ML20198F779

Forwards Realistic Accident Section of Des

ML20198F779
Person / Time
Site:	Columbia
Issue date:	08/02/1972
From:	Harold Denton US ATOMIC ENERGY COMMISSION (AEC)
To:	Muller D US ATOMIC ENERGY COMMISSION (AEC)
References
CON-WNP-0909, CON-WNP-909 NUDOCS 8605290087
Download: ML20198F779 (8)

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1 AUG 2 1372 ENVIRON, FILE (NEPA)

D. b iler, Assistant Director for Environmental Projects. L HANFORD ho. 2 REALISTIC ACCIDENT ASSESSMENI PLANT NAME: Hanford No. 2 Nuclear Power Plant LICENSING STAGE: CP DOCKET NUMBER: 50-397 RESPONSIBLE BRANCH: GCR Branch REQUESTED COMPLETION DATE: August 1, 1972 APPLICANTS RESPONSE DATE NECESSARY FOR NEXT ACTION PLANNED ON PROJECT: N/A DESCRIPTION OF RESPONSE: Realistic Accident Assessment REVIEW STATUS: Completed Enclosed is the Realistic Accident section for the Hanford No. 2 draf t Environmental Statement prepared by S. Miner, GOR Branch and K. Hurphy of the Accident Analysis Branch.

Original signed by II. It Denton Harold R. Denton, Assistant Director for Site Safety Directorate of Licensing

Enclosure:

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E!NIRO:"! ENTAL DIPACT OF ACCIDENTS Protection against the occurrence of postulated design basis accidents in the !!anford No. 2 Nuclear Power plant is provided through the defense in depth concept of design, nanufacture, 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 systcm.

These aspects are being considered in the Staff's safety evaluation for the llanford Ho. 2 facility. Off-design conditions that uay occur are limited by protection systems which place and hold the power plant in a safe condition. Notuithstanding this, the conservative postulate is nade that serious accidents might occur, even though unlikely; and engineered safety features are installed to mitigate the consequcnces of these postulated events.

The probability of occurrence of accidents and the spectrum of their consequences to be considered from an environmental effects standpoint have been analyzed using estimates of probabilities and realistic fission product release and transport assurptions. For site evaluation in the Staff safety review, extremely conservative assumptions were used for the purpose of evaluating the adequacy of engineered safety features and fer comparing calculated doses resulting from a hypothetical release of fission products from the fuel against the 10 CFR Part 100 siting guidelince.

The computed doses that would be received by the population and environment

from actual accidents would be significantly less than those to be presented in the Staff Safety Evaluation. 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 Amendments No. 1, 2 and 4, dated Jan. 14, 1972,

!! arch 24,1972 and July 5, 1972.

The Applicant's report has been evaluated, using the standard accidcnt assumptions and guidance issued by the Commission as a proposed amendment to Appendix D of 10 CFR Part 50 on December 1, 1971 (Federal Register, Vol.

36, Co. 231). Nine classes of postulated accidents and occurrences ranging in severity from trivial to very serious have been identified by the Commission. In general, accidents in the high potential consequence end of the spectrum have a very lou occurrence rate; and those on the low potential consequence end are characterized by a higher occurrence rate.

The Applicant's examples for these classes of accidents are shown in Table 1. The examples given are reasonably homogeneous in terms of probability within each class.

t Certain assumptions made by tNe 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 environmenta risk.

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Staff estimates of the doses 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 in man-rem that might be delivered to the population within 50 miles of the site are also presented in Table II. These man-rem estimates were based on the projected population (about 214,000) around the site for the year 1980.

To rigorously establish a realistic annual risk, the calculated doses in Table II would have to be rultiplied by estimated probabilities. The events in Classes 1 and 2 reprecent occurrences which are anticipated during plant operation and their consequences, which are very small, are considered within the framework of routine efflucats from the plant.

Except f or a limited amount of fuel f ailures, 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 Clasres 6 and 7 and small accidents la Class 8 are of similar or louer probability than accidents in Class 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 ,

probabilities, the environmental risk is very low. The postulated occurrences in Class 9 involve failures more severe than those required to be considered for the design basis for protective systems and engineered safety features (i.e., Class 8 accidents). These consequences could be ,

severe; however, the probability of their occurrence is so small that their t

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environmental risk is extremely low. Defense in depth (multiple physiec1 barriers), quality arsurance for design, manufacture, and operation, continued surveillance and testing, and conservative design are 411 applied to provide and maintain the required high degree of assurance that potential accidents in this class are, and will rcmain, sufficier.tly small in probability that the environmental risk in extrencly low.

The information given in Table II indicates that the realistically esticated radiological conocquences cf the postulated accidcnts vould result in exposurcs of an assuned individual at the site boundary to concentrations of radioactive t.:aterials within the !hxinun Permissible Concentrations (l!PC) listed in Tabic 11 of 10 CFr. Part 20. The tabulated information also shows.

that the estimated integrated exposure of the population within .50 miles of the plant f ron each pontuinted accideat vould be rauch smaller than that f ro a the naturally occurring radioactivity. The exposure frem naturally occurring radioactivity corresponds to approximately 82 man-ren per year within 10 miles and approximately 33,000 man-rem /yr within 50 milen of the site. These estimates are based on a natural background Icvel of 0.155 ren/yr. When considered within the probability of occurrence, the annual pottntial radiation exposure of the population from all the postulated accidents is an even smaller fraction of the exposure f rom natural background radiation and, in f act, is well within naturally occurring variations in the natural background. It in coacluded from the results of the realistic analysia that the environmental risks due to postulated radiologJcal accidents at the llanford No. 2 Nuclear Power plant are exceedingly small and need not be considered further.

I TABLE I CLASSIFICATION OF POSTU11TED ACCIDENTS AND OCCURRENCES AEC DESCRIPTION APPLICANTS EXAMPLE (S) 1.0 1rivial Incidenta None 2.0 Hisc. small releases outside Reactor Coolant leaks (below or just Containment above allovable tech spec limits) outside primary containment or reactor l

building 3.0 Raduaste System railures Any singic Equipment Failure or any singic operator error 4.0 Event s that Release Radio- Fuel defects during transients outside activity into the Primary the normal range of plant variables but f System within expected range of protective equipment and other parameter operation 5.0 Event s that release radio- Primary Coolant loop to auxil'Iary cool-activity into secondary system ing system secondary side of heet ex-changer leak 6.0 Refueling Accjdents inside Dropping of fuel assembly on reactor Containment core, spent fuel rack or against pool boundary Dropping of spent fuel shipping cask in pool or outside pool 7.0 Accidents to Spent Fuel Transportation incident involving spent and new fuel Shipnent on site but outside Primary Containment or reactor building 8.0 Accid en t Initiation Events a. Reactivity Transient considered in Design-Basis evaluat ton in the Safety

b. Losa of Reactor Coolant inside or Aaalysis Report outside primary containment

c. Offgas holdup failure or failure of liquid radwaste tank 9.0 Hypothetical Sequences of None failurcs more severe than Class 8

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TABLE 11 SUW1ARY OF RADIOLOGICAL CONSEQUENCES OF POSTULATED ACCIDENTS Estimated Estimated Fraction of 10 CFR Dose to populatio-Part 20 Limit y within 50 mile Event At Site' Boundary f radius, man-rem Class 1.0 Trivial incidents 2/ 2/

2.0 Small releases outside 2/ 2/

3.0 Radwaste system failures 3.1 Equipment leakage or malfunction 0.019 0.8 3.2 Releasc of waste gas storage tank contents 0.074 3.2 3.3 Release of liquid waste storage tank contents <.001 <0.1 4.0 Fission products to primary system (BWR) 4.1 Fuel cladding def ects 2/ 2/

4.2 off-design transients that induce fuel failures _above those expected 0.001 0.1 5.0 Fission products to primary and secondary systems (PWR) N. A. N. A.

6.0 Refueling accidents 6.1 Fuel assembly drop into core <.001 <0.1 6.2 Heavy object drop onto fuel in core 0.003 0.1 7.0 Spent fuel handling accident 7.1 Fuel assembly drop in fuel storage pool 0.001 <0.1 7.2 Heavy object drop onto fuel rack 0.001 0.1 7.3 Fuel cask drop 0.028 1.2 i

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Estimated Estimated Fraction of 10 CFR Dose to populatic Part 20 Limit within 50 mile  ;

Class Event At Site Boundary 77 radius, man-rem 8.0 Accident initiation events considered in design basis evaluation in the .

safety analysis report 8.1 Loss-of-coolant accidents inside containment Small break <0.001 <0.1 Large break' O.007 2.7

8. l(a) Break in instrument line outside reactor building <0.001 <0.1 8.2 (a) Rod Ejection Accident (PWR) N. A. N. A.

8. 2 (b) Rod drop accident (BWR) 0.001 0.1 8.3(a) Steamline break (PWR-outside

, containment) N. A. ,N. A.

8. 3 (b) Steamline breaks (BWR)

Small Break' O.001 <0.1 Large Break- 0.003 0.1 1/ Represents the calculated uhole body dose as a fraction of 500 mrem (or the equivalent dos'e to an organ).

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 arem/yr to an individual from either gasenns or liquid effluent).

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