ML20125B891

Forwards Realistic Accident Section for Plant Des.Changes Should Be Communicated to E Adensam

ML20125B891
Person / Time
Site:	Monticello
Issue date:	05/04/1972
From:	Gimes B US ATOMIC ENERGY COMMISSION (AEC)
To:	Knighton G US ATOMIC ENERGY COMMISSION (AEC)
References
NUDOCS 9212100204
Download: ML20125B891 (8)

Text

.

96.

ENVIRON, F;;$ (;:5pA)

MAY 4 1972 G - H .S G. W. Knighton, Chief , Project Branch No. ~ 1, DREP HONTICELLO REALISTIC ACCIDENT ASSESSMENT  ;

Enclosed is the Realistic Accident Section for the Honticello draf t '

1.nvironmental Statement prepared by E. Adensam.

If the natural background dose rate quoted in this section does not correspond to other values presented in the f.nvironmental Statement and it in to be changed, pleano Ict E. Adennam (Ext. 7323) know that it ir, being changed.

lirian Grimes, Chief Accident Analysis tiranch' Division of-Reactor Licensing Enclosures s (As Stated)  !

ces w/onclonare J. Shea til STRIBU110N, 15 . J. Youngbloot! DRL - Rd};.

W. Gammill DRL - Supp1, cc v/o enclosore St.RS Rdg.

D. !!uller AAB - Ed g.

11. Denton R. boyd D. Ziemann bcc E.-Adenaam w/ enclosure j.1 9212100204 720504 PDR ADOCK 05000263 D PDR omcr > . ..DREL ..., Ls s,o z DRL,..y.~.9 ~..

surmwe > f.ADEKSAM:mj . DZlD!ANC. --

.. fCS,a g. Ja R1

_.---. ogn > __

)]lJL _ ;5l)p2.; .

..... uc. min., w ,ucu om

$f, _ =l 7 2, . , , ,

e, , mo m m , m, . n, , n o, ,n , . . ,,,

u_,,_,u = _ . ,_ , _ , , , _ , . . , .,

. s.

i 1

ENVIRONMENTAL IMPACT OF ACCIDENTS l

Protection against the occurrence of postulated design basis acci-

\

idents in the Monticello Nuclear Generating Plant is provided through the defense in depth concept of design, manufacture, operation and testing, and the continued quality assurance program used to establish the necessary high degree of assurance for the integrity of the reactor primary system. These aspects were considered in the Commission's Safety Evaluation for the Monticello f acility, dated March 18, 1970.

Off-design conditions that may occur are limited by protection systems which place and hold the power plant in a safe condition. Notwithstanding this, the conservative postulate is made that serious accidents might

, . occur, even though unlikely; and engineered safety features are installed to mitigate the consequences of these postulated events.

The probability of occurrence of accidents and the spectrum of their consequences to be considered from an environmental effects standpoint a

have been analyzed using estimates of probabilities and realiste fission product release and transport assumptions. For site evaluation in the Commission's safety review, extremely conservative assumptions were used for the purpose of evaluating the adequacy of engineered safety features and for comparing calculated doses resulting from a hypothetical release of fission products from the fuel against the 10 CFR Part 100 siting guidelines. The computed doses that would be received by the.

population and environment from actual accidents would be significantly less than those presented in the Safety Evaluation.

i

! f

- - -. .-_ - _=

l

..r*~..

• _. l k.

l s

The Commission issued guidance to applicants on September 1, 1971, l requiring the consideration of a spectrum of accidents with assumptions as realistic as the state of knowledge permits. The applicant's response was contained in "Monticello Nuclear Generating plant Environ-mental Rep rt ," dated November 5,1971.

y/l> , / h Ayr./-L The e;f.fect ofiaccide.nt.s'havy been evaluated, using the standard-accident assumptions and guidance issued by the Commission as a proposed amendment to Appendix D of 10 CFR.Part 50 on December 1,1971 (Federal I

Register, Vol. 36, No. 231). Nine classes of postulated accidents and 1

occurrences ranging in severity from trivial to vary serious have been identified by the Commission. In general, accidents in the high potential consequence end of the spectrum have a very low occurrence rate, and these on the low potential consequence end are characterized by a higher 4

occurrence rate. .The applicant's examples for each class of accident are shown in Table I and are reasonably homogeneous in terms of probabilit within each class. Certain assumptions made by the Applicant such as the assumption of an iodine partition factor in the suppression pool during a loss-of-coolant accident and the efficiency. assigned to the charcoal filters in the standby gas treatment system, in the Staff view, are optimistic; but the use of alternative assumptions does not significantly affect the overall environmental risk.

Commission estimates of the dose which might be received by an r & fft h n ;- i,.E db $M individualstandingatthesiteboundarg,usingtheassumptionsinthe proposed Annex to Appendix D, are presented in Table II. Estimates of f

f

1

\

1 I the integrated exposure in man-rem that might,be delivered to the I

population within 50 miles of the site are als'o presented in Table 11.

l.

)These man-rem estimates were based on the projected population around

- the site for the year 2000.

To rigorously establish a realistic annual risk, the calculated doses in Table 11 would have to be multiplied by estimated probabil,ities, j

The events in Classes 1 and 2 represent occurrences which are anticipated j during plant operation and their consequences, which are very small, are considered within the framework of routine effluents from the plant.

l Except for a limited amount of fuel failures the events in Classes 3 through 5 are not anticipated during plant operation but events of this type could occur sometime during the 40 year plant lifetime. Accidents in Classes 6 and 7 and small accidents in Class 8 are of similar or lower probability than accidents in Classes 3 through.5 but are still possible.

The probability of occurrence of large Class 8 accidents is very small.

Therefore, when the consequences indicated in Table II are weighted by probabilitics, the environmental risk is very low. The postulated occurrences in Class 9 involve sequences of successive failures more i

severe than those required to be considered for the design basis of protection systems and engineered safety. features. Their consequences

, could be severe. However, the probability of their occurrence is so small that their environmental risk is extremely low. Defense in depth (multiple physical barriers), quality assurance for design, manufacture, and operation, continued surveillance and testing, and conservative l

?

- _= . .-

design are all applied to provide and maintain the required high de-gree of assurance that potential accidents in this class are, and j will remain, sufficiently small in probability that the environmental risk is extremely lov.

The information given in Table 11 indicates that the realistically estimated radiological consequences of the postulated accidents wonld be the-exposure of an individual assumed to be standing at the site boundary to concentrations of radioactive materials which were within the Maximum Permissible Concentrations (MPC) listed in Table II of 10 CFR part 20. The table also shows that the estdmated integrated i exposure of the populat1*on within 50 miles of the plant from each postulated accident would be orders of magnitude smaller than that from naturally occurring radioactivity which is approximately 303,000 man-rem year based on a natural background radiation level of 0.1

rem / year. When considered with the probability of occurrence, the annual potential radiatior exposure of the population frem all the postulated accidents is an even smaller fraction of the exposure from natural background radiation and, in fact, is well w'ithin naturally

occurring variations in the natural background. It is concluded from the results of the realistic analysis that the environmental risks due

to postulated radiological accidents at the Monticello Nuclear Generating Plant are exceedingly small and need not be considered further.

M

.---e- r *-tr,-- g ee -c

t-i.

< l 4

lt TABLE I f CLASSIFICATION OF POSTULATED ACCIDENTb 1-AND OCCURRENCES .

AEC Class Description Applicant 's Examples I

1 Trivial Incidents Primary coolant system leaks (below or

, just above allowabic tech spec. limits) within PC or RB (Not Considered) 2 Misc. Small Releases Reactor coolant leaks (below or just i above allowable tech spec limits) out--

side PC or RB l

3 Radwaste System Failures Single equipment failure j Single operator-error i

l 4 Events that Release Radio- Fuel failures dqring normal operation Transients within expected range of activity into the Primary l System ( EWR) protective equipment and normal parametc

. operation 5 Events that Release Radio- Primary coolant loop to auxiliary ~coolin

_ activity intoVcecondary system secondary' side of hea't exchanger j sys t em 6 (f #4 .j,;. .p k - leak (No events . identifled) i 6 Refueling Accidents inside Dropping of fuel assembly on reactor cor-

, Containment . spent fuelgrack or ag'ainst pool boundary '

i Dropping os, spent fuel shipping cask in ,

pool or outside pool l

Accidents to 8 pent Fuel

! 7 -Transportation incident involving spent l Outside Containment and new fuel t

-Shipnent equipment on site but outside P-or RB-8 ' Accident Initiation Events A, Reactivity-Transient

. Considered in Design Basis B. Loss of reactor coolant inside or ,

Evaluation in the Safety- outside primary containment Report 9 Hypothetical sequences of Successive failure of multiple-barriers, failures more severe than gafetysystemsandfissionproduct

Class 8 initigators-required and maintained, i

, (Not considered) -'

l i

L  !

i

.)

I

, i l:

_ , _ , _ _ _ _ , , . . . . . . _ _ . . . . _ . . , . . . . ~ . . . , . - , _ - . . , .. ..

W 4 i- ,

(.

b'

< TABLE Il 1

SUMMARY

OF RADIOLOGICAL CONSEQUENCES OF POSTULATED ACCIDENTS Estimated Estimated Dose Fraction of 10 CFR to Population j Class Event Part 20 Limit 1/ Within 50 mile

'At Site Boundarya Radius, man-rem

,- 1.0 Trivial incidents 2/ 2/

2.0 Small releases outside 2,/ j2 / = .

4 3.0 Radwaste system failures 3.1 Equipment. leakage or 0.19 7.6 J

malfunction l 3.2 Release of waste gas storage 4 tank contents 0.75 . 30.

I

3.3 Release of liquid waste storage <0.001 <0.1

- tank contents i

4.0 Fission products to primary system (E eC 4.1 Fuel cladding defects 2/ 2/

1 4.2 Off-design transients that induce- 0.008 0.78 fuel-failures above those expected 5.0 Fission products to primary and N.A. N.A.

j secondary systems (PWR) j 6.0 Refueling accidents 6.1 Fuel assembly dro,p into core <0.001 0.1

! 6.2 Heavy object drop onto. fuel in core 0.002 0.84 l

l 7.0 Spent fuel handling accident 7.1 Fuel assembly drop in fuel storage <0.001 '

O.18 pool t-l 7.2 Heavy object drop onto fuel rack <0.001 0;34 7.3 Fuel cask drop. 0.28 11-i L

t i

f L - _. . _ _ _. _. _ . , . __ . _

~ _ . . _ . _ _ _ _ _ .

Estimated Estimated Dost i e / Fra l.on of 10 FR to Population

' Part 20 Limit A ~

, Within 50 mite-Class Event At Site Boundary

• Radius , man-re:

is 8.0 Accident initiation events considered j- in design basis evaluation in the i safety analysis report 8.1 Loss-of-coolant accidents inside containment i

small break <0.001 <0.1 Large break 0.001 7.5 8.1(a) Break in instrument line inside <0.001 <0.1 reactor building

8. 2 (a) RodfjectionAccident(PWR) N.A. N. A.

4 8.2(b) Rod drop accident (BWR) 0.009 0.93 8.3 (a) Steamline break (PWR - outside containment) N.A. -

N.A.

9 1

8.3 (b) Steamline breaks (BWR) i i Small break -0.006 0.26 Large break 0.033 1.3 l

1 1/ Represents the calculated whole body dose as a fraction of 500 mrem j (or the equivalent dose to an organ),

i 2/. These releases will be comparable to the design objective indicated in the proposed-Appendix I to 10 CFR Part 50 for routine effluents (i.e., 5 mrem /yr

, to an individual from all sources).

a 3

.. - -- -- .. . .-.