ML20205T209

Application for Approval to Leave Inplace,Slightly Contaminated Soil Next to Reactor Water Storage Tank. Radiological Assessment Encl.Fee Paid

ML20205T209
Person / Time
Site:	Maine Yankee
Issue date:	11/02/1988
From:	Whittier G Maine Yankee
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
GDW-88-297, MN-88-107, NUDOCS 8811140170
Download: ML20205T209 (14)

Text

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MaineVankee naamt i Dacre sca vu.s s o ,e9 ,

EDISON ORtVE AUGUSTA. MAINE 04330 (200 f/.74868 i

November 2, 1988 '

MN-88-107 G0H-88-297 United States Nuclear Regulatory Commission  :

i- Washington, DC 20555 t Attention: Document Control Desk

Reference:

License No. OPR-36 (Docket No. 50-309)  :

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Subject:

Request for In-Place Disposal of Slightly Contaminated Soil in [

Accordance with 10CFR20.302(a)

Dear Sir:

Maine Yankee Atomic Power Company (Maine Yankee) requests NRC approval  !

pursuant to 10CFR20.302(a) for in-place disposal of residual contaminated  !

solls located on-site at the Haine Yankee Atomic Power Station in Hiscassett, l j Haine, as detailed in the attached application. The application specifically t requests hppioval to leave approximately 7,600 cuoic feet of sitehtly contamhated soll, resulting from a Reat. tor Mater Storage Tank (RHST) siphon  ;

heater leak, in the ground within the protected area at Maine Yankee.  ;

i Approxitately 600 cubic feet of soil from the immediate area of tne leak has [

, been removed for off-vite disposal as radioactive waste. It is not believed i

! practical to remove the remaining residual contamination due to the volume of  !

soil required to be excavated and its proximity to the foundation of the [

RHST. All significant concentrations of radioactive materials which might  ;

present an unnecessary risk to the public have been removed. The hole created i by the excavation has been backfilled with clean materials, with the major  ;

portion of the surface area paved over with asphalt to minimize the potential

! of translocating the rasidual activity by surface water run off or by winds. 1 1 .

l A radiological assessment based on an estimate of the residual soil activity from the RHST siphon heater leak is detailed in Attachment 1. Based on this analysis, Maine Yankee has determined that the potential radiological impact of any residual activity reaching the tidal waters adjacent to the plant will result in off-site doses to a maximally exposed member of the 4

t general public of less than one mrem / year to the whole body or any organ, ,

This dose which is about 100 times less than natural background radiation and would be indistinguishable from the normal variations in background radiation  ;

J' 1evels. It is below all limits currently under consideration by the NRC for  !

appilcation to materials which could be classified as Below Regulatory Concern )

(BRC).

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l MaineYankee United States Nuclear Regulatory Commission Page Two [

Document Control Desk MN-88-107 '

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Maine Yankee has determined that pursuant to 10CFR170.21 a fee of $150.00 l 1s required for this approval. Please find a check for that amount enclosed. (

Very truly your . l I i

MAINE YA!4KEE I e

jf}N i i G. D. Mbittler. Manager l Nuclear Engineering and Licensing 05:BJP i l Attachment l

c: Mr. Richard H. Messman I l Mr. Milliam T. Russell  !

j Mr. Patrick M. Sears j Mr. Cornelius F. Holden i

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MAINE YANKEE ATOMIC PONULCOMPANY I APPLICATION FOR APPROVAL TO LEAVI  ;

IN-PLACE SL1GlilLY CONTAMINATED SOIL NEXT 10_

TFE REACTOR NATER STORAGE TANC j 1 ,

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l, MaineYankee AUACHHENT 1 MAint_YADktt.At_omic Power Cc@pany Application for Approval to LAAte In-Platt Sligttil3_Conta mi n a t e LS atLN tJtt_to the Reatt0LBatiLilotAgt_IAah 1.0 INTR 000CUDN Haina Yankee Atomic Power Company (Haine Yankee) requests approval, pursuant to 10CFR20.302(a) to leave in. place residual radioactive I materia's in soll in the area of the excavation of contaminated soil associated with leakage from the Reactor Hater storage Tank (RHST).

2.0 DEiCRIPl10LQF EVENT CONTAMINATION i

On February 23, 1988, t small outdoor leak at the inlet flange connection l between the RHST siphon heater return litit and Isolation Valve CS-81 was discovered and subsequently contained. It could not be directly determined exactly when the leak had started, nor the actual water volume which had been lost. The leakage gave rise to a concern over possible ground contamination since part of the area below the leak was gravel which could allow radioactivity to seep into the soll below the asphalt pavement. Surveys of the area adjacent to the RHST indicated ground conta*.ination with concentrations as high as 6.6E-03 uC1/gm Cesium-137.

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As FF t ' contaminated soil was removed from the aree of the RHST and placed i , drums for future disposal off-site as radioactive waste.

During the contaminated soll removal, a second small leak at the base of  ;

the RHST siphon heater return line Isolation Valve CS-81 was also j discovered. The second leak was observed to be cnly a few drops per I

minute and was subsequently repaire). Sarple analysis of the soll [

removed frce the contaminated area also indicated the presence of l

1 MaineYankee Cesium-134, Antimony-125, and Cobalt-60 in addition to the principal radionuclide detected, Cesiun-137. The Cesium-134, Antimony-125, and Cobalt-60 were observed in some samples taken from the excavation to be present in concentrations approximately equal to 1.E-05 uCi/gm for Cesium-134, 2.E 05 uCi/gm for Cobalt-60, and 8.E-05 uCi/gm for Antimony-125. These levels are about two orders of magnitude below the highest Cesium-137 concer.trations as noted above.

Soil in the area of the RHST was excavated between two and five feet deep until the average Cesium-137 concentration had fallen to an equivalent MPC value in water of about 2.0E-05 uCi/ml. Approximately 600 cubic feet of - rth and asphalt that covered the area were removed for off-site raditactive waste disposal.

The hole was backfilled with clean fill and repaved, except for a small gravel area below the siphon heater. This limits the amount of rainfall and snce melt waters which could percolate down through the residual soil column to the grou..d water table. It also limits the potential for airborne transport of residual soil activity off-site, as well as eliminate any significant dose contribution to the plant's employees. l Table 1 lists the estimate of residual activity left in-place within the plant's protected area.

The following sections assess the potential impact associated with the  ;

assumption that the residual activity might be released to the off-site  !

envit onment. The release pathway postulated consist of the migration  !

downward of the residual soil activity to the ground water, with the subsequent transport through the water table to the tidal estuary.

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, 3.0 GEOLOGY AND HYOROLOGY CONSIDERATI0RS

( The soil at the Maine Yankee site consists of medium soft to medium l stiff silty clays with occasional sandy lenses and pebbly stones. The l soil is characterized as glacial till, with an average depth to bedrock 1

of 15 to 20 feet. The ground water pathway from the RHST location to the

MaineYankee l.

adjacent tidal waters is through this till, and possible in some places through compacted controlled backfill. The depth to groundwater has been conservatively estimated to be about 10 feet below grade. This is about 10 feet above tne adjacent tidal waters.

The flow of groundwater in the vicinity of the RHST is towards the surrounding adjacent tidal waters. There are no potable groundwater wells in the vicinity of the RHST which could be contaminated as a result  !

of the RHST related leaks.

The shortest distance between the soil contamination area and open waters associated with the estuary is estimated to be about 117 feet. Figure 1 shows the location of the RHST and adjacent open waters.

4.0 RADIOLOGICAL CONSIDERATIONS Residual Radioactivity: The remaining contamination in the soll was conservatively estimated by determining the average lateral radioactivity reduction factors between soil samples taken approximately 12 and 18 inches apart on the outer edge of the excavated area in all directions moving away from the RHST. Based on the Cesium-137 activity reduction factors, which averaged from about 4 per foot to as high as 106 per foot depending on which lateral direction outward from the trench wall one moved, the average concentration of residual activity is assumed to continue to decrease until an equivalent concentration equal to the Lower Limit of Detection (LLO) for Cesium-137 in sediments for environmental ,

samples, as required by plant Technical Specifications, is reached (i.e.,

1.8E-07 uCi/gm). No credit for reduction of residual activity with depth is assumed, even though the activity levels for Cesium-137 had generally fallen off at the bottom of the excavation to concentrations equivalent to the HPC value in water of 2E-05 uCi/ml. The column of residual activity was therefore assumed to extend down 10 feet from the surface to ground water. The resulting volume of soil containing residual activity L down to the concentration required as mini. mum detectable capabilities is k

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l conservatively estimated to be about 7,600 cubic feet. Residual activity concentrations were estimated based on a weighted average of the observed activities for Cesium-137, along the outer edge of the excavated trench.

For Cesium-137, the total activity remaining in the soil is estimated to be about 6.1 mC1, which is contained within the plant's protected area.

Table 1 lists the results of the estimates of residual contamination in soil. l Potential Exoosure: In order to bound the maximum possible dose to an individual, it is postulated that the residual activity in the soil near the RHST will migrate off-site via groundwater.

4 A conservative groundwater /redionuclide travel time analysis was -

performed for a minimum travel distance of about 117 feet from the RHST to the adjacent tidal waters. A groundwater travel time of 255 days was estimated from Darcey's Law for this location. This estimate is based on a soll permeability of 10 gpd/ft ,2a hydraulic gradient of 0.09 ft/ft, and a soi) porosity of 0.25. The analysis also conservatively assumed that tne RHST activity in soll was immediately available to the l

groundwater. However, due to ionic absorption of the radionuclides on l soil particles in the groundwater flow regime, most radionuclides travel at only a small fraction of the groundwater velocity. For the radionuclides present in the RHST rele.:se, retardation coefficients were estimated from data presented in NUREG/CR-3130, NUREG-0440, and NUREG/CR-1596, where the retardation coefficient is defined as the ratio of groundwater velocity to radionuclide velocity. The estimated r retardation coefficients and radionuclide travel times f rom the RHST to

, the tidal waters are summarized in Table 2. The travel time is the product of the groundwater travel time (i.e., 0.7 years) and the <

i appropriate retardation coefficient. I Due to the relatively long travel times for the nuclides listed in Table 2 in comparison to their respective half lives, the only nuclide j which could be expected not to decay away before it could reach tl.o estuary is Cesium-137. As a consequence, only Cesium-137 needs te be l considered in the off-site exposure analysis, i

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At the time when Cesium-137 is assumed to reach the estuary, it is postulated that all the residual activity noted in Table 1 is released ,

either to the shoreline sediment, or the tidal waters and aquatic food media. No credit for dispersion of activity through the soil media is taken.

Once the activity is ava'.lable to the estuary system, the exposure pathways of concern are direct radiation from the ground plane to anyone assumed to be working on the mud flats at lov tide, and the ingestion of fish and shellfish taken from the waters adjacent to the plant.

The dose models used in estimating the radiological impacts are taken l from Regula::ory Guide 1.109. For the ingestion pathway, the activity released into the tidal waters is assumed to be diluted in the 25-acre  !

surface mixing zone of the Maine Yankee discharge (FSAR Section 2.3.2) and a mean tidal range of about 8 feet (FSAR Table 2.3.2). The volume of j tidal waters available for dilution at high tide is therefore 0 3 7 about 8.7 x 10 ft or about 6.5 x 10 gallons. This dilution volume is conservative in that it accounts for only a fraction of the available tidal waters surrounding the plant.

I Table 3 indicates the liquid release pathway usage factors used in the dose analysis which were taken from the Maine Yankee Off-Site Oose Calculation Manual (00CH). Doses were calculated for the whole body and seven organs to each of three age groups: adults, teens, and children. l t

The resulting maximum potertlal individual doses a:e listed on Table 4.  !

Combining all three pathways, the maximum dose over the course of a t year's exposure is calculated to be 0.41 mrem to the whole body, and 0.55 ;

mrem to the liver of an adult, which is about 30 times less than the  !

internal exposure one receives from the natural Potassium-40 within our bodies. These doses are well below the "As Low As Reasonably Achievable" l (ALARA) objectives of 10CFR50, Appendix I, and all limits currently under L consideration by the NRC for application to materials which could be  ;

classified as Below Regulatory Concern (BRC).

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MaineYankee i 5.0 CONCLUS[QM Contaminated soil was located and removed to the extent practical with the residual radioactivity considered to be below any level of regulato y corcern since it presents no significant hazard to either the plant employees, general public, or the environment.

It is not expected that any significant transport of the residual radioactivity to any point off-site will occur. However, if transport were assumed, the dose consequences would be well below the naturally occurring background levels in the environment.

It is concluded that no further action is warranted with respect to the removal of any additional residual soil contamination. Maine Yankee, therefore, requests approval from the Commission to leave in-place the residual soil activity associated with the RHST leak. l I  :

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MaineYankee TABLE 1 Residual-RHST Soil Activities Heighted Average Total Residual Concentration Activity Nuclide -uCi/gm _ (Curies) {

Cesium-137 1.2E-05 6.1E-03 [

7.4E-05 Ceslum-134 1.5E-07 Antominy-125 3.2E-07 1.6E I Cobalt-60 1.1E-06 5.4E-04 '-

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MaineYankee TABLE 2 Nuclide Groundwater Travel Times y Retardation Travel Time (year) [

Nuclidt Coefficients in Tidal Waters ,

Cobalt-60 421 295 l Antimony-125 85 60 Cesium-134, 137 113 79 1

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MaineYankee TABLE 3

' Maine Yankee Liould Release Pathw&v Usaae Factors Fish Invertebrates Shoreline Agt (ka/vr) ,_(kg/vr) (hr/vr) '

Adult 21 5 334 Teen 16 3.8 67 Child 6.9 1.7 14 Infant 0 0 0 I

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MaineYankee i TABLE 4 Summary of Maximum Potential Doses Maximum Whole Body Dose Maximum Organ Dose in Any Age Group in Any Age Group ,

Pathway (mrem) (mres) i Fish 2.4E-01 3.7E-01 Shellfish 3.6E-02 5.5E-02 Ground Plane 1.3E-01 1.3E-01 f Total 4.1E-01 5.5E-01 (

p Age Group Adult Adult Organ Liver l [

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