ML20037A617
| ML20037A617 | |
| Person / Time | |
|---|---|
| Site: | Crystal River  |
| Issue date: | 07/28/1972 |
| From: | US ATOMIC ENERGY COMMISSION (AEC) |
| To: | |
| Shared Package | |
| ML20037A616 | List: |
| References | |
| NUDOCS 8003250620 | |
| Download: ML20037A617 (8) | |
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VI.
. ENVIRONMENTAL IMPACT OF POSTULATED ACCIDENTS A.
PLANT ACCIDESTS A high degree of protection against the occurrence of postulated
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acc1 dents at the Crystal River Plant Unit 3, is provided through correct-design, manufacture, and operation and the quality assurance program used to establish the necessary high integrity of the reactor system, as considered in the Cornission's Safety Evaluation dated June.6,1968.
Deviations that may occur are handled by protective systems to place and hold the plant in a safe condition.
Notwithstanding this, the conservative _ postulate is made that serious accidents might occur, in spite $f the fact that they are extremely 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'ccasidered f cm an environmental effects standpoint-have been analyzed using best estimates of probabilities and realistic fission product release and transport assumptions.
For site evaluation in the Cocsission's safety review, extremely conservative assumptions were used for-the purpose of comparing postulated doses resulting from a hypothetical release of fission products from the fuel, against the.
10 CFR Part 100 siting guidelines.
The ecmputed doses that would be received by the population and. environ =ent from actual accidents would be=
significantly less than those presented in the Safety Evaluation.
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.n The Commission issued guidance to applicants on September 1,l1971, 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 the " Applicant's Environmental Report," dated January 4, 1972.
The applicant's report has been evaluated, using the standard accident assumptions and guidance issued as a proposed amendment to Appendix D of 10 CFR Part 50 by.he Cc=nission on December.1,1971.
Nine: classes of postulated accidents and occurrences ranging in severity.from trivial ta very serious were identified by the Commission.
In general, accidents in the high potential consequence end of the spectrum have a lov occurrence rate, and those on the' low potential consequence.end have a higher occurrence rate.
The examples selected by the applicant for these cases are shown in Table VI-1.
The exampics selected are reasonably hemogeneous in terms of probability within each class,'although (1) the startup, rod withdrawal, moderator dilution, and cold water addition accidents are considered to be more appropriately in' Class 1, (2) a complete loss of electric power as more appropriately in Class 2,_(3) r l
the release of the waste gas decay tank contents as more appropriately l
l in Class 3, and (4) the steam generator tube rupture as more appropriately 6 l
Class 5.
Certain assumptions made by the applicant do not exactly agree with those in the proposed Ar.nex to Appendix D, but the use of alternative assumptions does not significantly affect overall environmental risk.
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Staff estimates of the dose which might be received by an assumed individual standing at the site boundary in the downwind' direction, using the assumptions in the proposed Annex to Appendix D, are presented in Table VI-2.
Staff estimates of the integrated exposure that might be delivered to the population within 50 miles of the site are also I-presented in Table VI-2.
The man-rem estimate was based on the projected population around the site for the year 2015, extrapolating the 1967 population data.
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TABLE VI-1 CLASSIFICATION OF POSTULATED ACCIDENTS AND OCCURRENCES Class AEC Description Applicant's Example (s) 1.0 Trivial Incidents Not considered-2.0 Small releases outside Small reactor coolant containment spill 3.0 Radwaste system failures Release of 157. of the activity in a waste gat decay tank 4.0 Fission products to primary Primary systen leakage systen to containment 5.0 lission products to primary Normal operation with and secondary syste=s fuel failures and secan generator Icakage 6.0 Refueling accident Mechanical damane-to fuel clerent during refueling inside containne 7.0 Spent fucI handling Mechanical danace to accident
-fuel ele =ent outside containcent 8.0 Accident initiation events Unce.maensated operating considered in design basis' reactivity changes, evaluation in the SAR startue accidents, rod
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withdrawal accidents, moderator dilution, cold water addition, loss c electrical load, stes= line failure, steam line Icakage
'* team generator tube failur ro'd ejection accider,c, vast gas decay tank ruuture, Ics of-coolant 9.0 Hypothetieni sequence of Not considered failures more severe than Class 8 t
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,y TABLE VI-2
SUMMARY
OF RADIOLOGICAL CONSEQUENCES OF POSTULATED ACCIDEh"fS Estimated Dose to Estimated Fraction population in of 10 CFR Part 20 50 mile radius, limit tt site boundarygj Class Event man-rem 1.0 Trivial Incidents 2/
2/
2.0 Small releases outside containment 2/
' 2_/
3.0 Radwaste. System f ailures 3.1 Equipment leakhge or mal-function 0.020 0.7 3.2 Release of waste gas storage tank contents.
0.078-2.9 3.3 Release of liquid waste storage contents 0.022 0.1 4.0 Fission products to primary system (BWR)
N. A.
N. A.
5.0 Fissica products to primary and sccendary systems (PUR) 5.1 Fuel cladding defects and stea= generator leaks 2/
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5.2 Off-design transients that induce fuel failure above-those expected and-steam
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gdnerator leak
<0.001
<0.1 5.3 Steam generator tube rupture 0.026
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6.0 Refueling accidents 6.1 Fuel bundle drop 0.004 0.2.
6.2 Heavy object drop onto fuel in core 0.072 2.6 I
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Estimated Does Estinated Fraction to population of 10 CFR Part 20 in 50 mile radius, site boundary j g
Class Event limit at man-rem 7.0 Spent fuel handling accident.
7.1 Fuel assembly drop in fuel rack 0.003 0.1 7.2 Heavy object drop-onto fuel rack 0.010 0.4 7.3 Fuel cask drop
.N. A.
N..A.
8.0 Accident initiation events considered in design basis evaluation in the SAR 8.1 Loss-of-Coolant Accidents Small Break-0.044
'2.9 Large Break 0.308
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69 8.1(a)
-Break in instrument line frem primary systen that penetrates the contair.=ent N. A.
N. A.
8.2(a)
Rod ejection accident (PWR) 0.030 6.9 8.2(b)
Rod drop accident (BWR)
N. A.
N. A.:
8.3(a)
Steanline breaks (PWR's cutside containment)
Small Break
<0.001
<0.1 Large Break
<0.001
<0.1 8.3(b)
Steamline break (BWR)
N. A.
N. A.
1/ Represents the calculated fraction of a whole body dose of'500 mrem, or the equivalent dose to an organ.
2/ These releases are expected to be in accord with proposed Appendix I for routine effluents (i.e., 5 mrem per year to an individual from either gaseous or liquid effluents).
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To rigsrtu31y settblith a rcelictic innual rick, thy calculat d doses in Table VI-2 would have to be multiplied by estimated probabilities.
The evente in. Classes 1 and 2 represent occurrences which are anticipated during plcnt operation and their consequences, which are very small, are considered within the framework of routine effluents from the plant.
Except for a limited amount o# fuel failures and sona steam generator leakage, the events in Classes 3 through. $
are not anticipated during plant operation; but events of this type could occur sometime during the 40 year plant lifetime. Accidente in Classes 6 and 7'and small accidents in Class 8 are of similar er lower probability.tban accidents in Classes 3 through 5 but are still possible.
The probsbility of occurrence of large Class 8 accidents 1
is very small.
Therefore, when the consequences indicated in Tabic VI-2 l
are weighted by probabilities, the environmental risk is very low.
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postulated occairences in Class 9 involve sequences of successive failures core severe than these required to be considered in the design bases of protectiln systems and engineered safety l features.
The conse-
. quencestcould be severe.
However, the probability of t'.teir occurrence is so scall that theirienviron= ental ~ risk is extremely low. Defense in der,th (=ultiple physical barriers), quality assurance for design, manufactur(
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and operation, cont 1nued surveillance and testing, and conservative design-I are all applied to provide and maintain the required'high degree of 1
assurance that potential accidencs in this class are, and will remain, e
u sufficiently snall. in probcbiligy that the environmental risk is extremely low.
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Table VI-2 indicated that the realistically estimated radiological consequences of the postulated accidents would result in exposures of an assumed individual at the site boundary to concentrations of radio--
active materials within or ecmparable to the Maximum Permissible Concentrations (MPC) of Appendix B, Table II,10 CFR Part 20.
Table VI-2 also shcws - that the esticated integrated exposure of the population within 50 miles of the plant from each postulated accident would be orders of magnitude smaller than that from naturally occurring radioactivity.
The exposure from naturally occurring radioactivity corresponds to approximately 3.,300 man-rem per year within a 10 mile. radius and approximately 46.900 man-rem per year within a 50 mile radius (based on a natural background of 125 mrem /yr.)
When considered with the probability of occurrence, the annual potential radiation exposure of the populaticn from all the postulated accidents 9 an even s= aller fraction of the exposure from natural background radiction and, in fcet, is well within naturally occurring variations in the natural background.
It is concluded frca the results of the realistic analysis that the environmental risks due to postulated radiological accidents are. exceedingly small.
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