specific features, will result in re-e detailed discussions of accident risks than in previous environmental 1

i staterents, particularly for those' related to conventional light water plants a: 1 ard-basec sites.

It is expected that these revised treatments will lead

c: :.uzicr.: regarding the environmental risks of accidents similar to those

~ a: :_1: :e reached by a continuation of current practices, particularly

1. r cases i.volving special circunstances where Class 9 risks have been con-s'dered t/ t' e s aff, as described above. Thus, this change in policy is

:e c:rstr:ed as any lack of confidence in conclusions regarding the e c'-:-.e.:al risks of accidents expressed in any previously issued Statements,

r, abse. a shswing of similar special circumstances, as a basis for open-

' ;, -e::e drg or expanding any previous or ongoing :roceeding.

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- 'ssi:.ers 3ilinsky and Bradford disagree with the inclusion of the

-e:ed# ; w: sentences. They feel that they are absolutely inconsistent w - ar even-handed reappraisal of the former, erronecus position on Class 9 e

a::icer.:s.

.g.

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.-e.er, it is also the intent cf the Commissicn that the suff take steps

ider.:i#y additional cases that right warrant early consideration of either a d di ti:r. E'. feat.:res or other actions which would prevent or nit'igate the con-se:uertes O' se-ious accidents. Cases for such consideration are those for enic. a.:inal Environmental Statement has already been issued at the Construc-ti:n Fem.it stage but for which the 6perating License review stage has not ye: been reached.

In carrying out this directive, the staff should consider re'.evant site features, including population density, associated with accident risk in c:mparison to such features at presently operating plants.

Sta ff sh:uld also c:nsider the likelihood that substantive changes in plant design features which may compensate further for adverse site features may be more easily in:orp: rated in plants when construction has not yet progressed very far.

Envircnnental Reports submitted by applicants for construction permits and fer o;erating licenses on or after July 1,1980 should include a discussion of the envire, mental risks associated with accidents that follows the guidance given herein.

F. elated P:liev Matters Under Consideration additi:n :: its responsibilities under NEPA, the ":.C also bears responsi-

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te ty under the Atenic Energy Act 'or the protection cf the public health and sa'ety fr:r the hazards associated with the use cf nuclear energy.

Pursuant t

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cris resp:nsi':ility the Corr.ission notes that there are currently a number

f cr.;;in; activities being considered by the Commission and its staff which l

ir.:i.ately relate to the " Class 9 accident" question and which are either the su:.'s:: cf cu-rent rulemaking or are candidate subjects for rulemaking.

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'i, ~ 375 -he C: rission issued for public ::mmen:6 a prooosed

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-:f: s';nificantly revise its requirenents in 10 CFR Part 50 for s s ;s :. ; at ' ; f:r nuclear :ower plants.

One of the considerations in

-is s a '.; -ts -he potential consequences of Class i accidents in a

sneri

sanss.

r. Au; :: 1575, :urs; ant to the Commission's recuest, a Siting Policy Task F rce r.ade re:ca-endations with respect to possible changes in NRC reactor sitir; ;:licy and criteria,8 currently set forth in 10 CFR Part 100.

As stated therein, its reco=mendations were made to accenplish (among others) tr.e f:lievin; goti:

'To take into consideration in siting the risk associated with accidents teytid -he design basis (Class 9) by establishing population density and distri b:tio criteria."

This atter is currently before the Commission.

1 J

i T'.is and other recommendations that have been made as a result of the investiga-tiens into tr.e Three Mile Island Accident are curren-ly being brought together 1

by tre Scariss'o 's staff in the form of proposed Action Plans.o Among other 1

53 s s, the:s ' ;;rocrate recc=mendations for rulemakir.; related to degraded c:re :cc'.ir; and core nelt accidents. The Commission ex:ects to issue deci-s' s :. t'ste

t'en Plans in the near future.

It is the Conrission's policy E-d ' :s ; :: date s NRC's major resou*ces to r.atter: d-ich -he Commi ssion

5".isces w'l' ske sxistin; and future nuclear power ;lar.:s safer, and to i..------

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#. '. :E5-: 15, ":iannin; Basis for the Develo; en c' State and Local G:.ern en: Raciciegical Energency Response Plans in Support of Light V3 e

'iuclear sewer Plants," November 1978.

E *:'.:E3

525,

e:crt cf the Siting Policy Task Force," August 1979.

• U:.E5-0550, " Action Plans for Implementing :.s:09 endations of the

te:

-ss':snt's ::=rission and Cther Studies of the TP:-2 Accider.t," December 1~,

--e.e-a -e: -rer.:e Of the ki.d cf a::ident tha: :::urre: a: Three Mile

's'a :.

- -.e ir.: erin, h: wever, and sending c:.:leti: O f rulemaking a:-','t'es i

~ e areas of e ergen:y ;ianning, sitin; criteria, and design a-d :: era:#:

t'. safety, all of which involve ccr.siderati:ns Of serieus acci-

E.: ::e. it, trs Co niisien finds i essential c i.;reve its precedures 1:r descri'ing and disciosing to the public the basis fer arriiing at conclu-

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s':r s regarding the environnental risks due to accidents at nuclear power

. ants.

On 20.pletion of the rulemaking activities in these areas, and based

r the experience gained with thii state ient cf ir. eri:n policy and

~a s:

ida.ce, the Sc

mission ir.tends to pursue possible

harges er additions to 1: CF:.' Par 51 to codify its position on the role of accident risks under W

ed at k'Esr.ingten, D.C. this day of u^C

1980,

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For the Nuclear F.egulatory Cot =ission l

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i Samuel J. Chil l Secretary of :M C =ission S

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