ML19343B854

Supplement to Draft Environmental Statement Related to the Operation of San Onofre Nuclear Generating Station,Units 2 & 3

ML19343B854
Person / Time
Site:	San Onofre
Issue date:	01/31/1981
From:	Office of Nuclear Reactor Regulation
To:
References
NUREG-0490, NUREG-0490-S01, NUREG-490, NUREG-490-S1, NUDOCS 8101290455
Download: ML19343B854 (37)

Text

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U.S. NUCLEAR CECUL ATO3Y COMMISSION BELIOGRAPHIC DATA SHEET NUREG-0490, Draft Supplement

• TITLE AND SUBT8TLE (Add Volume No. of appreersate)

2. lleave blankl Supplement to Draft Environmental Statement related to the Op; ration of San Onofre Nuclear Generating Station, Units 2

3. REC:PIENT'S ACCESSION NO.

and 3, Docket Nos. 50-361, 50-362

7. AUTHOR (S)

5. DATE REPORT COMPLETED l YEAR MONTH January 1981

9. PERFORMING ORGANIZATION NAME AND MAILING ADDRESS (include Zip Code)

DATE REPORT ISSUED MONTH l YEAR Office of Nuclear Reactor Regulation January 1981 U. S. Nuclear Regulatory Commission

s. (t,,ve be,nk)

Washington, D. C. 20555

8. (Leave blank)

12. SPONSORING ORGANIZATION NAME AND MAILING ADDRESS (/nclude Zip Code)

10. PROJECT /T ASK/ WORK UNIT NO.

same as above

11. CONTRACT NO.

13. TYPE OF REPORT PE RIOD COVE RE D //nc'usive dams)

Supplement to Draft Environmental Statement

15. SUPPLEMENTARY NOTES

14. (teave b/ek)

Docket Nos. 50-361 and 50-369

16. ABSTR ACT Q00 words'or less)

This is an addendum to thesummary and conclusions of the original Draf t Environmental Statement issued previously in November 1978. This Supplement relates to accident considerations related to the proposed operation of the San Onofre Nuclear Generating Station, Units 2 and 3, in San Diego County, California. The Supplement is being provided to Federal and State agencies for review and comment.

Comments are due by March 9,1981.

The Statement is available for public inspection at the Commission's Public Document Room in Washington, D.C. and the Mission Viejo Branch Library, 24851 Chrisanta Drive, Mission Viejo, California.

Comments on the Supplement from the public should be eddressed to the U.S. Nuclear Regulatory Comm5 ion, Washington, D.C.

20555, Attention:

Director, Division of Licensing.

Requests ft. copies of the Supplement should be addressed to the same.

17. KEY WORDS AND DOCUMENT ANALYSIS 17a. DESCRIPTORS 9

g/d/ M6 45C 17b. IDENTIFIERS /OPEN-ENDED TERMS

18. AVAILABILITY STATEMENT

19. SE CURITY CLASS (This reporf)

21. NO. OF PAGES unclass1fied Unlimited 20 SECURITY CLASS (Thss page)

22. P RICE S

N RC F T'EM 335 (7-77)

NUREG4190 Supplement to Draft Environmental Statement related to the operation of San Onofre Nuclear Generating Station, Units 2 and 3 Docket Nos. 50-361 and 50-362 Southern California Edison Company San Diego Gas & Electric Company The City of Riverside The City of Anaheim U.S. Nuclear Regulatory Commission Office of Nuclear Reactor Regulation January 1981 i

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l Summary and Conclusions This Supplement to the Draft Environmental Statement Related to Operation of San Onofre Nuclear Generating Station Unit No. 2 and 3, issued in November 1978, was prepared by the U.S. Nuclear Regulatory Comission, Office of Nuclear Reactor Regulation (the staff) in accordance with 10 CFR 51.23. The purpose of this supplement is to evaluate the site-specific environmental impacts attributable to plant-specific accident sequences that lead to releases of radiation and/or radioactive materials, including sequences that can rssult in inadequate cooling of reactor fuel and melting of the reactor core.

1.

The action is administrative.

2.

The proposed action is the issuance of Operating Licenses jointly to the Southern California Edison Company (SCE) and the San Diego Gas and Electric Company (SDG&E) (the applicant) for the startup and operation of Units 2 and 3 of the San Onofre Nuclear Generating Station, adjacent to San Onofre Unit 1, located on the Pacific coast in the State of California, County of San Diego (Docket Nos. 50-361 and 50-362).

Both units will employ pressurized water reactors to produce up to 3410 thermal megawatts (MWt) each.

Steam turbine generators will use this heat to provide a net power output of up to 1106 electrical megawatts (MWe) each. The exhaust steam will be cooled by once-through flow of water pumped from the Pacific Ocean and returned to it through a diffuser-type system.

3.

Summary of environmental impact and adverse effects:

The environmental impacts that have been considered include potential radiation exposures to individuals and to the population as a whole, the risk of health effects that such exposures could entail, and the potential economic and societal consequences of accidental contamination of the environment. These fepacts could be severe for specific accidents postulated, but the likelihood of their occurrence is judged to be acceptably remote.

4.

The following Federal and State agencies were asked to comment on the Supplement to the Draft Environmental Statement:

Department of Agriculture Department of the Army (Corps of Engineers)

Department of Commerce Department of Energy Department of the Interior Department of Health, Education and Welfare Department of Housing and Urban Development Department of Transportation Environmental Protection Agency Federal Energy Regulatory Commission Advisory Council on Historic Preservation California Department of Health (Water Pollution Control Commission, Air Pollution Control Commission, Occupational Health Office)

California Department of Natural Resources California Department of Parks and Recreation 5.

This Supplement is being made available to the public, to the Council on Environmental Quality, and to other specified agencies in January 1981.

6.

On the basis of the analysis set forth in this Supplement, the conclusions reached in the Draft Environmental Statement remain unchanged.

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TABLE OF CONTENTS Page i

111

SUMMARY

AND CONCLUSIDNS........

vi FOREWORO............................

1-1 1.

INTRODUCTION..

7.

ENVIRONMENTAL IMPACT OF POSTULATED ACCIDENTS..

7-1 7.1 PLANT ACCIDENTS 7-1 7.1.1 General Characteristics of Accidents 7-1 1

7.1.1.1 Fission Product Characteristics.........

7-1 7.1.1.2 Exposure Pathways..

7-2 7.1.1. 3 Health Effects...................

7-2 7.1.1. 4 Health Effects Avoidance 7-3 7.1. 2 Accident Experience and Observed Impacts 7-3 7-4 7.1.3 Nitigation of Accident Consequences..

7.1. 3.1 Design Features........

7-4 7.1.3.2 Site Features........

7-5 7-6 7.1.3.3 Emergency Preparedness'.

7.1. 4 Accident Risk and Impact Assessment......

7-6 7.1. 4.1 Design Basis Accidents.....,......................

7-6 7.1.4.2 Probabilistic Assessment of Severe Accidents.............

7-7 7.1. 4. 3 Dose and Health Impacts of Atmospheric Releases......

7-8 7-9 7.1.4.4 Economic and Societal Impacts....

7.1. 4. 5 Releases to Groundwater 7-9 7.1.4.6 Risk Considerations 7-10 7.1.4.7 Uncertainties...................................................

7-12 7.1. 5 Conclusions..............................

7-13 Re fe re nce s fo r Se c ti on 7..................................................................... 7-28

10. CONCLUSIONS AND RE-EVALUATE D BENEFIT-COST B ALANCE........................................... 10-1 T

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LIST OF TABLES AND FIGURES 1

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- Table 7.1.4 Approximate Radiation Doses from Design Basis Accidents......

7-14 Table 7.1.4-2 Sur,ary of Atmospheric Release Categories Representing Hypothetical Accidents in a PWR..

7-15 Table 7.1.4-3 Activity of Radionuclides in the San Onofre Reactor Core at 3560 MWt.

7-16 Ttble 7.1.4-4 Summary of Environmental Impacts and Probabilities....

7-18 I-Table 7.1.4-5 Annual Average Values of Envirormental Risks Due to Accidents 7-19 Fig. 7.1.4-1 Schematic Outline of Consecuence Model.........

7-20 Fig. 7.1.4-2 Probability DistriLutions of Individual Dose Impacts...

7-21 4

Fig. 7.1.4-3 Probability Distributions of Population Exposures..

7-22 Fig. 7.1.4-4 Probability Distribution of Acute Fatalities................

7-23 Fig. 7.1.4-5 Probability Distributions of Latent Cancer Fatalities......

7-24 Fig. 7.1.4-6 Probability Distribution of Cost of Offsite Mitigative Measures....

7-25

' Fig. 7.1.4-7 Annualized Risk to Individuals vs. Distance...............

7-26 Fig. 7.1.4-8

. Relative Directional Risk to Individuals...........

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I FOREWORD This Supplement to the Draf t Environmental Statement was prepared by the U.S. Nuclear Regulatory Commission (NRC), Office of Nuclear Reactor Regulation (staff), in accordance with the Commission's regulation, 10 CFR Part 51, which implements the requirements of the National Environmental Policy Act (NEPA) of 1969.

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The purpose of this supplement is to identify and evaluate the site-specific environmental impacts attributable to. accident sequences that lead to releases of radiation and/or radioactive materials, including sequences that can result in inadequate cooling of reactor fuel and to melting of the reactor core.

Ccpies of this supplement are being sent to Federal, State, and local agencies for comment. Interested per-sons are invited to comment. The period provided for receipt of such comments will conclude 45 days after The commen's received will i

publication in the Federal Reaister of a notice of the supplement's availability.

b3 considered by the NRC in the preparation of the Final Environmental Statement.

Comments should be addressed to the Office of Nuclear Reactor Regulation. U.S. Nuclear Regulatory Commission, Washington, D.C.

20555, Attention: Director, Division of Licensing. If there are any questions regarding the contents of this statement, the NRC. Project Nanager, Mr. Dino C. Scaletti, may be contacted on 301-492-8443, Single copies of this Supplement to the Draft Environmental Statement related to the operation of San Onofre 1

Nuclear Station Units No. I and 2 can be obtained, free of charge, by written request to the Division of Technical Information and Document Control, U.S. Nuclear Regulatory Commission, Washington, D.C.

20555. Single copies

'of the Draf t Environmental Statement will also be supplied on request.

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i List of Contributors Name Organization S. Acharya U.S. Nuclear Regulatory Commission R. Codell U.S. Nuclear Regulatory Commission C. M. Ferrell U.S. Nuclear Regulatory Commission R. L. Gotchy U.S. Nuclear Regulatory Commission R. W. Houston U.S. Nuclear Regulatory Commission J. A. Mitchell U.S. Nuclear Regulatory Commission D. Nash U.S. Nuclear Regulatory Commission H. Schierling U.S. Nuclear Regulatory Commission L. Soffer U.S. Nuclear Regulatory Commission vil

m 7.

ENVIRONMENTAL IMPACT OF POSTULATED ACCIDENTS 7.1 PLANT ACCIDENTS The staff has considered the potential radiological impacts on the environment of possible accidents at the Sen Onofre Nuclear Generating Station Units 2 and 3 in accordance with a Statement of Interim Policy published by the Nuclear Regulatory Commission on June 13, 1980.

The following discussion reflects these considera-tions and conclusions.

The first section deals with general characteristics of nuclear power plant accidents including a brief summary of safety measures to minimize the probability of their occurrence and to mitigate their consequences if they should occur. Also described are the important properties of radioactive materials and the pathways by which they could be transported to become environmental hazards. Potential adverse health effects and impacts on society associated with actions to avoid such health effects are also identified.

Next, actual experience with nuclear power plant accidents and their observed health effects and other societal impacts are then described. This is followed by a summary review of safety features of the San Onofre Units 2 and 3 facilities and of the site that act to mitigate the consequences of accidents.

The results of calculations of the potential consequences of accidents that have been postulated in the design basis are then given. Also described are the results of calculations for the San Onofre site using probabil-Istic methods to estimate the possible impacts and the risks associated with severe accident sequences of exceedingly low probability of occurrence.

7.1.1. General Characteristics of Accidents i

The term accident, as used in this section, refers to any unintentional event not addressed in Section 5.5 that results in a release of radioactive materials into the environment. The predominant focus, therefore, is on events hat can lead to releast. substantially in excess of permissible limits for normal operation.

Such limits are specified in the Commission's regulations at 10 CFR Part 20 and 10 CFR Part 50, Appendix I.

There are several features which combine to reduce the risk associated with accidents at nuclear power plants.

Safety features in the design, construction, and operation comprising the first line of defense are to a very large extent devoted to the prevention of the release of these radioactive materials from their normal places of confinement within the plant. There are also a number of additional lines of defenses that are designed to mitigate the consequences of failures in the first line. Descriptions of these features for the San Onofre Units 2 and 3 plant may be found in the applicant's Final Safety Analysis Report, and in the staff's forth-coming Safety Evaluation Report. The most important mitigative features are described in Section 7.1.3.1 below.

These safety features are designed taking into consideration the specific locations of radioactive materials within the plant, their amounts, their nuclear, physical, and chemical properties, and their relative tendency to be transported into and for creating biological hazards in the environment.

7.1.1.1 Fission Product Characteristics n

By far the largest inventory of radioactive material in a nuclear power plant is produced as a byproduct of the fission process and is located in the uranium oxide fuel pellets in the reactor core in the form of fission products.

These pellets are contained in the fuel rods which make up the fuel assemblies. During periodic refueling shutdowns, the assemblies containing these fuel pellets are transferred to a spent fuel storage pool so that the second largest inventory of radicactive material is located in this storage area. Much smaller inventories of radioactive materials are also normally present in the water that circulates in the primary coolant system and in the systems used to process gaseous and liquid radioactive wastes in the plant.

These radioactive materials exist in a variety of physical and chemical forms. Their potential for dispersion into the e,vironment is dependent not only on mechanical forces that might physically transport them, but also upon their inherent properties, particularly their volatility. The majority of these materials exist as non-volatile solids over a wide range of temperatures. Some, however, are relatively volatile solids and a few are gueous in nature. These characterist,1cs have a significant bearing upon the assessment of the environ-mental radiological impact of accidents.

The gaseous materials include radioactive forms of the chwdally inert noble gases krypton and xenon. These hive the highest potential for release into the atmosphere. If a reactor accident were to occur involving 7-1

degradation of the fuel cladding, the release of substantial quantities of these radioactive gases from the fuel is a virtual certainty. Such accidents are very low frequency but credible events (cf Section 7.1.2).

It is for this reason that the safety analysis of each nuclear power plant analyzes a hypothetical design basis accident that postulates the release of the entire contained inventory of radioactive noble gases from the fuel into the containment structure. If further released to the environment as a possible result of failure of safety features, the hazard to individuals from these noble gases would arise predominantly through the external gamma radiation from the airborne plume. The reactor containment structure is designed to minimize this type of release.

Radioactive forms of iodine are form *d in substantial quantities in the fuel by the fission process and in some chemical forms may be quite volatile. For this reason, they have traditionally been regarded as having a relatively high potential for release from the fuel. The chemical forms in which the fission product radio-iodines are found are generally solid materials at room temperature, however, so that they have a strong tendency to condense (or " plate out") upon cooler surfaces. In addition, most of the iodine compounds ire quite soluble in, or chemically reactive with, water. Although these properties do not inhibit the release of radiciodines from degraded fuel, they do act to mitigate the release from containment structures that have large internal surface areas and that contain large quantities of water as a result of an accident. The same properties affect the behavior of radioiodines that may " escape" into the atmosphere. Thus, if rainfall occurs during a release, or if there is moisture on exposed surfaces, e.g., dew, the radiolodines will show a strong tendency to be absorbed by the moisture. Because of radiolodine's relatively high solubility and distinct radiological hazard, its potential for release to the atmosphere has also been reduced by the use of special containment spray systems. If released to the environment, the principal radiological hazard associated with the radiciodines is ingestion into the human body and subsequent concentration in the thyroid gland.

Other radioactive materials formed during the operation of a nuclear power plant have lower volatilities and therefore, by comparison with the noble gases and iodine, a much smaller tendency to escape from degraded fuel unless the temperature of the fuel becomes quite high. By the same token, such materials, if they escape by volatilization from the fuel, tend to condense quite rapidly to solid form again when transported to a lower temperature region and/or dissolve in water when present. The former mechanism can have the result of pro-ducing some solid particles of sufficiently small size to be carried some distance by a moving stream of gas or air. If such particulate materials are dispersed into the atmosphere as a result of failure of the con-tainment barrier, they will tend to be carried downwind and deposit on surface features by gravitational settling or by precipitation (fallout),'here they will become " contamination" hazards in the environment.

w All of these radioactive materials exhibit the property of radioactive decay with characteristic half-lives ranging from fractions of a second to many days or years (cf. Table 7.1.4-3).

Many of them decay through a sequence or chain of decay processes and all eventually become stable (nonradioactive) materials. The radia-tion emitted during these decay processes is the reason that they are hazardous materials.

7.1.1.2 Exposure Pathways The radiation exposure (hazard) to individuals is determined by their proximity to the radioactive material, the duration of exposure, and factors that act to shield the individual from the radiation. Pathways for the transport of radiation and radioactive materials that lead to radiation exposure hazards to humans are generally the same for accidental as for " normal" releases. These are depicted in Section 5, Figure 5.23.

There are two additional possible pathways that could be significant for accident releases that are not shown in Figure 5.23.

One of these is the fallout onto open bodies of water of radioactivity initially carried in the air. The second would be unique to an accident that results in temperatures inside the reactor core sufficiently high to cause melting and subsequent penetration of the basemat underlying the reactor by the molten core debris. This creates the potential for the release of radioactive material into the hydrosphere through contact with ground water. These pathways may lead to external exposure to radiation, and to internal

. exposures if radioactivity is inhaled, or inqested from contaminated food or water.

It is characteristic of these pathways that during the transport of radioactive material by wind or by water, the material tends to spread and disperse, like a plume of smoke from a smokestack, becoming less concentrated in larger volumes of air or water. The result of these natural processes is to lessen the intensity of exposure to individuals downvind or downstream of the point of release, but they also tend to increase the number who may be exposed. Fo, a release into the atmosphere, the degree to which dispersion reduces the concentration in the plume at any downwind point is governed by the turbulence characteristics of the atmosphere which vary considerably with time and from place to place. This fact, taken in conjunction with the variability of wind direction and the presence or absence of precipitation, means that accident consequences are very much dependent upon the weather conditions existing at the time.

7.1.1.3 Health Effects The cause and effect relationships between radiation exposure and adverse health effects are quite complex ( a) but they have been more exhaustively studied than any other environmental contaminant.

Whole-body radiation exposure resulting in a dose greater than about 25 rem over a short period of time (hours) is necessary before any physiological effects to an individual are clinically detectable. Doses about ten to 7-2

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twenty times larger, also received over a relatively short period of time (hours to a few days), can be expected to cause some fatal injuries. At the sevtre, but extremely low probability end of the accident specttum, exposures of these magnitudes are theoretically possible for persons in the close proximity of such accidents if measures are not or cannot be taken to previde protection, e.g., by sheltering or evacuation.

Lower levels of exposures may also constitute a health risk, but the ability to define a direct cause and effect relationship between any given health effect and a known exposure to radiation is difficult given the backdrop of the many other possible reasons why a particular ef fect is observed in a specific individual.

For this reason, it is necessary to assess such effects on a statistical basis. Such effects include car:er and genetic changes in future generations after exposure of a prospective parent. The health consequentes model currently being used is based on the 1972 BEIR Report of the National Academy of Sciences.(4,5) gg assumes exposures of fetuses (in utero) will result in excess cancer risk beginning at birth and ending at age 10. For exposures af ter birth (any age), excess leukemia risk is assumed to begin 2 years af ter exposure and end 25 years later or at the end of life expectancy (whichever comes first).

For all other cancers except those of the bone and thyroid, no excess risk is assumed for exposures before the age of 10. For exposures af ter the age of 10, no excess cancers (except bone) are expected for 15 years af ter exposure, and are assumed to remain elevated for 30 years or to the end of life expectancy.

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In the case of bone and thyroid cancer, excess risk is assumed to begin 10 years af ter exposure and end l

30 years later or at the end of life expectancy (whichever comes first).

Most authorities are in agreement that a reasV&Ue and probably conservative estimate of the statistical relationship between low levels of radiation wposure to a large number of people is within the range of about 10 to 500 potential cancer deaths (although Zero is not excluded by the data) per million person-rem.

The range comes from the latest NAS BEIR III Report (1980) which also indicates a probable value of about 150. This value is virtually identical to the value of about 140 used in the current NRC health ef fects s)odel s.

In addition, approximately 220 genetic changes per million person-rem would be projected by BEIR III over succeeding generations. That also compares well with the value of about 260 per million person-rem currently used by the NRC staff.

7.1.1.4. Health Ef fects Avoidance Radiation hazards in the environment tend to disappear by the natural process of radioactive decay. Where the decay process is a slow one, however, and where the material becomes relatively fixed in its location as an environmental contaminant (e.g., in soll), the hazard can continue to exist for a relatively long period of time--months, years, or even decades. Thus, a possible consequential environmental societal impact of severe accidents is the avoidance of the health hazard rather than the health hazard itself, by restrictions 4

on the use of the contaminated property or contaminated foodstuffs, milk, and drinking water. The potential a

economic impacts that this can cause are discussed below.

7.1. 2 Accident Experience and Observed Impacts l

The evidence of accident frequency and impacts in the past is a useful indicator of future probabilities and impacts. As of mid-1980, there were 69 commercial nuclear power reactor units licensed for operation in the United States at 48 sites with power ger.erating capacities ranging from 50 to 1130 megawatts electric (MWe).

(The San Onofre Units 2 and 3 are designed for 1140 MWe each.) The combined experience with these units represents approximately 500 reactor years of operation over an elapsed time of about 20 years.- Accidents have occurred at several of these facilities.I ) Some of these have resulted in releases of radioactive material to the environment, ranging from very small fractions of a curie to a few million curies. None is known to have caused any radiation injury or f atality to any member of the public, nor any significant individual or collective public radiation exposure, nor any significant contamination of the environment.

This experience base is not large enough to permit a reliable quantitative statistical inference. It does.

7 however, suggest that significant environmental impacts due to accidents are _very unlikely to occur over time periods of a few decades.

Melting or severe degradation of reactor fuel has occurred in only one of these 69 operating units, during the accident at Three Mile Island - Unit 2 (TMI-2) on March 28, 1979. In addition to the release of a few

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nillion curies of xenon-133, it has been estimated that approximately 15 curies of radiolodine was also released to the environment at TMI-2. 0 This amount represents an extremely minute fraction of the total radiciodine inventory present in the reactor at the time of the accident. No other radioactive fission products were released in measurable quantity.

f It has been estimated that the mm.imum cumulative offsite radiation dose to an individual was less than 100 millirem.(7,8) The total population exposure has been estimated to be in the range from about 1000 to 3000 person-rem. This exposure could produce between none and one additional fatal cancer over the lifetime of the population. The same population receives each year from natural background radiation about 240,000 person-rem and approximately a half-million cancers are expected to develop in this group over its 1

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i lifetime.U,8) Trace quantities (barely above the limit of detectability) of radioiodine were found in a few samples of milk produced in the area. No uther food or water supplies were impacted.

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"The major health effect of the accident appears to have been on the mental health of the people living in the region of Three Mlle Island and the workers at TMI. There was immediate, short-lived mental distress produced by the accident among certain groups of the general population living witH n 20 miles of TMI. The highest levels of distress were found among adults (a) living within 5 miles of TMI, or (b) with preschool children; and among teenagers (a) living within 5 miles of TMI, (b) with preschool siblings, or (c) whose i

families left the area. Workers at TMI experienced more distress than workers at another plant studied for i

comparison purposes. This distress was higher among the nonsupervisory employees and continued in the months following the accident."(0}

4 Accidents at nuclear power plants have also caused occupational injuries and a few fatalities but none attri-i buted to radiation exposure. Individual worker exposures have ranged up to about 4 rems as a direct conse-quence of accidents, but the collective worker exposure levels (person-rem) are a small fraction of the exposures experienced during normal routine operations that average about 500 person-rem per reactor year.

Accidents have also occurred at other nuclear reactor facilities in the United States and in other countries.(6)

Due to inherent difference s in design, construction, operation, and purpose of most of these other facilities, i

their accident record has only indirect relevance to current nuclear power plants. Melting of reactor fuel occurred in at least seven of these accidents, including the one in 1966 at the Enrico Fermi Atomic Power Plant Unit 1.

This was a sodium-cooled fast breeder demonstration reactor designed to generate 61 MWe.

The damages were repaired and the reactor reached full power four years following the accident. It operated successfully and completed its mission in 1973. This accident did not release any radioactivity to the environment.

A reactor accident in 1957 at Windscale, England released a significant quantity of radiciodine, approximately 20,000 curies, to the environment. This reactor, which was not operated to generate electricity, used air rather than water to cool the uranium fuel. During a special operation to heat the large amount of graphite in this reactor, the fuel overheated and radiolodine and noble gases were released directly to the atmosphere i

i from a 405-foot stack. Milk produced in a 200-square mile area around the facility was impounded for up to 44 days. This kind of accident cannot occur in a reactor like San Onofre, however, because of its water-cooled l

design.

7.1.3 Mitigation of Accident Consequences The Nuclear Regulatory Commission is conducting a safety evaluation of the application to operate San Onofre Units 2 and 3.

Although this evaluation will contain more detailed information on plant design, the principal j

design features are presented in the following section.

7.1. 3.1 Design Features San Onofre Units ; and 3 are essentially identical units. Each contains features designed to prevent acci-dental release of radioactive fission products from the fuel and to lessen the consequences should such a l

release occur. Many of the design and operating specifications of these features are derived from the analysis of postulated events known as design basis accidents. These accident preventive and mitigative i

features are collectively referred to as engineered safety features (ESF).

Each steel-lined concrete containment building is a passive mitigating system which is designed to minimize accidental radioacthity releases to the environment. Safety injection systems are incorporated to provide j

cooling water to the reactor core during an accident to prevent or minimize fuel damage. The containment atmosphere cooling system provides heat removal capability inside the containment following steam release i

i accidents and helps to prevent containment failure due to overpressure. Similarly, the containment spray system is designed to spray cool water into the containment atmosphere. The spray water also contains an i

additive (sodium hydroxide) which will chemically react with any airborne radiciodine to remove it from the containment atmosphere and prevent its release to the environment.

The mechanical systems mentioned above are supplied with emergency power from onsite diesel generators in the event that normal offsite station power is interrupted.

The fuel handling area of each unit is located in a fuel building, a low leakage structure with a safety grade ventilation system for accident mitigation. The safety grade ventilation system is an internal recirculation system and contains both charcoal and high efficiency particulate filters. If radioactivity were to be released into the building, it would be drawn through the ventilation system, and radioactive iodine and t

particulate fission products would be removed from the flow stream, reducing the concentration within the building and hence the amount that might leak to the ata.osphere.

l There are features of each unit that are necessary for its power generation function that can also play a role in mitigating certain accident consequences. For example, the main condenser, although not classified as an ESF, can act to mitigate the consequences of accidents involving leakage from the primary to the i

secondary side of the steam generators (such as steam generator-tube ruptures).

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1 If normal offsite power is maintained, the ability of the plant to send contaminated steam to the condenser instead of releasing it through the safety valves or atmospheric dump valves can significantly reduce the amount of radioactivity released to the environment. In this case, the fission product removal capability of the normally operating off gas treatment system would come into play.

Much more extensive discussions of the safety features and characteristics of San Onofre Units 2 and 3 may be found in the applicant's Final Safety Analysis Report.

The staff evaluation of these features will be i

tddressed in a forthcoming Safety Evaluation Report. In addition, the implementation of the lessons learned from the TMI-2 accident, in the form of improvements in design and procedures, and operator training, will significantly reduce the likelihood of a degraded core accident which could result in large releases of fission products to the containment. Specifically, the applicant will be required to meet those THI-related requirements specified in NUREG-0737. As noted in Section 7.1.4.7, no credit has been taken for these actions and improvements in discussing the radiological risk of accidents in this supplement.

7.1.3.2 Site Features In the process of considering the suitability of the site of San Onofre Units 2 and 3, pursuant to NRC's Rtactor Site Criteria in 10 CFR Part 100, consideration was given to certain factors that tend to minimize i

the risk and the potential impact of accidents. First, the site has an exclusion area as required in 10 CFR Part 100. The exclusion area of the 83.6-acre site has a minimum exclusion distance of 600 meters from the containment centerlines to the closest site boundary. The applicant's authority to control all activities within the exclusion area was acquired by a grant of easement from the United States of America made by the Stcretary of the Navy. The exclusion area is traversed by old U.S. Highway 101, the San Diego Freeway (Interstate 5), and the Atchison, Topeka and Santa Fe Railroad. The exclusion area on the ocean side extends over a narrow strip of beach and into the Pacific Ocean.

The applicant's control of the landward portion of the exclusion area extends to the mean high tide line but does not include the strip of beach lying between high and low tide that is occasionally uncovered. This strip of " tidal beach" is owned by the State of California and is used primarily as a passageway for indi-viduals walking along the beach. The applicant's lack of control of this strip of tidal beach has been adjudicated in a Commission proceeding (see ALA8-432) and has been determined to be "de minimis" on the basis of its occasional use, together with *ne high probability that any radiation exposure to individuals in this zone will be within the guideline values of 10 CFR Part 100 in the event of an emergency.

i Activities within the exclusion area which are unrelated to plant operation include a gas pipeline, railroad traffic, through traffic on the San Diego Freeway, and local recreational traffic on old U.S. Highway 101.

RIcreational activities in the plant vicinity include swimming, camping, and surfing. Recreational activities, such as sunbathing or picnicking, are discouraged within the landward portion of the exclusion area (the area landward of the contour of mean high tide). The seaward portion of the exclusion area (the area seaward of

'the contour of mean high tide) may be occupied by small numbers of people for passageway transit between the pubife beach areas upcoast and downcoast from the plant. Additional small numbers of people may be antici-pated to occasionally be in the water within the exclusion ares.

Transient access to an approximate five-acre area at the southwest corner of the site for the purposes of viewing the scenic bluffs and barrancas will be on an unimproved walkway. The applicant has estimated that at any one time a maximum of 100 persons will be in the walkway and a five-acre barranca viewing area, and on the beach and water below the mean high tide. The improved walkway affords landward passage between the two brach areas.

In case of a radiological emergency, the applicants have made arrangements with agencies of the State and local governments to control all traffic on the railroad, roadways, and waterways.

$1cond, beyond and surrounding the exclusion area is a low population zone (LPZ), also required by Part 100.

This is a circular area of 1.95 miles outer radius. Within this zone the applicant must assure that there is reasonable probability that appropriate measures could be taken on behalf of the residents in the event of a serious accident.

The San Onofre State Beach northwest and southwest of the San Onofre exclusion areas represents a public water-front recreation area within a five-mile radius of the plant. The beach south of the nuclear facility is used for swiming, hiking, and vehicle parking. The 3,400-foot stretch of beach north of the site is used primarily for surfing.

Third, Part 100 also requires that the nearest population center of about 25,000 or more persons be no closer than one and one-third times the outer radius of the LPZ. As discussed in the Statement of Considerations accompanying 10 CFR Part 100 when promulgated, the purpose of this criterion is a recognition that since accidents of greater potential hazards than those cormnonly postulated as representing an upper limit are l -'

conceivable, although highly improbable, it was considered desirable to add the population center distance requirement to provide for protection against excessive exposure doses to people in large centers.

The largest connunities in the vicinity of the site are San Clemente, the nearest population center, located about 3 miles away, which had a 1976 estimated population of 23,000, and the U.S. tiarine Corp base Camp Pendleton, with a total estimated population of about 33,000. The Marine Corp base consists of several population clusters of camps located at distances from 1.5 miles to 12 miles away.

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The Mexican border lies about 75 miles from San Onofre, toward the southeast. ThecitiesofTijuana,Mexicali, l

and Ensenada are within 150 miles of the site.

1 The safety evaluaticn of the San Onofre site has also included a review of potential external hazards, i.e.,

activities of fsite that might adversely af fect the operation of the plant and cause an accident. This review Encompassed nearby industrial, transportation, and military facilities that might create explosive, missile, toxic gas, or similar hazards. The staff concluded at the construction permit stage that the hazards from the nearby military facility are negligibly small. However, the hazards from the nearby interstate highway, the railroad right of way, and natural gas pipelines, are still under review by the staff. Reevaluation of these hazards has been requested by the staff, and the results will be reported in a supplement to the staff's I

Safety Evaluation Report. it is anticipated that the review will show that either the risk are acceptably small or may be made acceptably small.

7.1.3.3 Emergency Preparedness Emergency preparedness plans including protective action measures for the San Onofre facility and environs are in an advanced, but not yet fully completed stage. In accordance with the provisions of 10 CFR 4

1 Section 50.47, effective November 3, 1980, no operating license will be issued to the applicant unless a finding is made by the NRC that the state of onsite and offsite emergency preparedness provides reasonable assurance that adequate protective measures can and will be taken in the event of a radiological emergency.

i Among the standards that must be met by these plans are provisions for two Emergency Planning Zones (EPZ). A plume exposure pathway EPZ of about 10 miles in radius and an ingestion exposure pathway EPZ of about 50 miles in radius are required. Other standards include appropriate ranges of protective actions for each of these j

zones, provisions for dissemination to the public of basic emergency planning information, provisions for rapid notification of the public during a serious reactor emergency, and methods, systems, and equipment for assessing and monitoring actual or potential offsite consequences in the EPZs of a radiological emergency ccndition.

NRC findings will be based upon a review of the Federal Emergency Management Agency (FEMA) findings and deter-Ginations as to whether State and local government emergency plans are adequate and capable of being imple-mented, and on the NRC assessment as to whether the applicant's onsite plans are adequate and capable of being implemented. NRC staff findings will be reported in the staff's forthcoming Safety Evaluation Report. Although the presence of adequate and tested emergency plans cannot prevent the occurrence of an accident, it is the 4

judgment of the staff that they can and will substantially mitigate the consequences to the public if one 4

should occur.

7.1.4 Accident Risk and Impact Assessment 7.1. 4.1 Design Basis Accidents As a means of assuring that certain features of tu San Onofre Units 2 and 3 plants meet acceptable design and performance criteria, both the applicant and the staff have analyzed the potential consequences of a number of postulated accidents. Some of these could lead to significant releases of radioactive materials to the environment, and calculations have been performed to estimate the potential radiological consequences to persons offsite. For each postulated initiating event, the potential radiological consequences cover a considerable range of values depending upon the particular course taken by the accident and the conditions, including wind direction and weather, prevalent during the accident.

In the safety analysis of the San Onofre Units 2 and 3 plants, three categories of accidents have been considered. These categories are based upon their probability of occurrence and include (a) incidents of 1

moderate frequency, i.e., events that can reasonably be expected to occur during any year of operation, (b) infrequent accidents, i.e., events that might occur once during the lifetime of the plant, and (c) limiting faults, i *, accidents not expected to occur but that have the potential for significant releasss of radioactivity. The radiological consequences of incidents in the first category, also called anticipated operational occurrences, are discussed in Section 5.

Initiating events postulated in the second and third categories for the San Onofre Units 2 and 3 are shown in Table 7.1.4-1.

These are collectively designated design basis accidents in that specific design and operating features as described above in Section 7.1.2.1 are provided to limit their potential radiological consequences. Approximate radiation doses that might be received by a person at the nearest site boundary (600 meters tros the plant) are also shown in the table, along with a characterization of the time duration of the releases.

The calculational.model used is a conservative one in that it is expected to provide a reasonable estimate of the potential upper bound for individual exposures. The results are used to implement the provisions of 10 CFR 100 and to establish performance requirements for certain engineered safety features. The conservative assumptions used in these analyses include: (1) large (upper bound) amounts of radioactive material released by the initiating event, (2) single failures ir. Important equipment, including operating the engineered safety features in,a degrad,ed mode," Q) very adverse meteorological conditions, and (4) no reduction in exposure due to possible prutective actions.

"The containment structure, however, is assumed to prevent leakage in excess of that which can be demonstrated by testing, as provided in 10 CFR Section 100.11(a).

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The results of these calculations show that, for these events, the limiting whole-body exposures are not expected to exceed 7 rem. They also show that radioiodine releases have the potential for offsite exposures rtnging up to about 100 rem to the thyroid. For such an exposure to occur, an individual would have to be located at a point on the site boundary where the radiolodine concentration in the plume has its highest value and inhale at a breathing rate characteristic of a person jogging, for a period of two hours. The h1alth risk to an individual receiving such a thyroid exposure is the potential appearance of benign or malignant thyroid nodules in about 4 out of 100 cases, and the development of a fatal cancer in about 2 out of 1000 cases.

Th2 realistically expected consequences, were one of these initiating events actually to occur, would be very substantially less. Therefore, the risk is judged to be extremely small for these design basis accidents.

The subject of risk is more fully discussed in Section 7.1.4.6 below.

7.1.4.2 Probabilistic Assessment of Severe Accidents In this and the following three sections, there is a discussion of the probabilities and consequences of accidents of greater severity than the design basis accidents identified in the previous section. As a class, they are considered less likely to occur, but their consequences could be more severe, both for the plant itself and for the environment. These severe accidents, heretofore frequently called Class 9 accidents, can be distinguished from design basis accidents in two primary respects: they involve substantial physical diterioration of the fuel in the reactor core, including overheating to the point of melting, and they involve deterioration of the capability of the containment structure to perform its intended function of limiting the release of radioactive materials to the environment.

Th2 assessment methodology employed is that described in the Reactor Safety Study (RSS) which was published in 1975.I9)* The San Onofre Units 2 and 3 are Combustion Engineering-designed pressurized water reactors (PWR) having similar design and operating characteristics to the Surry Unit 1 facility used in the RSS as a prototype for PWRs. This assessment has used as its starting point, therefore, the same set of accident siquences that were found in the RSS to be dominant contributors to risk in the prototype PWR. The same set i

of nine release categories, designated PWR 1 through 9. have also been used to represent the spectrum of stvere accident releases that are hypothesized for the San Onofre Units 2 and 3.

Characteristics of these categories are shown in Table 7.1.4-2.

A calculated probability per reactor year associated with each release category is also shown in the second column in Table 7.1.4-2.

These probabilities are' the result of a detailed engineering analysis of the proto-type PWR in the Reactor Safety Study. There are substantial uncertainties in these probabilities. This is due, in part, to difficulties associated with the quantification of human error and to inadequacies la the dita base on failure rates of individual plant components that were used to calculate the probabilities.(5)

(Ste Section 7.1.4.7 below.) Also, the detailed engineering analysis represents a plant designed by a different nuclear steam supply system designer (CE versus Westinghouse) with different detailed designs. The pr'.bability of accident sequences from the Surry plant were used to give a perspective of the societal risk tt San Onofre Units 2 and 3 because, although the probabilities of particular accident sequences may be substantially different, the overall effect of all sequences taken together is likely to be within the uncertainties. Except as indicated in the footnotes in Table 7.1.4-2, the staff has no present basis for judging whether the probabilities may be too high or too low. The error band for the probabilities of some of the event sequences could be as great as a factor of 100. The event sequences in categories PWR 1-7 lead to partial or complete melting of the reactor core while those in the last two categories do not involve melting of the core. In release categories 1 to 3, the event sequences include containment failure by steam sxplosion, hydrogen burning, or overpressure. In release categories 6 and 7, the dominant containment failure mode is by melt-through of the containment base mat. The other release categories contain event sequences in which the systems intended to isolate the containment fall to act properly.

The magnitudes (curies) of radioactivity releases for each category are obtained by multiplying the release fractions shown in Table 7.1.4-2 by the amounts that would be present in the core at the time of the hypo-thetical accident. These are shown in Table 7.1.4-3 for a San Onofre plant at the core thermal power level cf 3560 megawatts.

The potential radiological consequences of these releases have been calculated by the consequence model used in the RSS(10) and adapted to apply to a specific site. The essential elements are shown in schematic form in Figure 7.1.4-1.

As noted therein, the atmospheric dispersion and health effects parts of this model are treated probabilistically and are based upon cbserved statistical distributions. Environmental parameters specific to the San Onofre site have been used and include the following:

(1) Meteorological data for the site representing a full year of consecutive hourly measurements and seasonal variations.

Because this report has been the subject of considerable controversy, a discussion of the uncertainties surrounding it is provided in Section 7.1.4.7.

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(2) Projected population for the year 2000 extending throughout regions of 50 and 500 miles radius from the site.

(3) The habitable land fraction within the 500-mile radius, and (4) Land use statistics, on a state wide basis, including fare land values, farm product values including dairy production, and growing season information, for the State of California and each surrounding State within the 500-mile region.

(5) Land use statistics for Mexico on a country-wide basis. Fara land values, growing season information, and comparison between agriculture and dairy products are based on comparisen with U.S. values for nearby States. Fare product values are based on Mexico-average Gross National Product ano " agriculture" percentage.

The RSS consequence model also contains a provision for incorporating the consequence reduction benefits of evacuation. Except as otherwise indicated below, the results shown for San Onofre do not Sclude this pro-vision. With respect to this aspect of the calculations, therefore, the results are " worst case" estimates.

The model does however, provide for relocation of persens to avoid prolonged esposure to ground contamination.

Unless otherwise specified the calculations for San Onofre incorporate this provision for relocation following seven days of exposure.

There are also uncertainties in the estimates of consequences, and the error bounds may be as large as they are for the probabilities. It is the judgment of the staff, however, that it is more likely that the calcu-lated results are overestimates of consequences rather than underestimates.

The results of the calculations using this consequence model are radiological doses to individuals and to populations, health effects that might result from these exposures, costs of implementing protective actions, and costs associated with property damage by radioactive contamination.

7.1. 4. 3 Dose and Health Impacts of Atmospheric Releases The results of the calculations of dose ef fects and health impacts performed for the San Onof re f acility and site are presented in the for1a of probability distributions in Figures 7.1.4-2 through 5 and are included in the impact Summary Table 7.1.4-4.

All of the nine release categories shown in Table 7.1.4-2 centribute te the results, the consequences from each being weighted by its associated probability.

Figure 7.1.4-2 shows the probability distribution for the number of persons who might receive whole-body doses equal to or greater than 200 res and 25 rem, respectively, and thyroid doses equal to or greater than 300 rem, all on a per year basis. The 200 rem whole-body dose figure corresponds approximately to a thres-hold value for which hospitalization would be indicated for the treatment of radiation injury. The 25-ree whole-body (which has been identified earlier as the icwer limit for a clinically observable physiological ef fect) and 300-rem thyroid figures correspond to the Ccmmission's gaideline values for reactor siting in 10 CFR Part 100.

The figure shows in the lef t-hand portion that there is less than one Chance in 100,000 per year (i.e.,10 5) that one or more persons may receive doses equal to or greater than any of the doses specified. The fact that each of the three curves approacnes a horl20ntal line shows that if one person were to receive such doses the chances are about the same that several hundreds would be so exposed. The chances of larger numbers of persons beingexposedattheselevelsareseentobeconsiderablysmaller. For example, the chances are 2 in 10,000,000 (2 x 10- ) that 100,000 or more people might receive doses of 200 rem or greater. A majority of the exposures reflected in this figure would be expected to occur to persons within a 30-mile radius of the plant. Virtually all would occur within a 100-mile radius.

Figure 7.1.4-3 shows the probability distribution for the total population exposure in person-rem, i.e., the probability per year that the total population exposure will equal or exceed the values given. Mast of the population exposure up to 100 million person-rea would occur within 50 miles, but the more severe release categories (PhR l-6) would result in exposure to persons beyond the 50-mile range as shown.

For perspective, population doses shown in Figure 7.1.4-3 may be compared with the annual average dose to the population within 50 miles of the San Onofre site due to natural background radiation of 700,000 person-rem, and to the anticipated annual population dose to the general public from normal station operation of about 460 person-rem (excluding plant workers) (Section 5, Tables 5.3 and 5.5).

Figure 7.1.4-4 shows the probability distributions for acute fatalities, representing radiation injuries that would produce fatalities within about 60 days af ter exposure. Virtually all of the acute fatalities would be expected to occur within a 50-mile radius and the majority within a 30-mile radius. Three curves are shown, rtpresenting three possible respons?s to an accident: (1) no evacuation but relocate af ter 7 days, (2) relocate af ter remaining for one day in the area, and (3) begin to evacuate af ter one hour in a 10-mile radius from the plant. The benefits of protective actions are apparent. The response to any real accident would be dictated by conditions prevailing at the time; the responses chosen for the calculations are 7-8

i illustrative. The third response is judged to be conservatively consistent with the Commission's requiruents i

for emergency preparedness plans.

Figure 7.1.4-5 represents the 5,tatistical relationship between population exposure and the induction of fatal cancers that might appear over a period of many years following exposure. The impacts on the total population and the population within 50 miles are shown separately. Further, the fatal, latent cancers have been sub-divided into those attributable to iodine exposures (thyroid cancers) and all other cancers.

7.1.4.4 Economic and Societal Impacts As noted in Section 7.1.1, the various measures for avoidance of adverse health ef fects including those due to residual radioactive contamination in the environment are possible consequential impacts of severe acci-dints. Calculations of the probaollities and magnitudes of such impacts for the San Onofre facility and enviroas have also been made. Unlike the radiation exposure and adverse health effect impacts ciscussed above, impacts associated with adverse health effects avoidance are more readily transformed into economic impacts.

The results are shown as the probability distribution for costs of of fsite mitigating actions in Figure 7.1.4-6 and are included in the impact Summary Table 7.1.4.-4.

The factoi; contributing to these estimated costs include the following:

o Evacuation costs o

Value of crops contaminated and condemned o

Value of milk contaminated and condemned o

Costs of decontamination of property where practical o

Indirect costs due to loss of use of property and incomes derived therefrom.

The last named costs would derive from the necessity for interdiction to prevent the use of property until it is either free of contamination or can be economically decontaminated.

Figure 7.1.4-6 shows that at the extreme end of the accident spectrum these costs could exceed tens of billiors of dollars but that the probability that this would occur is exceedingly small, less than one chance in a hundred million per year.

Nditional economic impacts that can be monetized include costs of decontamination of the facility itself and

• osts of replacement power. Probability distributions for these impacts have not been calculated, but sre included in the discussion of risk considerations in Section 7.1.4.6 below.

i Psychological impacts that may or may not have economic consequences are also possible as has been demonstrated at Three Mile Island. These impacts are not readily quantifiable, however, and their consideration is limited hire to the recognition that they can accompany accidents.

I 7.1.4.5 Releases to Groundwater A pathway for public radiation exposure and environmental contamination that would be unique for severe reactor accidents was identified in Section 7.1.1.2 above. Consideration has been given to the potential environmental l

impact of this pathway for the San Onofre plant. The principal contributors to the risk are the core melt l

accidents associated with the PWR-1 through 7 release categories. The penetration of the basemat of the con-l tainment building can release molten core debris to the strata beneath the plant. Soluble radionuclides in l

this debris can be leached and transported with groundwater to downgradient domestic wells used for drinking or to surface water bodies used for drinking water, aquatic food and recreation. In pressurized water -

reactors, such as the San Onofre unit, there is an additional opportunity for groundwater contamination due to the release of contaminated sump water to the ground through a breach in the containment.

An analysis of the potential consequences of a liquid pathway release of radioactivity for generic sites was presented in the " Liquid Pathway Generic Study" (LPGS).UI) The LPGS compared the risk of accidents involving

(

the liquid pathway (drinking water, irrigation, aquatic food, swimming and shoreline usage) for four conven-tional, generic land-based nuclear plants and a floating nuclear plant, for which the nuclear reactors would l

be mounted on a barge and moored in a water body. Parameters for the land-based sites were chosen to represent avtrages for a wide range of real sites and are thus " typical," but represented no real site in particular.

t

' The discussion in this section is an analysis to determine whether or not the San Onofre site liquid pathway consequences would be unique when compared to land-based sites considered in the LPGS. The method consists i

of a direct scaling of the LPGS population doses based on the relative values of key parameters characterizing the LPGS " ocean" site and the San Onofre site. The parameters which were evaluated included amounts of radio-l active. materials entering the ground, groundwater travel time, sorption on geological media, surface water trinsport, aquatic food consumption, and shoreline usage.

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Doses to individuals and populations were calculated in the LPGS without consideration of interdiction methods such as isolating the contamei.;ted groundwater or denying use of the water. In the event of surface water contamination, commercial and y irts fishing, as well as many other water-related activities would be restricted. The consequences would therefore be largely economic or social, rather than radiological. In I

any event, the individual and population doses for the liquid pathway range from frections to very small fractions of those that can arise from the airborne pathways.

l The San Onofre reactors are situated above the San Mateo Formation, which is about 274 meters thick and f

consists of medium to coarse grained sandstone.I2) Grcundwater at the site occurs between elevation 0 and 1.5 meters Mean Low Low Water, under water table conditions. The basemat of the reactors would be peneath the water table.

The groundwatar gradient is clearly toward the ocean. There are no wells between the site and the ocean, so i

no groundwater users could be affected by an accidental contamination from the plant. There is virtually no 1

possibility of a reversal of the grrondwater gradient due to heavy pumping inland, particularly because such a reversal would at the same time cause an unacceptable intrusion of saltwater into the aquifer. Therefore, i

liquid radioactivity released from a core melt accident could only cause contamination by being transported through the groundwater and subsequently released to the Pacific Ocean.

The staff's most conservative estimate of the groundwater travel time would be 215 days. For groundwater travel times of this magnitude, it is clear that the most important radionuclide contributors to the liquid j

pathway population dose would be Sr-90 and Cs-lj7. Conservative values of the retardation factors, which reflect the ef'ects of sorption of the radionuclides on geologic materials, were estimated on media similar to the granular materials under the site to be 31 for Sr-90 and 2204 for Cs-137. The mean transport time from the reactor building to the Pacific Ocean is therefore conservatively estimated tc be about 16 years for Sr-90 and 1080 years for Cs-137. When thesa travel times are compcred to 5.7 years for Sr-90 and 51 years for Cs-137 in the LPGS land-based ocean site case, the relatively larger travel times for the San Onofre ',ite would allow a smaller portion of the radioactivity to enter the surface water. This reduces tha Sr-90 r#1 ease j

to about 78% of the LPGS value. Virtually all of the Cs-137 would have decayed before reaching surface mater.

I Contaminants released from the shoreline would disperse in the oceanic turbulence. The LPGS made no distinc-tion between the turbulence which would be found in the east, gulf, or west coasts of the United States. The only assumption whicn can be made without site-specific data is that the mixing at the San Onofre and LPGS sites are similar.

The two major liquid pathway exposure pathways for an ocean site are aquatic food consumption and direct shoreline exposure.

The commercial and recreational finfish harvest for a rectangular block 80 km along shore and stretching 40 km offshore has been estimated by the staff from data provided in the Environmental Report (13) to be about 13.1 x 108 kg.

For comparison, the same size block using the LPGS ocean site fish catch densities would yield 5.8 x 106 kg of finfish.

1 Approximately 62% of population dose due to finfish consump. ion calculated in the LPGS was due to Cs-137 and

(

approximately 38% was due to Sr-90.

The only significant radionuclide which could reach the ocean in the San Onof re case would be Sr-90.

The staff has conservatively estimated that the uninterdicted population dose in the San Onofre case would be about 69% of the LPGS land-based ocean case population dose for seafood consumption.

Nearly all of the direct shoreline exposure in the LPGS ocean-based site case was determined to emanate from Cs-137. Since virtually all of the Cs-137 would decay before reaching the ocean, the shoreline direct expo-sure can be eliminated from further consideration.

The San Onofre liquid pathway contribution to population dose has, therefore, been demonstrated to be smaller than that predicted for the LPGS land-based ocean site, which represents a " typical" ocean site. Thus, the San Onofre site is not unique in its liquid pathway contribution to risk.

There are measures which could be taken to minimize the impact of the liquid pathway. The staff estimated that the minimum groundwater travel time from the San Onofre site to the Pacific Ocean would be hundreds of j

days. In addition, the holdup of important radionuclides would provide additional time to utilize engineering i

measures such as slurry walls and well point dewatering to isolate the radioactive contaminants at the source.

j 7.1.4.6 Risk Considerations 1

The foregoing discussions have dealt with both the frequency (or likelihood of occurrence) of accidents and their impacts (or consequences). Since the ranges of both factors are quite broad, it is useful to combine 1

them to obtain average measures of environmental risk. Such averages can be particularly instructive as an aid to the comparison of radiological risks associated with accident releases and with normal operational i

releases.

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A common way in which this combination of factors is used to estimate risk is to multiply the probabilities by the consequences. The resultant risk is then expressed as a number of consequences expected per unit of time. Such a quantification of risk does not at all mean that there is universal agreement that people's attitudes about risk, or what constitutes an acceptable risk, can or should be governed solely by sLch a measure. At best, it can be a contributing factor to a risk judgment, but not necessarily a decisive factor.

In Table 7.1.4-5 are shown average values of risk associated with population dose, acute fatalities, latent fatalities, and costs for two possible responses: (1) remaining in the area for seven days (column labeled "without protective actions") and (2) early evacuation of the population within 10 miles. These average values are cbtained by summing the probabilities multiplied by the consequences over the entire range of the distr:butions. Since the probabilities are on a per year basis, the averages shown are also on a per year ba',s.

Again, the benefits of protective actions are apparent.

The population exposure risk due to accidents may be compared with that for normal operational releases.

These are shown in Section 5, Tables 5.3 and 5.5, for San Onofre Units 2 and 3 operating concurrently. The radiological dose to the population from normal operational releases may result in:

(1) late somatic effects in the form of fatal and nonfatal cancer in various body organs--following age and organ-specific latency periods--of the exposed population, and (2) fatal and nonfatal genetic disorders in the future generations of the exposed population.

Because of the randomness of these ef fects, calculations of these ef fects are made f rom the population dose (person-rem). Absolute risk estimators of 140 deaths f rom expression of latent cancer in various body organs per 106 total-body person-rem in the exposed population and 260 cases of all forms of genetic disorders per 109 total-body person-rem in the future generations of the exposed population were derived from the 1972 BEIR report.

This derivation assumes a linear and nonthreshold dose-ef fect relationship at all sublethal dose levels. Using these risk estimators and 228 person-rem as the annual population dose (Table 5.5, adjusted for one reactor), the staf f calculated that there may occur 0.03 cancer deaths in the exposed population and 0.06 genetic disorders in all future generatons of the exposed population from each year of operation of one reactor.

The comparison of 0.03 cancer deaths given above with about 0.2 latent cancer deaths from Table 7.1.4-5 shows that the accident risks are about ten times larger whsa the possible effectiveness of protective actions is discounted. Estimates of risk reduction by evacuation of the public within the 10-mile emergency planning zone show that the population exposure risks for accidents can be reduced by a f actor of 10 to 20 so that the risks would then be comparable to those for normal operational releases.

There are no acute fatality nor economic risks associated with protective actions and decontamination for normal releases; therefore, these risks are unique for accidents. For perspective and understanding of the meaning of the acute fatality risk of 0.014 per year, however, we note that to a good approximation the population at. isk is that within about 10 miles of the plant, about 92,000 persons in the year 2000.

Accidental fatalities per year for a population of this size, based upon overall averages for the United States, are approximately 20 for motor vehicle accidents, 7 from falls, 3 f rom drowning, 3 from burns, and 1 from firearms.(3b) i l

l As a separate item under acute fatalities in Table 7.1.4-5 is an entry of 0.0003 for " Beach visitors." As discussed in Section 7.1.3.2, the beaches near the site are heavily used for recreation. The average number of visitors has been estimated, based on seasonal and daily variation. The effects on the visitors are tallied separately because in actuality they are likely to be permanent residents from other nearby locations.

Figure 7.1.4-7 shows the calculated risk expressed as whole-body dose to individuals versus the distance from the plant. The values are on a per year basis for seven-day exposures and all categories of accidents contri-buted to the dose, weighted by their associated prrhabilities. Wind speeds measured at the site have been taken into account in calculating plume dispersion properties. This " average" risk by distance can be combined with the frequencies of the wind by direction from the plant, producing a relative directional risk. The results of such a calculation, arbritrarily normalized, are displayed in Figure 7.1.4-8.

Relative to the

" average" results, it can be seen that the risks are hipaer for larger distances f rom the plant in directions to which the wind blows for larger fractions of the time and correspondingly reduced for directions that are downwind less often.

The economic risk associated with protective actions and decontamination could be compared with property damage costs associated with alternative energy generation technologies. The use of fossil fuels, coal or oil, for exas.ple, would emit substantial quantities of sulfur dioxide and nitrogen oxides into the atmosphere, and, among other things, lead to environmental and ecological damage through the phenomenon of acid rain.( C)

This effect has not, however, been sufficiently quantified to draw a useful comparison at this time.

There are other economic impacts and risks that can be monetized that are not included in the cost calculations discussed in Section 7.1.4.4.

These are accident impacts on the facility itself that result in acded costs I

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to the public, i.e., ratepayers, taxpayers, and/or shareholders. These are costs associated with decontamina-j tion of the facility itself and costs for replacement power.

No detailed methodology has been developed M r estimating the contribution to economic risk associated with clsanup and decontamination of a nuclear,

' plant that has undergone a serious accident toward either a decommissioning or a resumption of operat',

imperience with such costs is currently being accumulated as a result of the Three MHe Island accident. L is already clear, however, that such costs can approach or even 7

4xceed the original capital cost of such a facility. As an illustration of the possible contribution to the economic risk, if the probability of an accident serious enough to require extensive cleanup and decontamina-tion is taken as the sum of the nine categories in Table 7.1.4-2, i.e., about 5 chances in 10,000 per year, cnd if the " average" decontamination cost for these nine categories is assumed to be one billion dollars, then the estimated economic risk would be about $500,000 per year.

Other costs, besides damage to or loss of the facility, result from accidents. The major additional costs are replacement power and replacement of the capacity. These costs are affected by the point in the lifetime of the plant at which an accident might occur. The present worth cost is highest for an accident occurring at the beginning of the plant operating life and decreases over the plant life. It is assumed for these calculations that one unit of San Onofre 2 or 3 is permanently lost and replaced by new capacity after eight ytars and the undamaged unit is shut down for three years before restart. For illustrative purposes, the costs and economic risk have been estimated for a " worst case" situation for the approximately 2200-megawatt i

I (electric) San Onofre Units 2 and 3 complex by postulating a total loss of one of the units in the first year of a projected 30 year operating life. Net replacement power cost of 45 rills /kWh is assumed (nearly all fossil units in southern Califorria are oil-fired). Using a 60% capacity factor, the annual cost of replace-ment power would be $520 million for the two units in 1980 dollars. The additional capital costs as a result of having to construct a new facility are $60 alliton per year, again in 1980 dollars.

If the probability of sustaining a total loss of the original facility is taken as the probability of the occurrenar of a core melt accident (approxfmately by the sum of probabilities for the categories PWR-1 through 7 in Table 7.1.4.2, f.e., about 5 chances in 100,000 per year), then the average contribution to economic risk that would result from a loss early in the operating life of a San Onofre unit is about $29,000 for each of the first three years until the undamaged plant is returned to service, then $16,000 per year until the damaged unit is replaced, and $3000 per year additional capital costs for the assumed remaining 22 years of plant strwice.

i 7.1. 4. 7 Uncertainties The foregoing probabilistic and risk assessment discussion has been based cpon the methodology presented in 1

tha Reactor Safety Study (RSS) which was published in 1975.

In July 1977, the NRC organized an Independent Risk Assessment Review Group to (1) clarify the achievements and limitations of the Reactor Safety Study Group, (2) assess the peer comments thereon and the responses to the comments. (3) study the current state of such risk assessment methodology, and (4) recommend to the Commission how and whether such methodologcan be used fri the regulatory and liceasing process. The results of this study were issued September 1978 This report, called the Lewis Report, contains several findings and recommendations concerning the RSS. Some of the more significant findings are summarized below.

(1) A number of sources of both conservatism and nonconservatism in the probability calculations in RSS were found, which were very difficult to balance. The Review Group was unable to determine whether the overall probability of a core melt given in the RSS was high or low, but they did conclude that the error bands were understated.

(2) The methodology, which was an important advance over earlier methodologies that had been applied to reactor risk, was sound.

(3) It is very difficult to follow the detailed thread of calculations through the RSS. In particular, the.

Executive Summary is a poor description of the contents of the report, should not be used as such, and has lent itself to misuse in the discusslun of reactor risk.

On January 19, 1979, the Commission issued a statement of policy concerning the RSS and the Review Group Report. The Commission accepted the findings of the Review Group.

7 The accident at Ihree Mile Islano occurred in March 1979 at a time when the accumulated experience record was thout 400 reactoa years. It is of interest to note that this was within the range of frequencies estimated by the RSS for an accident of this severity.(3d) It should aleo be noted that the Three Mile Island accident has resulted in a very comprehensive evaluation of reactor accidents like that one, by a significant number cf investigative groups both within NRC and outside of it. Actions to improve the safety of nuclear power plants have come out of these investigations, including those from the President's Commission on the Accident at Three Mile Island, and NRC staff investigations and task forces. A comprehensive "NRC Action Plan Developed as a Result of the TMI-2 Accident," NUREG-0660 Vol. I, May 1980 collects the various recommendations of these o

7-12

i groups and describes them under the subject areas of: Operational Safety; Siting and Design; Emergency Preparedness and Radiation Effects; Practices and Procedures; and NRC Policy, Organization and Management.

4 The action plan presents a sequence of actions, some already taken, that will result in a gradually increasing improvement in safety as individual actions are completed. The San Onofre plant is receiving and will receive the benefit of these actions on the schedule indicated in NUREG-0660. The improvement in safety from these actions has not been quantified, however, and ti3 radiological risk of accidents discussed in this chapter does not reflect these improvements.

7.1. 5 Conclusions The foregoing sections consider the potential environmental impacts from accidents at the San Onofre facility.

These have covered a broad spectrum of possible accidental releases of radioactive materials into the environ-ment by atmospheric and groundwater pathways. Included in the considerations are postulated design basis accidents and more severe accident sequences that lead to a severely damaged reactor core or core melt.

The environmental impacts that have been considered include potential radiation exposures to individuals and to the population as a whole, the risk of near-and long-term adverse health effects that such exposures could entall, and the potential economic and societal consequences of accidental contamination of the environment.

These impacts could be severe, but the likelihood of their occurrence is judged to be small. This conclusion is cased on (a) the fact that considerable experience has been oained with the operation of siellar facilities without significant degradation of the environment; (b) that, in order to obtain a license tc operate the San Onofre facility, it must comply with applicable Commission regulations and requirements; (c) a proDa-bilistic assessment of the risk wased upon the methodology developed in the Peactor Safety Study. The overall assessment of environmental risk of accidents, assuming protective action, shows that it is roughly comparable to the risk for normal operational releases although accidents have a potential for acute fatalities and economic costs that cannot arice from norwal operations. The risk of a:ute fatalities from potential accidents at the site are small in comparison with the risk of acute fatalities from other human i

activities in a comparably-sized population.

Be have concluded that there are no special or unique features about the San Onofre site and environs that would warrant special or addittor.al engineered safety featurcs for the San Onofre plants.

4 I

F i

7-13

TABLE 7.1.4-1 Approximate Radiation Doses from Design Basis Accidents Conservative Calculational Model Dose (rem at 600 meters (l)

Duration Infrequent Accidents of Release Whole Body Thyroid Waste Gas Tank Failure

< 2 hr

<3

< 30 I2)

Steam Generator Tube Rupture

<2he

<3 2

Fuel Handling Accident

< 2 hr 7

40 Limiting Faults Main Steam Line Break

< 2 hr 6

10 Control Rod Ejection hrs-days

<6 60 Large-Break LOCA hrs-days 3

100 (I)The nearest site boundary.

(2)See NUREG-0651 (Reference 6) for descriptions of three steam generator tube rupture accidents that have occurred in the United States.

< means "less than" 7-14

Table 7.1.4-2 Summary of Atmospheric Release Categories Representing Hypothetical Accidents in a PWR Fraction of Core Inventory Released *I I

Release Probability SI ICI Category (reactor yr 8)

Xe-Kr I

Cs-Rb Te-Sb Ba-Sr Ru La PWR 1 5.1 x10 *Id) 0.9 0.7 0.4 0.4 0.05 0.4 3 x 10 8 PWR 2 7 x 10 5 0.9 0.7 0.5 0.3 0.06 0.02 4 x 10 8 PWR 3 2.3 x 10.s 0.8 0.2 0.2 0.3 0.02 0.03 3 x 10 8 PWR 4 2.1 x 10.as 0.6 0.09 0.04 0.03 5 x 10 8 3 x 10 3 4 x 19..

PWR 5 5 x 10 8 0.3 0.03 9 x 10 8 5 x 10 8 1 x 10 8 6 x 10

• 7 x 10 5 PWR 6 6 x 10 7 0.3 3 x 10 8 8 x 10

• 1 x 10 8 9 x 10 5 7 x 10 5 1 x 10 5

?

G PWR 7 4 x 10 5 6 x 10 8 4 x 10 5 1 x 10 5 2 x 10 5 1x 10.s 1 x 10 5 2 x 10 7 PWR 8 4 x 10 5 2 x 10 8 1 x 10

• 5 x 10

• 1 x 10 8 1 x 10 8 0

0 PWR 9 4 x 10

• 3 x 10 8 1 x 10 7 6 x 10 7 1 x 10

• 1 x 10 88 0

0 (a) Background on the isotope groups and release mechanisms is presented in Appe*, dix VII, WASH 1400 (Ref. 9).

I Includes Ru, Rh, Co, Mo, Tc.

(c)!ncludes. Y La, Ir, Nb, Ce, Pr, Nd, Np, Pu, Am, Ca.

' rrent understanding of the phenomenon of containment f ailure by steam explosion embodied in this release category indicate *,

> probability should be lower than stated.

NOTE: Please refer to Section 7.1.4.6 for a discussion of uncertainties in risk estimates.

TABLE 7.1.4-3 Activity of Radionuclides in a San Onofre Reactor Core at 3560 mit Radioactive Inventory Group /Radionuclide in Millions of Curies Half-Life (days)

A.

NOBLE GASES Arypton-85 0.63 3,950 Krypton-85e 27 0.183 Krp ton-87 52 0.0528 Krypton-88 76 0.117 Xenon-133 190 5.28 Xenon-135 38 0.384 B.

IOO!hES Iodine-131 95 8.05 Iodine-132 130 0.0958 lodine-133 190 0.875 lodine-134 210 0.0366 lodine-135 170 0.280 C.

ALKALI METALS Ru0idiun-86 0.029 18.7 Cesium-134 8.3 750 Ceslum-136 3.3 13.0 Cesium-137 5.2 11,000 D.

TELLURItM-ANTIMONY Tellurium-12/

6.6 0.391 Te11urt w 127m 1.2 109 Te11urium-129 34 0.048 Tellurlue-129s 5.9 34.0 Tellurium-131m 14 1.25 Te11urium-132 130 3.25 Antimony-127 6.8 3.88 Antimony-129 37 0.179 E.

AutINE EARTHS Strontium-89 100 52.1 Strontium-90 4.1 11,030 Stronti w 91 120 0.403 Barium-140 180 12.8 F.

MOBLE METAL 5 Ccbalt-58 0.87 71.0 Cobalt-60 0.32 1,920 Molybdenum-99 180

2. 8 Technetiw99m 160 0.25 Ruthenium-103 120 39.5 Ruthenium-105 80 0.185 Rutheni w 106 28 366 Rhodium-105 55 1.50 1-16

Table 7.1.4-3 (Continued)

Radioactive Inventory Group /Radionuclide in Millions of Curles Half-Life (days)

G.

CARE EARTHS, REFRACTORY OXIDES AND TRAN50RANICS Yttrium-90 4.3 2.67 Yttrium-91 130 59.0 Zirconium-95 170 65.2 Zirconium-97 170 0.71 Niobium-95 170 35.0 Lanthanum-140 180 1.67 Cerium-141 170 32.3 Cerium-143 150 1.38 Cerium-144 95 284 Praseodymium-143 150 13.7 Neodymium-147 67 11.1 Neptunium-239 1800 2.35 Plutonium-238 0.063 32,500 Plutonium-239 0.023 8.9 x 108 Plutonium-240 0.023 2.4 x 108 Plutonium-241 3.8 5,350 Americium-241 0.0019 1.5 x 105 Curium-242 0.56 163 Curium-244 0.026 6,630 NOTE: The above grouping of radionuclides corresponds to that in Table 7.1.4-1.

7-17

- ~. -

Table 7.1.4-4 Summary of Environmental Impacts and Probabilities

• l Population Latent **

Probability Persons Persons.

Exposure

. Cancers Cost of Offsite ef Impact Exposed Exposed Acute Millions of person-50 al/

Mitigating Actions Per Year over 200 ren over 25 rem Fatalities rea 50 mi/ Total Total Millions of Oo11ars 10 *

<1

<1

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<.001 10 5

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< 30 12

[

1

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<1 70/130 5,400/8,100 400

-5 x 10.s 10' 8 10,000 150,000 2,000 400/600 33,000/45,000 5,000 10 7 15,000 700,000.

30,000 1,100/2,000 132,000/171,000 15,000 I

l 10 8 50.000 1,000.000 130,000 30,000/40,000 300,000 35,000 7g Related.

Figure' 7.1.4-2 7.1.4-2 7.1.4-4 7.1.4-3 7.1.4-5 7.1.4-6 aNo protective actions are assumed except for cost impacts. Reasonable protective actions would reduce the radiological exposures and acute fatalities to small fractions of the numbers shown.

anGenetic effects would be approximately twice the number of latent cancers. Thirty times the values shown in the Figure 7.1.4-5 are shown in this column reflecting the thirty year period over which they might occur.

[

I NOTE: Please refer to Section 7.1.4.6 for a discussion of uncertainties in risk estimates.

r P

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TABLE 7.1.4-5 Annual Average Values of Environmental Risks Due to Accidents Without With Protective Protective Actions Actions Population exposure person-rem within 50 miles 1500 170 person-rem total 2600 380 Acute Fatalities permanent residents 0.014 0.001 beach visitors 0.0003 0.00002 Latent cancer fatalities all organs excluding thyroid 0.18 0.022 thyroid only 0.03 0.011 Cost of protective actions and decontamination not applicable

$19,000 NOTE: Please see Section 7.1.4.6 for discussions of uncertainties in risk estimates.

7-19

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REFERENCES 1.

Statement of Inteiin Policy, " Nuclear Power Plant Accident Considerations Under the National Environmental Policy Act of 1%9," 45 FR 40101-40104, June 13,1980.

2.

" Final Safety Analysis Report (FSAR), San Onofre Nuclear Generating Station Units 2 and 3, Docket Numbers 50-361 and 50-362." Southern California Edison Company and San Diego Gas and Electric Company, December 1, 1976, as amended.

3a. " Energy in Transition 1985 - 2010 " Final Report of the Committee on Nuclear and Alternative Energy Systems (CONAES), National pesearch Council,1979, Chapter 9, pp. 517-534; also C.E. Land Science 20],

1197, September 12, 1980.

3b. CONAES Report, loc cit, pp 577.

3c. CONAES Report, loc cit, pp 559-560.

3d. CONAES Report, loc cit, p 553.

4.

"The Effects on Populations of Exposure to Low Levels of Ionizing Radiation," Advisory Consittee on the Biological Effects of Ionizing Radiations (BEIR), National Academy of Sciences / National Research Council (November 1972).

5.

" Risk Assessment Review Group Report to the U.S. Nuclear Regulatory Commission," H.W. Lewis et al.,

NUREG-CR-0400, September 1978.

6.

" Descriptions of Selected Accidents that Have Occurred at Nuclear Reactor Facilities," H.W. Bertini et al., Nuclear Safety Information Center, Oak Ridge National Laboratory, ORNL/NSIC-176, April 1980; also,

" Evaluation of Steam Generator Tube Rupture Accidents," L.B. Marsh, NUREG-0651, March 1980.

7.

"Three Mile Island - A Report to the Commissioners and the Public " Vol. I, Mitchell Rogovin, Director, Nuclear Regulatory Commission Special Inquiry Group, January 1980, Summary Section 9.

- 8.

" Report of the President's Commission on the Accident at Three Mile Island," October 1979, Cosnission Findings B, Health Effects.

9.

- " Reactor Safety Study " WASH-1400 (NOREG-75/014), October 1975.

10. " Overview of the Reactor Safety Stuay Consequences Model," NUREG-0340, October 1977.

11. " Liquid Pathway Generic Study," NUREG-0440, Febra ry 1978.

12. Isherwood, Dana, " Preliminary Feport on Retardation Factors and Radionuclides Migration," Lawrence Livermore Laboratories, UCID-A3.44, August 5, 1977.

13. San Onofre Nuclear Generating Station Units 2 and 3. Applicant's Environmental Report, Operating License Stage, Volume 2, November 1976.

l l

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10. CONCLUSIONS AND RE-EVALUATED BENEFIT-COST 8ALANCE The staff has re evalated the environmental costs of the San Onofre Nuclear Station Unit No. 2 in light of the potential environmental fapacts from accidents at the facility, including severe accident sequences that lead to a severely damaged reactor core or core melt. The annualized risks of such accidents (the product of the consequences of associated releases and the probability of their occurrence) were compared to the risks associated with routine operation, which were considered in the Draft Environmental Statement. Based on its consideration of all the material set forth in Section 7.1, giving due consideration to both the consequences af releases that may be associated with accidents and to the probability of occurrence of such releases, the sttff concludes that the environmental risks considered in this supplement do not change the results of the ecst-benefit balance contained in the Draf t Environmental Statement (Section 10).

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