ML20030B417
| ML20030B417 | |
| Person / Time | |
|---|---|
| Site: | Limerick, Saint Lucie  |
| Issue date: | 08/06/1981 |
| From: | Lear G Office of Nuclear Reactor Regulation |
| To: | Houston R Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20030B418 | List: |
| References | |
| NUDOCS 8108170276 | |
| Download: ML20030B417 (9) | |
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!!D10RA!(DUM FOR:
R. Wayne Houston, Chief Accident Evaluation Branch s
1 Division of Systems Integration THRU:
James P. Knight Assistant Director for Components and Stnictures Engineering Division of Engineering FRM1:
George Lear, Chief Hydrologic and Geotechnical Engineering Branch Division of Engineering
SUBJECT:
EtNIR0!!!EllTAL STATD!E!R IllPUT FOR ST. LUCIE UNIT 2
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CORE MELT LIQUID PATHWAY ANALYSIS
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The Rydrologic Engineering Section has anIalyzed the core melt accident liquid pathway consequences for the subject site and has prepared input for your 3
i use in preparing the Environmental Statement. The conclusions of the staff are that the liquid pathway consequences would be substantially smaller than those for the ocean based site in the " Liquid Pathway Generic Study." This 3
,i study was performed by Richard Codell and Rex IIescott.
i Original'signes by George Lear
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George Lear, Chief Hydrologic and Geotechnical Engineering Branch Division of Engineering i
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Enclosure:
As stated s
cc: w/o enclosure R. Vollmer W. Kreger i
w/ enclosure V. Herses
- 8. Richter G. Lear M. Fliegel R. Code 11 R. Hescott
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6.1.d.5 Releases to Groundwater A pathway for public radiation exposure and environmental contamination that would be unique for severe reactor accidents was identified in Section 6.1.1.2 Consideration has been given to the potential environmenta'l impact above.
of this pathway for the St. Lucie plant. The principal t;ontributors to the risk' are the core melt accident associated with the PWR-1 through 7 release categories.
The penetration of the basemat of the containment building can release molten core debris to the strata beneath the the plant. Soluble radio-nuclides in t'is debris can be leached and transported with groundwater to downgradient domestic wells used for drinking or to surface water bodies used for aquatic food and recreation. In pressurized water reactors, such as the St, Lxie units, there is an additional opportunity for groundwater contamination due to the release of contaminated sump water to the ground through a breach f
in the containment.
An analysis of the potential consequences of a liquid pathway release of radioactivity far generic sites was presented in the " Liquid Pathway Generic
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Study" (LPGS).II) The LPGS compared the risk of accidents involving the liquid pathway -(drinking water, irrigation, aquatic food, swiarning and shoreline usage) for four conventional, generic l'and based nuclear plants and a floating nuclear plant, for which the nuclear reactors would be mounted on a barge and moored in a water body. Parameters for the land-based sites were chosen to represent averages fcr a wide range of real sites and are thus " typical," but represented no real site in particular.
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The d siussion in this-section is an analysis to detennine whether or not 1
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- g thhAt. Lucie site liquid pathway consequences would be unique when compared s
to land-based sites considered in the LPGS. The method consists of a direct scaling of the LPGS populaticn doses based on the relative values of key The parameters characterizing the LPGS " ocean" site and the St. Lucie site.
parameters which were evaluated. included amounts of radioactive materials entering the ground, groundwater travel time, sorption on geological media, surface water transport, aquatic food consumption, and shoreline usage.
Doses to individuals and populations wer,e calculated in the LPGS without consideration of interdiction methods such as isolating the contaminated groundwater or denying use of the water. In the event of surface water 4
contamination, commercial and sports fishing, as well as many other water-related a:tivities would be restric.ed. The consequences would therefore be.
largely economic or social, rather than radiological. In any event, the individual and population doses for the liquid pathway range from fractions to I
very small fractions of those that can arise from the airborne pathways.
The Saint Lucie site is located on Hutchinson Island, whicft is a typical east coast barrier island in southern Florida. The site is bordered by the Indian River (an estuarine bay) on the southwest, the Atlantic ~ 0cean on the north-east and Big Mud Creek (a backwater off the Indian River) on the northwest.
l-Ground water flows in several layers under the site, but the only flows which i
concern the liquid pathway analysis are in the unconsolidated sand and silt water table aquifer of the Anastasia formation.
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The hda's.tasia formation is roughly 50 meters (150 feet) thick at the site.
1" Groun,d water flows in this formation are generally toward the Atlantic Ocean.
g caused by recharge from precipitation on the mainlandi The Indian River comes L-between Hutchinson Is1cnd and the mainland, but is too shallow to intercept the
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Piezometers located on 4
major portion of ground water flow toward the ocean.
4 Hutchinson Island generally show a Glight gradient of 0.00016 tovard the ocean (Ref.1). Using the applicant's site parameters shown in Table 1, we V
calculated a ground water travel time of 1180 years to the Atlantic Ocean.
This compares to a ground water t vel time of 0.61 years used in the LPGS 1
ocean-based case, (Ref. 2) which would clearly demonstrate the superiority i
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of the Saint Lucie' site for the liquid pathway contribution to risk if it could be determined that this is the only pathway for contaminants released to ground water to reach the surface water.
n There exists, however, the possibility of an alternative pathway for contamination of surface water via ground water travel to Big Mud Creek. The placement of j
piezometers on Hutchinson Island is not adequate to show the existance of a gradient toward Big Mud Creek, which is the closest body of surface water. A phenomenon on many islands is the presence of a fresh watar lens in the water table r
which flodts over sal't water. The lens is supported by the infiltration of fresh water from precipitation. It is thickest in the middle of the island and thinnest at the coasts. It is the possibility of'a gradient in the fresh i
water lens towards Big Mud Creek, that is of concern here.
The staff analyzed the transport of radicactively contaminated water released l
to the postulated fresh water lens using an analytical method based on the d
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Ghybek-Hertzberg approximation for fresh water lenses (Ref. 3)s The estimated i:
1-mfbimum travel time for groundwater to reach Big Mud Creek is 29 years.
4 For ground water travel times on the order of years, the staff has shown (Ref. 2) that the only significant radionuclide contributors to the liquid
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pathway population dose from an assumed core melt accident would be Sr 90 and Cs 137. These 2 nuclides interact chemically with most geologic media and thus travel slower than the groundwater. Conservative values of the retardation factors, which reflect the effects of sopption of the radionuclides on geologic materials, were estimated by the applicant to be 9.5 for Sr and 86 for Cs. The staff considers these values to be conservative, and consistent with ranges of retardation factors displayed by geologic materials similar to those found underthesite(Ref.4). Using these values the staff estimated that the mean groundwater transport time from the reactor buildings to. Big Mud Creek would be 278 years for Sr 90 and 2520 years for Cs 137. Groundwater travel times to the Atla'ntic Ocean would be much longer, about 11,000 years for Sr 90 and 100,000 years for Cs 137.
When these travel times are compared to the 5.7 years for Sr 90 and 51 years for Cs-137 used in the LPGS land-based ocean site case, the relatively larger travel times for the St. Lucie site would allow a much smaller fraction of the released radioactivity to escape to the surface water. This reduction would be about a factor of 775 for Sr 90 in the pathway to Big Mud Creek. Virtually all of the Cs 137 would have decayed before reaching surface water via either pathway as would the Sr 90 for the pathway to the Atlantic Ocean.
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s ConIab'nated water reaching Big Mud Creek would subsequently be transported The two intogthe Indian River and then be carried to the Atlantic Ocean.
potential liquid exposure pathways for the site are aquatic food consumption and direct shoreline exposure.
The applicant astimated the comercial and recreational finfish and shellfish 7
harvests within 80 km (50 mi) of the St. Lucie site to be about 2.6 x 10 Kg/ year. (2.9 x 10 tons /yr, Ref 5). This value includes all brackish inland 4
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waterways. The staff considers these values to be conservative for the reason that much of these waters would be unaffected by the assumed releases from the plant. The-LPGS evaluation considered only the recreational and commercia.'
6 fishing offshore, which is taken to be about 1.9 x 10 Kg/yr (2100 ton:;/yr).
Therefore, the St. Lucie catch is taken to be a factor of about 14 times 4
greater than the LPGS catch.
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Approximately 62 percent of the population dose from aquatic food consumption i
calculated in the LPGS was due to Cs 137.and approximately 38 percent was due 4
to Sr 90. The only significant radionuclide which could enter the ocean from j
i the liquid pathway in the St. Lucie case is Sr 90 via the Big Mud Creek pathway.
The staff has conservatively estimated, therefore, that the uninterdicted l
population dose in the St. Lucie case would be at least a factor 930 smaller than the LPGS case for seafood consumpthn.
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- 1, Nea'r 11 of the direct shorelire exposure in the LPGS case was detennined te be caused by Cs-137. Since virtually all of the Cs-137 would decay before
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reaching the ocean, the direct exposure pathway can be eliminated from further consideration. Results of these analyses are summarized in table 1.
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Table 1 - Comparison of St. Lucie and LPGS Land Based Ocean Site Liquid Pathway Consequences St. Lucie-Ground Water St. Lucie-Groundwater i
Parameter LPGS Flow to Atlantic Ocean Flow to Big Mud Creek i
Ground Water 2m/ day
.00173 m/ day N/A Velocity (6.7 ft/ day)
(.00568 ft/ day)
Distance to 450m (1500 ft) 745m (2444 ft) 218m (700 ft) i Surface water Effective Porosity 0.2 0.4 0.4
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-3 Permeability N/A 5 x 10 cm/sec 5 x 10 cm/sec (5173 ft/yr) 4 Ground Water 0.61 1180 29 Travel Time (years) i Retardation Sr 9.2 9.5 9.5
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Coefficient Cs 83 86 86
't Radionuclide 114000 278 Travel time i,S r 5.7 C s 51 100,000 2520 (years) s Fraction' Sr 90 0.87
-0 0.0013
-26 Reaching Csl37 0.31 a0 6.3 x 10 surface p
water s 0
7 7
K 2.6 x 10 Kg Total finfish 1.9 x 10 Kg
-2.6 x 10 4g 3
& shellfish (2.1 x 10 tons)
(2.9 x 10 tons) annual harvest within 80 km Population dose relative to LPGS-aquatic food 1.0
^' O 0.0078 shoreline 1.0 u0 fv 0 <
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kt9 The St. Lucie liquid pathway contribution to population dose has, therefore, been. demonstrated to be smaller than that predicted for the LPGS land based ocean site, which represents a " typical" ocean site. Thus the St. Lucie site is not unique in its liquid pathway contribution to risk.
There are measures which could be taken to minimize the impact of the liquid pathway. The staff estimated that the minimum groundwater travel time from In addition, the St. Lucie site to Big Mud Creek would be at least 29 years.
the holdup of-important radionuclides would provide additional time to utfitze engineering measures such as slurry walls and well point dewatering to isolate the radiaactive contaminants at the source (Ref. 6).
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Refer'ences 1.\\ klorida Power and Light, " Final Safety Analysis Report, St. Lucie Nuclear Plant, Units 2," Chapter 2.4.13,
- 2..U.S. Nuclear Regulatory Commission, " Liquid Pathway Generic Study' NUREG 0440, 1978.
3.
Bear, J., Hydraulics of Groundwater, McGraw Hill, Inc.1979, p 379-433-4.
Isherwood, D., "Geosciences Data Base Handbook foi Modeling a Nuclear Waste Repository," Vol.1. NUREG/CR-0912, Jan 1981.
5.
Florida Pcwer and Light, " Environmental Report, Operating License Stage.
St. Lucie Nuclear Plant, Unit 2, Response to Question E240.3.
6.
Harris, V.. Ya rs,-J., and Warkensteen J., " Accident Mitigation-Slurry Wall Barriers," Draft report to staff of Hydrologic Engineering Section, HGEB.,DE. NRR, from Argonne National Laboratories,1981.
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