ML20049J427
| ML20049J427 | |
| Person / Time | |
|---|---|
| Site: | Callaway  |
| Issue date: | 08/22/1981 |
| From: | NRC |
| To: | |
| Shared Package | |
| ML20049J425 | List: |
| References | |
| FOIA-81-448 NUDOCS 8203180177 | |
| Download: ML20049J427 (70) | |
Text
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CAltN5/ Job K 2nd Draft 5-61 22 Aug 81 (1)
,c 5.9.4 Postulated Accidents On 13 June 1980 the Commission published in the " Federal Register" a statement of interim policy regarding accident considarations (Ref.1). This statement
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withdrew the proposed Annex to Appendix 0 of 10 CFR Part 50 and suspended the i
rulemaking proceedings associated with it.
It also put forth the Commission's interim policy that:
"... Environmental Impact Statements shall include consi-derations of the site-specific accident sequences that lead to releases of radiation and/or radioactive materials, including sequencu that can result in inadequate cooling of reactor fuel and to melting of the reactor core.
In this regard, attention shall be given both to the probability of occurrence of sucn releases and to the environmental consequences of such releases." This section presents an analysis of accidents, including those commonly referred to as Class 9 accidents.
The staff has considered the potential radiological impacts on the environment of possible accidents at the Callaway Plant Units 1 and 2 in accordance with the statement of interim policy.
The following discussion reflects these considerations and conclusions.
The first section deals with general characteristics of nuclear power plant accidents including a brief summary of safety measures to minimize the prob-ability of their occurrence and to mitigate their consequences if they should Also described are the important properties of radioactive materials occur.
and the pathways by which they could be transported to become environmental l
hazards.
Potential adverse health effects and impacts on society associated
.wi+hsactions,td avoid such health effects are also identifie'd.'
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8!203180177 811123 PDR FOIA BACKUS B1-448 PD'
CALMY5/ Job K 2nd Draft 5-61 22 Aug 81 (2)
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 facilities of Callaway Units 1 and 2 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 Callaway site using probabilistic methods to estimate the possible impacts and the risks associated with severe accident sequences of exceedingly low probability of occurrence.
5.9.4.1 General Characteristics of Accidents The term accident, as used in this section, refers to any unintentional event 7
not addressed in Section 5.9.3 that results in a release of radioactive mate-rials into the environment.
Therefore, the predominant focus is on events that can lead to releases 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 that combine to reduce the risk associated with accidents at nuclear power plants.
Safety features in the design, construc-tion, 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 cefense that are designed to mitigate the conse-quences of failures in the first line.
9escriptic~ns of these features for v.
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CALUYS/ Job K 2nd Oraft 5-61 22 Aug 81 (3)
Callaway Units 1 and 2 may be found in the applicant's Final Safety Analysis k
Report (Ref. 2), and in the staff's forthcoming Safety Evaluation Report.
The most important mi.tigative features are described in Section 5.9.4.3 Design Features.
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.
Fission-Product Characteristics By far the largest inventory of radioactive material in a nuclear power plant is produced as a by product of the fission process and is located in the uranium oxide fuel pellets in the the reactor core in the form of fission products.
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 radioactive material is located in this storage area.
Much smaller inventories of radioactive materials are also normally present in the water that circulates in the reactor coolant system and in the systems used to process gaseous and liquid radioactive wastes in the plant.
l These radioactive materials exist in a variety of physical and chemical forms.
Their potential for dispersion into the environment is dependent not only on mechanical forces that might physically transport them, but also on their j
inherent properties, particularly their volatility.
The majority of these materials. exist as nonvolatile solids over a wide range of temperatures.
CAltN5/ Job X 2nd Draft 5-51 22 Aug 81 (4)
However, some are relatively volatile solids and a few are gaseous in nature.
These characteristics have a significant bearing on the assessment of the environmental radtological impact of accidents.
The gaseous materials include radioactive '.'orms of the chemically inert noble gases krypton and xenon.
These have the highest potential for release into the atmosphere.
If a reactor accident were to occur involving degradation of the fuel cladding, the release of substantial quantitt es of these radioactive gases from the fuel is a virtual certainty.
Such accidents are very low fre-quency but credible events (cf. Sec. 5.9.4.2).
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 system.
If fur-(~
ther released to the environment as a possible result of failure of safety A
features, the hazard to individuals from these noble gases would arise predomi-nantly through the external gamma radiation from the airborne plume.
The reactor containment system is designed to minimize this type of release.
Radioactive forms of iodine are formed 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.
However, the chemical forms in j
which the fission product radiciodines are found are generally solid materials
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at room temperature, so that they have a strong tendency to condense (or
" plate out") onto cooler surfaces.
In addition, most of the iodine compounds are quite soluble in, or chemically reactive with, water.
Although these properties do not prevent the release of radiciodines from degraded fuel, l
CALUVS/Jcb K 2nd Draft 5-61 22 Aug 81 (5) they do act to mitigate the release from containment systems 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 radiofodines will show a strong tendency to be absorbed by the moisture.
Because of radio-iodine's distinct radiological hazard, its potential for release to the atmo-sphere has also been reduced by the use of special filter systems and/or containment spray systems.
If released to the environment, the principal radiological hazard associated with the radioiodines 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 "7ble 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 producing 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 containment barrier, they will tend to be carried downwind and deposit on surface features by gravitational settling or by precipitation (fallout),
where they will become " contamination" hazards in the environment.
All of these radioactive m'aterials exh' bit. t.1 property of radioactive decay with characteristic half-lives ranging from fractions of a second to many days
CAWY5/ Job K 2nd Draft 5-61 22 Aug 81 (6) or years (see Table 5.15).
Many of them decay through sequence or chain-of-M decay processes and all eventually become stable (nonradioactive) materials.
The radiation emitted during these decay processes is the reason that they are hazardous materials.
Excosure Pathways The rartiation 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 Figure 5.1.
There are two additional possible pathways that
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could be significant for accidental releases that are not shown in that figure.
One of these is the fallout onto open bodies of water of radioactivity ini-tially 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 radio-active material into the hydrosphere through contact with groundwater. These pathways may lead to external exposure to radiation, and to internal exposures if radioactivity is inhaled or ingested 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 tv' ural processes is to lesser
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Taele 5.15.
Activity of Racionuclides in a Callaway Reactor Care at 3636 MWt Radioactive Inventory Half-Life Radionuclide (sillion C1)
(days)
Noble Cases Kr-85
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27.5 0.183 0.64 3,950 Kr-85e Kr-87 53 0.0528 Kr-88 77 0.117 Xe-133 194 5.28 Xe-13S 39 0.394 lodines I-131 97 8.05 1-132 133 0.0954 I-133 194 0.875 I-134 214 0.0366 I-135 173 0.280 Alkali Metals Rb-86 0.03 18.7 Cs-134 8.5 750 Cs-136
- 3. 4 13.0 Cs-137 5.3 11,000 Telluri ve-Anti mony Te-127 6.7 0.391 Te-127m 1.2 109 Te-129 34.7 0.048 Te-129s 6.0 34.0 Te-131m 14.3 1.25 Te-132 133 3.25 Sb-127 6.9 3.88 Sb-129 37.7 0.179 Alkaline Earths S r-89 102 52.1 S r-90 4.2 11.030 S r-91 122 0.403 8a-140 184 12.8 Cobalt and Noble Metals Co-58 0.89 71.0 Co-60 0.33 1,920 Mo-99 184 2.8 Tc-99e 163 0.25 Ru-103 122 39.5 Ru-105 82 0.185 Ru-106 29 366 Rh-105 56 1.50 Rare Earths. Refractory 0xides, and Transuranics Y-90 4.4 2.67 Y-91 133 59.0 Z r-95 173 5.2 Z r-97 173 0.71 Mb-95 173 35.0 La-140 184 1.67 Ce-141 173 32.3 Ce-143 153 1.38 Ce-144 97 284 Pr-143 153 13.7 Nd-147 68 U.1 Mp-239 1,836 2.35 Pu-238 0.064 32,500 Pu-239 0.023 8,900,000 Pu-240 0.023 2.400,000 Pu-241 3.9 5,350 An-241 0.0019 150,000 fa-242 0.57 163 Ca-244 0.027 6,630
CALWY5/ Job K 2nd Draft 5-61 22 Aug 81 (7) the intensity of exposure to individuals downwind or downstream of the point of release, but they also tend to increase the number of individuals who may be exposec.
For~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 vari-ability of wind direction and the presence or absence of precipitation, means that accident consequences are very much dependent on the weather cond):. ions existing at the time.
Health Effects The cause-and-effect relationships between radiation exposure and adverse kf/
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health effects are quite complex (Ref. 3, pp. 517-534, and Ref. 4), but they
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have been more exhaustively studied than any other environmental contaminant.
Whole-body radiation exposure resulting in a dose greater than about 10 rem A
for a few persons and about 25 rems for nearly all people over a short period of time (hours) is necessary before any physiological effects to an individual are clinically detectable.
Doses about 10 to 20 times larger, also received over a relatively short period of time (hours to a few days), an be expected to cause some fatal injuries. At the severe but extremely low probability end of the accident spectrum, exposures of these magnitudes are theoretically possible for persons in the proximity of such accidents if 'neasures are not or cannot be taken to provide protection, e.g. by sheltering or evacuation.
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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 knosn exposure to radiation is difficult given the backdrop of the many other possible reasons why a particular effect is observed in a specific individual.
For this reason, it is necessary to assess such effects on a statistical basis.
Such effects include cancer in the exposed population and genetic changes in future generations after exposure of a prospective parent.
Cancer in the exposed population may begin to develop only after a lapse of 2 to 15 years (latent period) from the time of exposure and then continue over a period of about 30 years (plateau period). However, in the case of exposure of fetuses (,in utero), cancer may begin to develop at birth (no latent period) and end at age 10 (i.e. the plateau period is 10 years).
The health-consequences model currently being used is based on the 1972 BEIR
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Report of the National Academy of Sciences (Ref. 5).
Most authorities are in agreement that a reasonable and probably conservative estimate of the statistical relationship between low levels of radiation expo-i sure to a large number of people is within the range of about 10 to 500 poten-tial 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
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also indicates a probable value of about 150. This value is virtually iden-tical to the vAlue of about 140 used in the current NRC health-effects models.
In addition, about 220 genetic changes per million person ren would be pro-
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jected 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 y
staff.
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Health-Effects Avoidance Radiation hazards. in the environment tend to disappear by the natural process of radioactive decay.
However, where the decay process is a slow one, and where the material becomes relatively fixed in its location as an environ-mental contaminant (e.g. In soil), 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 on the use of the contaminated property or contaminated food-stuffs, milk, and drinking water.
The potential economic impacts that this can cause are discussed below.
5.9.4.2 Accident Experience and Observed Impacts The evidence of accident frequency and impacts in the past is a useful indi-cator of future probabilities and impacts. As of mid-1981, there were 73 com-mercial nuclear power reactor units licensed for operation in the United States at 51 sites with power generating capacities ranging from 50 to 1130 megawatts electric (We).
(The Callaway Units 1 and 2 are designed for 1188 We each.) The combined experience with these units represents about 500 reactor years of operation over an elapsed time of about 20 years.
Acci-h dents have occurred at several of these facilities (Refs. 6 and 7).
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 fatality to any member of the public, any significant individual or collective public radi'tica exposures or
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CAltf(5/ Job K 2nd Draft 5-61 22 Aug 81 (10) any significant contamination of the environment. This experience base is not large enough to permit a reliable quantitative statistical inference.
- However, it does 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 units, during the accident at Three Mile Island - Unit 2 (TMI-2) on 28 March 1979.
In addition to the release of a few million curies of xenon-133, it has been estimated that a release of about 15 curies of radiofodine to the environment occurred at THI-2 (Ref. 8).
This amount represents an extremely N
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.
It has been estimated that the maximum cumulative offsite radiation dose to an individual was less than 100 millirems (Refs. 8 and 9).
The total population f
exposure has been estimated to be in the range of about 1000 to 3000 person-
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X rems.
This exposure could produce between zero 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-remy, and about a
,X half-million cancers are expected to develop in this group over its lifetime, primarily from causes other than radiation (Refs. 8 and 9). Trace quantities h
(barely above the limit of detectability) of radiofodine were found in a few I
samples of milk produced in the area.
No other food or water supplies were impacted.
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Accidents at nuclea power plants ha"O, Plso::aused occupational injuries and a few fatalities, but none attributed to radiation exposure.
Individual worker
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A exposures have ringed up to about 4 rems as a direct consequence of accidents,
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but the collective worker exposure levels (person-rems () are a small fraction
.A of the exposures-experienced during normal routine operations that average S
i about 410 person rems per reactor year.
Accidents have also occurred at other nuclear reactor facilities in the United States and in other countries (Refs. 6 and 7).
1;e to inherent differences in design, construction, operation, and purpose of cost of these other facili-ties, their accident records have 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 Atcmic 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 in 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 quan-tity of radiciodine, about 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 radiciodine and noble gases were released directly to the atmosphere from a 123-m (405-ft) stack. Milk produced in a 520-km2 (200-mi2) area around the facility was impounded for up to 44 days.
However, this kind of accident cannot occur in a water-cooled reactor like that at Callaway.
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CALWYS/Jon K 2nd Oraft 5-61 22 Aug 81 (12) 5.9.4.3 Mitigation of Accident Consequences Pursuant to the Atomic Energy Act of 1954, the Nuclear Regulatory Commission is conducting a safety (valuation of the application to operate Callaway Units 1 and 2.
Although this evaluation will contain more detailed informa-tion on plant design, the principal design features are presented in the fol-lowing section.
Design Features Callaway Units 1 and 2 are essentially identical units.
Each contains features designed to prevent accidental release of radioactive fission products from the fuel and to lessen the consequences should such a 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 features are collectively referred to as engineered safety features (ESF). The possibilities or probabilities of failure of these systems are incorporated in the assessments discussed in Section 5.9.4.4.
Each steel-lined concrete containment building is a passive mitigating system that is designed to minimize accidental radioactivity releases to the envi-ronment.
Safety injection systems are incorporated to provide cooling water to the reactor core during an accident to prevent or minimize fuel damage.
The containment spray system is' designed to spray cool water into the contain-ment atmosphere.
The operation of the spray system after a loss-of-coolant accident (LOCA) would prevent containment-system overpressure by quenching the steam generf ted, as a result of reactor caelant f1-as,hing into the containment
CALBYS/ Job X 2nd Draft 5-61 22 Aug181 (13) atmosphere. The spray water also contains an additive (sodium hydroxide) that will chemically react with any airborne radioiodine to remove it from the con-tainment 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 located in the fuel building also has accident mitigat-ing systems.
The ventilation system 'contains both charcoal and high efff-ciency particulate filters. This ventilation system is also designed to keep the area around the spent-fuel pool below the prevailing barometric pressure during fuel-handling operations so as to prevent exfiltration through building g-openings.
If radioactivity were to be released from the building, it would be drawn through the ventilation system and most of the radioactive iodine and particulate fission products would be removed from the flow stream before exhausting to the environment.
There are features of the plant 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 prie:ry so the secondary side of the steam generators (such as steam generator tube ruptures).
If normal offsite power is maintained, the ability of the plant to send conta-
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minated steam to the condenser instead of releasing it through the safety
CALWY5/J:b K 2nd Oraft 5-61 22 Aug 81 (14) valves or power-operated relief valves can significantly reduce the amount of radioactivity released to the environment.
In this case, the fission product-removal capability of the normally operating water processing system would come into play.
Much more extensive discussions of the safety features and characteristic t of the Callaway Plant may ba found in the applicant's Final Safety Analysh i
Report (Ref. 2).
The staff evaluation of these features will be addressed 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 that could result in large releases of fission products to the containment.
Specifically, the applicant is expected to follow the guidance on TMI-related matters specified in NUREG-0737.
As noted in Section 5.9.4.4 Uncertainties, no credit has been taken for these actions and improvements in establishing the radiological risk of accidents in this environmental statement.
Site Features In the process of considering the suitability of the site of Callaway Units 1 and 2, pursuant to NRC's reactor-site criteria in 10 CFR Part 100, consid-eration was given to certain factors that tend to minimize the risk and the potential impact of accidents.
First, the site has an exclusion area as pro-vided in 10 CFR Part 100.
The exclusion area of the 1290-ha (3188-acre) site has a minimum exclusion distance of 1200 m (3900 ft) from the midpoint between the reactor buildings, ard, lies entirely within the plant site.
Tra"ahilicant
CALWY5/Jon K 2nd Draf2 5-61 22 Aug 81 (15) owns all the surface rights within the exclusion area, including the mineral rights. The authority of the applicant to determine all activities within the exclusion area, which is required by Part 100, has been established by right of ownership.
Activities within the exclusion area that are unrelated to plant operation are limited to agricultural activities.
There are no industrial, recreational, or residential structures within the plant area.
The staff has determined that these activities will not interfere with normal plant operation, as required by Part 100.
Second, beyond and surrounding the exclusion area is a low population zone (LPZ), also required by 10 CFR Part 100.
This is a circular area with a radius of 4 km (2.5 mi).
Within this zone the applicant must assure that
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there is a reasonable probability that appropriate and effective measures could be taken on behalf of the residents and other members of the public in the event of a serious accident.
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 tne LPZ.
The purpose of this criterion is a :< cognition that, l
although accidents of greater potential hazards than those commonly postulated as representing an upper limit are conceivable, but highly improbable, it was considered desirable to add the population-center distance requirement to provide for protection against excessive doses to people in large centers.
No commercial or industrial facilities are located within the LPZ.
In 1970, i
l 116 residents lived within it, and the 1980 population has been estimated at
CALUYS/ Job K 2nd Oraf2 5-61 22 Aug 81 (16)
- 76. There are no sources of seasonal population in the LPZ with the exception of Lost Canyon Lake (a trailer park used seasonally), and the Reform Wildlife Management Area, which attracts hunters and fishermen.
There is no working-day concentration that woul.d create a significant transient population.
The nearest population center is Jefferson City, Missouri, located about 40 km (25 mi) west-southwest of the plant.
The City of Fulton, Missouri, located about 16 km (10 mi) southeast of the plant, had a 1970 population of 12,248.
Fulton is not expected to reach a population of 25,000 by 2020. The population-center distance is more than one and one-third times the LPZ, as required by Part 100.
The safety evaluation of the Callaway site has also included a review of potential external hazards, i.e. activities offsite that might adversely affect the operation of the plant and cause an accident. This review encom-passed nearby industrial, transportation, and military facilities that might create explosive, missile, toxic gas, or similar hazards.
The staff has con-cluded that the hazards from nearby industrial and military facilities, pipe-lines, air transportation, waterways, and railways are acceptably low. A more detailed discussion of the site features will be included in the staff's safety evaluation report.
Emergency Preoaredness Emergency preparedness plans including protective-action measures for the Callaway Plant and environs are in an advanced, but not yet fully completed, stage.
In accordance with the provisions of 10 CFR Section 50.47, effective t'
3 November 1980, an operating license will not be issued to the applicant s--
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CALWY5/ Job K 2nd Dr+'t 5-61 22 Aug 81 (17) unless a finding is made by the NRC that the state of onsite and offsite emer-gency preparednes jeovides reasonable assurance that adequate protective measures,can and 'will be taken in the event of a radiological emergency.
Among the standards that must be met by these plans are provisions for two Emernency Planning Zones (EPZ).
A plume-exposure pathway EPZ of about 16 km (10 mi) in radius and an ingestion-exposure pathway EPZ of about 80 km (50 mi) in radius are required. Other standards include appropriate ranges of protec-tive actions for each of these EPZs, provisions for dissemination to the public of basic emergency planning information, provisions for rapid notifi-cation of the public during a ser,ious reactor emergency, and methods, systems, and equipment for assessing and monitoring actual or potential offsite conse-quences in the EPZs of radiological-emergency conditions.
The NRC findings will be based on a review of the Federal Emergency Management Agency findings and determinations as to whether state and local government emergency plans are adequate and capable of being implemented, and on the NRC assessment as to whether the applicant's onsite plans are adequate and capable of being implemented. Although the presence of adequate and tested emergency plans cannot prevent the occurrence of an accident, it is the judgment of the staff that they can and will substantially mitigate the consequences to the l
public should one occur.
l 5.9.4.4 Accident Risk and Impact Assessment Desian-Basis Accidents Asi 2.means of.(assur:.7g that certain features ' f the Callaway Units 1 and 2 o
meet acceptable design and performance criteria, both the applicant and the l
CALUY5/ Job K
' 2nd Draf2 5-61 22 Aug 81 (18)
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staff have analyzed the potential consequences of a number of postulated
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accidents.
Some of these could lead to significant relaases of radioactive materials tc the environment, and calculations have been performed to estimate the potential radiological consequences to persons offsite.
For each postu-lated initiating event, the potential radiological consequences cover a consi-derable range of values depending on the particular course taken by the acci-dent and the conditions, including wind direction and weather, orevalent during the accident.
In the safety analysis and evaluation of Callaway U. sits 1 and 2. three cate-gories of accidents have been considered by the applicant and the staff.
These categories are based upon their probability of occurrence and include (1) incidents of moderate frequency, i.e. events that can reasonably be expected
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to occur during any year of operation; (2) infrequent accidents, i.e. events
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that might occur once during the lifetime of the plant; and (3) limiting faults, i.e. accidents not expected to occur but that have the potential for significant releases of radioectivity.
The radiological consequences of inci-dents in the first category, also called anticipated operational occurrences, are discussed in Section 5.9.3.
Initiating events postulated in the second and third categories for the Callaway Units 1 and 2 are shown in Table 5.16.
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These are celect4vely' designated design-basis accidents in that specific
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design and operating features as described in Section 5.9.4.3 Design Features are provided to limit their potential radiological consequences. Approximate radiation doses that might be received by a person at the most adverse location along the site boundary (1200 m or 3900 ft from the plant) are also shown in the table, along with a characterization of the time duration of the releases.
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Table 5.16.
ApproximateRadiationOosesfrgmDesign-Basis Accidents at the Callaway Plant Dose at 1200 mb (rems)
Design-Basis Accidents Thyroid Whole Body Infrecuent Accidents Rod-ejection accident 43.0 0.1 Steam generator tube rupture 72.0
- 1. 0 Fuel-handling accident 4.0 1.0 Limiting Faults Main steam-line break 3.6 0.1 C
Large-break LOCA 91.0
- 2. 2
.a Duration of release less than two hours.
b The site boundary distance that yields the highest radiologi-cal dose following an accident.
c Loss-of-coolant accident.
{*
i g
s m
CALWYS/ Job K 2nd Draft 5-61 22 Aug 81 (19)
The staff has used conservative models for calculations to estimate the poten-tial upper bounds for individual exposures summarized in Table 5.16 for the Q//
l purpose of imple~menting the provisions of 10 CFR Part 100, " Reactor Site Criteria."
For these calculations, pessimistic (conservative or worst case) assumptions are made as to the course taken by the accident and the prevailing conditions.
These assumptions include much larger than expected amounts of radioactive material released by the initiating events, additional single l
failures in equipment, operation of ESFs in a degraded mode,* and very poor meteorological-dispersion conditions.
The results of these calculations show that, for these events, the limiting whole-body exposures are not expected to exceed 2.2 rems /
to any individual at i
the site boundary.
They also show that radiofodine releases have the poten-tial for offsite exposures ranging up to about 91 rem to the thyroid.
For X
such an exposure to occur, an individual would have to be located at a point on the site boundary where the radioiodine 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 health risk to an individual receiving such a thyroid exposure is the potential appearance of benign or malignant thyroid nodules in about 3 out of 100 cases, and the development of a fatal cancer in about 1 out of 1000 cases.
l None of the calculations of the impacts of design-basis accidents described in,
this section takes into consideration possible reduction in individual or population exposures as a result of taking any protective action.
-a-
"However, the containment system is assumed to prevent leakage in excess of, '
that demonstrable by testing, as provided in 10 CFR Part 100.11(a).
... 7 ' '" 2'~.-.:.
p.r 3 s.
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CALWYS/ Job K 2nd Oraft 5-61 22 Aug 81 (20)
Probabilistic Assessment of Severe Accidents In this and the following three sections, there is a discussion of the proba-bilities and consequences of accidents of greater-severity than the design-basis accidents discussed in the previous section. They are considered less likely to occur, but their consequences could be severe, both for the plant itself and for the environment.
These severe accidents can be distinguished from design-basis accidents in two primary respects:
they involve substantial physical deterioration 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.
Heretofore, these acci-dents have frequently been called Class 9 accidents.
As a class, they include all accidents involving sequences of failures more severe than those postu-lated for the design basis of the protective systems and engineered safety features.
The consequences of such accidents could be severe.
The assessment methodology employed is that described in the Reactor Safety Study (RSS), which was published in 1975 (Ref.10).*
However, the sets of f
accident sequences that were found in the RSS to be the dominant contributors to the risk in the prototype PWR (Surry Unit 1) have recently been updated or "rebaselined" (Ref.12).
The rebaselining has been done largely to incorpo-k rate peer group comments (Ref.12) and better data and analytical techniques p
resulting from research and development after the publication of the RSS.
- Because this report has been the subject of considerable controversy, a discus-7 sion of the uncertainties surrounding it is provided-in Section 5.0.4.4
(~
Uncertainties.
CALUYS/ Job K 2nd Oraf2 5-61 22 Aug 81 (21)
Entailed in the rebaselining effort was the evaluation of the individual domi-nant accident sequences as they are understoort to evolve. The earlier tech-nique of grouping a number of accident sequences into the encompassing release categories, as was done in. the RSS, has been largely (but not completely) eliminated.
The Callaway Units 1 and 2 are Westinghouse-designed PWRs having design and operating characteristics similar to those of Surry Unit 1, which was used in the RSS as a prototype for PWRs. Therefore, the present assessment for Callaway has used as its starting point the rebaselined accident sequences and release jg[
categories referred to above, and more fully described in Appendix E.
Charac-e teristics 'of the sequences (and release categories) usee Oli of which involve partial to complete melting of the reactor core) are shown in Table 5.17.
Q/7 Sequences initiated by natural phenomena such as tornados, flood, or seismic events, and those that could be initiated by deliberate acts of sabotage, are not included in these event sequences.
The radiological consequences of such events would not be different in kind from those that have been treated.
Moreover, it is the staff's judgment, based on design requirements of 10 CFR Part 50, Appendix A, relating to effects of natural phenomena, and safeguards requirements of 10 CFR Part 73, that these events do not contribute signifi-cantly to risk.
Calculated probability per reactor year associated with each accident sequence k/7 (or sequence group) used is shown in the second column in Table 5.17.
As in the RSS there are substantial uncertainties in these probabilities. This is due, in part, to difficulties associated with the quantification of human
{
errcr sad to inadquacies ia' the t'ata 'Jase oi:*ailure rutes.of individual
/
.tO Table 5.17.
Summary of Atmospheric Releases in ligpothetical Accident Sequences in a PWR (Rebaselined)
Accident l
Fraction of Core Inventory Released ee e Probability per C
Category Reactor Year Xe-Kr I
Cs-Rb Te-Sb Ba-Sr Ru La*
Event V 2.0(-6)I 1.0 0.64 0.82 0.41 0.1 0.04 0.006 TMLB' 3.0(-6) 1.0 0.31 0.39 0.15 0.044 0.018 0.002 y
si PWR 3 3.0(-6) 0.8 0.2 0.2 0.3 0.02 0.03 0.003 g
N PWR 7 4.0(-5) 6(-3) 2(-5) 1(-5) 2(-5) 1(-6) 1(-6) 2(-7) a See Section 5.9.4.4 Uncertainties for a discussion of uncertainties in risk estimates.
h b
Background on the isotope groups and release mechanisms is presented in Appendix VII of
" Reactor Safety Study," WASH-1400, NUREG-75/014, October 1975.
(
c See Appendix E for a description of accident sequences and release categories.
d Includes Ru, Rh, Co Mo, Tc.
e Includes Y, La, Zr, Nb, Ce, Pr, Nd, Np, Pe,, Am, Ca.
f Exponential notation: 2.0(-6) = 2.0 x 10 0
,y l
e
CALUY5/ Job K 2nd Oraft 5-61 22 Aug 81 (22) plant components that were used to calculate the probabilities (Ref.12) (see Sec. 5.9.4.4 Uncertainties).
The probability of accident sequences from the Surry plant were used to give a perspective of the societal risk at Callaway Units 1 and 2 because, although the probabilities of particular accident sequences may be substantially different for Callaway, the overall effect of all sequences taken together is likely to be within the uncertainties (see Sec. 5.9.4.4 Uncertainties).
The magnitudes (curies) of radioactivity releases for each accident sequence or release category are obtained by multiplying the release fractions shown in Table 5.17 by the amounts that would be present in the core at the time of the TA'//
hypothetical accident.
These are shown in Table 5.15 for a Callaway reactor core at the thermal power level of 3636 megawatts.
The potential radiological consequences of these releases have been calculated by the consequence model used in the RSS (Ref.13) and adapted to apply to a h
specific site.
The essential elements are shown in schematic form in Figure 5.2.
Environmental parameters specific to the Callaway site have been Fo used and include the following:
1.
One full year of consecutive hourly averages of 1974/1975 meteorological data from the site meteorological-monitoring systems, and precipitation data obtained from Columbia, which is about 24 km (15 mi) from the site; 2.
Projected population for the year 2000 extending throughout regions of 80- and 560-km (50- and 350-mi) radii from the site;
,.Q-l
b -//
22+
l weather cata isi.... Cat. sori.. y.t
..ne,4 l31soorsion O* 'I"* *U Healta Effects o
Cloud Oeoletion Property Oamage Population Ground Contamination Evacuation Figure 5.2.
Schematic Outline of Consequence Model, t
s i
e
^;
G:
CALUY5/Jcb K 2nd Draft 5-61 22 Aug 81 (23) 3.
The habitable land fraction within the 560-km (350-mi) radius; and 4.
1.and-use statistics, on-a state-wide basis, including farm land values, farm product values including dairy production, and growing-season infor-mation, for the State of Missouri and each surrounding state within the 560-km (350-mi) region.
To obtain a probability distribution of consequences, the calculations are performed assuming the occurrence of each accident release sequence at each of 91 different " start" times throughout a one year period.
Each calculation uses the site-specific hourly meteorological data and seasonal information for the time period following each " start" time.
The consequence model also contains provisions for incorporating the consequence-reduction benafits of evacuation and other protective actions.
Early evacuation of people would considerably reduce the exposure from the radioactive cloud and the contami-nated ground in the wake of the cloud passage. The evacuation model used, as discussed in Appendix F, has been revised from that used in the RSS for better
.[
site-specific application. The quantitative characteristics of the evacuation model used for the Callaway site are best-estimate values made by the staff and based on evacuation-time estimates prepared by the applicant.
Actual evacuation effectiveness could be greater or less than that characterized, but would not be expected to be very much different.
The other protective actions include:
(1) either complete denial of use l
(interdiction) or permitting use only at a sufficiently later time after appropriate decontamination of foodstuffs such as crops and milk, (2) decon-
{,
tamination of'seve' rely contaminated environment (land and property) when it is
CALUYS/ Job K 2nd Draft 5-61 22 Aug 81 (24) considered to be economically feasible to lower the levels of contamination to protective-action guide (PAG) levels, and (3) denial of use (interdiction) of severely contaminated land and property for varying periods of time until the contamination levels reduce to such values by radioactive decay and weathering that land and property can be economically decontaminated as in (2) above.
w These actions would reduce the radiological exposure to the people from the immediate and/or subsequent use of, or living in, the contaminated environment.
Early evacuation within the plume-exposure pathway EPZ and other protective actions as mentioned above are considered as essential sequels to serious nuclear reactor accidents involving significant release of radioactivity to the atmosphere.
Therefore, the results shown for Callaway include the bene-fits of these protective actions.
(
There are also uncertainties in the estimates of consequences, and the error bounds may be as large as they are for the probabilities.
However, in the judgment of the staff, it is more likely that the calculated 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 asso-ciated with property damage by radioactive contamination:
1 Dose and Health Impacts of Atmospheric Releases The results of the calculations of dose effects and health impacts performed 4
for the Callaway Plant and site are presented 1. the form of probability 1
l l
CALWYS/ Job K 2nd Oraft 5-61 22 Aug 81 (25) fx3 f.
distributions in Figures 5.3 through 5.6 and are included in the impact-summary Table 5.18.
All of the four accident sequences and release categories shown Ff/
T*.(*/8' in Table 5.17 contribute to the results, the consequences from each being Th'If t
weighted by its associated probability.
O Figure 5.3 shows the probability distribution for the number of persons who might receive whole-body doses equal to or greater than 200 rems lland 25 rems,d j
and thyroid doses equal to or greater than 300 rem [from early exposure," all X
on a per-reactor year basis.
The 200-rem whole-bcdy dose figure corresponds approximately to a threshold value for which hospitalization would be indicated
. for the treatment of radiation injury.
The 25-rem whole-aody (which has been identified earlier as the lower limit for a clinically observable physiological effect) and 300-rem thyroid figures correspond to '.he Commission's guideline r,
values for reactor siting in 10 CFR Part 100.
(s The figure shows in the left-hand portion that there are less than eight chances in a million per year (i.e. 8 x 10 8) that one or more persons may receive doses equal to or greater than any of the doses specified. The' fact that the three curves run almost parallel and horizontal ows that if one 5
person were to receive such doses, the chances are about the same that several tens to hundreds would be so exposed. The chances of larger numbers of persons
'~
being exposed at those levels are seen to be considerably smaller.
For example, the chances are about one in a hundred million per reactor year (i.e.10.s) that 6000 or more people might receive doses of 200 rem r greater. A majority
)(
"Early exposure to an individual includes external doses from thi radioactkve
/
cloud and the contaminated ground, and the dose from internally.eposited radionuclides from inhalation of contaminated air during the cloud passage.
Other pathways of exposure are excluded.
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Sb is-id 16 18 1d 16 1d 16 16 g$ "1 11GEND E~
g a = WHoLE BODY DOSE 25 REM x
o = THYR 0!D DOSE 300 REM yo a = WHOLE BODY DOSE 200 REM 3
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'id-X=NUNBER or AFrECTED PERSONS Figure 5.3.
Probability Distribution of Individual Dose Impacts.
(See Sec. 5.9.4.4 Uncertainties for a discussion of uncertainties in risk estimates.)
(50 mi = 80 km)
C.
, 16 16 18 1,8
. Ad 18,
- 1 LECEND
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o = ENTIRE EXPOSED POPULAT!oM o = POPULATION WITHIN SO MILES AS a=.
8 lD 1
o.
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l X= TOTAL PERSON REM whole body l
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Figure 5.4.
Probability Distribution of Population Exposure.
s.
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kf gid 16 Id 16, "1
LEGEND
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o = EVAC. TO 10 MILE 5 :
x
- 4. <
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Do' Ib g!
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i X= ACUTE FATALITII3 Figure 5.5.
Probability Distribution of Acute Fatalities.
(See Sec. 5.9.4.4 Uncertainties for a discussion of uncertainties
(
in risk estirrates.)
(10 mi = 16 km, 50 mi = 80 km) 18 Id
_ _1,8 1d, "I
LEGEN D r"
E o = ENTIRE EXPOSED POPULATION-EXC1. THYROID p
o = ENTIRE EXPOSED POPULATION-THYROID ONLY l
- g a = WITHIN SO MILES-EXCLUDIMC THYROID g
+ = WITHIN SO MILI3-THYHOID ONLY r-g-l I
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gg
'gg
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-gg I= LATENT CANCER FATALITIES PER YEAR FOR 30 YEARS
- f..
J Figure 5.6.
Probability Distribution of Cancer Fatalities.
1
--a.
n.
', *. 3 i
a Table 5.18.
Summary of Environmental Impacts and Probabilities i
I Number of Fatalities l
Prrbability Population Exposur Lateng Hitigating Per Ex sed 3
per Year y (million person rem )
Cancer Actions j
. ll !
of Impact
> 200 res(f > 25 remi" 80 km/ total Acute 80 km/ total
($ million) j-
[g 10 4 0
0 0/0 0
0/0 0
10 5 0
0 0.0065/0.01 0
0/0 2.5 5 x 10 a -
0 2,500 0.6/10.0 0
45/530 280 Vg i
10 s 300 13,000 2/30 19 210/1,860 1,000 g
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N 10 7 2,000 40,000 4.5/70 260 570/4,400 2,800 i
10 s 6,000 650,000 60/105 1,100 810/8,400 7,000 l'
Related figure
' 5. 3 5.3 5.4 5.5 5.6 5.7 O g
. M Q
t
,,' I a
See Section 5.9.4.4 Uncertainties for a discussion of uncertainties in risk estimates.
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b Thirty times the values in Figure 5.6 are shown in this column, reflecting the 30 year period over which if they might occur. Genetic effects would be about twice the number of latent cancers.
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CALWYS/ Job K 2nd Draft 5-61 22 Aug 81 (26) of the exposures reflected in this figure would be expected to occur to persons
(
within an 80-km (50-mi) radius of the plant. Virtually all would occur within
~
a 160-km (100-mi) radius.
[h[
Figure 5.4 shows the probability distribution for the total population expo-sure in person-rem [i.e. the probability per reactor year that the total K
For the more population exposure will equal or exceed the values given.
severe accidents (first three accidents in Table 5.17) the population exposure T3,'/ 7
/
up to 1 million person-rems"would occur within 80 km (50 mi), and exposure greater than 10 million person-remskould result to person beyond the 80-km Y
(50-mi) range as shown.
m For perspective, population doses shown in Figure 5.4 may be compared with the f$
annual average dose to the population within 80 km (50 mi) of the Callaway v
~"
f site due to natural-background radiation of 50,000 person-rem [and to the X
anticipated annual population dose to the general public from normal plant kW person-rems (excluding plant workers) (App. C, Table W
l operation of about
~
and C.9)..
74
[I '
Figure 5.5 shows the probability distrib ions for acute fatalities, repre-senting radiation injuries that would produce fatalities within about one year l
after exposure. Virtually all the acute fetalities would be expected to occur within the 24-km (15-mi) radius.
The results of the calculations shown in this figure and in Table 5.18 reflect the effect of evacuation within the
~.67/7 16-km (10-mi) plume-exposure pathway EPZ only.
For the very low probability accidents having t,he potential for causing radiation exposures above the threshol'd for acute f a'tality at distances boyend 16 ka'(In 'mi), it would ba
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.. :... =. -.,..,.. 74 4. -.e
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3 4
CALWYS/ Job K 2nd Draf2 5-61 22 Aug 81 (27) realistic to expect that authorities would evacuate persons at all distances at which such exposures might occur.
Therefore, acute-fatality consequences would be expected to be less than the numbers shown.
Figure 5.6 represents the statistical 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 popula-tion within 80 Ln (50 mi) are shown separately.
Further, the latent fatal cancers have been subdivided into those attributable to exposures of the thyroid and all other organs.
Economic and Societal Impacts As noted in Section 5.9.4.1, the various measures for avoidance of adverse health effects, including those due to residual radioactive contamination in the environment, are possible consequential impacts of severe accidents.
Calculations of the probabilities and magnitudes of such impacts for the Callaway Plant and environs have also been made. Unlike the radiation exposure and adverse health-effect impacts discussed 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 offsite mitigating actions in Figure 5.7 and are included in the impact-sumary FC Table 5.18.
The factors contributing to these estimated costs include the fg following:
e q
5- //
47 ~)
,11 11 td 11 ad 11 td
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- tot, it.tc E.w u !-
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--I l-Aq g.S I
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8, '
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~d td Id td id id td t( '
it' t
X= TOTAL Co37 IN Do!LARS 1980 Figure 5.7.
Probability Distribution of Mitigation-Measures Cost.
(See Sec. 5.9.4.4 Uncertainties for a discussion of uncertainties in risk estimates.)
s 9
9 e
e G
,r a
=
CAlb'YS/ Joe K 2nd Draft 5-61 22 Aug 81 (28) 1.
Evacuation costs, 2.
Value of crops contaminated and condemned, 3.
Value of milk contaminated and condemned, 4.
Costs of decontamination of property where practical, and 5.
Indirect costs due to loss of use of prcperty 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 5.7 shows that at the extreme end of the accident spectrum these costs
[a7 could approach ten t;illion dollars, but that the probability that this would occur is exceedingly small, less than one chance in one billion per reactor year.
Additional economic impacts that can be monetized include costs of decontami-nation of the facility itself and the costs of replacement power.
Probability distributions for these impacts have not been calculated, but they are included
~
in the discussion of risk considerations in Section 5.9.4.4 Risk Considerations.
.C.
g.,
Q.,
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CALUYS/ Job K 2nd Oraf2 5-61 22 Aug 81 (29)
Release to Groundwater A pathway for public radiation exposure and environmental contamination that could be associated with severe reactor accidents was identified in Section 5.9.4.1 Exposure Pathways.
Consideration has been given to the poten-j tial environmental impact of this pathway for the Callaway Plant. The prin-cipal contributors to the risk are the core-melt accidents..The penetration of the basemat of the containment buildings can release molten core debris to the strata beneath the plant.
Soluble radionuclides in 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 Callaway units, 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) (Ref. 14).
The LPGS compared the risk of accidents involving the liquid pathway (drinking water, irrigation, aquatic food, swimming and shoreline usage) for four conventional, generic land-based nuclear plants and a floating nuclear plant, for which the nuclear reactors would be mounted on a I
barge and moored in a water body.
Parameters for the land-based sites were chosen to represent averages for a wide range of real sites and are thus l
" typical," but represented no real site in particular.
t e
The. discussion in this section is an analysis to determine whether or not the v
Callaway site liquid pathway consequences would be unique when compared to l
CALBYS/ Job K 2nd Draft 5-61 22 Aug 81 (30) land-based sites considered in the LPGS.
The method consists of a direct scaling of LPGS population doses based on the relative values of key param-eters characterizing the LPGS "small-river" site and the Callaway site.
The parameters that are normally evaluated included amounts of radioactive mate-rials entering the ground, groundwater travel time, sorption on geological media, surface-water transport, drinking-water use, aquatic-food consumption, and shoreline use.
Individual and population doses were calculated in the LPGS without consider-ation of interdiction methods such as isolating the contaminated groundwater or denying use of the water.
In the event of surface-water contamination, alternative sources of water for drinking, irrigation, and industrial use would be expected to be found, if necessary. Commercial and sport fishi..,3, as well as many other water-related activities, would be restricted. Therefore, the consequences would be largely economic or social, rather than radiological.
In any event, the individual and population doses for the liquid pathway range from fractions to very small fractions of those that can arise from the air-borne pathways.
The Caliaway site is located above several aquifers.
However, contamination from an assumed core-melt accident would affr.ct only the upper water-table aquifer.
This is because of the deptns of tiu lower aquifers and the lack of hydraulic connection to the upper aquifer due to intervening aquicludes.
In its analysis of liquid tank spills in Section 2.4.13 of the Final Safety Analysis Report (Ref. 2), the applicant estimated groundwater transport time from the s}te to the nearest surface-water, drainage feature, a tributary of
~.
m
CALWYS/ Job K 2nd Oran 5-61 22 Aug 81 (31)
Mud Creek.
Groundwater transport was assumed to occur in the Graydon Chert conglomerate, the Burlington Limestone, and Bushberg Sandstone. A conservative value of of 5.0 x.10 4 cm/s was used for horizontal permeability, the effective porosity was estimated to be 0.12, and the hydraulic gradient was chosen to be 0.0144. The staff considers these parameters to be conservative.
Using these parameters, a minimum travel time of about 60 years was calculated for ground-water released at the site to reach the tributary of Mud Creek and subsequently the Missouri River. This compares to a travel time of about 0.6 year used for the LPGS river site.
For groundwater travel times of several years or longer, the LPGS showed that the only significant contributors to population dose frcm an assumed core-melt accident would be Sr-90 and Cs-137.
To estimate the travel times of these nuclides the applicant estimated values of the retardation factors, which reflect the effects of sorption within the aquifer.
Base (. on data obtained from similar geologic media, these values were 7.1 for Sr-90 cnd 14.5 for Cs-137.
The staff considers these estimates to be consistent with ranges of retardation factors observed in a wide variety of geologic materials similar to those at the site (Ref.15).
Using these estimates, the transport time f
from the reactor building to Mud Creek is estimated to be 426 years for Sr-90 and 870 years for Cs-137.
i l
When these times are compared to 5.7 years for Sr-90 and 5.1 years for Cs-137 in the LPGS land-based river case, the relatively larger travel times for the I
Callaway site would allow a much smaller portion of the radioactivity to enter ue surface water.
For an equal source of radioactive material, the quantity of materials entering the river would be reduced by a factor of at least 17,000 for Sr-90 and 1.8 x 10s for Cs-137, compared to the LPGS case.
l l
l l
CALWYS/ Job K 2nd Draft 5-61 22 Aug 81 (32)
The nearest water well that could be affected by liquid releases to groundwater is about 2650 m (8700 ft) downgradient.
The minimum groundwater travel time to this well has been conservatively calculated to be greater than 200 years.
Therefore, direct contamination of groundwater drinking supplies has not been considered to contribute in any significant way to population dose.
Without further analysis it can be concluded that, because of the relatively long travel times, little or no radioactive materials could enter and contam-inate surface water near the Callaway site.
Therefore, the Callaway liquid-pathway contribution to population dose has been shown to be much smaller than that predicted for the LPGS river site, which represents a " typical" river site.
Thus, the Callaway site is not unique in its liquid pathway contri-bution to risk.
Furthermore, there are measures that could be taken to minimize the impact of the liquid pathway.
The staff estimates that the minimum groundwater travel time from the site to Mud Creek would be about 60 years, and that the holdup radioactivity would be much greater, which would allow ample time for engine-ering measures such as slurry walls and well point dewatering to isolate the radioactive contaminants at the source.
Risk Considerations The foregoing discussions have dealt with both the frequency (or likelihood of occurrence) of accidents and their impacts (or consequences).
Because the ranges of both factors are quite broad, it is useful to combine them to obtain average measures of environmental risk.
Such averages can be particularly
CA WYS/ Job K
- 2nd Draft 5-61 22 Aug 81 (33) l instructive as an aid to the comparison of radiological risks associated with o
(
accident releases and with normal operational releases.
A common way in which this combination of factors is used to estimate risk is The resultant risk is then to multiply the probabilities by the consequences.
Such a expressed as a number of consequences expected per unit of time.
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 such a measure.
At best, it can be a contributing factor to a risk judgment, but not necessarily a decisive factor.
In Table 5.19 are shown average expected values of risk associated with popu-7g/y lation dose, acute fatalities, latent fatalities, and costs for evacuation and r.
other piotective actions.
These average values are obtained by summing the probabilities multiplied by the consequences over the entire range of distri-i ts butions.
Because the probabilities are on a per reactor year basis, the averages shown are also on a per reactor year basis.
The population-exposure and latent-cancer-fatality risks may be compared with fffy,$
j those for normal-operation releases, shown in Appendix C, Tables C.7 and C.9.
7gy I6,9 The radiological dose to the population due to normal operation of each unit j
may be abou person-rem per year. TMs-dosc - ay-restrit-+n-O:c0067-4etent-K cancer-death-to-the exposed population.-The -1atent-cancer-death. predicted-to
' res'M t 5m-sec4 dents-is-expected-to-be-Or0077-(Table-h-19)r--The-comparisorr gj7 shows-that-accident-risks-are-comparable to normal-operation-risks.
There are no acute-fatality or ecormmic risks associated wif.N' protective
/-
actions' and decontamination for nonnal releases; therefore, these risks are '
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Annual Average Expected Values of EnvironmentalRisksDuetogccidentsat the Callaway Plant Population. exposure (person-rems 8 b
Within 80 km (50 mi) 9 Total 126 Number of acute fatalities 0.0001 Number of latent-cancer fatalities All organs excluding thyroid 0.0065 Thyroid only 0.0012 Cost of protective actions a.
and decontamination ($)
4300 a
See Section 5.9.4.4 Uncertainties for dis-cussions of uncertainties in risk estimates.
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CAulY5/ Job K 2nd Oraft 5-61 22 Aug 31 (34) unique for accidents.
However, for perspective and understanding of the meaning of the acute-fatality risk of 0.0001 per year the staff notes that, to a good approximaticn, the population at risk is that within about 16 km (10 mi) of the plant, about 12,000 persons in the year 2000. Accidental fatalities per year for a population of this size, based on overall averages for the United States, are about two fiom motor-vehicle accidents, one from falls, one from drowning, and one from burns (Ref. 3).
Figure 5.8 shows the calculated risk expressed as whole-body dose to an indi-
[b,T vidual from early exposure as a function of the distance from the plant within the plume-exposure pathway EPZ.
The values are on a per-reactor year basis, and all accident sequences and release categories in Table 5.17, weighted by y
their associated probabilities, contributed to the doso.
Within the 16-km (10-mi) radius plume-exposure pathway EPZ, the calculations show that the best-estimate evacuation can reduce the risk of acute fatality to an individual to near zero.
Evacuation and other protective actions also reduce the risk to an individual of latent-cancer fatality.
Figures 5.9
[b![
and 5.10 show curves of constant risk per reactor year to an individual living
[3[jp I
within the plume-exposure pathway EPZ of the Callaway Plant of acute death and I
of death from latent cancer, respectively, as a function of distance due to potential accidents in a reactor.
Directional variation of these curves reflects the variation in the average fraction of the year the wind would be
(
blowing into each direction from the plant.
For comparison, the following 1
risks of fatality per year to an individual living in the United States may be noted:
automobile accident 2.2 x 10 4, falls 7.7 x 10 5, drowning 3.1 x10 5, burning 2.9 x 10 5, and firearms 1.2 x 10 5.(Ref. 3).
h 1
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INDIVIDUAL RISK 0F DOSE AS A FUNCTION OF DISTANCE
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Individual Risk of Dose as a Function of Distance.
(See Sec. 5.9.4.4 Uncertainties for a discussion of uncertainties in risk estimates.)
(To con-vert mi to km, multiply by 1.6097.)
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Isopleths of Risk of Acute Fatality per Reactor Year to an Individual.
(To convert mi to km, multiply by 1.6093.)
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Figure 5.10.
Isopleths cf Risk of Latent-Cancer Fatality per Reactor Year to an Individual.
(To convert mi to km, multiply by 1.6093.)
l
CALWY5/ Job X 2nd Oraft 5-61 22 Aug 81 (35)
The economic risk associated with evacuation and other protective actions could be compared with property-damage costs associated with alternative energy generation-technologies.
The use of fossil fuels, coal or oil for example, 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 (Ref. 3, pp. 559-560).
However, this effect has not 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 5.9.4.4 Economic and Societal Imoacts.
These impacts relate to the added cost to the public due to the loss of the nuclear unit itself.
The costs associated with this loss include those for decontamination, repair or replacement of the plant, and replacement power.
No detailed methodology has been developed for estimating the contribution of an accident to the economic risk to the licensee for decontamination and restoration of the plant.
Experience with such costs is currently being accu-mulated as a result of the Three Mile Island acciae nt.
If an accident occurs during the first year of the Callaway Unit 1 operation, the economic penalty in present-worth dollars, reflected to the initial year of Unit 1 operation, is estimated at $1.3 billion for decontamination and restoration of the plant and $600 million for replacement power during the period the plant is being restored.
This estimate assumes that the plant would be out of commission for eight years and that tr e energy that would have been forthcoming from the "r
Callaway unit (assuming 60% capacity factor) would be replaced largely by coal-fired generation within the general area.
CALWYS/ Job K 2nd Oraft 5-61 22 Aug 81 (36)
If the probability of sustaining a total loss of the original plant is taken as the sum of the probabilities of the occurrence of core-melt accidents, there would be about 4.8 chances in 100,000 (i.e. probability of 4.8 x 10 5) 4 that a disabling accident cid happen during each year of service life of the units.
Multiplying the previously estimated cost of $1900 million for an accident to Callaway Unit 1 during the initial year of its operation by the 4.8 x 10 5 probability r'esults in an economic risk of $91,000 applicable to Callaway Unit 1 during that year. This is also the approximate economic risk during the second and each subsequent year of its operation.
Although the nuclear units depreciate in value and probably operate at reduced capacity factors such that the economic consequer.ces due to an accident become less as the units become ' cider, this is offset by higher cost (due to inflation) of decontamination and restoration of the units in the later years.
Uncertainties The foregoing probabilistic and risk-assessment discussion has been based on the methodology presented in the Reactor Safety Study (RSS), which was pub-lished in 1975.
In July 1977, the NRC organized an Independent Risk Assessment Review Group to l
(1) clarify the achievements and limitations of the RSS 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 methodology can be used in the regulatory and licensing 3
process.
The results of this study were issued in September 1978 (Ref.12).
f
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CALW5/ Job K 2nd Draft 5-61 22 Aug 81 (37)
This report, called the Lewis Report, contains several findings and recommen-dations concerninj the RSS.
Some of the more significant findings are summa-rized below:
1.
A rw::ter of sources of both conservatism and nonconservatism in the prob-ability 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 methodolo-gies 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 discussion of reactor risk.
On 19 January 1979, the Connission issued a statement of policy concerning the RSS and the Review Group Report.
The Commission accepted the findings of the Review Group.
The acci. dent at Three Mile Island occurred in March 1979 at a time when the accumulated experience record was about 400 reactor 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 (Ref. 3, p. 553).
It should also be noted that r
the Three Mile Island accident has resulted in a very comprehensive evaluation l
of reactor accidents like that one, by a significant number of investigative l
l CALMY5/ Job K 2nd Ora 9t 5-61 22 Aug 81 (38) groups both within NRC and outside it.
Actions to improve the safety o 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 Devel-oped as a Result of the TMI-2 Accident," NUREG-0660, Vol. I, May 1980, collects the various recommendations of these groups and describes them under the sub-ject areas of: Operational Safety; Siting and Design; Emergency Preparedness and Radiation Effects; Practices and Procedures; and NRC Policy, Organization, and Management.
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 Callaway Plant is receiving and will receive the benefit of these actions on the schedule indicated in NUREG-0660.
However, the improvement in safety from these actions has not been quantified, and the radiological risk of accidents discussed in this section does not reflect these improvements.
S.9.4.5 Conclusions The foregoing sections consider the potential environmental impacts from acci-dents at the Callaway Plant. These have covered a broad spectrum of possible accidental releases of radioactive materials into the environment by atmo-spheric and groundwater pathways.
Included in the considerations are postu-lated 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 radia-tion exposures to individuals Ped-tb ~the popul,ation as a whole, the risk of
i CALWYS/ Job K
~ 2nd Draft 5-61 22 Aug 81 (39) g near-and long-term adverse health effects that such exposures could entail, and the potential economic and societal consequences of accidental contamina-tion of the environment. These impacts could be severe, but the likelihood of their occurrence is judged to be small. This conclusion is based on (1) the fact that considerable experience has been gained with the operation of simi-lar facilities without significant degradation of the anvironment; (2) that, in order to obtain a license to operate the Callaway Plant, it must comply with the applicable Commission regulations and requirements; and (3) a probabi-listic assessment of the risk based on the methodology developed in the RSS.
The overall assessment of environmental risk of ac'cidents, assuming protective ri M \\c.y action, shows that it is.less-than the risk for normal operational rele,ases, Y
A although accidents have a potential for acute fatalities and economic costs that cannot arise from normal operations.
The risks of acute fatality from potential accidents at the site are small in comparison with the risks of e-acute fatality from other human activities in a comparably sized population.
The staff concludes that there are no special or unique features about the Callaway site and environs that would warrant special mitigation feature's for the Callaway Plant.
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CALMY5/ Joe K 2nd Draft 5-61 22 Aug 81 (40)
References (Sec. 5.9.4) 1.
" Nuclear Power Plant Accident Considerations Under the National Environ-mental Policy Act of 1969."
Statement of Interim Policy, 45 FR 40101-40104, 13 June 1980.
2.
" Final Safety Analysis Report, Callaway Plant Units 1 and 2."
Docket Numbers STN 50-483 and STN 50-486. Union Electric Company, August 1980.
3.
" Energy in Transition 1985-2010."
Final Report of the Committee on Nuclear and Alternative Energy Systems (CONAES), National Research Coun-cil, 1979.
4.
C.E. Land, Science 209:1197, 12 September 1980.
5.
"The Effects on Populations of Exposure to Low Levels of Ionizing Radi-ation." Advisory Committee on the Biological Effects of Ionizing Radia-tions (BEIR), National Academy of Sciences / National Research Council, November 1972.
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.
7.
L.B. Marsh.
Evaluation of Steam Generator Tube Rupture Accidents."
NUREG-0651, U.S. Nuclear Regulatory Commission, March 1980.
e m
e
CALWY5/ Job K
-2nd Draf2 5-51 22 Aug 81 (41) 8.
"Three Mile Island - A Report to the Commissioners and the Public."
Vol. I, Summary Section 9, Mitchell Rogovin, Director, Nuclear Regulatory Commission Special Inquiry Group, January 1980.
9.
" Report of the President's Commission on the Accident at Three Mile Island." Commission Findings B, Health Effects, October 1979.
4 10.
" Reactor Safety Study." WASH-1400, NUREG-75/014, U.S. Nuclear Regulatory Commission, October 1975.
11.
" Task Force Report on Interim Operation of Indian Point." NUREG-0715, U.S. Nuclear Regulatory Commission, August 1980.
12.
H.W. Lewis et al.
" Risk Assessment Review Group Report to the U.S.
Nuclear Regulatory Commission." NUREG/CR-0400, U.S. Nuclear Regulatory Commission, September 1978.
13.
" Overview of the Reactor Safety Study Consequences Model." NUREG-0340, U.S. Nuclear Regulatory Commission, October 1977.
14.
" Liquid Pathway Generic Study."
NUREG-0440, U.S. Nuclear Regulatory Commission, February 1978.
15.
"Geosciences Data Base Handbook for Modeling a Nuclear Waste Repository."
NUREG/CR-0912, U.S. Nuclear Regulatory Commission, January 1981.
l l
l
CALUY4/ Job E 3rd Oraft E-1 8 Aug 81 AFPENDIX E.
REBASELINING OF THE RSS RESULTS FOR PWRs The results of the Reactor Safety Study (RSS) have been updated. The update was done largely to incorporate results of research and development conducted after the October 1975 publication of the RSS and to provide a baseline against which the risk associated with various LWRs could be consistently compared.
Primarily, the rebaselined RSS results reflect use of advanced modeling of the processes involved in meltdown accidents, i.e., the MARCH computer code model-ing for transient and LOCA initiated sequences and the CORRAL code used for 7
calculating magnitudes of release accompanying various accident sequences.
These codes
- have led to a capability to predict the transient and small LOCA initiated sequences that is considerably advanced beyond what existed at the time the RSS was completed.
The advanced accident process models (MARCH and l
CORRAL) produced some changes in our estimates of the release magnitudes from various accident sequences in WASH-1400.
These changes primarily involved release magnitudes for the iodine, cesium, and tellurium families of isotopes.
In general, a decrease in the iodines was predicted for many of the dominant accident sequences while some increases in the release magnitudes for the cesium and tellurium isotopes were predicted.
"It should be noted that the MARCH code was used on a number of scenarios in connec. ion with the TMI-2 recovery efforts and for post 'iMI-2 investigations
- te explore possible alternative scenarios that TMI-2 could have experienced.
CALUY4/ Job E 3rd Oraft E-2 8 Aug 01 Entailed in this rebaselining effort was the evaluation of individual dominant accident sequences as we understand them to evolve rather than the technique of grouping large. numbers of accident sequences into encompassing, but syn-thetic, release categories as was done in WASH-1400.
The rebaselining of the RSS also eliminated the " smoothing technique" that was criticized in the report by the Risk Assessment Review Group (sometimes known as the Lewis Report, NUREG/CR-0400).
In both of the RSS designs (PWR and BWR), the likelihood of an accident sequence leading to the occurrence of a steam explosion (a) in the reactor vessel was decreased.. (A key to accident-sequence symbols is given in b-l Table E.1.)
This was done to reflect both experimental and calculational indi-cations that such explosions are unlikely to occur in those sequences involving
[
small size LOCAs and transients because of the high pressures and temperatures expected to exist within the reactor coolant system during these scenarios.
Furthermore, if such an explosion were to occur, there are indications that it would be unlikely to produce as much energy and the massive' missile-caused breach of containment as was postulated in WASH-1400.
For rebaselining of the RSS-PWR design, the release magnitudes for the risk dominating sequences, e.g., Event V, TMLB' 6, y, and 5 C-6 (described later) 2 were explicitly calculated and used in the consequence modeling rather than being lumped into release categories as was done in WASH-1400. The rebase-lining led to a small decrease in the predicted risk to an individual of early fatality or latent cancer fatality relative to the original RSS-PWR predictions.
This result is believed to be largely attributable to the decreased likelihood of occurrence for sequences involving severe steam explosions (a) that breached 9
CALWY4/ Job E 3rd Draft E-3 8 Aug 81 containment.
In WASH-1400, the sequences involving severe steam explosions (a) were artificially elevated in their risk significance (i.e., made more likely) by use of'the " smoothing technique."
In summary, the rebaselining of the RSS results led to small overall differ-ences from the predictions in WASH-1400.
It should be recognized that these small differences due to the rebaselining efforts are likely to be far out-weighed by the uncertainties associated with such analyses.
The accident sequences which are expected to dominate risk from the RSS-PWR design are described below.
These sequences ari assumed to represent the approximate accident risks from the Callaway PWR design. Accident sequences are designated by strings of identification characters in the same manner as
('
in the RSS.
Each of the characters represents a failure in one or more of the important plant systems or features that ultimately would result in melting of the reactor core and a significant release of radioactive materials from con-tainment.*
Event V (Interfacing System LOCA)
During the RSS a potentially large risk contributor was identified due to the configuration of the multiple check valve barriers used to separate the high pressure reactor coolant system from the low design pressure portions of the ECCS (i.e., the low pressure injection subsystem - LPIS).
If these valve barriers were to fail in various modes, such as leak-rupture or rupture-rupture,
~~
- For additional information detail see Appendix V of " Reactor Safety Study',"
WASH-1400, NUREG-75/014, October 1975.
CALUY4/ Job E 3rd Oraft E-4 8 Aug 81 and suddenly exposed the LPIS to high overpressures and dynamic loadings, the RSS judged that a high probability of LPIS rupture would exist.
Since the LPIS is largely located outside of containment, the Event V scenario would be a LOCA that bypassed containment and those mitigating features (e.g., sprays) within containment. The RSS assumed that if the rupture of LPIS did not entirely fail the LPIS makeup function (which would ultimately be needed to prevent core damage), the LOCA environment (flooding, steam) would.
Predictions of the release magnitude and consequences associated with Event V have indicated that this scenario represents one of the largest risk contributors from the RSS-PWR design. The NRC has recognized this RSS finding, and has taken steps to reduce the probability of occurrence of Event V scenarios in both existing ana future LWR designs by requiring periodic surveillance testing of the interfacing valves to assure that these valves are properly functioning as pressure boundary isolation barriers during plant operations. Accordingly, Event V pre-dictions for the RSS-PWR are likely to be conservative relative to the design and operation of the Callaway PWR.
TM LB ' -6, y
i l
This sequence essentially considers the loss and nonrestoration of all AC power sources available to the plant along with an independent failure of the steam turbine driven auxiliary feedwater train which would be required to operate to remove shutdown heat from the reactor core. The transient event is initiated by loss of offsite AC power sources which would result in plant trip (scram) and the loss of the normal way that the plant removes heat from the reactor core (i.e., via the power conversion system consisting of the turbine, con-denser, the condenser cooling syste'm, ind the main feedwater and condensate 6
CALBY4/ Job E 3rd Draf2 E-5 8 Aug 81 delivery system that supplies water to the steam generators).
This initiating event would then demand operation of the standby onsite emergency AC power sup-plies (2 diesel generators) and the standby auxiliary feedwater system, two trains of which are electrically driven by either onsite or offsite AC power.
With failure and nonrestoration of AC and the failure of the steam turbine driven auxiliary feedwater train to remove shutdown heat, the core would ulti-mately uncover and melt.
If restoration of AC was not successful during (or following) melt, the containment heat removal and fission product mitigating systems would not be operational to prevent the ultimate overpressure (6, y) failure of containment and a rather large, energetic release of activity frem the containment.
Next to the Event V sequence, TMLB'6, y is predicted to domi-nate the overall accident risks in the RSS-PWR design.
S C-6 (PWR 3) 9 In the RSS the S C-6 sequence was placed into PWR release Category 3 and it 2
actually dominated all other sequences in Category 3 in terms of probability and release magnitudes.
The rebaselining entailed explicit calculations of the consequences from S C-6 and the results indicated that it was next in over-2 all risk importance following Event V and TMLB'6, y.
The S C-6 sequence included a rather complex series of dependencies and inter-2 actions that are believed to be somewhat unique to the containment systers (subatmospheric) employed in the RSS-PWR design.
In essence, the S C-6 sequence included a small LOCA occurring in a specific 2
region of the-clant-(reactor vessel cavityT; failure of the recirculating con-tainment heat removal systems (CSRS-F) because of a dependence on water
CALWY4/ Job E 3rd Draf?.
E-6 8 Aug 81 draining to the recirculation sump from the LOCA and a resulting dependence 1
imposed on the quench spray injection system (CSIS-C) to provide water to the i
susp. The failure of the CSIS(C) resulted in eventual overpressure failure of j
containment (6) due to the loss of CSRS(F). Given the overpressure failure of containment the RSS assumed that the ECCS functions would be lost due either to the cavitation of ECCS pumps or from the rather severe mechanical loads that could result from the overpressure failure of containment. The core was then assumed to melt in a breached containment leading to a significant release of radioactive materials.
s.
Approximately 20% of the iodines and 20% of the alkali metals present in the core at the time of release would be released to the atmosphere. Most of the release would occur over a period of aoout 1.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />. The release of radio-(
active material from containment would be caused by the sweeping action of gases generated by the reaction of the molten fuel with concrete.
Since these gases would be initially heated by contact with the melt, the rate of sensible energy release to the atmosphere would be moderately high.
l PWR 7 This is the same as the PWR release Category 7 of the original RSS which was made up of several sequences such as S D-c (the dominant contributor to the 2
risk in this category), S D-c, 5 H-c, S H-e, AD-c, AH-c, TML-c, and TKQ-c.
2 2
t 1
All of these sequences involved a containment basemat melt-through as the con-tainment failure mode.
With exception of TML-c and TKQ-c, all involve the potential failure of the emergency core cooling system following occurrence of a LOCA with the etintainment ESFs continu'ing to operate as designed until the-l
i CALWY4/ Job E 3rd Oraft E-7 8 Aug 81 base mat was penetrated.
Containment sprays would operate to reduce the con-tainment temperature and pressure as well as the amount of airborne radioac-tivity.
The containment barrier would retain its integrity until the molten core proceeded to melt through the concrete containment basemat.
The radio-active materials would be released into the ground, with some leakage to the atmosphere occurring upward through the ground.
Most of the release would occur continuously over a period of about 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br />. The release would include approximately 0.002% of the iodines and 0.001% of alkali metals present in the core at the time of release.
Because leakage from containment to the atmo-sphere would be low and gases escaping through the ground would be cooled by contact with the soil, the energy release rate would be very low.
e J
l
G4 Table E.1.
Key to PWR Accident-Sequence Symbols Symbol Definition A
Intermediate to large LOCA.
8 Failure of electric power to ESFs.
B' Failure to recover either onsite or offsite electric power within about one to three hours following an initiating transient that is a loss of offsite AC power.
C Failure of the containment spray injection system.
D Failure of the emergency core cooling injec-tion system.
F Failure of the containment spray recirculation system.
G Failure of the containment heat removal system.
H Failure of the. emergency core cooling recircu-lation system.
K Failure of the reactor protection system.
L Failure of the secondary system steam relief valves and the auxiliary feedwater system.
M Failure of the secondary system steam relief valves and the power conversion system.
Q Failure of the primary system safety relief valves to reclose after opening.
R Massive rupture of the reactor vessel.
S A small LOCA with an equivalent diameter of t
about 5 to 15 cm (2 to 6 in).
S A small LOCA with an equivalent diameter of 2
about 1.3 to 5 cm (0.5 to 2 in).
T Transient event.
V LPIS check valve failure.'
a Containment rupture due to a reactor vessel steam explosion.
S Containment failure resulting from inadequate isolation of containment openings and pene-trations.
y Containment failure due to hydrogen burning.
6 Containment failure due to overpressure.
[
c Containment vessel melt-through.
CAlb'Y4/ Job F 2nd Oraft F-1 8 Aug 81
~
APPENDIX F.
EVACUATION MODEL
" Evacuation", used in the context of offsite emergency response in the event of a substantial amount of radioactivity released to the atmosphere in a reactor accident, denotes an early and expeditious movement of people to avoid exposure to the passing radioactive cloud and/or to acute ground contamination in the wake of the cloud passage.
It should be distinguished from " relocation",
which denotes a postaccident response to reduce exposure to long-term ground contamination.
The " Reactor Safety Study" (RSS) (Ref.1) consequence model Y
p-contains provision for incorporating radiological-consequence-reduction bene-fits of public evacuation.
Benefits of a properly planned and expeditiously carried out public evacuation would be well manifested in reduction of acute health effects associated with early exposure; namely, in the number of cases of acute fatality and acute radiation sickness that would require hospital-ization. The evacuation model originally used in the RSS consequence model is described in WASH-1400 (Ref.1) as well as in NUREG-0340 (Ref. 2).
- However, the evacuation model used herein is a modified version (Ref. 3) of the RSS p
model and is, to a certain extent, oriented to site emergency planning. The modified version is briefly outlined below:
The model uses a circular area with a specified radius, such as a 16-km (10-mi) plume-exposure pathway emergency planning zone (EPZ), with the reactor at the cente r.,
It is assumed that people living within portions of this area would
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CALBY4/ Job F 2nd Draft F-2 8 Aug 81 evacuate if an accident should occur involving imminent or actual release of significant quantities of radioactivity to the atmosphere.
Significant atmospheric releases of radioactivity would, in general, be pre-ceded by one or more hours of warning time (postulated as the time interval between the awareness of impending core melt and the beginning of the release q
of radioactivity from the containment building).
For f.he purpose of calcu,
lation of radiological exposure, the model assumes that all people who live in a fan-shaped area (fanning out downwind from the reactor) within the circular zone--who would potentially be under the radioactive cloud that would develop following the release--would leave their resideer.es after lapse of a specified delay time
- and then evacuate. The delay time is reckoned from the beginning of the warning time and is the sum of the times required by the reactor opera-(
tors to notify responsible authorities; by the authorities to interpret the data, decide to evacuate, and direct the people to evacuate; and by the people to mobilize and get underway.
The model assumes that each evacuee would move radially downwind with an average effective speed * (obtained by dividing the zone radius by the average time taken to clear the zone after the delay time) over, a fixed distance
- from the evacuee's starting point.
This distance is selected to be 24 km (15 mi),
8 km (5 mi) more than the 16-km (10-mi) plume-exposure pathway EPZ radius.
After reaching the end of the travel distance the evacuee is assumed to receive no further radiation exposure.
(An important assumption incorporated in the RSS consequence model is that if the calculated ground dose to the total z.
- Assumed to be a constant value, which would be the same for all evacuees.
CALWY4/ Job F 2nd Oraft F-3 0 Aug 81 marrow over a 7-day period were to exceed 200 rems in the regions beyond the
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evacuation zone, then this high dose rate would be detected by actual field measurements following the accident, and people from those regions would be relocated immediately. Therefore, the model limits the period for ground-dose calculation to only 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> for those regions. When no evacuation at all is assumed, this manner of ground-dose calculation applies to all regions, begin-ning at the reactor location.
CRAC code implements this feature irrespective of the evacuation model used.)
The model incorporates a finite length of the radioactive cloud in the down-wind direction that would be determined by the product of the time over,whicn the atmospheric release would take place and the average wind speed during the release.
It is assumed that the front and the back of the cloud formed would move with equal speeds that would be the same as the prevailirg wind speed; therefore, its length would remain constant at its initial value. At any time after the release, the concentration of radioactivity is assumed to be uniform over the length of the cloud.
If the delay time were less than the warning time, then all evacuees would have a head start; i.e. the cloud would'be initially trailing behind the evacuees. On the other hand, if the delay time l
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were more than the warning time, depending on initial locations of the evacuees 4
the possibilities are that (1) an evacuee would still have a head start, (2) the cloud would be already overhead when an evacuee starts to leave, or j
(3) an evacuee would be initially trailing behind the cloud. However, this initial picture of relative position would change as the evacuees travel, l
depending on the relative speeds of the cloud and people.
It may become l
possible that the cloud and an evacuee would overtake each other one or more times before;the evacuee would reach his or her destination.
In.the model, e
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CA wye / Job F 2nd Draf2 F-4 8 Aug 8A the radial position of an evacuee, while stationary or in transit, is ccmpared to the front and the back of the cloud as a function of time to determine a realistic period of exposure to airborne radionuclides.
The model calculates the periods during which people are exposed to radionuclides on the ground while they are stationary and while they are in transit.
Because radionuclides would be deposited continually from the cloud as it passed a given location, a person under the cloud would be exposed to ground contamination less concen-trated than if the cloud had completely passed.
To account for this, at least in part, the revised model assumes that persons are exposed to the total calculated ground-contamination concentration (that existing after complete passage of the cloud) when completely passed by the cloud, to one-half the calculated concentration when anywhere under-the cloud, and to no concentration when in front of the cloud.
The model provides for use of different values of
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the shielding protection factors for exposure from airborne radioactivity and contaminated ground, and the breathing rates for stationary and moving evacuees during delay and transit periods.
It is realistic to expect that authorities would evacuate persons at distances from the site where exposures above the threshold for causing acute fatalities could occur regardless of the plume-exposure pathway EPZ distance.
Figure F.1 illustrates a slight reduction in acute fatalities that can occur by extending evacuation to a larger distance, such as 24 km (15 mi), from the Callaway site.
Calculation shows that if the evacuation distance is increased to 32 km (20 mi),
there would be no reduction in acute fatalities at all probability levels for this site.
Also illustrated in the figure is a pessimistic case for which no early evacuation is assumed:
all persons are assumed to be exposed for the f.irst 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> fol, lowing an accident and are then relocated.
CAttfY4/Jcb F 2nd Draft F-5 8 Aug 81 1
i The model has the same provision for calculation of the economic cost associ-ated with implementation of evacuation as in the original RSS model.
For atmospheric releases with durations of threa hours or less, the model assumes that all people living within a circular area of 8-km (5-mi) radius centered at the reactor, plus all people within a 45' sector centered on the downwind direction within the plume-exposure pathway EPZ, would evacuate and tempo-rarily relocate.
However, if the duration of release were to exceed three hours, the cost of evacuation is based on the assumption that all people within the entire plume-exposure pathway EPZ would evacuate and temporarily relocate.
For either of these situations, the cost of evacuation and reloca-tion is assumed to be 5125 per person (1980 dollars), which includes the cost of food and temporary shelter for one week.
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Sensitivity of Acute Fatalities to Evacuation Characteristics.
(15 mi = 24 km) i (For evacuation to 32 km or more, the acute fatalities do not change.
See Sec. 5.9.4.4 Uncertainties for a discussion of uncer-tainties in risk estimates.)
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CALUY4/ Job F 2nd Draft F-6 8 Aug 81 References 1.
" Reactor Safety Study."
U.S. Nuclear Regulatory Ccamission, WASH-1400, NUREG-75/014, October 1975.
2.
" Overview of the Reactor Safety Study Consequences Model."
U.S. Nuclear "egulatory Commission, NUREG-0340, October 1977.
3.
"A Model of Public Evacuation for Atmospheric Radiological Releases."
SAND 78-0092, June 1978.
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