ML20198F103
| ML20198F103 | |
| Person / Time | |
|---|---|
| Site: | Washington Public Power Supply System |
| Issue date: | 10/01/1974 |
| From: | Harold Denton US ATOMIC ENERGY COMMISSION (AEC) |
| To: | Muller D US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| CON-WNP-1216 NUDOCS 8605280413 | |
| Download: ML20198F103 (11) | |
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UNITED STATES
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ATOMIC ENERGY COMMISSION
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,!nres CCT 1 M4 D. Muller, Assistant Director for Environmental Projects, L REALISTIC ACCIDENT ASSESSMENT-WPPSS Nuclear Project No.1 & 4 PLAlff NAME: WPPSS Nuclear Project No. 1 and 4 LICENSING STAGE: CP DOCKET NUMBER: 50-460; 50-513 RESPONSIBLE BRANCH:
LWR 2-3, EP-3 REQUESTED COMPLETION DATE:
September 23, 1974 APPLICANTS RESPONSE DATE NECESSARY FOR NEXT ACTION PLANNED ON PROJECT: N/A DESCRIPTION OF RESPONSE:
Realistic Accident Assessment REVIEW STATUS: Accident Analysis Branch input complete Enclosed is the Realistic Accident section for the WPPSS Nucicar Project No.
1&4 Draft Environmental Statement prepared by H. !!. Fontecilla of the Accident Analysis Branch.
l b
Harold R. Denton, Assistant Director for Site Safety Directorate of Licensing
Enclosure:
As stated cc w/o encl.:,
i A. Ciambusso W. Mcdonald SS BC's A. Kenneke J. Panzarella cc w/cncl.:
S. llanauer F. Schroeder R. DeYoung B. Crimes A. Schwencer W. Regan T. Cox R. Loose E. Adansam L. Soffer
- 11. Fontecilla
1
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' ' " ' ~
f Environmental Impact of Postulated Accidents A high degree of protection against the occurrence of postulated accidents in the WPPSS Nuclear Project No. 1 & 4 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 will be considered in the Commission's Safety Evaluation.
Deviations that may occur are handled by protective systems to place and hold the plant in a safe condition. Notwiths'tanding this, the conservative postulate is made that serious accidents might occur, even though they may be extremely unlikely; and engineered safety feat.ures are installed to mitigate the consequences of those postulated events which are judged credible.
The probability of occurrence of accidents and he spectrum of their consequences to be considered from an envir nmental effects standpoint have been analyzed using best estimates of ' probabilities and realistic fission product release and transport assumptions.
For site evaluation in the Commission's safety review, extremely conservative assumptions are used for the purpose of comparing calculated doses resulting from a hypothetical release of fission products from the fuel against the 10 CFR Part 100 siting guidelines.
Realistically computed doses that would be received by the population and environment from the accidents which are postulated would be significantly less than those to be-presented in the Safety Evaluation.
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The Commission issued guidance to applicants on September 1, 1971, 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 Environmental Report dated July 10, 1974.
The applicant's report has been evaluated, using the standard accident assumptions and guid,ance issued as a proposed amendment to Appendix D of 10 CFR Part 50 by the Commission on December 1,1971. Nine classes of postulated accidents and occurrences ranging in severity from trivial to very serious were identified by the Commission.
In general, accidents in the high potential consequence end of the spectrum, pave a low occur-rence 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 I.
The examples selected are reasonably homogeneous I
in terms of probability within each class.
t Commission 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 II.
Estimates of the integrated exposure that might be delivered to the population within 50 miles of the site are also pre-sented in Table II.
The man-rem estimate was based on the projected Population within 50 miles of the site for the year 2010.
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.j To rigorously establish a realistic annual risk, the calculated
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l doses in Table II would havs to be multiplied by estimated probabili-
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i ties. The! events in Classda 1 and 2 represent occurrences which 5
l are anticipated during plant operations; and their consequences ~,
which are very small, are considered within the framework of routineefluentsfrodtheplant.
Except for a limited amount l
.'. of fuel failures and some steam generator leakage, the events in Classes 3 through 5 are not anticipated during plant operation; but even s. 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 ocdurrence of large Class 8 accidents is very small. Therefore, f,
when the consequences indicated in Table II are weighted by probabilities, the env'ironniental risk is very low. The postulated
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occurreiicis in Class 9 involve sequences of' successive failures f
more severe than thc,se required to be considered in the design -
bases of protection systems and engineered safety'fcatures. Their consequences could be severe. However, the p'robabili~ty of their
/.
occurrence is judged so small that their envifotoental risk is
~
extremely low.
Defense in Oepth (multiple physical barriers), qual-ity assurance for design, manufacture and operation, continued sur-veillance and testing, and conservative design are all applied to
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j provide and maintain a high degree of assurance that potential accidents in this class are.and will remain, sufficiently small in probability that the environmental rish is extremely low.
k The AEC is currently performing a study to assess core quantitatively these risks.
The initial results of these efforts were made available for comment.in draft form on August 20, 1974.
This study is called the Reactor Safety Study and is an effort to develop realistic data on the probabilitics and sequences of accidents in water-cooled power reactors, ':ba orber to improve the quantification of available knowledge related to nuclear reactor accident probabilities.
The Co= mission organized a special group of about 50 specialists under the direction jr 9>
of Professor Norman Rasmussen of MIT to conduct the study. The scopa.
of the study has been discussed with EPA and describcd in correspondence
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with EPA which has been placed in the AEC Public Document Room (letter, Doub to Dominick, dated June 5, 1973).
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As with all new information developed uhich might have an effect on the health and safety of the public, the results of these studies q
will be made public and will be cssessed on a timely basis uithin the Regulatory process on generic or specific bases as may be warranted.
Table II indicates that the realistically estimated radiological consequences of the postulated accidents would result in exposures
- " Reactor Safety Study:
An Assessment of Accident Risks in U. S.
Commercial Nuclear Power Plants, Draf t," UASil-1400,. August 1974.
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of an assumed individual at the site Loundary which are less than that i
which would result from a year's exposure to the Maximum Permissible I
Concentrations (MPC) of 10 CFR Part 20.
The table also shows the estimated integrated exposure of the population within 50 miles of the plant from each postulated accident. Any of these integrated exposures would be much smaller than that from naturally occurring radioactd vity. When considered with the probability of occurrence, dhe annual potential radiation exposure of the population from all the postulated accidents is an even smaller fraction of the exposure from natural background radiation and, in fact, is well within t
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 are 1
exceedingly small and need not be considered further.
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- .t, Table I.
Classification of Postulated Accidents and Occurrences Class AEbDescription Applicant's Examples i
1.
Trivial incidents Included in the evaluation of routine releases.
2.
qmall releases outside Included in the evaluation of routine containment releases.
3.
Fadioactive waste system Waste gas and liquid decay tank ailure failures.
4.
Fission products to pri-Not applicable.
j mary system (BWR) 5.
Fission products to pri-Fuel failures and steam generator mary and secondary systems leaks.
Steam generator tube rupture.
(PWR) 6.
Refueling accident Fuel bundle drop. Heavy object drop onto fuel in core.
7.
Spent fuel handling Fuel assembly drop in fuel storage accident
- pool, licavy object drop onto fuel rack.
Fuel cask drop.
8.
Accident initiation events Loss of coolant accident.
Steam Line considered in design-basis breaks.
Instrument line rupture.
evaluation in the Safety Rod ejection accident.
Analysis Report 9.
Hypothetical sequence of Not considered.
failures more severe than Class 8 f
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f TABLE II
SUMMARY
OF RADIOLOGICAL CONSEQUENCES OF POSTULATED ACCIDENTS Estimated Fraction Estimated Dose of 10 CFR Part 20 to Population in limit at 50 mile radius, boundary 71te 2
Class Event man-rem 1.0 Trivial Incidents 3/
3/
2.0 Small releases outside 3/
3/
containment 3.0 Radwaste System failures 3.1 Equipment leakage or mal-function 0.010 0.78 3.2 Release of waste gas storage taak contents 0.041 3.1 3.3 Release of liquid waste storage contents 0.001
<0.1 4.0 Fission products to primary N. A.
N. A.
system (BUR)
--1/
Thedosescalculatedasconsequencesofthd~postulatedaccidentsare based on airborne transport of radioactive materials resulting in both a direct and an inhalation dose.
Our evaluation of the accident doses assumes that the applicant's environmental monitoring program and appropriate additional monitoring (which could be initiated subsequent to a liquid release incident detected by in-plant monitoring) would detect the presence of radioactivity in the environment in a timely manner such that remedial action could be taken if necessary to limit exposure from other potential pathways to man.
--2/
Represents the calculated fraction of a whole body dose of 500 mrem, or the equivalent dose to an organ.
--3/
These releases are expected to be in accord with proposed Appendix I for routine ef fluents (i.e., 5 mrem per year to the whole body from either gaseous or liquid effluents).
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Estimated Fraction Estimated Dose H
of 10 CFR Part 20 to population limit ac in 50 mile boundary 71te Class Event 2
_ radius, man-rem 5.0 Fission products to primary and secondary systems (PWR) 5.1 Fuel cladding defects and 3/
steam generator leaks 3/
5.2 off-design transients that induce fuel failure above those expected and steam generator leak
<0.001
<0.1 5.3 Steam generator tube rupture 0.014 1.0 6.0 Refueling accidents 6.1 Fuel bundle drop 0.002 0.16
' 6.2 Heavy object drop onto fuel in core 0.038 2.8 7.0 Spent fuel handling accident 7.1 Fuel assembly drop in fuel rack
.0.001 7.2 Heavy object drop onto 0.10 fuel rack l0.005 0.41 7.3 Fuel cask drop
'0.033-2.5 8.0 Accident initiation events considered in' design basis evaluation in the SAR 8.1 Loss-of-Coolant Accidents Small Break 0.025 3.1 Large Break 0.22 110 r
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TABLE II - Continued Estimated Fraction Estimated Dose of 10 CFR Part 20 to population limit at in 50 mile boundary 71te 2
Class Event radius, man-rem 8.1(a)
Break in instrument line from N. A.
N. A.
I primary system that penetrates the containment 8.2(a)
Rod ejection accident (PWR) 0'.022 11 8.2(b)
Rod drop accident (HRR)
N. ' A..
N. A.
8.3(a)
Steamline breaks (PWR's outside containment)
Small Break
<0.001
<0.1 Large Break
<0.001:
<0.1 8.3(b)
Steamline break (BUR)
N. A.
N. A.
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