NUREG-0440, Forwards Class 9 Liquid Pathway Assessment Input to Chapter 6.1 of Des

Forwards Class 9 Liquid Pathway Assessment Input to Chapter 6.1 of Des

ML20213D733
Person / Time
Site:	Columbia
Issue date:	06/12/1981
From:	Lear G Office of Nuclear Reactor Regulation
To:	Houston R Office of Nuclear Reactor Regulation
References
CON-WNP-0363, CON-WNP-363, RTR-NUREG-0440, RTR-NUREG-440, RTR-NUREG-440-C-81062 NUDOCS 8106220368
Download: ML20213D733 (8)

Text

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Docket fio. 50-397 fb,7' (1 Ll )e s 3U,JU:115 G81>--HF u.s, . casa Q'

f!EfiORAfiDUtt FOR: R. }Iayne Houston, Chief Accident Evaluation Branch N X Division of Systems Integration # #

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THRU: James P. Knight. Assistant Director for Components and Structures Engineering Division of Engineering i FROM: George Lear. Chief t

flydrologic and Geotechnical Engineering Branch Division of Engineering i

SUBJECT:

CLASS 9 LIQUID PATlalAY ASSESS!!EffT It!PUT TO !!ASHI!;GT0f!

HUCLEAR POUER PLAffT UflIT 2 l

Plont flame: liashington fluclear Power Plant, Unit 2 Licensing Stage: OL

. Docket flo. 50-397 l

Date Due: June 30, 1981 i

Enclosed is our input to Chapter 6.1 of the lifiP-2 EIS. He conclude that the liquid pathway consequences would be much smaller than those for the "large river" site considered in the " Liquid Pathway Generic Study"

(?!UREG 0440). The review was conducted by R. Codell and G. Staley of the flydrologic Engineering Section.

Original signed by George Lear George Lear. Chief Hydrologic and Geotechnical Engineering Cranch Division of Engineering

Enclosure:

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Hydrologic Engineering Section Hydrologic & Geotechnical Engineering Branch Input to DES Washington fluclear Power Plant Unit 2 Docket flumber 50-397 6.1.4.5 Releases to Ground Water 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 above. Consideration has been given to the potential environmental . impacts of this pathway for the WilP_-2 fluclear Plant. The principle contributers to the risk are the core melt accidents associated with the Boiling Water Reactor release categories in WASH-1400. The penetration of the basemat of the containment building can release molten core debris to the strata beneath the plant. The soluble radionuclides in the debris can be leached and transported with ground water to down-gradient domestic wells used for drinking water or to surface water bodies used for drinking water, aquatic food and recreation. Releases of radioactivity to the ground water underlying the site could also occur via

! depressurization of the containment atmosphere or radioactive ECCS and .

suppression pool water through the failed containment.

An analysis of the potential consequences of a liquid pathway release of radioactivity for generic sites was presented in the " Liquid Pathway l Generic Study" (LPGS). The LPGS compares 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 reactor would l

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1 be mounted on a barge and moored in a water body. Parameters for each l

generic land-based site were chosen to represent averages for a w'ide 1 l

range of real sites and were thus " typical" but represented no real l sites in particular. The discussion in this section is a summary of an analysis performed to determine whether or not the liquid pathway consequences of a postulated accident at the UNP-2 site would be unique when compared to the generic "large river" land-based site considered in the LPGS. The method of comparison consists of a direct scaling up or down of the LPGS population doses based on the relative values of key parameters characterizing the LPGS large river site and the subject site.

The parameters which were evaluated in this case include the amounts and rate of release of radioactive materials to the ground, ground water travel time and sorption on geological media. .

All of the reactors considered in the LPGS were Westinghouse pressurized water reactors (PWR) with ice condenser containments. There are likely to be significantly different mechanisms and probabilities of releases of ,

radioactivity for the WNP-2 boiling water reactors (BWR). The staff is not aware of any studies which indicate the probabilities or magnitudes l

of liquid releases for boiling water reactors. It is unlikely however that the liquid release for a BWR would be any larger than that conservatively estimated for similarly sized PWR's in the LPGS. " e source term used

! for WNP-2 in this comparison therefore is assumed to be equal to that used in the LPGS.

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3 Doses to individuals and populations were 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 contamination, alternative sources of water for drinking, irrigation and industrial uses would be expected to be found, if necessary. Commercial and sports fishing, as well as many other water-related activities could be restricted. The consequences would, therefore, be largely economic or societal, 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 airborne pathways.

The WNP-2 site is located in the Hanford reservation about 3 miles west of the Columbia River. Ground water at the site exists in both a water table aquifer and several confined, artesian aquifers largely in unconsoli-dated alluvial and glacial sediments. The water table aquifer at the site is about 60 feet below thesurface and is 120 to 160 feet thick. Flow in the unconfined aquifer is toward the Columbia River, which is its sink.

There is no recharge of the water table at the site.

The plant buildings are located on highly permeable glaciofluvial outwash sands and gravels. Contaminated water released from the plant would travel vertically until it reached the water table, and would then move downgradient toward the Columbia River. Although there are many wells on the site,

they are closely monitored and are not used for public water consumption.

In the event of a core melt accident, use of water from affected wells would, presumably be halted. Therefore, our analysis focused on potential contamination of the Columbia River by way of contaminated ground water from the site.

Large releases to the ground of radioactive water resulting from chemical reprocessing of reactor fuel have occurred at the Hanford reservation.

From 1944 to 1972, over 130 billion gallons of waste water and millions of curies of fission products have been discharged from seepage pits to the ground. There have been extensive measurements of the ground water plumes of several radioactive isotopes and other chemicals released from the seepage pits. Because of this large body of information obtained over the years, the movement of radionuclides in groundwater at the site is relatively well understood. Several constituents of leached waste have migrated up to about 15 miles in the direction of the Columbia River in the timespan 1944 to 1975. On the basis of the observed plume migration we have estimated the ,

l ground water velocity in the unconfined aquifer under the site to be about 7 feet per day toward the Columbia River. Contaminated water released from the plant in the event of a core melt accident could migrate to the river in i

a minimum of about 6 years. This compares to a minimum groundwater travel time of about 0.6 years used for the LPGS site. '

For holdup times on the order of years the LPGS showed that the only significant contributors to population dose to surface water users would be the isotopes Cs-137 and Sr-90. Actual observation of the movement

.of Cs-137 and Sr-90 in site soil columns and in situ measurements at the seepage pits indicate that these two isotopes are strongly bound to the soil.* While the plumes of substances not easily sorbed, such as tritium and nitrate, can be seen to extend tens of miles, most of the cesium and strontium has remained within a few tens of feet from the points of release. Based upon these data, the staff has estimated retardation factors, which reflect the effects of sorption of the radionuclides within the aquifer, to be about 8400 for Cs and 1400 for Sr. Using these values of the retardation factors, we estimate that it would take a minimum of 50,400 years for Cs-137 and 8400 years for Sr-90 to reach the Columbia River. These travel times compare to 51 years for Cs-137 and 5.7 years for Sr-90 employed in the LPGS. Because their half-lives are approximately 30 years, virtually all the Cs-137 and Sr-90 would decay in the ground water before it could reach the Columbia River. Since nearly all of the population dose for a liquid pathway release can be shown to be due to these two isotopes, the staff concludes that the liquid pathway

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consequences at the Hanford site, resulting from a postulated Class 9 accident, would be significantly less than that calculated for the LPGS large river site and would present no unique contribution to risk.

• 0. J. Brown, " Migration Characteristics of Radionuclides Through Sediments Underlying the Hanford Reservation", in Disposal of Radioactive Wastes into the Ground, IAEA, Vienna,1967, pp 215-228.

s Finally, there are measures which could be taken, if necessary, to .

isolate liquid contaminants such as tritium before they could contaminate the river. The staff's estimate of a 6 year minimum travel time would allow ample time for engineering measures such as slurry walls and dewatering to isolate the radioactive contamination near the source.

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