ML011560290

Section 6: Ltp Compliance with Radiological Dose Criteria

ML011560290
Person / Time
Site:	Maine Yankee
Issue date:	06/01/2001
From:	Williamson T Maine Yankee Atomic Power Co
To:	Document Control Desk, NRC/FSME
References
+sisprbs20060109, -nr, -RFPFR
Download: ML011560290 (336)

Text

MYAPC License Termination Plan Revision 1 June 1, 2001 MAINE YANKEE LTP SECTION 6 COMPLIANCE WITH RADIOLOGICAL DOSE CRITERIA

MYAPC License Termination Plan Page 6-i Revision 1 June 1, 2001 TABLE OF CONTENTS 6.0 COMPLIANCE WITH THE RADIOLOGICAL DOSE CRITERIA . . . . . . . . . . . . . . . . 6-1 6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1 6.2 Site Condition After Decommissioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1 6.2.1 Site Geology and Hydrology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-2 6.3 Critical Group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3 6.4 Conceptual Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-4 6.5 Environmental Media and Dose Pathways . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-5 6.5.1 Contaminated Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-5 6.5.2 Environmental Media . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-5 6.5.3 Dose Pathways . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-5 6.5.4 Radionuclide Concentrations in Environmental Media . . . . . . . . . . . . . . . . 6-6 6.6 Material Specific Dose Assessment Methods and Unitized Dose Factors . . . . . . . . 6-7 6.6.1 Contaminated Basement Surfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-8 6.6.2 Activated Basement Concrete/Rebar . . . . . . . . . . . . . . . . . . . . . . . . . 6-19 6.6.3 Embedded Pipe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-24 6.6.4 Surface Soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-26 6.6.5 Deep Soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-27 6.6.6 Groundwater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-28 6.6.7 Surface Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-31 6.6.8 Buried Piping/Conduit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-32 6.6.9 Forebay Sediment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-34 6.6.10 Circulating Water Pump House . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-36 6.7 Material Specific DCGLs and Total Dose Calculation . . . . . . . . . . . . . . . . . . . . . 6-38 6.7.1 Conceptual Model for Summing Contaminated Material Dose . . . . . . . . 6-40 6.7.2 Method and Calculations for Summing Contaminated Material Dose

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-41

MYAPC License Termination Plan Page 6-ii Revision 1 June 1, 2001 6.8 Area Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-45 6.8.1 Basement Contamination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-45 6.8.2 Surface Soil and Deep Soil Area Factors . . . . . . . . . . . . . . . . . . . . . . . . 6-46 6.9 Standing Building Dose Assessment and DCGL Determination . . . . . . . . . . . . . . 6-46 6.9.1 Dose Assessment Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-46 6.9.2 Standing Building DCGLs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-47 6.9.3 Standing Building Area Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-47 6.10 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-49 Attachments -1 Fill Direct Dose Microshield Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-50 -2 BNL Kd Report for Fill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-51 -3 BNL Kd Report for Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-52 -4 Irrigation Memorandum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-53 -5 Concrete Density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-54 -6 Activated Concrete Inventory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-55 -7 Embedded Piping List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-56 -8 Deep Soil Microshield Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-57

MYAPC License Termination Plan Page 6-iii Revision 1 June 1, 2001 -9 Deep Soil RESRAD Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-58 -10 Buried Piping/Conduit List and Projected Concentration Calculation . . . . . . . . . . . . . . . . 6-59 -11 Buried Piping/Conduit RESRAD Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-60 -12 Buried Piping/Conduit Microshield Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-61 -13 DCGL/Total Dose Spreadsheets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-62 -14 Soil Area Factor Microshield Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-63 -15 Standing Building Area Factor Microshield Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-64 -16 Forebay Sediment Dose Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-65 -17 Unitized Dose Factors for Activated Rebar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-66 -18 NRC Screening Levels for Contaminated Basement and Annulus Trench Surfaces . . . . . . 6-67 List of Tables Table 6-1 Environmental Media Affected by Transfer from Contaminated Materials . . . . . . . . . . . . . . . . . . . 6-7 Table 6-2 Environmental Media and Dose Pathways for the Resident Farmer Scenario . . . . . . . . . . . . . . . . . 6-7

MYAPC License Termination Plan Page 6-iv Revision 1 June 1, 2001 Table 6-3 Selected Kd Values (g/cm3) for Basement Fill Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-16 Table 6-4 Contaminated Basement Surface Unitized Dose Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-21 Table 6-5 Activated Concrete Unitized Dose Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-24 Table 6-6 Embedded Piping Unitized Dose Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-25 Table 6-7 Surface Soil Unitized Dose Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-26 Table 6-8 Site Specific Parameters used in RESRAD Deep Soil Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . 6-28 Table 6-9 Deep Soil Unitized Dose Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-28 Table 6-10 Buried Pipe and Conduit Unitized Dose Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-34 Table 6-11 Contaminated Material DCGL and Total Annual Dose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-37 Table 6-12 Area Factors for Surface Soil and Deep Soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-46 Table 6-13 Gross Beta DCGL For Standing Buildings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-48 Table 6-14 Area Factors for Standing Buildings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-48

MYAPC License Termination Plan Page 6-1 Revision 1 June 1, 2001 6.0 COMPLIANCE WITH THE RADIOLOGICAL DOSE CRITERIA 6.1 Introduction The goal of the MY decommissioning project is to release the site for unrestricted use in compliance with the NRCs annual dose limit of 25 mrem/y plus ALARA and the enhanced State of Maine clean-up criteria of 10 mrem/y or less for all pathways and 4 mrem/y or less for groundwater sources. Both the State and NRC dose limits apply to residual radioactivity that is distinguishable from background. This section provides the methods for calculating the annual dose from residual radioactivity that may remain when the site is released for unrestricted use.

The dose assessment methods are used to determine Derived Concentration Guideline Levels (DCGLs) for nine different potentially contaminated materials. The DCGLs are the levels of residual radioactivity that correspond to the enhanced state clean-up criteria of 10 mrem/y or less for all pathways and 4 mrem/y or less for groundwater sources to the average member of the critical group. The DCGLs developed to demonstrate compliance with the enhanced State criteria are intended to also serve to demonstrate compliance with the NRCs 25 mrem/y plus ALARA regulation.

Maine Yankee intends to dismantle equipment and systems and remediate structures and land areas (per LTP Sections 3 and 4) to ensure that residual radioactivity levels are at, or below, the DCGLs. After remediation is completed, a final site survey will be performed (per LTP Section 5) to verify compliance with the DCGLs. The final survey report will document that the DCGLs have been met and serve to demonstrate that the Radiological Criteria for License Termination, as codified in 10 CFR 20 Subpart E and Maine State Law LD 2688-SP 1084 have been fully satisfied.

A dose assessment will be performed for each of the following materials: 1) contaminated building basement surfaces; 2) embedded pipe; 3) activated concrete/rebar; 4) groundwater;

5) surface water; 6) surface soils; 7) buried piping/conduit; 8) deep soils; and 9) Forebay sediment. Appropriate dose models and model input parameters were developed and justified for each material. The dose from each material was evaluated and summed with that from other materials as necessary to determine the total dose to the average member of the critical group.

MYAPC License Termination Plan Page 6-2 Revision 1 June 1, 2001 6.2 Site Condition After Decommissioning This section provides a brief overview of the planned site condition after decommissioning as well as a summary of site geology and hydrology. Detailed information on the planned final site condition is provided in Section 3.2.4. LTP Section 8.4 provides a more detailed overview of the geological and hydrological characteristics of the site.

In general, when decommissioning is complete the site will be predominantly a backfilled and graded land area restored with indigenous vegetative cover. The only above grade structures remaining per the current plans include the 345 KV switchyard. The former Low-Level Waste Storage Building (now the ISFSI Security Operations Building) will remain in place until the fuel is removed from the ISFSI. Building basements and foundations greater than three feet below grade will be backfilled and left in place. Buried piping that is at least three feet below grade will be remediated as necessary, surveyed, and abandoned in place.

6.2.1 Site Geology and Hydrology The site geology consists of a series of ridges and valleys striking north-south that reflect the competency and structural nature of the underlying bedrock. Deep valleys are filled with glaciomarine clay-silt soil and ridges are characterized by exposed bedrock or thin soil cover over rock. Surface drainage moves both to the north and south along the axes of the topographic valleys and also runs east and west down the flanks of the ridges. In the plant area, where the ground surface is relatively flat, manmade underground storm drains and catch basins control the surface runoff. In the area south of Old Ferry Road, drainage from a large area north of Old Ferry Road and the northern half of Bailey Point discharges in underground manmade piping to Bailey Cove.

The groundwater regime at the Maine Yankee facility is comprised of two aquifers: (1) a discontinuous surficial aquifer in the unconsolidated glaciomarine soils and fill material; and (2) a bedrock aquifer. The surficial aquifer is not present continuously across the site, as the overburden soils are thin to non-existent in some portions of the site. This is especially true in the southern portion of Bailey Point. The bedrock aquifer is present below the entire site and vicinity.

Groundwater originating near the surface in the northern portion of the site generally moves vertically into the soil except in the wetland areas where groundwater discharge locally occurs. After slow movement through the soil, the groundwater moves into the

MYAPC License Termination Plan Page 6-3 Revision 1 June 1, 2001 deeper bedrock and travels toward the bay, discharging upward in the near-shore area.

In the southern portion of the site, groundwater originating near ground surface generally stays near the surface, rather than penetrating deep into the bedrock.

During plant operation, impacts to the groundwater flow regime were limited to draw-down of the groundwater surface caused by foundation drains around the containment structure and, to a lesser extent, draw-down caused by active water supply wells.

Following decommissioning of the containment structure, groundwater levels will recover to approximate pre-construction levels.

6.3 Critical Group The regulations in 10 CFR 20 Subpart E require the dose to be calculated for the average member of the critical group. The critical group is defined in 10CFR20.1003 as the group of individuals reasonably expected to receive the greatest exposure to residual radioactivity for any applicable set of circumstances. The average member of the critical group is a conservative approach and is also used for demonstrating compliance with the dose criteria in Maine State Law LD 2688-SP 1084. The critical group selected for the MY site dose assessment is the resident farmer.

The resident farmer is a person who lives on the site after the site is released for unrestricted use and derives all drinking and irrigation water from an onsite well. In addition, a significant portion of the residents diet is assumed to be derived from food grown onsite. NRC guidance in NUREG-1727, Regulatory Guide DG-4006, NUREG-1549, and NUREG-5512 identify the resident farmer as a conservative onsite critical group. The resident farmer critical group applies to existing open land areas and all site areas where standing buildings have been removed to three feet below grade.

It is unlikely that other future site uses would result in a dose exceeding that calculated for the hypothetical resident farmer. It is more probable that actual future occupants of the site would engage in behaviors that would result in lower doses. For example, it is more likely that a hypothetical future resident would use the municipal water supply, as opposed to well water, since this is the common practice in the vicinity of the site and the yield from onsite test wells has been determined to be low and not suitable for consumption. Further, it is most likely that the site will be limited to industrial use. In this case the future site occupant would be a worker as opposed to the resident farmer. A third example would be an onsite resident who does not derive a significant fraction of dietary needs from an onsite farm. The important conclusion from

MYAPC License Termination Plan Page 6-4 Revision 1 June 1, 2001 these examples is that the dose calculated for the hypothetical resident farmer will likely be a conservative estimate of the dose that an actual site occupant or site visitor would receive.

Maine Yankee has assessed the potential for the filled basements to be excavated and occupied at some time in the future and does not believe that this scenario meets the reasonable expectation threshold required by the definition of a critical group in 10 CFR 20.1003. As stated in NUREG-1727, page C26, compliance with the dose limit does not require an investigation of all possible scenarios and the use of the average member of the critical group is intended to emphasize the uncertainty and assumptions needed in calculating potential future dose, while limiting boundless speculation on possible future exposure scenarios. As discussed above, selecting the resident farmer critical group is a sufficiently conservative projection of future land use. Further assuming that an individual excavates filled basements and attempts to renovate and occupy the basements is not considered plausible and results in excessive conservatism.

Notwithstanding the very low probability of excavation occurring, Maine Yankee will limit the potential activity on basement fill to concentrations below the surface soil DCGL level corresponding to 10 mrem/y. In addition, cost studies conducted to date indicate that it is more expensive to remediate soil than basement surface contamination. As discussed in Section 6.9, the selected Basement Contamination DCGLs are limited in order to maximize soil DCGL levels. The cost optimization process supported selecting Basement Contamination DCGLs that are below the NRC screening values for standing building surfaces. At these levels, the resident farmer dose was calculated to be 0.59 mrem/y from contamination on basement surfaces and ensures very low dose for any future land use.

6.4 Conceptual Model The Conceptual Model for dose to the resident farmer critical group is different to some extent for each contaminated material due to the different physical characteristics of the materials and different source term radionuclides. The Conceptual Model for each material is described in detail in Section 6.6.

In general, the overall site Conceptual Model includes a resident farmer who lives on the site after release for unrestricted use, draws drinking water and irrigation water from the worst-case onsite well location, and derives a substantial percentage of annual food requirements from the onsite resident farm.

MYAPC License Termination Plan Page 6-5 Revision 1 June 1, 2001 The hypothetical dose from each potentially contaminated material is evaluated independently.

However, the total resident farmer dose results from the summation of the contributions from all materials and all pathways. The method for summing the doses and selecting DCGLs for all contaminated materials is provided in Section 6.7.

6.5 Environmental Media and Dose Pathways 6.5.1 Contaminated Materials There are nine contaminated materials that could contribute to dose:

a. Embedded pipe

b. Buried pipe/conduit

c. Activated concrete/rebar

d. Groundwater

e. Surface Water

f. Basement surfaces

g. Surface soil

h. Deep soil

i. Forebay Sediment 6.5.2 Environmental Media After considering radionuclide transfer from the nine contaminated materials, there are five environmental media that could deliver dose to the resident farmer. These are groundwater, surface soil, deep soil, surface water, and basement fill. Groundwater concentration may increase through the transfer of radionuclides from contaminated basement surfaces, activated concrete/rebar, deep soil, and embedded pipe. Note that the groundwater environmental medium includes contributions from water contained in building basements as well as other sources. Basement fill may also become slightly contaminated through the transfer of contamination from basement surfaces, embedded piping, and activated concrete/rebar. Table 6-1 indicates which environmental media are affected by the transfer of radionuclides from contaminated materials.

The residual contamination in the Forebay sediment is not transferred to any of the five environmental media and is evaluated independently. Therefore, Forebay sediment is not included in Table 6-1.

MYAPC License Termination Plan Page 6-6 Revision 1 June 1, 2001 6.5.3 Dose Pathways The five environmental media listed in Table 6-1 deliver dose to the resident farmer through one or more of the following dose pathways: 1) drinking water; 2) direct exposure; 3) ingesting soil, plants, animals, or fish; and 4) inhaling resuspended soil.

These pathways are consistent with those listed in NUREG-1549 for the resident farmer.

A given environmental medium will not contribute dose through all pathways. For example, the basement fill will result in dose by direct exposure through the earthen cover that will be placed over the filled basements. However, there will be no ingestion or inhalation associated with the fill because of the presence of the cover. Ingestion or inhalation could occur if the fill were excavated at some time in the future. To account for this possibility, the projected basement fill concentration is limited to ensure that the concentration will not exceed the surface soil DCGL and that the dose will not increase over that calculated with the earthen cover in place. In fact, the hypothetical dose would decrease if the fill were excavated at some time in the future.

Table 6-2 lists the dose pathways applicable to each environmental medium. Note that groundwater contributes to the plant and animal pathways through irrigation.

6.5.4 Radionuclide Concentrations in Environmental Media To calculate the dose from each pathway the radionuclide concentrations in each environmental medium must be calculated. The concentrations in the surface soil, deep soil, and surface water can be used directly in the dose assessment since there is no contribution from other contaminated materials. However, the final concentrations in groundwater and basement fill, and the resulting dose, will depend on the transfer of contamination from other materials. Final concentrations in the five environmental media are calculated by summing contributions from various materials as listed below.

The contaminated materials that contribute to each of the environmental media are summarized below. The materials in brackets are those requiring transfer evaluations.

• Groundwater Concentration = [basement surface contamination] + [embedded pipe] + [activated concrete/rebar] + [deep soil] + [buried pipe/conduit] +

existing groundwater concentration

MYAPC License Termination Plan Page 6-7 Revision 1 June 1, 2001

• Basement Fill Concentration = [basement surface contamination] + [embedded pipe] + [activated concrete/rebar]

• Surface Soil Concentration = surface soil concentration

• Deep Soil Concentration = [buried pipe/conduit] + deep soil concentration

• Surface Water Concentration = surface water concentration Table 6-1 Environmental Media Affected by Transfer from Contaminated Materials Ground Surface Deep Surface Basement Water Soil Soil Water Fill Basement X X Contamination Surface Soil X Deep Soil X X Groundwater X Embedded pipe X X Surface Water X Activated X X concrete/rebar Buried X X

Pipe/Conduit Table 6-2 Environmental Media and Dose Pathways for the Resident Farmer Scenario Direct Drinking Plant, Inhalation Fish Radiation Water Animal, Soil Ingestion Ingestion Surface Soil X X X Deep Soil X Basement Fill X Groundwater X X* X*

Surface X X Water

• These pathways result through irrigation

MYAPC License Termination Plan Page 6-8 Revision 1 June 1, 2001 6.6 Material Specific Dose Assessment Methods and Unitized Dose Factors Each material has unique characteristics that must be considered when developing the conceptual and mathematical model for dose assessment. This section provides the dose assessment methods and results for each material in a unitized format by expressing the dose as a function of unit concentrations such as 1 dpm/100 cm2 or 1 pCi/g. The unitized format facilitates the summation of doses from all materials and the selection of material specific DCGLs (see Section 6.7).

6.6.1 Contaminated Basement Surfaces

a. Conceptual Model The Dose Model for contaminated basement surfaces assumes that the buildings are demolished to three feet below grade. The remaining basements are then decontaminated as necessary, filled with a suitable material (current plans call for fill with Bank Run Sand) and the area restored to grade, which results in a three-foot cover over the top of the filled basements. After the site is restored, rainwater and groundwater infiltrate into the basements and occupy the void space in the fill material. The available void space volume is a function of the fill material porosity.

The entire inventory of contamination on the basement surfaces, including the concrete and steel liner, is assumed to be instantaneously released and mixed with the water that has infiltrated into the basements. In this context, surface is intended to include all radioactivity, at all depths (this does not include activated concrete, which is treated as a separate material). Analyses of Maine Yankee concrete have indicated that, on average, the contamination is about 1 mm deep in the concrete. The liner contamination should be true surface contamination, i.e., not at any significant depth.

Using a mass balance approach, the radionuclides that are released from the surfaces are assumed to instantaneously reach equilibrium between the water, fill, and concrete. The relative equilibrium concentrations in the water, fill, and concrete are a function of the material Kd, mass, and porosity.

The critical group is the resident farmer who is assumed to drill a domestic water well into the worst case basement, i.e., that with the highest basement

MYAPC License Termination Plan Page 6-9 Revision 1 June 1, 2001 surface area to volume ratio. The amount of activity available for release is assumed to be directly proportional to the surface area of contaminated material. Therefore, the highest surface area/volume ratio results in the maximum radionuclide inventory and maximum concentrations in the water, fill, and concrete. The resident farmer is also assumed to occupy the land immediately above the basement, which maximizes direct exposure through the 3-foot cover.

The conceptual model results in three dose pathways to the resident farmer: 1) drinking water from the well; 2) irrigating with water from the well; and 3) direct radiation from radionuclides in the fill.

b. Mathematical Model A mathematical model was developed to calculate the equilibrium radionuclide concentrations in the basement water, fill, and concrete after the infiltration of rainwater and groundwater. Contamination is assumed to diffuse into and re-adsorb on concrete surfaces since concrete is a porous media. The re-adsorption on the steel liner is expected to be less than the concrete and is considered to be bounded by the concrete analysis. The mathematical model includes calculations to determine the resident farmer dose from drinking water derived from a well drilled directly into the basement fill, irrigating with the water, and being directly exposed to the covered fill. The model is intended to be a simple, conservative, screening approach.

The radionuclide inventory, water volume, fill volume, and concrete volume subject to re-adsorption are the quantities required to determine the equilibrium radionuclide concentrations in the three materials. The initial condition of the model is that a volume of water has infiltrated into the basement that is equal to the annual volume required for drinking, domestic use, and irrigation by the resident farmer. As stated above, the well is placed directly into the basement fill containing the water. From this initial condition the volumes and masses of the three materials, and the maximum radionuclide inventory released to the water, can be calculated.

The annual resident farmer well-water usage is assumed to be 738 m3 (justification provided below). This implies that the fill volume is 738 m3 divided by the porosity of the soil, which is assumed to be 0.3 (justification provided

MYAPC License Termination Plan Page 6-10 Revision 1 June 1, 2001 below). Therefore, the model fill volume is 2460 m3. This is the minimum fill volume required to contain the annual resident farmer water volume.

Depending on the infiltration rate, smaller fill volumes could supply the required 738 m3/y water volume, but this would result in slightly lower average annual concentrations. Assuming a model volume of 2460 m3, and no dilution through infiltration recharge, is the most conservative approach.

The actual basement open volumes of the PAB, Spray, and Fuel buildings are less than 2460 m3, but the containment basement volume is greater, i.e., 8217 m3. The larger containment volume has no effect on the result since the additional hypothetical water volume does not affect the radionuclide concentrations in the water, or the assumed annual water use. In fact, as explained below, using actual containment basement dimensions, including volume and surface area, would reduce water concentrations by a factor of 3.7 since the surface area to volume ratio for the containment basement is lower than that used in the model. The effect of surface area to volume ratio and the rationale for selecting the value used in the model are described below.

The basement surface area to open volume ratios have a direct effect on the results and are necessary for determining two parameters. The most important affected parameter is the maximum radionuclide inventory. Less important, but also related, is the volume of concrete available for re-adsorption of radionuclides. Using the maximum surface area/volume ratio from the four basements maximizes the radionuclide inventory and the resulting water, fill, and concrete concentrations.

The maximum ratio of concrete surface area/basement open volume of 1.7 m2/m3 is found in the Spray building basement. The surface area/volume ratios for the Containment, PAB, and Fuel buildings are 0.46 m2/m3, 1.03 m2/m3, and 0.49 m2/m3, respectively. Using the maximum ratio of 1.7 m2/m3 results in conservative dose calculations for the Containment, PAB, and Fuel buildings by factors of 3.7, 1.65, and 3.5 respectively. If necessary, as the project proceeds, Maine Yankee may use building-specific surface area/volume ratios based on the data presented in Section 6.6.1(d)(2) to calculate building-specific DCGLs.

Multiplying the 1.7 m2/m3 ratio by the fill volume (2460 m3) results in the maximum contaminated surface area that could contribute to the source term

MYAPC License Termination Plan Page 6-11 Revision 1 June 1, 2001 for a given 738 m3 of water. Accordingly, the maximum surface area in the model would be 4182 m2, which exceeds the actual surface area of any of the building basements. This occurs because the 1.7 m2/m3 ratio is from the Spray building and the maximum surface area of 3775 m2 is in the Containment building. However, consistent with a conservative screening approach, and to maintain the correct mathematical relationships between porosity, annual water volume, and surface area, the 4182 m2 surface area will be used in the model.

Note that using 3775 m2 would reduce the available source term and thereby reduce water concentrations.

Assuming that the water penetrates to a depth of 1 mm in the concrete, the concrete volume available to re-adsorb radionuclides from contaminated water is 4.2 m3. The 1 mm depth is based on analyses of contaminated Maine Yankee concrete. Although the conditions are different, i.e., water saturation after decommissioning versus periodic wet contamination events during operation, the penetration of water into the concrete after the basements are filled with water is also assumed to be 1 mm. This is considered a conservative assumption since increasing the concrete penetration depth will decrease the concentrations in the fill and in the water.

The model uses two approximations related to re-adsorption onto concrete that have a very small effect on the final results. First, the fill volume is calculated assuming all of the 738 m3 water volume is contained in the fill, not mixed between the fill and concrete. An exact solution would require consideration of both the fill and concrete volumes simultaneously. However, the affected concrete volume is very low and the corresponding water volume in the concrete is about 1 m3. This is less than 1% of the 738 m3 total and is insignificant. Second, the porosity of 0.3 is assumed to apply to both fill and concrete. The same porosities are used in the model in order to produce the simplified solution provided in Equation 7. However, site-specific measurements indicate that the actual concrete porosity is 0.15. Using a porosity of 0.15 would decrease the volume of water in the concrete to about 0.5 m3.. An exact solution to these two approximations would have a very small effect on the results and is an unnecessary level of detail considering the conservative screening approach used in the model.

The approach assumes uniform mixing among the soil, water, and concrete.

Uniform mixing within the fill is not unreasonable considering the surface area to

MYAPC License Termination Plan Page 6-12 Revision 1 June 1, 2001 volume ratio of 1.7 m2/m3. Assuming a planar geometry, this means that the water is required to mix over a distance of 0.6 m in the backfill. Although assuming planar geometry is a simplification, it demonstrates that water mixing over long distances in the fill is not intrinsic to the validity of the screening model.

The calculations for determining the equilibrium concentrations in the basement water, fill, and concrete are based on a mass balance approach. The total mass in the system, Mt, is the sum of the mass in the water (Mw), the mass sorbed to the fill (Mb), and the mass sorbed to the concrete (Mc). For these calculations, mass is expressed as activity, A. The total activity, At, is the total radionuclide inventory in the 4182 m2 basement concrete surface under consideration.

Equations (1) through (7) described below are solved for each radionuclide in the Maine Yankee Radionuclide Mixture.

At = Aw + Af + Ac (1)

Where: At is total activity (pCi)

Aw is the total activity in water (pCi)

Af is the total activity in the fill (pCi)

Ac is the total activity in the concrete (pCi)

The activity in the water is defined as:

Aw = çC Vt (2)

Where: ç is the porosity of the fill and concrete C is the concentration in solution (pCi/l) and, Vt is the total system volume (sum of the volume of fill and concrete, m3).

At equilibrium the activity adsorbed to the fill and concrete is directly proportional to the concentration in the water. The proportionality constant used in these calculations is the distribution coefficient, Kd, and has units of cm3/g. Distribution coefficients are widely accepted measures of sorption onto the solid phase, and the solid/liquid phase ratio, and are accepted for use in risk assessments by national and international regulatory agencies and scientific

MYAPC License Termination Plan Page 6-13 Revision 1 June 1, 2001 organizations including the U.S. Nuclear Regulatory Commission and the U.S.

Environmental Protection Agency.

The activity adsorbed on the fill and the concrete can be represented as:

Af = nf Kdf C Vf (3)

Where: nf is fill bulk density (g/cm3)

Kdf is fill distribution coefficient C is water concentration(pCi/l)

Vf is fill volume (m3) and Ac = nc Kdc C Vc (4)

Where: nc is concrete bulk density (g/cm3)

Kdc is concrete distribution coefficient C is water concentration (pCi/l)

Vc is concrete volume (m3)

The bulk density of the fill is assumed to be 1.5 g/cm3 based on analyses of potential fill (reference provided below). For the concrete, a site-specific value of 2.2 g/cm3 was used (reference provided below). V is the volume of the solid phase; Vf is 2460 m3 and Vc is 4.2 m3.

Combining the terms from Equations (2), (3), and (4) gives:

At = çC Vt + nf Kdf C Vf + nc Kdc C Vc (5)

Multiplying the second and third terms by (çVt)/(çVt), i.e., 1, and rearranging gives:

At = çC Vt + (çVt C)( nf Kdf Vf) /(çVt ) + (ç Vt C)(nc Kdc Vc)/(ç Vt) (6)

MYAPC License Termination Plan Page 6-14 Revision 1 June 1, 2001 Recognizing from Equation (1) that the term, çC Vt is the activity in the water phase, Aw, allows Equation 6 to be rewritten as:

At = Aw(1 + nf (Kdf/ç)(Vf/Vt) + nc (Kdc/ç)(Vc/Vt)) (7)

To calculate the water concentration, drinking water dose, concentration in the fill, and concentration on the concrete surfaces, Equation (7) is first solved for Aw. All of the terms in Equation (7) are known except Aw. The water concentration, C, is then calculated using Equation (2). After solving for C, the backfill and concrete concentrations are calculated using Equations (3) and (4).

c. Dose Calculations The concentrations in the basement water and fill are used to calculate dose.

There are three dose pathways to the resident farmer after the fill is placed in the basements, the three-foot cover is completed, and water infiltrates the basements. These are drinking water dose, irrigation dose, and direct dose.

The dose calculations are described in Equations (8) through (10). The equations are used to calculate dose for each radionuclide in the Maine Yankee mixture.

1. Drinking Water Dose Drinking water dose is calculated from the radionuclide concentrations in the basement water. As shown in Table 6-1, the basement water is one of several contributors to drinking water dose. The annual water intake is assumed to be 478 L/y consistent with the default values in the NRC screening code, DandD, Version 1. Dose conversion factors are taken from Federal Guidance Report No. 11.

Dosedw = ( C pCi/l)(478 L/y)(DCF mrem-y/pCi) (8)

Where: C is water concentration in pCi/L DCF is FGR 11 dose conversion factor

MYAPC License Termination Plan Page 6-15 Revision 1 June 1, 2001

2. Irrigation Dose Including irrigation dose is conservative because irrigation in Maine is uncommon due to relatively high annual precipitation. However, consistent with a screening approach it is included. The irrigation rate is assumed to be 0.274 L/m2/d (justification provided below). The source of the water is the resident farmer well placed in the building basement. The annual irrigation volume is mixed in a 15 cm depth of soil, which is consistent with the NRC DandD model as described in NUREG-5512, Volume 1. The dose from the resulting soil concentrations were calculated using the NRC screening values in NUREG-1727, Table C2.2 , converted to mrem/y per pCi/g.

Doseirrigation = (C soil pCi/g)(NUREG-1727 mrem/y per pCi/g) (9)

Where: Doseirrigation is the annual dose from irrigation (mrem/y)

Csoil is soil concentration in pCi/g (NUREG-1727) is the soil screening value from NUREG-1727, Table C2.3 converted to mrem/y per pCi/g Csoil = (pCi/L in water)(0.274 L/m2/d)(365 d)(1 m2)

(1m2)(0.15 m)(1E+06 cm3/m3)(1.6 g/cm3) (10)

3. Direct Dose The direct dose was calculated using the Microshield code assuming a three-foot soil cover, 10,000 m2 area, and 5.8 m depth. The 5.8 m depth represents the deepest basement, i.e., containment. The Microshield result for Deep Dose Equivalent, Rotational Geometry, was used and is generally referred to as exposure. The resulting exposure rate was multiplied by the annual outdoor occupancy time of 964 hours0.0112 days <br />0.268 hours <br />0.00159 weeks <br />3.66802e-4 months <br /> (0.1101 x 365 days x 24 hr/day) from the NRC DandD, Version 1, screening code to calculate the annual direct exposure dose.

The Microshield output reports are provided in Attachment 6-1.

MYAPC License Termination Plan Page 6-16 Revision 1 June 1, 2001

d. Model Input Parameters The following section describes and justifies the parameters used in the concentration and dose calculations.

1. Distribution Coefficients, Kd Fill Kd values were either derived from literature (mean values) or from the results of analyses of site-specific fill materials. The site-specific Kd analyses were performed by Brookhaven National Laboratory (BNL)

(results provided in Attachment 6-2). At this time, the most likely fill material is Bank Run Sand. Therefore, the average Kds for Bank Run Sand from Attachment 6-2 were used in the model. Table 6-3 lists the fill Kds, and the reference, for each radionuclide.

Concrete Kd values were either derived from literature or from the results of site-specific Kd analyses. The site-specific Kd analyses were performed by BNL (results provided in Attachment 6-3). Table 6-3 lists the concrete Kds, and the reference, for each radionuclide. It is seen that for cement, a few Kds were left blank. This indicates data were not available and a value of 0 was used in the calculations. A Kd of 0 maximizes the concentration in water. In addition, the Krupka reference did not contain Kd information for cobalt or iron. It was assumed that the Kds for these two metals were the same as nickel.

However, the overall effect of the concrete is small, regardless of Kd.

2. Maximum Surface Area to Volume Ratio The building basements that will remain following demolition of site structures include the Containment, PAB, Spray and Fuel Building basements. The open-air volumes of the basements are 8217 m3, 1584 m3, 1136 m3, and 837 m3 respectively. This represents the volume of fill required in each basement. The wall and floor surface areas are 3775 m2, 1637 m2, 1883 m2, and 409 m2 respectively. The basement volumes and surface areas were determined in Maine Yankee calculation EC 01-00(MY). The maximum surface area to volume ratio of 1.7 m2/m3 is found in the Spray building basement.

MYAPC License Termination Plan Page 6-17 Revision 1 June 1, 2001 Table 6-3 Selected Kd Values (g/cm3) for Basement Fill Model Radionuclide Mean Reference for Mean Kd Concrete Reference for Kd Fill Kd Kd in cement H-3 0 0 Fe-55 25 Baes, Table 2.13 100 Krupka Table 5.1 Ni-63 12 Attachment 6-2 100 Krupka Table 5.1 Mn-54 50 Sheppard, Table A-1 Co-57 13 Attachment 6- 2 100 Krupka Table 5.1 Co-60 13 Attachment 6-2 100 Krupka Table 5.1 Cs-134 56 Attachment 6-2 3 Attachment 6-3 Cs-137 56 Attachment 6-2 3 Attachment 6-3 Sr-90 6 Attachment 6-2 1.0 Attachment 6-3 Sb-125 45 Sheppard, Table A-1 Pu-238 550 Sheppard, Table A-1 5000 Krupka Table 5.1 Pu-239/240 550 Sheppard, Table A-1 5000 Krupka Table 5.1 Pu-241 550 Sheppard, Table A-1 5000 Krupka Table 5.1 Am-241 1900 Sheppard, Table A-1 5000 Krupka Table 5.1 Cm243/244 4000 Sheppard, Table A-1 5000 Krupka Table 5.1 C-14 5 Sheppard, Table A-1 Eu-152 400 Onishi, Table 8.35 Eu-154 400 Onishi, Table 8.35

3. Porosity The porosity of the fill material is assumed to be 0.3. The range of mean porosities for a wide variety of soil types are listed in NUREG-5512, Volume 3, Residual Radioactive Contamination From Decommissioning. Parameter Analysis, Page 6-64, Table 6.41. The porosities listed in NUREG-5512 ranged from 0.36 to 0.49.

MYAPC License Termination Plan Page 6-18 Revision 1 June 1, 2001 The projected dose from contaminated concrete in the basement fill model decreases with increasing porosity. However, the projected doses from the embedded pipe and activated concrete increase with increasing porosity. This is because the source term for embedded and buried piping is constant and the source term for contaminated concrete is a function of surface area. All three dose assessment models are conservative. However, the activated concrete and embedded piping source term assumptions are much more conservative than those used for the basement concrete and the resulting dose is a small fraction of that from contaminated concrete. Therefore, the porosity effect on the contaminated concrete dose is used to select a porosity at the lower end of the range, e.g., 0.3.

4. Annual Drinking Water Volume The annual drinking water volume was assumed to be 478 l/y. This is the default volume from NRC DandD, Version 1 screening code.

5. Irrigation Rate and Annual Irrigation Volume Annual irrigation volume was based on interviews with representatives of the Maine USDA-NRCS. The individuals contacted are documented in a memorandum provided in Attachment 6-4. The USDA representatives indicated that irrigation in Maine is uncommon, but that in drought years irrigation may occur. The Maine USDA representatives indicated that the drought irrigation rate for a family garden would not be expected to exceed 4-5 in/y (10 to 12 cm/y).

The 10 cm/y rate was used in the model, which can be converted to 0.274 l/m2/d. To calculate total annual volume, the 10 cm/y rate was multiplied by the default cultivated area of 2400 m2 from the DandD screening model (NUREG-1727, Appendix C, Section 2.3.2). This results in the annual irrigation volume of 240,000 l/y.

6. Annual Domestic Water Use Annual domestic water volume is derived from NUREG-5512, Volume 3, Page 6-37, Table 6-19. The per capita consumption rate for the State of Maine is listed as 124,422 l/y. Assuming a family of

MYAPC License Termination Plan Page 6-19 Revision 1 June 1, 2001 four, this corresponds to a total domestic water volume of 497,688 l/y.

The assumption of four occupants is based on the land occupancy rate from NUREG-1727, Table D2, of 0.0004 persons/m2 and an assumption that the resident farm size is 10,000 m2.

7. Total Resident Farmer Annual Well Water Volume The total annual volume of water from the resident farmer well is the sum of the domestic use plus irrigation use. Domestic use is 497,688 l/y and irrigation use is 240,000 l/y for a total of 737,688 l/y.

A rounded value of 738 m3/y was used in the model.

8. Concrete Density Concrete density was determined by site-specific analysis to be 2.2 g/cm3 (Attachment 6-5).

9. Fill Material Density Density of the possible fill material is 1.5 g/cm3 (Attachment 6-2). This corresponds to Bank Run Sand.

10. Soil Density Density of soil is 1.6 g/cm3 based on an average of the densities of Bank Run Sand and Bank Run Gravel from Attachment 6-2. This average is assumed to be representative of the site soil, which is comprised primarily of backfill.

11. Dose Conversion Factors (DCFs)

The DCFs are in units of Committed Effective Dose Equivalent (CEDE) and are taken from Federal Guidance Report No. 11, Limiting Values of Radionuclide Intake and Air Concentration and Dose Conversion Factors for Inhalation, Submersion, and Ingestion, Table 2.2, EPA-520/1-88-020.

MYAPC License Termination Plan Page 6-20 Revision 1 June 1, 2001

12. Outdoor Occupancy Time The DandD, Version 1, default value of 0.1101 y or 965 hr/y is used.

e. Unitized Dose Factors for Contaminated Basement Surfaces Using Equations 1-10 above, the radionuclide concentrations in basement water, fill, and concrete, and the dose to the resident farmer were calculated using a simple spreadsheet application. The activity of each radionuclide in the Maine Yankee mixture for contaminated surfaces was set to1 dpm/100 cm2 of surface area. The surface was assumed to be concrete for the purpose of the calculation to evaluate the potential effect of re-adsorption on concrete. The spreadsheet output and the resulting unitized dose factors are provided in Table 6-4 (see next page).

6.6.2 Activated Basement Concrete/Rebar

a. Conceptual Model Activated concrete and rebar is present in the ICI sump area in the containment building. The current plan is to remediate activated concrete exceeding 1 pCi/g total activity (sum of all radionuclides) and any rebar associated with this concrete. The walls and floors consist primarily of concrete with rebar being a small percentage. Characterization results indicate that the total activity concentration in rebar is about 1.9 times higher than the concrete surrounding the rebar. In addition, the radionuclide mixtures for concrete and rebar differ as indicated in Table 2-9. However, as shown in Attachment 6-17, the calculated dose from the rebar is less than the dose from the surrounding concrete (see Table 6-11 for activated concrete dose), accounting for both the higher relative concentration and the rebar radionuclide mixture. The concrete dose was 4.63 E-2 mrem/y and the rebar dose was 1.93 E-2 mrem/y. Therefore, the walls and floors are conservatively assumed to be comprised entirely of activated concrete in the dose calculation.

MYAPC License Termination Plan Page 6-21 Revision 1 June 1, 2001 Table 6-4 Contaminated Basement Surfaces Unitized Dose Factors Key Parameters Porosity 0.30 Bulk Density 1.50 g/cm3 Yearly Drinking Water 478.00 L/yr 2

Wall Surface Area 4182.0 m Fill Volume 2460.00 m3 Surface Area/Open Volume 1.70 m2/m3 Concrete Volume 4.18 m3 Concrete Density 2.20 g/cm3 Annual Total Well Water Vol 738.00 m3 Irrigation Rate 0.274 L/m2-d Surface Soil Depth 0.15 m DOSE CALCULATION FACTORS SOURCE TERM Kd WATER, FILL, CONCRETE CONTAMINATED CONCRETE ANNUAL DOSE CONCENTRATION Nuclide NUREG-1727 FGR 11 Mcroshield Inventory Inventory Kd Fill Kd Adsorption Water Fill pCi/g Concrete Nuclide Drinking Irrigation Direct Total mrem/y per mrem/ mrem/y per dpm/100 pCi cm3/gm Concrete Factor pCi/L pCi/g Water Dose Dose Dose Dose pCi/g pCi pCi/g cm2 cm3/gm mrem/y mrem/y mrem/y mrem/y Sr-90 1.47E+01 1.42E-04 0.00E+00 1.00E+00 1.88E+05 6.00E+00 1.00E+00 3.10E+01 8.23E-03 4.94E-05 8.23E-06 Sr-90 5.59E-04 5.38E-05 0.00E+00 6.12E-04 Cs-134 4.39E+00 7.33E-05 6.09E-05 1.00E+00 1.88E+05 5.60E+01 3.00E+00 2.81E+02 9.08E-04 5.09E-05 2.72E-06 Cs-134 3.18E-05 1.77E-06 3.10E-09 3.36E-05 Cs-137 2.27E+00 5.00E-05 1.20E-05 1.00E+00 1.88E+05 5.60E+01 3.00E+00 2.81E+02 9.08E-04 5.09E-05 2.72E-06 Cs-137 2.17E-05 9.16E-07 6.10E-10 2.26E-05 Co-60 6.58E+00 2.69E-05 6.30E-04 1.00E+00 1.88E+05 1.30E+01 1.00E+02 6.71E+01 3.80E-03 4.93E-05 3.80E-04 Co-60 4.88E-05 1.11E-05 3.11E-08 5.99E-05 Co-57 1.67E-01 1.18E-06 2.80E-08 1.00E+00 1.88E+05 1.30E+01 1.00E+02 6.71E+01 3.80E-03 4.93E-05 3.80E-04 Co-57 2.14E-06 2.82E-07 1.38E-12 2.42E-06 Fe-55 2.50E-03 6.07E-07 0.00E+00 1.00E+00 1.88E+05 2.50E+01 1.00E+02 1.27E+02 2.01E-03 5.01E-05 2.01E-04 Fe-55 5.82E-07 2.23E-09 0.00E+00 5.84E-07 H-3 2.27E-01 6.40E-08 0.00E+00 1.00E+00 1.88E+05 0.00E+00 0.00E+00 1.00E+00 2.55E-01 0.00E+00 0.00E+00 H-3 7.80E-06 2.57E-05 0.00E+00 3.35E-05 Ni-63 1.19E-02 5.77E-07 0.00E+00 1.00E+00 1.88E+05 1.20E+01 1.00E+02 6.21E+01 4.10E-03 4.92E-05 4.10E-04 Ni-63 1.13E-06 2.17E-08 0.00E+00 1.15E-06

MYAPC License Termination Plan Page 6-22 Revision 1 June 1, 2001 With the exception of the source term calculation, the conceptual model for activated concrete is identical to the conceptual model for contaminated basement surfaces described above. A conservative screening approach was used to account for the activated concrete source term by assuming that the entire inventory of the residual activity in the activated concrete, at all depths, is immediately released into the 738 m3 of water in the basement fill. A more realistic model would account for the fact that the activated inventory would be released very slowly over time and that the concentration would decrease with depth. Concentration decreases with depth since the most highly activated concrete will have been removed during remediation. In addition, the concrete concentration at all depths is assumed to be equal to the surface concentration of 1 pCi/g. This is conservative since the concentration will actually decrease with depth. However, since the dose using the screening approach was very low, the detailed analyses required to justify release rates and actual concentrations with depth were not necessary.

b. Unitized Dose Factors for Activated Concrete Although activated concrete is present at depth beneath the surface, the unit dose calculation for activated concrete is based on a concentration of 1 pCi/g total activity (sum of all radionuclides) at the surface of the floors and walls of the ICI sump. The surface activity (measured volumetrically) is the measurable quantity that will be used to demonstrate compliance during the final status survey. However, the total inventory, i.e., source term, includes the radionuclides in the entire volume of activated concrete, including surface and subsurface. The total inventory was determined to be 3.43E+08 pCi as described in Attachment 6-6. This inventory may change if the remediation level (i.e., DCGL) for activated concrete is changed. The final dose assessment will be based on the actual remediation level selected.

To determine the inventory of each radionuclide, the total 3.43E+08 pCi inventory must be multiplied by the radionuclide fraction in the activated concrete mixture. The resulting radionuclide specific inventories are input to the inventory column in the spreadsheet developed for the contaminated basement surfaces. All of the resulting water, fill, and concrete concentrations and dose calculations are identical to those described for the contaminated basement surfaces in Section 6.6.1.

The Activated Concrete/Rebarspreadsheet is provided in Table 6-5, which lists the unitized dose factors for all radionuclides in the activated concrete mixture assuming a unit inventory of 1 pCi/g total activity at the surface of activated concrete.

MYAPC License Termination Plan Page 6-23 Revision 1 June 1, 2001 Table 6-5 Activated Concrete Unitized Dose Factors 1.0 pCi/g Key Parameters Porosity 0.30 Bulk Density 1.50 g/cm3 Yearly Drinking Water 478.00 L/yr 2

Wall Surface Area 4182.0 m Fill Volume 2460.00 m3 Surface Area/Open Volume 1.70 m2/m3 Concrete Volume 4.18 m3 Concrete Density 2.20 g/cm3 Annual Total Well Water Vol 738.00 m3 Irrigation Rate 0.274 L/m2-d Surface Soil Depth 0.15 m Activated Concrete 3.43E+08 Total pCi Total Inventory per pCi/g DOSE CALCULATION FACTORS SOURCE TERM Kd WATER, FILL, CONCRETE CONTAMINATED CONCRETE ANNUAL DOSE CONCENTRATION Nuclide NUREG-1727 FGR 11 Mcroshield Nuclide Inventory Inventory Kd Fill Kd Concrete Adsorption Water Fill pCi/g Concrete Nuclide Drinking Irrigation Dose Direct Dose Total Dose mrem/y per mrem/ mrem/y per Fraction pCi/g pCi cm3/gm cm3/gm Factor pCi/L pCi/g Water mrem/y mrem/y mrem/y pCi/g pCi pCi/g Dose mrem/y Cs-134 4.39E+00 7.33E-05 6.09E-05 4.00E-03 4.00E-03 1.37E+06 5.60E+01 3.00E+00 2.81E+02 6.62E-03 3.70E-04 1.98E-05 Cs-134 2.32E-04 1.29E-05 2.26E-08 2.45E-04 Co-60 6.58E+00 2.69E-05 6.30E-04 4.00E-02 4.00E-02 1.37E+07 1.30E+01 1.00E+02 6.71E+01 2.76E-01 3.59E-03 2.76E-02 Co-60 3.55E-03 8.09E-04 2.26E-06 4.37E-03 C-14 2.08E+00 2.09E-06 0.00E+00 5.80E-02 5.80E-02 1.99E+07 5.00E+00 1.00E+02 2.72E+01 9.89E-01 4.95E-03 9.89E-02 C-14 9.88E-04 9.15E-04 0.00E+00 1.90E-03 Eu-154 3.13E+00 9.55E-06 3.10E-04 9.00E-03 9.00E-03 3.09E+06 4.00E+02 0.00E+00 2.00E+03 2.09E-03 8.36E-04 0.00E+00 Eu-154 9.54E-06 2.90E-06 2.59E-07 1.27E-05 Fe-55 2.50E-03 6.07E-07 0.00E+00 1.24E-01 1.24E-01 4.25E+07 2.50E+01 1.00E+02 1.27E+02 4.53E-01 1.13E-02 4.53E-02 Fe-55 1.31E-04 5.03E-07 0.00E+00 1.32E-04 H-3 2.27E-01 6.40E-08 0.00E+00 6.47E-01 6.47E-01 2.22E+08 0.00E+00 0.00E+00 1.00E+00 3.00E+02 0.00E+00 0.00E+00 H-3 9.18E-03 3.03E-02 0.00E+00 3.95E-02 Eu-152 2.87E+00 6.48E-06 2.09E-04 1.11E-01 1.11E-01 3.81E+07 4.00E+02 0.00E+00 2.00E+03 2.58E-02 1.03E-02 0.00E+00 Eu-152 7.99E-05 3.29E-05 2.16E-06 1.15E-04 Ni-63 1.19E-02 5.77E-07 0.00E+00 7.00E-03 7.00E-03 2.40E+06 1.20E+01 1.00E+02 6.21E+01 5.23E-02 6.27E-04 5.23E-03 Ni-63 1.44E-05 2.76E-07 0.00E+00 1.47E-05

MYAPC License Termination Plan Page 6-24 Revision 1 June 1, 2001 6.6.3 Embedded Pipe

a. Conceptual Model Embedded pipe includes pipes that are encased in the basement concrete walls or floors that will remain after demolition and remediation. The conceptual dose model is identical to that described for contaminated basement surfaces.

However, analogous to activated concrete, the source term calculation includes the entire radionuclide inventory contained in all embedded piping, regardless of location. The entire inventory is assumed to be instantaneously released into the worst case 738 m3 of basement water.

b. Unitized Dose Factors for Embedded Pipe The total embedded pipe inventory is calculated assuming a unit contamination level of 1 dpm/100 cm2 over the entire internal surface area of all embedded pipe remaining after decommissioning. A list of the embedded piping planned to remain after decommissioning is provided in Attachment 6-7. The internal surface area of the embedded piping is 172 m2. Assuming a unit inventory of 1 dpm/100 cm2 the total inventory was determined to be 7.75E+03 pCi.. The 7.77E+03 pCi inventory applies to each radionuclide at a unit concentration of 1 dpm/100 cm2. Based on this value, an inventory was calculated and input into the spreadsheet developed for the contaminated basement surfaces. The spreadsheet inventory column input was calculated by multiplying the pipe surface contamination level, in this case a unitized level of 1 dpm/100 cm2, by the 7.75E+03 pCi unit inventory. This form facilitates the use of the spreadsheet in the total dose and DCGL calculations provided in Section 6.7.

All of the resulting water, fill, and concrete concentrations, and dose calculations are identical to those described for the contaminated basement surfaces in Section 6.6.1.

The Embedded Pipe spreadsheet is provided in Table 6-6. The results represent the unit dose factors for embedded piping assuming a source term of 1 dpm/100 cm2, for each radionuclide, on the internal surfaces of the pipe.

MYAPC License Termination Plan Page 6-25 Revision 1 June 1, 2001 Table 6-6 Embedded Piping Unitized Dose Factors Key Parameters Porosity 0.30 Bulk Density 1.50 g/cm3 Yearly Drinking Water 478.00 L/yr 2

Wall Surface Area 4182.0 m Fill Volume 2460.00 m3 Surface Area/Open Volume 1.70 m2/m3 Concrete Volume 4.18 m3 Concrete Density 2.20 g/cm3 Annual Total Well Water Vol 738.00 m3 Irrigation Rate 0.274 L/m2-d Surface Soil Depth 0.15 m Embedded Pipe 7748.0 pCi per Conversion Factor dpm/100 cm2 DOSE CALCULATION FACTORS SOURCE TERM Kd WATER, FILL, CONCRETE CONTAMINATED CONCRETE ANNUAL DOSE CONCENTRATION Nuclide NUREG- FGR 11 Mcroshield Inventory Inventory Kd Fill Kd Adsorption Water Fill Concrete Nuclide Drinking Irrigation Direct Total 1727 mrem/ mrem/y per dpm/100 pCi cm3/gm Concrete Factor pCi/L pCi/g pCi/g Water Dose Dose Dose mrem/y pCi pCi/g cm2 cm3/gm Dose mrem/y mrem/y mrem/y per pCi/g mrem/y Sr-90 1.47E+01 1.42E-04 0.00E+00 1.00E+00 7.75E+03 6.00E+00 1.00E+00 3.10E+01 3.39E-04 2.03E-06 3.39E-07 Sr-90 2.30E-05 2.21E-07 0.00E+00 2.32E-05 Cs-134 4.39E+00 7.33E-05 6.09E-05 1.00E+00 7.75E+03 5.60E+01 3.00E+00 2.81E+02 3.74E-05 2.09E-06 1.12E-07 Cs-134 1.31E-06 7.29E-09 1.27E-10 1.32E-06 Cs-137 2.27E+00 5.00E-05 1.20E-05 1.00E+00 7.75E+03 5.60E+01 3.00E+00 2.81E+02 3.74E-05 2.09E-06 1.12E-07 Cs-137 8.93E-07 3.77E-09 2.51E-11 8.97E-07 Co-60 6.58E+00 2.69E-05 6.30E-04 1.00E+00 7.75E+03 1.30E+01 1.00E+02 6.71E+01 1.56E-04 2.03E-06 1.56E-05 Co-60 2.01E-06 4.57E-08 1.28E-09 2.05E-06 Co-57 1.67E-01 1.18E-06 2.80E-08 1.00E+00 7.75E+03 1.30E+01 1.00E+02 6.71E+01 1.56E-04 2.03E-06 1.56E-05 Co-57 8.81E-08 1.16E-09 5.68E-14 8.92E-08 Fe-55 2.50E-03 6.07E-07 0.00E+00 1.00E+00 7.75E+03 2.50E+01 1.00E+02 1.27E+02 8.25E-05 2.06E-06 8.25E-06 Fe-55 2.39E-08 9.17E-12 0.00E+00 2.39E-08 H-3 2.27E-01 6.40E-08 0.00E+00 1.00E+00 7.75E+03 0.00E+00 0.00E+00 1.00E+00 1.05E-02 0.00E+00 0.00E+00 H-3 3.21E-07 1.06E-07 0.00E+00 4.26E-07 Ni-63 1.19E-02 5.77E-07 0.00E+00 1.00E+00 7.75E+03 1.20E+01 1.00E+02 6.21E+01 1.69E-04 2.02E-06 1.69E-05 Ni-63 4.65E-08 8.92E-11 0.00E+00 4.66E-08

MYAPC License Termination Plan Page 6-26 Revision 1 June 1, 2001 6.6.4 Surface Soil

a. Conceptual Model Surface soil includes all soil within the first 15 cm of the ground surface. The NRC screening values for soil from NUREG-1727, Table C2.3, are used for the unitized dose calculations Therefore, the conceptual model is identical to that described in NUREG-1727. The screening values include the dose from all pathways. The groundwater contribution to the screening value dose is negligible and is entered as zero. The screening values are used because they were specifically generated by NRC to be conservative calculations of the resident farmer dose and are recommended for use in NUREG-1727.

b. Unitized Dose Factors for Surface Soil The unitized dose factors are generated for each radionuclide directly from the NUREG-1727 screening values by converting the values to mrem/y per pCi/g.

Table 6-7 provides the Surface Soil unitized dose spreadsheet. The results represent the dose from a unit source term if 1 pCi/g for each radionuclide in the soil mixture.

Table 6-7 Surface Soil Unitized Dose Factors 1.0 pCi/g Cs-137 Key Parameters:

Soil Depth 0.15 m DOSE CALCULATION FACTORS SOURCE TERM SURFACE SOIL ANNUAL DOSE NUREG-1727 Total mrem/y per Soil Dose Nuclide pCi/g pCi/g mrem/yr Cs-137 2.27E+00 1.00E+00 2.27E+00 Co-60 6.58E+00 1.00E+00 6.58E+00 H-3 2.27E-01 1.00E+00 2.27E-01 Ni-63 1.19E-02 1.00E+00 1.19E-02

MYAPC License Termination Plan Page 6-27 Revision 1 June 1, 2001 6.6.5 Deep Soil

a. Conceptual Model Deep soil is defined as soil at depths greater than 15 cm. A separate calculation is required for deep soil because the NRC soil screening values apply to the top 15 cm of soil only. The resident farmer is exposed to deep soil through the direct exposure pathway and groundwater. The deep soil could be brought to the surface at some time in the future through the activities of the resident farmer. Therefore, the deep soil concentration will be limited to the surface soil DCGL.

The conceptual model for deep soil assumes a 15 cm layer of uncontaminated soil for the purpose of calculating the additional direct radiation exposure. The 15 cm cover represents the layer of surface soil. The direct radiation from residual contamination in the top 15 cm soil layer was accounted for in the surface soil screening values. A very large volumetric source term was assumed, i.e., 48,500 m3, for the purpose of conservatively determining the potential for groundwater contamination. from deep soil. This is considered a bounding source term volume and essentially represents the entire volume of soil within the restricted area down to bedrock. After remediation and backfill, the remaining volume of deep soil will be a very small fraction of 48,500 m3.

b. Unitized Dose Factors for Deep Soil Unitized dose factors were calculated using unit concentrations of each of the radionuclides in the soil mixture. The contribution from direct radiation was calculated using the Microshield code assuming a 15 cm cover and default values from DandD for indoor occupancy time (0.6571 y), outdoor occupancy time (0.1101 y), and external radiation shielding factor (0.5512). The Microshield output reports, deep dose direct radiation calculations, and resulting dose factors are provided in Attachment 6-8.

The maximum groundwater concentrations were calculated using RESRAD and unit concentrations of each radionuclide in the mixture. The RESRAD groundwater parameters used in the analysis are listed in Table 6-8. Only the parameters pertaining to groundwater transport are listed since the groundwater concentration is the only RESRAD output used. The RESRAD parameters affecting groundwater transport were reviewed by a local hydrologist who is very familiar with the site hydrogeological characteristics (Mr. Robert Gerber, P.E. and Certified Geologist). The parameters in Table 6-3 are recommended site-specific values. The Kds were derived from Maine Yankee analyses of

MYAPC License Termination Plan Page 6-28 Revision 1 June 1, 2001 Bank Run Sand and Bank Run Gravel. The average of these two materials was assumed to represent the material used to backfill the site during plant construction. Finally, site-specific effective porosity was identified as variable at the site. To account for this variability, a sensitivity analysis was conducted over a range of 0.01 to 0.001. The highest groundwater concentration resulted from a value of 0.01, which was used in the analysis.

Table 6-8 Site Specific Parameters used in RESRAD Deep Soil Analysis Parameter Value Units Contam. Zone site specific hydraulic conductivity 32 m/y Contam. Zone site specific b factor 4.05 Site Specific Effective Porosity 0.01 Unsat. Zone Site Specific Hydraulic Conductivity 1000 m/y Co 9.4 cm3/g Sr 4.4 cm3/g Site Specific Soil Kds:

Cs 34.6 cm3/g Ni 8.0 cm3/g Attachment 6-9 provides the RESRAD output report. The attachment provides the results for the radionuclides that were projected to migrate to groundwater over a 1000 year period. The RESRAD code was used only to estimate maximum groundwater concentrations, not calculate dose. The dose from the groundwater concentrations listed in Attachment 6-9 were calculated using the same parameters as in the water dose calculations performed for contaminated basement surfaces, activated concrete/rebar, and embedded piping, i.e, 478 l/y annual water intake and FGR 11 Dose Factors. The spreadsheet output and the unitized dose factors for deep soil are provided in Table 6-9.

6.6.6 Groundwater This calculation applies to existing groundwater only. As described above, there are additional contributions to the projected total groundwater dose from other contaminated materials.

Groundwater dose is calculated directly from the highest individual groundwater sample result from site monitoring well locations. As reported in Section 2, Attachment B, the

MYAPC License Termination Plan Page 6-29 Revision 1 June 1, 2001 only radionuclide identified in site groundwater is H-3 and the maximum concentration was identified in the containment foundation sump at a concentration of 6812 pCi/l.

The range of H-3 concentrations identified during characterization sampling of site wells was 441 pCi/l to 6812 pCi/l, for the most part consistent with background levels. The containment sump was re-sampled during continued characterization with 900 pCi/l H-3 identified. In addition, routine containment sump water samples have been collected since February 2000. None of these samples have exceeded the MDC level of about 2500 pCi/l.

In general, it appears that current containment sump H-3 water concentrations are within the range expected in area water background. However, to ensure that a conservative water concentration is applied and to avoid the potentially extensive sampling and analyses necessary to demonstrate that the concentrations are at background levels, the 6812 pCi/l H-3 concentration is used in the dose assessment.

If, prior to unrestricted release of the site, additional groundwater monitoring data are collected that indicate higher H-3 concentration, or identify other radionuclides, the higher concentrations will be used in the final dose assessment for demonstrating compliance with the 10/4 mrem/yr dose limit.

Table 6-9 Deep Soil Unitized Dose Factors Key Parameters Porosity 0.30 Bulk Density 1.6 g/cm3 Yearly Drinking Water 478.00 L/yr 2

Irrigation Rate 0.274 L/m -d Surface Soil Depth 0.15 m DOSE CALCULATION FACTORS SOURCE TERM DEEP SOIL ANNUAL DOSE Water NUREG-1727 Mcroshield Deep Soil Drinking Irrigation Direct FGR 11 Inventory Total Dose Nuclide mrem/y per mrem/y Inventory Water Dose Dose Dose mrem/pCi pCi/L per mrem/y pCi/g per pCi/g pC/gi mrem/y mrem/y mrem/y pCi/g Cs-137 2.27E+00 5.00E-05 4.00E-01 1.00E+00 1.10E+00 2.63E-02 1.04E-03 4.00E-01 4.27E-01 Co-60 6.58E+00 2.69E-05 2.40E+00 1.00E+00 6.60E-01 8.49E-03 1.81E-03 2.40E+00 2.41E+00 H-3 2.27E-01 6.40E-08 0.00E+00 1.00E+00 7.10E+03 2.17E-01 6.72E-01 0.00E+00 8.89E-01 Ni-63 1.19E-02 5.77E-07 0.00E+00 1.00E+00 9.40E+01 2.59E-02 4.66E-04 0.00E+00 2.64E-02

MYAPC License Termination Plan Page 6-30 Revision 1 June 1, 2001 There are no unit dose factors or DCGLs for groundwater. The actual dose from the highest measured concentration will be used in the total dose calculation. The groundwater dose is calculated using the FGR 11 DCF for H-3 and a 478 l/y intake.

The resulting dose is 0.21 mrem/y. The method for factoring the groundwater dose into the total dose calculation and the DCGL determination for other contaminated materials is described in Section 6.7.

The dose calculation for existing groundwater is provided below.

DoseGW = (6812 pCi/l H-3)(478 l/y)(6.4E-08 mrem/y/pCi) = 0.21 mrem/y (12) 6.6.7 Surface Water Site surface water from the Fire Pond and Reflecting Pond was sampled during characterization. The results indicated no plant derived radionuclides in the Fire Pond and a low potential in the Reflecting Pond. Therefore, only the Reflecting Pond was considered in the dose assessment.

Tritium was detected in the Reflecting Pond at a maximum concentration of 960 pCi/l.

This activity is not believed to be attributable to Maine Yankee operations. However, a review of available literature on H-3 concentrations in surface water could not conservatively demonstrate that the H-3 concentrations identified were consistent with background levels in the region. Additional characterization and literature review may provide the information needed to demonstrate that the H-3 was not plant derived.

However, given the very low dose from these H-3 concentrations, it was not considered cost effective to perform more analyses.

As for groundwater, the dose from surface water was calculated using existing data.

The maximum H-3 concentration of 960 pCi/l was used. As with groundwater, if higher concentrations or additional radionuclides are identified at any time prior to unrestricted release of the facility, the higher concentrations will be used in the final dose assessment for demonstrating compliance.

The surface water dose results from drinking water and ingesting fish from the pond.

The water dose is calculated using the parameters described above assuming that the resident farmer drinks directly from the surface water source. The dose from fish ingestion is calculated using a water to fish transfer factor of 1 for H-3 (NUREG-5512,

MYAPC License Termination Plan Page 6-31 Revision 1 June 1, 2001 Vol. 3, Table 6.30), 20.6 kg fish consumption per year (DandD default value), and using DCFs from FGR No.11.

The calculations for water and fish consumption from onsite surface water with a H-3 concentration of 960 pCi/l is provided below.

DoseSW = (960 pCi/l H-3)(478 l/y)(6.4E-08 mrem/y/pCi) = 2.9E-02 mrem/y (13)

DoseFish = (960 pCi/l)(1.0 pCi/kg per pCi/l)(20.6 kg/y))(6.4E-08 mrem/y/pCi) = 1.3E-03 mrem/y (14) 6.6.8 Buried Piping/Conduit

a. Conceptual Model After decommissioning is completed, some piping and conduit will remain underground at depths greater than three feet below grade. This contaminated material category includes the piping and conduit buried in open land, not pipe embedded in concrete basements, which were described in Section 6.6.3. A list of the buried piping/conduit that current plans call to remain after decommissioning is provided in Attachment 6-10. The buried piping/conduit is expected to contain very limited levels of contamination, if any. The radionuclide mixture is assumed to be the same as for contaminated materials.

The conceptual dose model for the buried piping/conduit is very simple and conservative. The piping/conduit is assumed to be uniformly contaminated over the entire internal surface area. The piping is further assumed to eventually disintegrate resulting in the total inventory in the pipe mixing with a volume of soil equal to the pipe volume. Without the assumption of the pipe disintegrating, there is essentially no dose pathway from buried piping/conduit. The resulting calculated soil concentrations are treated as deep soil and the dose was calculated using the same methods as described above for deep soil. However, the direct exposure is calculated assuming a three foot cover as opposed to a 15 cm cover. Although not required by the conceptual model, the buried piping/conduit DCGLs will be limited to ensure that the projected soil concentrations are below the surface soil DCGLs. This additional measure of

MYAPC License Termination Plan Page 6-32 Revision 1 June 1, 2001 conservatism was also applied to deep soil to account for hypothetical future excavation of the buried contamination.

b. Unitized Dose Factors for Buried Piping/Conduit The total surface area and total volume were calculated for all of the buried piping/conduit planned to remain after decommissioning. Assuming a unit inventory of 1 dpm/100 cm2 on the internal surfaces, the total inventory of each radionuclide was determined. This total inventory was divided by the total volume and converted to grams of soil assuming a density of 1.6 g/cm3 to calculate the projected pCi/g soil concentration of each radionuclide. The list of Buried Piping/Conduit and the calculation of projected pCi/g soil concentration are provided in Attachment 6-10. The resulting concentration is 2.59E-04 pCi/g.

The resulting projected pCi/g soil concentration was entered as the source term in RESRAD for each applicable radionuclide. The RESRAD analysis was performed using the same parameters used for deep soil (Table 6-8) with the exception of the source term geometry. For the buried piping/conduit, the source term geometry was assumed to be a 142 m2 area 1 m deep. This corresponds to the total volume of all buried piping/conduit of 142 m3. This is a conservative assumption since, in reality, the piping is distributed over a fairly large surface area which would result in dilution through groundwater transport compared to the maximum concentration assuming all the pipe is contiguous.

The RESRAD output report is provided in Attachment 6-11.

Microshield runs were performed on the unit source term assuming the same 142 m2 x 1m deep source. The source is assumed to be covered by three feet of soil. The resulting exposure rate was multiplied by the default outdoor occupancy time (0.1101 y) from DandD, Version 1. The Microshield reports and Buried Piping/Conduit Direct Radiation Dose Factors are provided in Attachment 6-12.

The spreadsheet output and resulting unitized dose factors (1 dpm/100 cm2) for buried piping/conduit are provided in Table 6-10.

MYAPC License Termination Plan Page 6-33 Revision 1 June 1, 2001 Table 6-10 Buried Pipe and Conduit Unitized Dose Factors Key Parameters Porosity 0.30 Bulk Density 1.6 g/cm3 Yearly Drinking Water 478.00 L/yr 2

Irrigation Rate 0.274 L/m -d Surface Soil Depth 0.15 m Buried Pipe CF 2.59E-04 pCi/g per dpm/100 cm2 DOSE CALCULATION FACTORS SOURCE TERM DEEP SOIL ANNUAL DOSE Water NUREG-1727 Mcroshield Soil Drinking Irrigation Direct FGR 11 Inventory Pipe Surface Total Dose Nuclide mrem/y per mrem/y Inventory Water Dose Dose Dose mrem/pCi pCi/L per Inventory mrem/y pCi/g per pCi/g pC/gi mrem/y mrem/y mrem/y pCi/g dpm/100cm 2 Sr-90 1.42E-04 1.47E+01 0.00E+00 3.69E+00 1.00E+00 2.59E-04 6.49E-05 5.85E-06 0.00E+00 7.07E-05 Cs-134 7.33E-05 4.39E+00 2.21E-05 0.00E+00 1.00E+00 2.59E-04 0.00E+00 0.00E+00 5.72E-09 5.72E-09 Cs-137 5.00E-05 2.27E+00 3.97E-06 1.02E-03 1.00E+00 2.59E-04 6.31E-09 2.50E-10 1.03E-09 7.59E-09 Co-60 2.69E-05 6.58E+00 2.53E-04 2.96E-03 1.00E+00 2.59E-04 9.86E-09 2.10E-09 6.55E-08 7.75E-08 Co-57 1.18E-06 1.67E-01 9.44E-09 3.39E-20 1.00E+00 2.59E-04 4.95E-27 6.11E-28 2.45E-12 2.45E-12 Fe-55 6.07E-07 2.50E-03 0.00E+00 0.00E+00 1.00E+00 2.59E-04 0.00E+00 0.00E+00 0.00E+00 0.00E+00 H-3 6.40E-08 2.27E-01 0.00E+00 1.61E+02 1.00E+00 2.59E-04 1.28E-06 3.94E-06 0.00E+00 5.22E-06 Ni-63 5.77E-07 1.19E-02 0.00E+00 2.80E+00 1.00E+00 2.59E-04 2.00E-07 3.60E-09 0.00E+00 2.04E-07 6.6.9 Forebay Sediment The forebay consists of a water-filled canal which is lined on both sides by rip-rap dikes and runs from the circulating water pipe discharge point to the inlet of the diffuser pipes. The bottom of the forebay is bare rock. The forebay area is part of the liquid effluent release pathway.

Initial Site Characterization reported positive sample results for forebay sediment with Co-60 in the range of 0.04 to 11.2 pCi/g and Cs-137 in the range of less than MDA to 0.53 pCi/g. Attempts were made to collect additional samples of sediment from the forebay. The bottom appeared to be free of sediment and no sample material could be obtained. Small amounts of sediment were however present between the rip-rap at low tide. The lack of significant volumes of sediment in the forebay is not unexpected since the flow through the forebay during plant operations exceeded 400,000 gpm. Due to

MYAPC License Termination Plan Page 6-34 Revision 1 June 1, 2001 the small volumes and geometry, the dose from forebay sediment is expected to be very low.

A total of fifteen additional characterization samples were collected between the rip-rap from the sides and the north end of the forebay. The fifteen samples were combined into a single composite and analyzed for HTD and gamma emitting radionuclides. The results showed Co-60 at 31.7 pCi/g, Fe-55 at 13.6 pCi/g, Ni-63 at 8.9 pCi/g, Cs-137 at 1.2 pCi/g and Sb-125 at 0.4 pCi/g.

Additional characterization is planned for Spring 2001. This will include an investigation of the potential for sediment to have settled on the rock bottom and additional characterization of sediment between the rip-rap. If contaminated sediment is identified on the bottom, Maine Yankee will evaluate the dose and determine an appropriate DCGL, if necessary.

Since small volumes of contamination were identified between the rip-rap, the dose from this contamination was evaluated. The dose assessment assumes an individual stands or randomly walks over the rip-rap. Performing the dose assessment assuming the rip-rap remains in place is a conservative scenario. If the rip-rap is excavated or disturbed in some way, the small amount of contamination that is present will be mixed within the excavated volume and diluted.

The assessment assumes an inch of sediment uniformly distributed under all of the rip-rap. This appears to be a conservative source term assumption based on the characterization results to date. The rip-rap was assumed to be 2 foot diameter rock spheres. This assumption will be confirmed or modified after the additional characterization is completed.

The pathways evaluated were direct exposure and ingestion of the sediment. Inhalation was not considered a credible pathway because the material is submerged a portion of the time and essentially always remains damp. The resulting dose rate from the rip-rap sediment was compared to the dose from deep soil and surface soil combined. The soil concentrations were assumed to be equal to the DCGL.

The dose to the resident farmer will not be increased by the contamination in the forebay sediment if the dose rate from the rip-rap sediment is less than the dose rate from the soil. This is based on the assumption that the person will be located either on

MYAPC License Termination Plan Page 6-35 Revision 1 June 1, 2001 the soil or on the rip-rap, but not at both locations at the same time. Therefore, the outdoor occupancy time is split between the soil area and the rip-rap area.

A detailed description of the forebay sediment dose assessment is provided in Attachment 6-16. The dose rates from the forebay sediment and soil were 2.3E-04 mrem/h and 2.0E-03 mrem/h, respectively. The soil dose rate was over 8 times higher than the forebay dose rate. Based on these data, the forebay sediment could be present at concentrations over 8 times higher than concentrations identified during characterization to date and not result in additional dose to the resident farmer. If additional characterization and final survey do not identify rip-rap sediment concentrations that result in dose exceeding the resident farmer soil dose, no remediation of the forebay rip-rap sediment will be performed.

6.6.10 Circulating Water Pump House The circulating water pump house (CWPH) was the intake for the plant circulating water (CW) system. The water intake was directly from the Back River at high volumes (about 400,000 gpm). The CWPH will be demolished to three feet below grade, backfilled, and stabilized on the river side with rock rip-rap. The intake structure which is below water level will remain in communication with the river. The contamination potential in this structure is very low.

There are three, albeit low potential, exposure pathways from the material that will remain in the demolished and backfilled CWPH: (1) exposure to radionuclides that have leached to the tidal water that saturates the remaining backfilled structure, (2) exposure from the excavation of the limited amount of silt currently on the bottom of the pump house bays, and (3) exposure from contamination that leaches from the structure surfaces, is adsorbed onto fill material, and is excavated at some time in the future.

Exposure to the excavated silt is limited to the same pathways as surface soil.

Therefore, the DCGL for the silt will be the same as calculated for surface soil. In addition, the radionuclide mixture is assumed to be the same as that identified for surface soil. This assumption has essentially no effect since the samples will be counted by gamma spectroscopy, which will specifically identify the radionuclides of concern.

Limiting the silt DCGL to the surface soil DCGL ensures that there will be no additional dose to the resident farmer, above that already accounted for through the surface soil DCGL, from the hypothetically excavated silt.

MYAPC License Termination Plan Page 6-36 Revision 1 June 1, 2001 The potential for radionuclide leaching from the surfaces of the CWPH is very remote considering the extremely low potential of contamination being present as a result of past operations and the fact that if contamination were present from past operations, the constant tidal flushing of the pump house bays would have already removed any leachable material. Notwithstanding this low potential, one water sample will be collected from each of the four pump house bays prior to draining the bays for final survey. The analytical detection sensitivity will be at the environmental LLD level. If no activity is detected, the water leaching pathway will be eliminated from consideration.

Potential leaching to water will be evaluated by direct water sampling only.

If activity above the environmental LLD is detected in the water samples, the positive results will be used to evaluate exposure from fish ingestion using the bioaccumulation factors from NUREG-5512, Vol. 3, Table 6.30, i.e., 20.6 kg fish consumption per year (DandD default value), and DCFs from FGR No.11. If a dose calculation is necessary, the dose will be added to the total dose from the other contaminated materials listed in Table 6-11. Adjustments will be made to the DCGLs for other contaminated materials, if necessary, to ensure compliance with the 10/4 mrem/yr unrestricted use criteria.

Since potential leaching into water is accounted for by direct water sampling, the only remaining exposure pathway to consider is the excavation of fill material hypothetically contaminated by radionuclide transfer from structure surfaces to the fill. The conceptual model developed for the contaminated basement surfaces is adequate to apply to this very low potential pathway. As shown in Attachment 6-13, the DCGL for building basements in Table 6-11 resulted in very low radionuclide concentrations on the basement fill, with all concentrations being less than 1 pCi/g. Note that one of the criteria applied to the selection of the basement fill DCGL is that the calculated fill concentration be less than the surface soil DCGL. In addition, the Kds used for the basement fill model (Bank Run Sand) are generally higher than the Kds for Bank Run Gravel which is being considered for backfill. This indicates that the CWPH fill would have lower concentrations than those calculated for basement fill. However, regardless of the fill material used, it is unlikely that the fill concentration would exceed the surface soil DCGL.

Considering all of the arguments presented above, the DCGL calculated for the building basements is appropriate and conservative for application to CWPH surfaces for the purpose of limiting hypothetical dose from the excavated fill pathway (as stated above, the potential leaching to water is addressed by direct sampling of the water).

MYAPC License Termination Plan Page 6-37 Revision 1 June 1, 2001 Compliance with the basement fill DCGL will ensure that the fill concentration will not exceed the surface soil DCGLs. Since the concentration of the hypothetically excavated fill would be below the surface soil DCGLs, there will be no additional dose to the resident farmer beyond that already accounted for through the surface soil and no addition to the total dose calculated in Table 6-11 is necessary.

6.7 Material Specific DCGLs and Total Dose Calculation As described above, calculations were performed to develop conservative dose assessment models and generate unitized dose factors for all contaminated materials at the Maine Yankee site and all radionuclides in the Maine Yankee mixture applicable to each material. When the dose pathways for the resident farmer were evaluated, it was evident that the resident farmer could receive dose from more than one contaminated material. A detailed discussion of the various contaminated materials and dose pathways was provided above. The total dose results from the summation of the contributions from each of contaminated materials. Therefore, the final DCGLs for each of the contaminated materials are inter-dependent.

This section describes the method used to account for the dose from all materials and select the final DCGLs for all materials. The method ensures that the summation of doses from all pathways, at the selected DCGL concentrations for all materials, does not exceed 4 mrem/y drinking water dose and 10 mrem/y total dose. Table 6-11 provides the DCGLs that were selected for the Maine Yankee Site and the resulting total dose for all contaminated materials.

Attachment 6-13 contains the dose calculations for all contaminated materials listed in Table 6-

11. The radionuclide mixture for the containment annulus trench differs from the rest of the basement surfaces. Therefore, a separate DCGL was selected and a separate dose calculation was performed for the trench.

The DCGLs listed in Table 6-11 are target project DCGLs. The formal unrestricted use criteria are the enhanced State dose criteria of 10 mrem/y or less from all pathways and 4 mrem/y or less from groundwater drinking sources. The DCGL values in Table 6-11 may be adjusted as the project proceeds using the methods and limitations described in this section as long as the dose criteria are satisfied.

MYAPC License Termination Plan Page 6-38 Revision 1 June 1, 2001 Table 6-11 Contaminated Material DCGL Basement Contaminated Concrete (gross beta dpm/100 cm2): 18,000.00 Note: Annulus Trench Concrete DCGL = 9,500 (gross beta dpm/100 cm2)

Basement Activated Concrete (pCi/g): 1.00 Surface Soil (Cs-137 pCi/g): 3.00 Deep Soil (Cs-137 pCi/g): 3.00 Embedded Piping, (gross beta dpm/100 cm2): 18,000.00 Ground Water (H-3, pCi/L): 6812.00 Surface Water (H-3, pCi/L): 960.00 Buried Piping, Conduit and Cable, (gross beta dpm/100 cm2): 9,800.00 Contaminated Material Annual Dose Drinking Direct, Inhalation Total Material Water & Ingestion Annual Dose (mrem/y) (mrem/y) (mrem/y)

Contaminated Concrete 5.00E-01 5.63E-02 5.56E-01 Activated Concrete 1.42E-02 3.21E-02 4.63E-02 Surface Soil 0.00E+00 7.05E+00 7.05E+00 Deep Soil 1.22E-01 1.95E+00 2.07E+00 Embedded Piping 2.05E-02 2.34E-04 2.08E-02 Ground Water 2.08E-01 0.00E+00 2.08E-01 Surface Water 2.94E-02 1.27E-03 3.06E-02 Buried Piping, Conduit & Cable 4.56E-03 1.83E-03 6.40E-03 Total 0.90 mrem/y 9.09 mrem/y 9.99 mrem/y The dose summation method is a conservative screening approach. For example, the environmental pathway analysis for deep soil indicated that a low concentration of tritium would reach groundwater three years after the site is released for unrestricted use. The location of the deep soil and corresponding groundwater contamination are obviously different from the location of building basements where the hypothetical resident farmer well was placed. In addition, the peak time for H-3 water concentration from deep soil is different from the peak time for the basement water concentration. Nonetheless, consistent with a screening approach, the peak H-3 concentration in groundwater from deep soil is fully added to the peak basement water concentration and the sum is used in the dose assessment. There was no reduction in concentration due to the differences in peak dose time or dilution through groundwater

MYAPC License Termination Plan Page 6-39 Revision 1 June 1, 2001 transport. A more realistic and less conservative environmental pathway analysis would consider these effects.

The Maine Yankee commitment to a conservative screening approach is also seen in the methods for adding the dose contributions from embedded piping, activated concrete/rebar, and contaminated surfaces in the building basements, as well the other contaminated materials.

It is important to recognize that the conservative results from the dose summation are in addition to the conservatism already built into the unitized dose factor calculations for the individual contaminated materials.

Soil areas outside of the RA boundary will not require consideration of dose from any other materials. The area of the RA is approximately 10,000 m2, which represents the size of the resident farmer survey unit and contains the other contaminated materials considered. The other contaminated materials have essentially no effect outside of the RA and the dose is assumed to result from the contaminated soil only. In this case, the DCGLs will be based on the NUREG-1727 screening values corrected to represent 10 mrem/y. The soil radionuclide mixture applied to areas outside the RA boundary are assumed to be the same as the mixture listed in Table 6-13 in Attachment D.

6.7.1 Conceptual Model for Summing Contaminated Material Dose The conceptual model for summing doses to the resident farmer essentially combines the dose from surface soil and deep soil with the dose from water derived from a well drilled directly into the worst case building basement. The well water is used for irrigation and drinking.

The source term for the well water concentrations includes contributions from basement contamination, activated concrete/rebar, and embedded piping. The model assumes that the residual contamination in all three materials is instantaneously released and mixed with water that has infiltrated the building basement.

The instantaneous release of all contamination is conservative for several reasons.

Concrete contamination will be released at a rate associated with the diffusion coefficient for the various radionuclides. Activated concrete/rebar will actually be released to the water at a relatively slow rate more closely linked to physical dissolution of concrete, which is expected be very slow. For embedded piping, the actual contamination release rate is expected to be close to zero because any open pipe end

MYAPC License Termination Plan Page 6-40 Revision 1 June 1, 2001 that could be a point of release into a basement will be sealed. Another conservatism is the assumption that all of these sources are mixed in the same worst case 2460 m3 of basement volume. In actuality, the various sources are in different areas and different buildings. Finally, the source term contributions from groundwater, surface water, and deep soil were added directly to the basement well concentrations without consideration of transport or dilution.

6.7.2 Method and Calculations for Summing Contaminated Material Dose The primary inputs to the dose summation are the unitized dose factor calculations developed for each contaminated material. The unitized dose spreadsheets were used for the dose calculations without modification. However, the input concentrations and inventories required modification to represent the selected DCGLs as opposed to unit concentrations. The additional calculations required to convert the DCGL values into radionuclide concentrations and inventories are described in the sections below.

To perform the summation and to provide a method to efficiently adjust the DCGLs for various materials, each of the individual material unitized dose spreadsheets was copied and linked in a single spreadsheet entitled DCGL/Total Dose. The spreadsheet output for the DCGL dose calculation for each material is provided in Attachment 6-13.

These spreadsheets provide the calculations for the dose values reported in Table 6-11.

Contaminated Basement Surfaces The DCGL for contaminated concrete is expressed as dpm/100 cm2 detectable gross beta. This form was required because the final survey will be performed using gross beta measurements. The primary criteria for selecting the gross beta DCGL for basement surfaces was to ensure that the total dose, from all contaminated materials, was less than the 10/4 mrem/yr dose limit. There were two secondary criteria applied to the selection of the DCGL; 1) the DCGL would result in calculated basement fill concentrations below the surface soil DCGL, and 2) the DCGL was less than the NRC surface screening values from NUREG-1727, Table C2.2 (see Attachment 6-18).

To calculate the dose from a given gross beta DCGL, the gross beta concentration is converted to individual radionuclide concentrations based on their respective fractions in the radionuclide mixture. The individual concentrations are then input to the dose calculation spreadsheet for contaminated basement concrete. Characterization data indicated that the radionuclide mixtures for the containment annulus trench differs from

MYAPC License Termination Plan Page 6-41 Revision 1 June 1, 2001 the other the basement surfaces (see Table 2-8). Therefore, a separate mixture is applied to the dose assessment for the annulus trench, resulting in a different DCGL for the trench. The DCGL selected for the annulus trench resulted in a lower dose than that calculated for the rest of the basement surfaces (see Attachment 6-13). Therefore, the total dose shown in Table 6-11 is based on the higher dose calculated for the general radionuclide mixture and DCGL, not the trench mixture.

The individual radionuclide concentrations are calculated as follows:

Convert the detectable gross beta concentration to total radionuclide concentration:

Total dpm/100 cm2 = (gross beta dpm/100 cm2)/(Ggross beta radionuclide fractions) (15)

Where: Total dpm/100 cm2 is the summation of activity from all radionuclides Gross beta is the detectable gross beta concentration Ggross beta radionuclide fractions is the sum of the fractions of each radionuclide in the Maine Yankee mixture with detectable beta Calculate each individual radionuclide concentration as follows:

CR dpm/100 cm2 = (NFR)(Total dpm/100 cm2) (16)

Where: CR is the concentration of a given radionuclide NFR is the nuclide fraction of a given radionuclide Surface Soil The DCGL for surface soil is expressed in pCi/g Cs-137. The surface soil dose is calculated by first determining the individual radionuclide concentrations by ratio to Cs-137 using the relative fractions in the Maine Yankee mixture and then entering the individual concentrations into the inventory column in the dose calculation spreadsheet for surface soil.

The final survey and final site dose assessment will be based on gamma spectroscopy results of individual soil samples, radionuclide specific DCGLs based on NUREG-1727 screening values (corrected to 10 mrem/y), and a unity rule approach. The dose contributions from the other contaminated materials will be accounted for by comparing

MYAPC License Termination Plan Page 6-42 Revision 1 June 1, 2001 the unity summation to a dose corrected value. The dose corrected value will be calculated by dividing the surface soil dose in Table 6-11 by 10 mrem/y. However, the surface soil dose value may change if different DCGLs are ultimately selected for the remaining contaminated materials. In no case will the total dose from all materials exceed the State of Maine enhanced criteria.

During final survey, and in the final site dose assessment, the non-gamma emitting radionuclides will be accounted for using Cs-137 as a surrogate as described in Equation 17 (from NUREG-1505, Page 11-2, Equation 11-4). As seen in Attachment 6-13, the contribution from the HTD radionuclides in soil (Ni-63 and H-3) is less than 1% of the Cs-137 dose. Therefore, the effect of the surrogate calculation on the Cs-137 DCGLw value will be minimal.

To adjust 137Cs for HTD: (17) 1 CS 137s =

1 R2 R 3 R

+ + + ...+ n D1 D 2 D3 Dn Where:Cs-137s is the surrogate Cs-137 DCGLw Rn is the ratio of the HTD radionuclide mixture fraction to the Cs-137 mixture fraction Dn is the DCGLw of the HTD radionuclide The unitized dose factors were used in the total dose and DCGL calculations. This allowed the dose contribution of each radionuclide to be calculated and reviewed to understand the relative significance of the nuclides in the mixture. The dose calculated from the Cs-137 concentration shown in Table 6-11 will be the same regardless of whether a surrogate Cs-137 DCGLw is used or the unitized dose factors for all radionuclides are used.

The Cs-137 to Co-60 ratio will vary in the final survey soil samples and this will be accounted for using a unity rule approach as described previously. However, absent sample-specific information from the final survey, using the radionuclide mixture fractions to represent the final Cs-137/Co-60 ratios is the best method available to estimate dose and determine target soil concentrations for remediation planning.

MYAPC License Termination Plan Page 6-43 Revision 1 June 1, 2001 Activated Concrete/Rebar The DCGL for activated concrete/rebar is in units of pCi/g total activity at the wall and floor surfaces. Total activity includes all radionuclides in the Maine Yankee mixture.

The target remediation concentration is 1 pCi/g of activated concrete. Therefore, no modification of the unit dose factor spreadsheet for activated concrete was required to account for the DCGL concentration.

Deep Soil The DCGL for deep soil, as for surface soil, is expressed in pCi/g Cs-137. The deep soil dose is calculated by first determining the individual radionuclide concentrations by ratio to Cs-137 using the relative fractions in the Maine Yankee surface soil mixture and then entering the individual concentrations into the inventory column in the dose calculation spreadsheet for deep soil. The surface soil radionuclide mixture is assumed to be representative of the deep soil mixture.

The issues related to compliance using final survey results for gamma emitters and the use of Cs-137 as a surrogate for the HTD radionuclides that were described for surface soil also apply to deep soil.

Groundwater The existing groundwater concentrations are entered directly into the DCGL/Total Dose spreadsheet. This allows the dose from current groundwater contamination to be accounted for. The entered concentration is not intended to be a DCGL. If Maine Yankees estimate of existing groundwater concentration changes, the value(s) input to the final dose calculation for compliance with the 10/4 dose criteria will use the most applicable concentrations.

Surface Water The maximum concentration identified was used in the dose assessment. As with the groundwater concentration, the entered concentration is not a DCGL. If new sample data, if collected, indicates higher concentrations in site surface water, the new data will be used in the final dose assessment to demonstrate compliance with the 10/4 dose criteria.

MYAPC License Termination Plan Page 6-44 Revision 1 June 1, 2001 Buried Piping/Conduit The buried piping/conduit DCGL is expressed as dpm/100 cm2 gross beta. The DCGL/Total Dose spreadsheet converts gross beta concentration to individual radionuclide concentrations analogous to contaminated basement surfaces. The resulting concentrations are entered in the dpm/100 cm2 inventory column in the dose calculation spreadsheet.

6.8 Area Factors 6.8.1 Basement Contamination The basement contamination conceptual model described in Section 6.6.1 was based on a worst case surface area of 4182 m2. The model assumes uniform mixing within a 0.6 m layer of fill in direct contact with the 4182 m2.surface area. The conceptual model assumes that the activity released from the wall is mixed with the 738 m3 volume of water contained in the 0.6 m fill layer, but does not require the contamination to be uniformly distributed over the entire 4182 m2 surface area. The model source term is the total inventory over the surface and is not dependent on the distribution of the contamination on the surface. Therefore, consistent with the conceptual model, the area factor could be a simple linear relationship between total activity and area. The area factor formula would then be described using the following equation:

AF = 4182 m2/(elevated area) (18) where: AF is the area factor (elevated area) is the size of the area exceeding the DCGLW Maine Yankee evaluated this potential approach and believes that it is consistent with NUREG-1575 and NUREG-1727 guidance which acknowledges that the area factors should be based on the dose model used to calculate the DCGL. However, it appears that substantially better remediation performance can be achieved than is reflected in Equation (18) and that leaving elevated areas at the levels allowed by the equation is not sufficiently conservative. Accordingly, the area factors for contaminated basement concrete will be calculated using Equation (19), which represents a considerably more conservative approach.

MYAPC License Termination Plan Page 6-45 Revision 1 June 1, 2001 AF = 50 m2/(elevated area) (19) where: AF is the area factor (elevated area) is the size of the area exceeding the DCGLW The 50 m2 area was selected after qualitative consideration of the potential residual contamination that could remain in elevated areas after a comprehensive remediation effort. Areas greater than 50 m2 are required to be at or below the DCGL w. Area factors can apply to elevated areas on any surface, but are expected to be applied primarily to contamination in cracks and crevices, or other geometries, that are not efficiently remediated. It is not expected that a large number of elevated areas will remain. The number of elevated areas allowed to remain is limited by the formula presented in Section 5.6.3.

6.8.2 Surface Soil and Deep Soil Area Factors The NRC screening values were used to calculate the surface soil DCGLs. This approach does not provide a direct method of linking the area factor calculation to the dose model. The surface soil area factors were determined based on the change in direct radiation as a function of area. The relative exposure was determined using Microshield. The output reports are provided in Attachment 6-14.

Using direct radiation only is a conservative approach since area factors based on the ingestion and inhalation dose pathways increase at a faster rate than those based on the direct radiation pathway. This is evident from inspection of Table 5.6 in NUREG-1575 which shows, for example, the higher area factors for Am-241 as compared to Cs-137 and Co-60. The area factors for surface and deep soil are listed in Table 6-12.

Table 6-12 Area Factors for Surface Soil and Deep Soil Survey Unit = 10,000 m2 Area m2 1 2 4 6 8 16 25 50 100 500 1,000 10,000 Area Factor 12.0 6.8 4.1 3.2 2.8 2.0 1.7 1.5 1.3 1.2 1.1 1.0

MYAPC License Termination Plan Page 6-46 Revision 1 June 1, 2001 6.9 Standing Building Dose Assessment and DCGL Determination 6.9.1 Dose Assessment Method This dose assessment applies to the occupancy of a standing building and does not apply to the filled building basement. Current plans call for only one building to remain standing after decommissioning, i.e., the switchyard relay house. The NRC screening values from NUREG-1727, Table C2.2 were used for building occupancy dose assessment and DCGL determination. The screening values were adjusted to correspond to 10 mrem/y.

6.9.2 Standing Building DCGLs The standing building DCGL was calculated as shown in Table 6-13. The DCGLs were calculated using Equation 4-4 in NUREG-1727 as adjusted for gross beta by multiplying the results by the gross beta radionuclide fraction in the mixture. The DCGL was expressed as gross beta since the final survey of a standing building, if necessary, will be performed using gross beta measurements.

6.9.3 Standing Building Area Factors As discussed above for soil, using the NRC screening values for DCGL determination does not allow for direct determination of area factors. Consistent with the method used for soil, Microshield runs were used to generate the area factors by starting with an area of 100 m2 and calculating the relative exposure rate as the area is decreased.

The ratio of the 100 m2 exposure rate to the respective smaller area exposure rate represents the area factor for the given elevated area size. Attachment 6-15 contains the Microshield runs and Table 6-14 provides the resulting area factors.

MYAPC License Termination Plan Page 6-47 Revision 1 June 1, 2001 Table 6-13 Gross Beta DCGL For Standing Buildings (Not Applicable to Basements to be Filled)

Nuclide Screening Beta Nuclide Fraction Level nf/Screening Level Fraction (nf) dpm/100 cm2 H-3 2.36E-02 4.96E+07 4.75E-10 Fe-55 4.81E-03 1.80E+06 2.67E-09 Co-57 3.06E-04 8.44E+04 3.63E-09 Co-60 5.84E-02 2.82E+03 5.84E-02 2.07E-05 Ni-63 3.55E-01 7.28E+05 4.88E-07 Sr-90 2.80E-03 3.48E+03 2.80E-03 8.04E-07 Cs-134 4.55E-03 5.08E+03 4.55E-03 8.95E-07 Cs-137 5.50E-01 1.12E+04 5.50E-01 4.91E-05 Sum 6.16E-01 7.20E-5 DCGL 8.554E+03 dpm/100 cm2 (10 mrem/y)

Table 6-14 Area Factors for Standing Buildings (Does Not Apply to Building Basements To Be Filled)

Survey Unit Size = 100 m2 Area m2 0.5 1 2 4 8 16 25 50 100 Area Factor 23.5 12.6 7.1 4.3 2.8 1.9 1.6 1.2 1.0

MYAPC License Termination Plan Page 6-48 Revision 1 June 1, 2001 6.10 References 6.10.1 Baes, C.F., R.D. Sharp, A.L. Sjorren, and R.W. Shor, 1984. A Review and Analysis of Parameters for Assessing Transport of Environmentally Released Radionuclides through Agriculture, ORNL-5786, Oak Ridge National Laboratory.

6.10.2 U.S. Environmental Protection Agency, 1988. External Exposure to Radionuclides in Air Water and Soil, Federal Guidance Report No. 11, EPA 520/1-88-020, U. S.

EPA Office of Radiation and Indoor Air.

6.10.3 Krupka, K.M., and R.J. Serne, 1998. Effects on Radionuclide Concentrations by Cement/Ground-Water Interactions in Support of Performance Assessment of Low-Level Radioactive Waste Disposal Facilities, NUREG/CR-6377, PNNL-14408.

6.10.4 Onishi, Y., R.J. Serne, R.M. Arnold, C.E. Cowan, and F.L. Thompson, 1981.

Critical Review: Radionuclide Transport, Sediment Transport, and Water Quality Mathematical Modeling; and Radionuclide Adsorption/Desorption Mechanisms, NUREG/CR-1322, PNL-2901.

6.10.5 Sheppard, M.I. and D.H. Thibault, 1990. Default Soil Solid/Liquid Partition Coefficients.