ML20030D639

Forwards Hydrologic & Geotechnical Engineering Branch Input Re Class 9 Accident Liquid Pathway Consequences,In Response to NRC 810813 Request

ML20030D639
Person / Time
Site:	Saint Lucie, Limerick, Callaway
Issue date:	08/20/1981
From:	Calkins G Office of Nuclear Reactor Regulation
To:	Honan D PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
Shared Package
ML20030B418	List: ML20030B417 ML20030D639
References
NUDOCS 8109140090
Download: ML20030D639 (1)

Text

{{#Wiki_filter:', 'AUS 2 0 1981 Docket Nos. 50-152/151 ~ "r. Oavid IIcnau Philadelphia Flect. ic Company '/1n1 Parket Street Philade'obia, Pennsylvania 19101

Dear rave:

This is in reference to your telephone request of Aunust 73, 1981, for clarification of nuestion E2an.21 in our acceptance L *,ter of l 1ulv f. In91. Enclosed are three inputs provided by ou" rdyde Ooofc i Fnaineerina Section. They relate to responses to the sam stion l concernino Class o accident lioufd pathway consequences. refer l to St. Lucie, finit 7 and the other to Callaway, i 11tr Sincerely. G. Donald Calkins, Project Manager Licensing Branch No. 2. OL Enclosures as stated Distribution:

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Dear Mr. Eisenhut:

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//. Re: St. Lucie Unit 2 '/* Docket No. 50-389 +fyg Liquid Pathway Study The attached report, " Comparability Of St. Lucie Site And Liquid Pathway Generic Study From The Standpoint Of Liquid Pathway", is provided in response to the May 5,1981 Hydrologic Engineering Section/ Hydrologic and Geoter.hnical Engineering Branch request for additional infonnation (Question 240.3). The report concludes that the aquatic radiological impact of a core melt accident at the St. Lucie site is estimated to be less than the impact derived in the Liquid Pathway Generic Study, NUREG-0440, for a " typical" coastal land based site. Thus, the St. Lucie site is not unique in its liquid pathway cont'ribution to risk. Very truly yours, l %D ert E. Uhrig v Vice President Advanced Systems & Technology REU/TCG/ah Attachment cc: Harold F. Reis Esquire J. P. O'Reilly, Director, Region II = n zL,,1 p\\ l m a i c et!is M IT t m H kt PDR ADOCK 05000389 A PDR

COMPARABILITY OF ST. LUCIE SITE AND LIQUID PATHWAY g O GENERIC STUDY FPOM THE STANDPOINT OF LIQUID PATHWAY , 5'9 f'$ \\ 1. Introduction i This report represents an evaluation of the offsite radiological impacts which are unique to a hypothetical accident that results in temperatures inside the reactor core which are sufficiently high to cause core melting and subsequent penetration of the basemat underlying the reactor. Such an accident creates the potential fo'e releases of radioactive material into the hydrosphere through contact with groundwater, which in turn may lead to external ~ exposure to radiation and internal exposures if contaminated food or water is ingested. A discussion is also presented of engineered systems which could be effective in mitigating the impacts of such an accident by isolating the contaminated groundwater aquifer from I the hydrosphere. The penetration of the basemat of the Reactor Building can release molten core debris to the strata beneath the plant. Soluble i radionuclides in this debris can be leached and transported with groundwater downgradient to surface water bodies used for aquatic j food and recreation. In pressurized water reactors, such as the St. Lucie Unit 2 plant, there is an additional opportunity for i groundwater contamination due to the release of contaminated sump water to the ground through a breach in the containment. i t An analysis of the potential consquences of a liquid pathway release of radioactivity for generic sites was presented in the " Liquid Pathway Generic Study" (LPGS).Cl)The LPGS compared the risk of accidents j involving the liquid pathway (drir. king water, irrigation, aquatic, food, swimming and shoreline usage) for four conventional, generic land-based 4 nuclear plants and a floating nuclear plant, for which the nuclear 1 l r 9 9 O

~4. J s i N , l\\ reactors would be mounted on a barge and moored in a. vater body. \\, g Parameters for the land-based sites were chosen to represent averages for a wide range of real sites and are thus " typical," but represented no reAl site in particular. This report presents an analysis to determine whether or not the I St Lucie site liquid pathway consequences would be unique when compared to land-based sites considered in the LPGS. The method 3 consists of comparing key parameters which characterize the St Lucie site and the " typical" land based ocean site evaluated in the LPGS. The parameters which are compared include groundwater travel time, sorption on geologic media, surface water transport, aquatic food consumption and shoreline usage. l Doses to individuals and populations were calculated in the LPGS j i without consideration of interdiction methods such as isolating 1 l the contaminated groundwater or denying use of the water. In the i event of surface water contamina' tion, cc=mercial and sports fishing, as well as many other water-related activities would be restricted. The consequences would therefore be largely economic or social, rather than radiological. In any event, the individual l and population doses for the liquid pathway range from fractions to very scall fractions of those that can arise from the airborne J pathways. 1 2. Comparison of St Lucia Site to LPGS Figures 1 and 2 (taken from the St Lucie 2 FSAR) present scaled diagrams of the relevant features of the site. The plant is located f on Hutchinson Island, a barrier island bounded along the east by the Atlantic Ocean and on the west by the Indian River which, in I fact, is not a river but a tidal lagoon. The distance from the e Reactor Building to the ocean is abcut 2500 fret. The distance to the closest water body (i.e. Big Mud Creek) is about 700 feet. . I l l O O 9 I

y i. \\ s. t(. The plant grade around the structure is at elevation plus 18.5 ,(\\ feet mean low water (MLW). The facility is underlain by \\k Class I, high grade, compacted fill to a depth of -60 feet MLU. The base mat beneath the Reactor Building is at elevation -25.5 MWLI A. The groundwater study region beneath the Class I fill includes a shallow, non artesian aquifer and a deep artesian aquifer.- The top of the deep aquifer is typically 600 to 800 feet beneath the surface and therefore is not considered further in this study ~ ~ The unconfined aquifer beneath the Class I fill is the Anastasia formation. This formation extends to elevation -135 to -155 feet and consists of grey slightly silty fine to medium sand with varyir.. amounts of fragmented shells. It also contains discontinuous pockets of cemented sand with shells and sandy limestone. Occasionr.11y, discontinuous thin plastic clay lenses are found in the upper part of the formation. The Anastasia formation is the relevent strata in the evaluation. It is divided into three zones. The upper :.one which extends to about -60 feet is a loose to medium dense sand with small amounts of silt l and clay and containing isolated pockets of shell fragments and 4 limestone nodules. The intermediate zone begins at about -60 feet and extends to about-150 feet. It is denser than the upper zone, contains l a greater percentage of fines and very few pockets of shells and limestone fragments. This zone would probably receive the melted core j j' and sump water because it covers the range of depths over which a molten core may penetrate. = 4 l f l I

The charactoristics of tha intsrm2 dicto zen 3 Gro as follsws: N 25%(4) i Water content x 3 (4) i 5. 107 lbs per.ft ~(DryUnitwt b) " tiet Unic Ut 133 lbs per f t \\ \\ pecified Cravity 2.73(4) S 77%(4) Relative Density 0.66 ') I Void Ratio 40% ') I Porosity Crain Size Sand (%90%) (.1 to 10 mm)(5) Silt (%5%) (.1 to.001 c:n)(5) .00016 (toward ocean) Slope 5 x 10-3 cm/sec(6) Permeability I7) Dispersivit/ 2 ft Distance to Ocean 2444 ft 4 The groundwater gradient of.00016 towards the ocean is obtained from Figures 3 and 4. Figure 3 shows certain piezometer locations, originally installed in the initial subsurface investigation of the site. Figure 4 shows the range of piezometer levels and average level fc,r the month of April 1968. Also, shown on this figure is the slope of the groundwater towards the Atlantic Ocean. The piezameter used for this determination is found at approximately the depth the molten core may penetrate and therefore indicates the groundwater gradient at that elevation. These parameters establish that the groundwater flows generally toward the ocesn and would require about 1164 years to flow from a location immediately beneath the Reactor Building to the ocean. There exists the possibility of an alternative p'athway for contamina-tion of surface water via ground water travel to Big Mud Creek. A phencmenon present on most islands is the presence of a fresh water lens in the water table which floats over the salt water. Extending the procedures presented in " Hydraulics of Groundwater" by Jacc> Bear the following equation has been derived and is used to cal: late the tre.rel time to Big Mud Creek. l e rr

t N&d 3 - (L-d)2 L 2 l ~ _14 J g g,, L g, i 7 Q.. $ Nk I ( L-d / \\.\\ s ~ I where t = travel time (years) a = effective porosity s 3 = ratio of. unit weights of water = 40 N = infiltration rste of precipitation (ft/ year) k = permeability (ft/ year) L = % width of island d = distance of reactor from shore Inserting the appropriate values into the equation a travel time of 54 years is obtained. The effective travel time of radionuclides which may con mmfnate the e aquifer regardless of the flow path following a core melt through would be considerably greater due to adsorption and ion exchange on the sand. The distribution coefficients (Kd) for cesium and strontium, the critical radionuclides, are assumed to be 20 and 2, respectively. These values were taken from Table VII 3-7 of Appendix VII of WASH-1400 and are conservative when compared to values reported in E ) the literature The calculated retention factors using these values for Kd, a porosity (n) of 0.4 and a bulk dry weight density of 1.7, are 86 for cesium and 9.5 for strontium. Using these reten-tion factors, the travel time for Cs-137 and Sr-90 for transport to the Atlantic Ocean and Big Mud Creek are given in the Table below. A comparison of the above parameters to t!$ose used in the LPGS is presented below: i e l

f 9 St Lucie (towards St Lucia (towards Parameter LPGS Atlantic Ocean)_ Bie Mud Creek) 1.}$oundwatervelocity ',g s'to surface water 6.7 feet / day 0.00568 feet / day N/A ) i \\\\ Distance to surface 1500 feet 2,444 700 water 4 Porosity 0.2 0.4 0.4 Sediment retention factor: Sr-90 9.2 9.5 9.5 i Cs-137 83 86 86 Time to Surface 4 Water (yrs): Sr-90 5.7 11,000 510 Cs-137 51 99,000 4600 I j Number of half lives to reach surface water: 4 Sr-90 0.2 380 17 Cs-137 1.7 3,300 150 l j-Based on this comparison, the time for contaminated ground water to i reach a surface water location at the St Lucie site is considerably greater than travel time which characterizes the ocean site La the I r LPCS.. I Once the contaminated water reaches the ocean, it is reasonable to I assume that dilution for St Lucie site is represented by the LPGS l since the standard land based ocean site in the LPGS is located on f the east coast of Florida. Accordingly, dilution factors can be considered comparable. For example, the offshore current of 0.4 to 1.6 feet per second at the St Lucie site is comparable to dhe velocity used in the LPCS.. The only comparison which remains is the fishery catch and shoreline usage factors. e F O O 9

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. - L. " The annual commercial and recreational finfish and shellfish catch . within 50 miles of the St Lucia site, including brackish. inland (I} \\g' vaterways, is estimated to be the following (kg/yr) n s ,s .\\ 0-3 miles _ > 3 miles _ Coc=ercial ~~ Finfish 8.26 x 10 ~ 6 Shellfish 1.58 x 10 6 6 Recreational

• 9.55 x 10

-6.84 x 10 The recreational use of the beaches within a 50 mile radius of the site has been estimated from the data. presented in Table 2.1-26 in the St Lucie Unit 2 Environmental Report (0.L. Stage). Based on an annual per capita participation rate of 6.57 days for residents and 13 days i for tourists. assuming 3 hours of beach activities per beach day, the annual beach usage by the year 2000 population is estimated to be approximately 3.3 x 10 user-hours, i The following presents a comparison of the values to those used in the LPGS: LPGS St Lucia _ Fishery (kg/ha/yr) 0-5 Km 120 227 5-19 Km 7.3 30 19-80 Km 1.1 Beach Activities 1.1 x.10 3.3 x 10 user brs/yr user hrs /yr These results reveal that the usage factors for the St Lucie site are somewhat higher than those used'in the LPGS for a land based ocean site. However, factoring in the transport time, the aquatic radiological impact of a core melt accident at the St Lucie site is estimated to be less than the impact derived in the LPGS for a " typical" coastal land based site. Thus the St Lucie site is not unique in its ' liquid pathway contribution to risk. The recreational catch is based on the number of fish estimated 'in Reference 9 and assuming an average of 0.43 Eg/ fish. l l 3 p. e -.7.

. se s \\s 134[. Putigative Phasures .j\\,The udnimum ground water travel time from the St Lucie site to the \\ k Atlantic Ocean and Big Mud Creek was estimated to be roughly 1164 and 54 years respectively, and because of the filtering ' pro-perties of soil the holdup of much of the radioactivity would be even greater. This would allow ample tLee for engineering measures, such as slurry walls, to isolate the radioactive con-tamination near the source. As a means of isolating coataminated groundwater in the St Lucia ~ site area, the feasibility of constructing an impermeable membrane was investigated. Alternate means, such as pumping or sheet piling were also considered. Pumping a large volume of water would impose unreasonable treatment requirements. Sheet piles will corrode in the salt water. A slurry trench was thought to be the most ef ficient method of isolation for this site. Two types of slurry trenches are available, cement bentonite and soil bentonite. Based upon previous experience, a cement bentonite slurry wall was investigated. Cement bentonite is used where slope support is needed for dewatering excavation sites and for groundwater control. The cement bentonite requires 24 hours to cure. The bentonite can either be installed into 2-3 foot wide trenches directly, or pumpsd by use of adapters to drive piles. Cement bentonite construction is a much slower and expensive process than for soil bentonite but provides added strength. oil bentonite is more flexible and less expensive since the trenching soil is used in the backfilling. Soil bentonite is quicker to install but must be installed in a continuous fashion." The native mat'erial can be used in the backfilling operation if it is sand, such as exists at St Lucie, prefer. ably a poorly graded mixture. No curing time is required for the soil bentonite and dewatering can begin immediately af ter construction whereas cement bentonite requires 24 hours for curing prior to any dewatering -measures. j' y

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1. A'ySince the St Lucie Site consists of fine sands, excavation in this

,^ material would be relatively easy and the. excavated material could be mixed with the bentonite to produce a soil bentonite mixture. There is nothing at the St Lucie Site that would preclude the use of this method of groundwater isolation. e 9 O e 6 1 4 -f a G A S S e e 8 e e e-

~ (1)',NUREG-0440 Liquid Pathway Generic Study. February, 1978. (2 See Figures 2.4-1 of FSAR 3)' See FSAR Section 2.4.13.1 (pg 2.4-40) -(4) See Table 2.5-5 of the FSAR (pg 2.5-93) (5) See Appendix 2.5.A of the FSAR (6) See Section 2.5.4.2.2 of the FSAR (7) See Section 2.4.13.3 (pg 2.4-45) of the FSAR (8) NUREG/CR-0912 Volume 1. Geoscience Data Base Handbook for Modeling a Nuclear Wasth Repository. January 1981. (9) kesponse to NRC questions 291.8 and 291.10. ~ e e s e e I 4 e

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