ML022970089: Difference between revisions

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| number = ML022970089
| number = ML022970089
| issue date = 10/15/2002
| issue date = 10/15/2002
| title = Maine Yankee'S License Termination Plan, Section 6, Table of Contents - Attachment 6-19
| title = Maine Yankees License Termination Plan, Section 6, Table of Contents - Attachment 6-19
| author name =  
| author name =  
| author affiliation = Maine Yankee Atomic Power Co
| author affiliation = Maine Yankee Atomic Power Co
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=Text=
=Text=
{{#Wiki_filter:MYAPC License Termination Plan Revision 3 October 15, 2002 MAINE YANKEE LTP SECTION 6 COMPLIANCE WITH RADIOLOGICAL DOSE CRITERIA
{{#Wiki_filter:}}
 
MYAPC License Termination Plan                                                                                                        Page 6-i Revision 3 October 15, 2002 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 . . . . . . . . . . . . . . . . . . . . . . . . . . . .                          6-4 6.5.1 Contaminated Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .                  6-4 6.5.2 Environmental Media . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .                6-5 6.5.3 Dose Pathways . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .            6-5 6.5.4 Radionuclide Concentrations in Environmental Media . . . . . . . . . . . . .                                      6-5 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 . . . . . . . . . . . . . . . . . . . . . . . . . 6-20 6.6.3 Embedded Pipe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-24 6.6.4 Surface Soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-27 6.6.5 Deep Soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-29 6.6.6 Groundwater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-31 6.6.7 Surface Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-32 6.6.8 Buried Piping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-33 6.6.9 Forebay and Diffuser . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-35                  l 6.6.10 Circulating Water Pump House . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-42 6.7    Material Specific DCGLs and Total Dose Calculation . . . . . . . . . . . . . . . . . . 6-44 6.7.1 Conceptual Model for Summing Contaminated Material Dose . . . . . 6-46 6.7.2 Method and Calculations for Summing Contaminated Material Dose
                          . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-47 6.8    Area Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-53 6.8.1 Basement Contamination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-53 6.8.2 Surface Soil and Deep Soil Area Factors . . . . . . . . . . . . . . . . . . . . . . . 6-54
 
MYAPC License Termination Plan                                                                                                    Page 6-ii Revision 3 October 15, 2002 6.8.3 Embedded Piping Area Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-55 6.8.4 Buried Piping Area Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-55 6.8.5 Activated Concrete/Rebar Area Factors . . . . . . . . . . . . . . . . . . . . . . . . 6-56 6.9      Standing Building Dose Assessment and DCGL Determination . . . . . . . . . . .                                    6-56 6.9.1 Dose Assessment Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .                  6-56 6.9.2 Standing Building DCGLs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .                  6-57 6.9.3 Standing Building Area Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .                  6-58 6.10    References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-59 Attachments -1 Fill Direct Dose Microshield Output -2 BNL Kd Report for Fill -3 BNL Kd Report for Concrete -4 Irrigation Memorandum -5 Concrete Density -6 Activated Concrete Inventory -7 Remaining Embedded Piping -8 Deep Soil Microshield Output -9 Deep Soil RESRAD Output
 
MYAPC License Termination Plan                                                                              Page 6-iii Revision 3 October 15, 2002 -10 Buried Piping List and Projected Concentration Calculation -11 Buried Piping RESRAD Output -12 Buried Piping Microshield Output -13 DCGL/Total Dose Spreadsheets -14 Soil Area Factor Microshield Output -15 Standing Building Area Factor Microshield Output -16 Forebay Sediment Dose Assessment (Has been replaced by Attachment 2H)                                          l -17 Unitized Dose Factors for Activated Rebar -18 NRC Screening Levels for Contaminated Basement and Special Areas                                              l -19                                                                                                        l Special Areas Unitized Dose Factors                                                                            l 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 Table 6-3 Selected Kd Values (cm3/g) for Basement Fill Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-16
 
MYAPC License Termination Plan                                                                                              Page 6-iv Revision 3 October 15, 2002 Table 6-4 Contaminated Basement Surfaces Unitized Dose Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-21 Table 6-5 Activated Concrete Unitized Dose Factors 1.0 pCi/g . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-23 Table 6-6A                                                                                                                            l BOP Embedded Piping Unitized Dose Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-25                l Table 6-6B                                                                                                                            l Embedded Spray Pump Piping Unitized Dose Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-26                      l Table 6-7 Surface Soil Unitized Dose Factors 1.0 pCi/g Cs-137 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-29 Table 6-8 Site Specific Parameters used in RESRAD Deep Soil Analysis . . . . . . . . . . . . . . . . . . . . . . . 6-30 Table 6-9 Deep Soil Unitized Dose Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-31 Table 6-10 Buried Piping Unitized Dose Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-35 Table 6-10A                                                                                                                            l Estimated Media Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-37  l Table 6-10B                                                                                                                            l Excavated Soil Direct Dose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-39  l Table 6-11 Contaminated Material DCGL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-45 Table 6-12 Area Factors (AF) for Surface Soil and Deep Soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-54 Table 6-13 Gross Beta DCGL For Standing Buildings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-58 Table 6-14 Area Factors (AF) for Standing Buildings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-59
 
MYAPC License Termination Plan                                                                Page 6-1 Revision 3 October 15, 2002 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; 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.
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
 
MYAPC License Termination Plan                                                                  Page 6-2 Revision 3 October 15, 2002 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 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.
 
MYAPC License Termination Plan                                                                  Page 6-3 Revision 3 October 15, 2002 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, 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 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
 
MYAPC License Termination Plan                                                                  Page 6-4 Revision 3 October 15, 2002 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 for contamination on              l basement surfaces was shown to be low (per Table 6-11) for any credible future land use.        l 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.
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                                                                    l
 
MYAPC License Termination Plan                                                                  Page 6-5 Revision 3 October 15, 2002
: 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.
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.
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,
 
MYAPC License Termination Plan                                                                Page 6-6 Revision 3 October 15, 2002 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]
                        + existing groundwater concentration
* Basement Fill Concentration = [basement surface contamination] +
[embedded pipe] + [activated concrete/rebar]
* Surface Soil Concentration = surface soil concentration
* Deep Soil Concentration = [buried pipe] + deep soil concentration            l
* Surface Water Concentration = surface water concentration
 
MYAPC License Termination Plan                                                              Page 6-7 Revision 3 October 15, 2002 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 Pipe                X                                                          l X
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 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).
 
MYAPC License Termination Plan                                                                  Page 6-8 Revision 3 October 15, 2002 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 or flowable fill)      l 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 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. (Since the resident farmer is assumed to receive dose from exposure to surface soil based on 100% stay-time, the additional direct dose from basement fill is a
 
MYAPC License Termination Plan                                                                Page 6-9 Revision 3 October 15, 2002 conservative addition to dose. Thus, no credit is taken overall for the absence or presence of 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 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
 
MYAPC License Termination Plan                                                                Page 6-10 Revision 3 October 15, 2002 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 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
 
MYAPC License Termination Plan                                                                  Page 6-11 Revision 3 October 15, 2002 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 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.
 
MYAPC License Termination Plan                                                                Page 6-12 Revision 3 October 15, 2002 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 = C Vt                                                (2)
Where:        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 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 = f Kdf C Vf                                          (3)
Where:            f is fill bulk density (g/cm3)
Kdf is fill distribution coefficient C is water concentration(pCi/l)
 
MYAPC License Termination Plan                                                                Page 6-13 Revision 3 October 15, 2002 Vf is fill volume (m3) and Ac = c Kdc C Vc                                          (4)
Where:          c 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 = C Vt + f Kdf C Vf + c Kdc C Vc                    (5)
Multiplying the second and third terms by (Vt)/(Vt), i.e., 1, and rearranging gives:
At = C Vt + (Vt C)( f Kdf Vf) /(Vt ) + ( Vt C)(c Kdc Vc)/( Vt)    (6)
Recognizing from Equation (1) that the term, C Vt is the activity in the water phase, Aw, allows Equation 6 to be rewritten as:
At = Aw(1 + f (Kdf/)(Vf/Vt) + c (Kdc/)(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
 
MYAPC License Termination Plan                                                                Page 6-14 Revision 3 October 15, 2002 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.
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.
: 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
: 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
 
MYAPC License Termination Plan                                                                    Page 6-15 Revision 3 October 15, 2002 screening values in NUREG-1727, Table C2.3 , converted to                    l mrem/y per pCi/g.
Doseirrigation = (Csoil 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 hours (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.
: 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 or flowable              l fill. Therefore, the average Kds for Bank Run Sand or flowable              l
 
MYAPC License Termination Plan                                                                  Page 6-16 Revision 3 October 15, 2002 fill from Attachment 6-2 were used in the model. Table 6-3 lists          l 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 zero (0) was        l used in the calculations. A Kd of zero (0) maximizes the                  l 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.
Table 6-3 Selected Kd Values (cm3/g) for Basement Fill Model                              l Radionuclide  Mean            Reference for Mean Kd      Concrete    Reference for Kd Flowable                                        Kd            in cement          l Fill Kd H-3                  0                                            0 Fe-55              25                    Baes, Table 2.13    100          Krupka Table 5.1 Ni-63              128                    Attachment 6-2      100          Krupka Table 5.1  l Mn-54              50                Sheppard, Table A-1 Co-57              128                    Attachment 6- 2      100          Krupka Table 5.1  l Co-60              128                    Attachment 6-2      100          Krupka Table 5.1  l Cs-134              79                    Attachment 6-2        3            Attachment 6-3  l Cs-137              79                    Attachment 6-2        3            Attachment 6-3  l 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
 
MYAPC License Termination Plan                                                                  Page 6-17 Revision 3 October 15, 2002 Table 6-3 Selected Kd Values (cm3/g) for Basement Fill Model                              l Radionuclide  Mean          Reference for Mean Kd      Concrete    Reference for Kd Flowable                                      Kd            in cement          l Fill Kd 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
: 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.
: 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.
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
 
MYAPC License Termination Plan                                                              Page 6-18 Revision 3 October 15, 2002 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 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.
 
MYAPC License Termination Plan                                                                Page 6-19 Revision 3 October 15, 2002
: 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.
: 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
 
MYAPC License Termination Plan                                                                  Page 6-20 Revision 3 October 15, 2002 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 4.07 E-2 mrem/y and the rebar dose was 3.54 E-3 mrem/y.                  l 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 3 October 15, 2002 Table 6-4 Contaminated Basement Surfaces Unitized Dose Factors Key Parameters 3
Porosity                    0.30                Fill Volume                2460.0 m            Annual Total Well Water Vol        738.0  m3 3                                              2  3 Bulk Density                1.50  g/cm          Surface Area/Open Vol        1.70 m /m          Irrigation Rate                    0.274  L/m2-d 3
Yearly Drinking Water      478.0  L/yr          Concrete Volume              4.18    m          Surface Soil Depth                  0.15  m Wall Surface Area        4182.0  m2            Concrete Density            2.20    g/cm3 WATER, FILL, CONCRETE                      CONTAMINATED CONCRETE DOSE CALCULATION FACTORS                        Source Term                Kd CONCENTRATION                                    ANNUAL DOSE NUREG-1727  FGR 11    Microshield                              Kd          Kd                                                          Drinking  Irrigation  Direct  Total Nuclide      mrem/y per mrem per  mrem/y per      Inventory  Inventory    Fill    Concrete  Adsorption    Water      Fill  Concrete  Nuclide  Water Dose    Dose      Dose    Dose pCi/g      pCi        pCi/g      dpm/100 cm2      pCi    cm3/gm      cm3/gm      Factor      pCi/L    pCi/g    pCi/g            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  6.02E+01    1.00E+00    3.02E+02    8.45E-04 5.09E-05  8.45E-07    Sr-90  5.74E-05  5.52E-06  0.00E+00 6.29E-05 Cs-134        4.39E+00  7.33E-05    6.09E-05        1.00E+00    1.88E+05  7.91E+01    3.00E+00    3.96E+02    6.44E-04 5.09E-05  1.93E-06  Cs-134  2.26E-05  1.26E-06  3.10E-09 2.38E-05 Cs-137        2.27E+00  5.00E-05    1.20E-05        1.00E+00    1.88E+05  7.91E+01    3.00E+00    3.96E+02    6.44E-04 5.09E-05  1.93E-06  Cs-137  1.54E-05  6.49E-07  6.11E-10 1.60E-05 Co-60        6.58E+00  2.69E-05    6.30E-04        1.00E+00    1.88E+05  1.28E+02    1.00E+02    6.40E+02    3.98E-04 5.09E-05  3.98E-05    Co-60  5.12E-06  1.16E-06  3.20E-08 6.32E-06 Co-57        1.67E-01  1.18E-06    2.80E-08        1.00E+00    1.88E+05  1.28E+02    1.00E+02    6.40E+02    3.98E-04 5.09E-05  3.98E-05    Co-57  2.25E-07  2.96E-08  1.42E-12 2.54E-07 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  1.28E+02    1.00E+02    6.40E+02    3.98E-04 5.09E-05  3.98E-05    Ni-63  1.10E-07  2.11E-09  0.00E+00 1.12E-07
 
MYAPC License Termination Plan                                                                  Page 6-22 Revision 3 October 15, 2002 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 3.30E+08 pCi as            l 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 3.30E+08 pCi            l 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 3 October 15, 2002 Table 6-5 Activated Concrete Unitized Dose Factors 1.0 pCi/g Key Parameters 3
Porosity                  0.30                          Fill Volume                      2460.0 m                      Annual Total Well Water Vol                738.0      m3 3                                                            2  3 Bulk Density              1.50  g/cm                  Surface Area/Open Volume          1.70 m /m                    Irrigation Rate                            0.274    L/m2-d 3
Yearly Drinking Water    478.0  L/yr                  Concrete Volume                    4.18  m                    Surface Soil Depth                          0.15      m Wall Surface Area      4182.0  m2                    Concrete Density                  2.20  g/cm3                Activated Concrete Total Inventory      3.30E+08 Total pCi per pCi/g Activated Concrete Total Conc.              1.00    pCi/g WATER, FILL, CONCRETE                        ACTIVATED CONCRETE DOSE CALCULATION FACTORS                    SOURCE TERM                      Kd CONCENTRATION                                  ANNUAL DOSE NUREG-1727  FGR 11    Microshield                                    Kd        Kd                                                        Drinking  Irrigation  Direct    Total Nuclide  mrem/y per  mrem/pCi  mrem/y per Nuclide    Inventory  Inventory    Fill  Concrete  Adsorption    Water      Fill  Concrete  Nuclide Water Dose    Dose      Dose    Dose pCi/g                  pCi/g  Fraction      pCi/g      pCi    cm3/gm      cm3/gm      Factor    pCi/L      pCi/g      pCi/g            mrem/y    mrem/y    mrem/y  mrem/y Cs-134      4.39E+00  7.33E-05    6.09E-05  8.40E-03    8.40E-03  2.77E+06  7.91E+01  3.00E+00  3.96E+02  9.74E-03  7.49E-04  2.84E-05 Cs-134  3.32E-04  1.85E-05  4.56E-08 3.50E-04 Co-60      6.58E+00  2.69E-05    6.30E-04  4.00E-02    4.00E-02  1.32E+07  1.28E+02  1.00E+02  6.40E+02  2.79E-02  3.56E-03  2.79E-03  Co-60  3.59E-04  8.16E-05  2.25E-06 4.43E-04 C-14      2.08E+00  2.09E-06    0.00E+00  5.80E-02    5.80E-02  1.91E+07  5.00E+00  1.00E+02  2.72E+01  9.52E-01  4.76E-03  9.52E-02  C-14    9.51E-04  8.80E-04  0.00E+00 1.83E-03 Eu-154      3.13E+00  9.55E-06    3.10E-04  9.00E-03    9.00E-03  2.97E+06  4.00E+02  5.00E+03  2.06E+03  1.95E-03  7.80E-04  9.75E-03 Eu-154  8.90E-06  2.71E-06  2.42E-07 1.19E-05 Fe-55      2.50E-03  6.07E-07    0.00E+00  1.24E-01    1.24E-01  4.09E+07  2.50E+01  1.00E+02  1.27E+02  4.36E-01  1.09E-02  4.36E-02  Fe-55  1.26E-04  4.84E-07  0.00E+00 1.27E-04 H-3      2.27E-01  6.40E-08    0.00E+00  6.47E-01    6.47E-01  2.14E+08  0.00E+00  0.00E+00  1.00E+00  2.89E+02  0.00E+00    0.00E+00  H-3    8.84E-03  2.91E-02  0.00E+00 3.80E-02 Eu-152      2.87E+00  6.48E-06    2.09E-04  1.11E-01    1.11E-01  3.66E+07  4.00E+02  5.00E+03  2.06E+03  2.41E-02  9.62E-03  1.20E-01 Eu-152  7.45E-05  3.07E-05  2.01E-06 1.07E-04 Ni-63      1.19E-02  5.77E-07    0.00E+00  7.00E-03    7.00E-03  2.31E+06  1.28E+02  1.00E+02  6.40E+02  4.88E-03  6.24E-04  4.88E-04  Ni-63  1.35E-06  2.58E-08  0.00E+00 1.37E-06
 
MYAPC License Termination Plan                                                                Page 6-24 Revision 3 October 15, 2002 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 154 m2. Assuming a unit inventory of 1 dpm/100 cm2 the total inventory          l was determined to be 6.95E+03 pCi.. The 6.95E+03 pCi inventory applies          l 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 6.95E+03 pCi unit inventory. Because two distinct areas (Embedded Spray          l Pump Piping and BOP Embedded Piping) were created to address                    l embedded piping, two different DCGL calculations (and spreadsheets) were        l created. Each spreadsheet addresses separate unit inventories that sum to        l the above total inventory (Spray Pump and BOP embedded inventories are          l 1.19E+03 and 5.75E+03 respectively). These forms facilitate the use of the      l spreadsheets 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 BOP Embedded Piping and Embedded Spray Pump Piping                          l spreadsheets are provided in Tables 6-6A and 6-6B. The results represent        l 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            l associated pipe.                                                                l
 
MYAPC License Termination Plan                                                                                      Page 6-25 Revision 3 October 15, 2002 Table 6-6A BOP Embedded Piping Unitized Dose Factors Key Parameters 3
Porosity                  0.30                Fill Volume                2460.0 m                      Surface Soil Depth                      0.15          m 3
Bulk Density              1.50  g/cm          Surface Area/Open Vol        1.70  m2/m3                  Irrigation Rate                        0.274      L/m2-d Yearly Drinking Water    478.0  l/yr          Concrete Volume              4.18  m3                    Annual Total Well Water Vol              738          m3 Wall Surface Area        4182.0  m2            Concrete Density            2.20  g/cm3                  Embedded Pipe Conversion Factor        5754.5    pCi per dpm/100 cm2 Total Inventory                      1.00E+00  dpm/100 cm2 WATER, FILL, CONCRETE DOSE CALCULATION FACTORS                        Source Term                Kd                                                          EMBEDDED PIPE ANNUAL DOSE CONCENTRATION NUREG-1727  FGR 11      Microshield                              Kd        Kd                                                      Drinking  Irrigation  Direct  Total Nuclide    mrem/y per  mrem/pCi    mrem/y per      Inventory    Inventory    Fill  Concrete  Adsorption    Water      Fill  Concrete Nuclide  Water Dose    Dose      Dose    Dose pCi/g                  pCi/g    dpm/100 cm2        pCi    cm3/gm    cm3/gm    Factor      pCi/L    pCi/g    pCi/g            mrem/y      mrem/y    mrem/y  mrem/y Sr-90    1.47E+01    1.42E-04    0.00E+00        1.00E+00    5.75E+03  6.02E+01  1.00E+00  3.01E+02    2.58E-05 1.55E-06  2.58E-08  Sr-90    1.75E-06  1.69E-07  0.00E+00 1.92E-06 Cs-134    4.39E+00    7.33E-05    6.09E-05        1.00E+00    5.75E+03  7.91E+01  3.00E+00  3.96E+02    1.97E-05 1.56E-06  5.90E-08 Cs-134    6.89E-07  3.84E-08  9.47E-11 7.27E-07 Cs-137    2.27E+00    5.00E-05    1.20E-05        1.00E+00    5.75E+03  7.91E+01  3.00E+00  3.96E+02    1.97E-05 1.56E-06  5.90E-08 Cs-137    4.70E-07  1.98E-08  1.87E-11 4.90E-07 Co-60    6.58E+00    2.69E-05    6.30E-04        1.00E+00    5.75E+03  1.28E+02  1.00E+02  6.40E+02    1.22E-05 1.55E-06  1.22E-06  Co-60    1.56E-07  3.56E-08  9.79E-10 1.93E-07 Co-57      1.67E-01  1.18E-06    2.80E-08        1.00E+00    5.75E+03  1.28E+02  1.00E+02  6.40E+02    1.22E-05 1.55E-06  1.22E-06  Co-57    6.86E-09  9.03E-10  4.35E-14 7.76E-09 Fe-55      2.50E-03  6.07E-07    0.00E+00        1.00E+00    5.75E+03  2.50E+01  1.00E+02  1.27E+02    6.13E-05 1.53E-06  6.13E-06  Fe-55    1.78E-08  6.81E-11  0.00E+00 1.78E-08 H-3      2.27E-01  6.40E-08    0.00E+00        1.00E+00    5.75E+03  0.00E+00  0.00E+00  1.00E+00    7.78E-03 0.00E+00  0.00E+00  H-3    2.38E-07  7.85E-07  0.00E+00 1.02E-06 Ni-63      1.19E-02  5.77E-07    0.00E+00        1.00E+00    5.75E+03  1.28E+02  1.00E+02  6.40E+02    1.22E-05 1.55E-06  1.22E-06  Ni-63    3.35E-09  6.43E-11  0.00E+00 3.42E-09
 
MYAPC License Termination Plan                                                                                      Page 6-26 Revision 3 October 15, 2002 Table 6-6B Embedded Spray Pump Piping Unitized Dose Factors Key Parameters 3
Porosity                0.30                  Fill Volume                2460.0 m                      Surface Soil Depth                        0.15    m Bulk Density            1.50  g/cm3          Surface Area/Open Vol        1.70 m /m 2  3 Irrigation Rate                          0.274  L/m2-d Yearly Drinking Water  478.0  l/yr          Concrete Volume              4.18  m3                    Annual Total Well Water Vol                738    m3 Wall Surface Area      4182.0  m2            Concrete Density            2.20  g/cm3                  Embedded Pipe Conversion Factor        1191.7    pCi per dpm/100 cm2 2
Total Inventory                        1.00E+00 dpm/100 cm WATER, FILL, CONCRETE DOSE CALCULATION FACTORS                    SOURCE TERM                  Kd                                                            EMBEDDED PIPE ANNUAL DOSE CONCENTRATION NUREG-1727  FGR 11    Microshield                              Kd        Kd                                                        Drinking  Irrigation  Direct  Total Nuclide    mrem/y per mrem/pCi    mrem/y per      Inventory  Inventory    Fill    Concrete Adsorption    Water      Fill  Concrete  Nuclide Water Dose      Dose      Dose    Dose pCi/g                  pCi/g      dpm/100 cm2      pCi    cm3/gm    cm3/gm    Factor        pCi/L    pCi/g    pCi/g              mrem/y      mrem/y    mrem/y  mrem/y Sr-90    1.47E+01  1.42E-04    0.00E+00        1.00E+00    1.19E+03  6.02E+01 1.00E+00  3.01E+02    5.35E-06 3.22E-07 5.35E-09    Sr-90    3.63E-07  3.50E-08    0.00E+00 3.98E-07 Cs-134    4.39E+00  7.33E-05    6.09E-05      1.00E+00    1.19E+03  7.91E+01 3.00E+00  3.96E+02    4.07E-06 3.22E-07 1.22E-08  Cs-134    1.43E-07  7.95E-09    1.96E-11 1.51E-07 Cs-137    2.27E+00  5.00E-05    1.20E-05      1.00E+00    1.19E+03  7.91E+01 3.00E+00  3.96E+02    4.07E-06 3.22E-07 1.22E-08  Cs-137    9.73E-08  4.11E-09    3.87E-12 1.01E-07 Co-60      6.58E+00  2.69E-05    6.30E-04      1.00E+00    1.19E+03  1.28E+02 1.00E+02  6.40E+02    2.52E-06 3.22E-07 2.52E-07  Co-60    3.24E-08  7.37E-09    2.03E-10 4.00E-08 Co-57      1.67E-01  1.18E-06    2.80E-08      1.00E+00    1.19E+03  1.28E+02 1.00E+02  6.40E+02    2.52E-06 3.22E-07 2.52E-07  Co-57    1.42E-09  1.87E-10    9.01E-15 1.61E-09 Fe-55      2.50E-03  6.07E-07    0.00E+00        1.00E+00    1.19E+03  2.50E+01 1.00E+02  1.27E+02    1.27E-05 3.17E-07 1.27E-06  Fe-55    3.68E-09  1.41E-11    0.00E+00 3.70E-09 H-3      2.27E-01  6.40E-08    0.00E+00        1.00E+00    1.19E+03  0.00E+00 0.00E+00  1.00E+00    1.61E-03 0.00E+00 0.00E+00    H-3    4.93E-08  1.63E-07    0.00E+00 2.12E-07 Ni-63      1.19E-02  5.77E-07    0.00E+00        1.00E+00    1.19E+03  1.28E+02 1.00E+02  6.40E+02    2.52E-06 3.22E-07 2.52E-07    Ni-63    6.95E-10  1.33E-11    0.00E+00 7.08E-10
 
MYAPC License Termination Plan                                                                  Page 6-27 Revision 3 October 15, 2002 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.
Verification Conditions (for Surface Soil Screening Values). NUREG-1727, NMSS Decommissioning Standard Review Plan, Appendix C, describes the justification necessary to allow direct use of these screening. Per the NUREG, the following conditions must be satisfied:
: 1. The initial residual radioactivity (after decommissioning) is contained in the top layer of the surface soil [that is, approximately 6 inches (15cm)].
: 2. The unsaturated zone and the groundwater are initially free of contamination.
: 3. The vertical saturated hydraulic conductivity at the specific site is greater than the infiltration rate.
The above conditions are satisfied for the Maine Yankee site.
Condition One. The direct use of these screening values is only for surface soil (approx. 6 inches). Section 6.6.5 calculated a dose from deep soil (that is, greater than 6 inches) separate from the use of the surface soil screening values. (See Section 6.6.5)
Condition Two. Maine Yankee does not use the surface soil screening values to address potential site groundwater contamination from H-3. H-3 presence in the groundwater and surface water is assumed based upon the highest measured readings and is covered by separate dose assessments. (See Sections 6.6.6 and 6.6.7)
Condition Three. The soils at Maine Yankee that are in areas currently containing nuclides elevated above background, and those soils that are
 
MYAPC License Termination Plan                                                                Page 6-28 Revision 3 October 15, 2002 planned to be used to fill the foundations are bank run sand and gravel. The Adams or Hinckley USDA Soil Series would provide the closest approximation. The minimum saturated vertical hydraulic conductivity of these soils is 0.001 cm/sec or 1.417 inches per hour. Average saturated hydraulic conductivity rates would be about 10 times this, or 14 inches per hour. Infiltration capacity is based on land cover type, antecedent moisture condition prior to a rainfall or snowmelt event, and the rate of water supply available for infiltration. The permanent water table at the Maine Yankee site in the area of interest is approximately elevation 10 to 15 feet above Mean Sea Level, indicating a distance of 6 to 11 feet from the existing ground surface to the average water table position. Therefore, this much of the sand fill will be unsaturated. Infiltration capacity is limited by the unsaturated hydraulic conductivity of the soil. The unsaturated hydraulic conductivity of the sand fill is typically from 1/10 to 1/100 of the saturated hydraulic conductivity. Precipitation rates rarely exceed one inch per hour in Maine.
Therefore, because the typically expected maximum precipitation rate is less than the minimum saturated hydraulic conductivity, and because the fill is unsaturated for 6 or more feet down and unable to transmit water downward at a rate exceeding the saturated vertical hydraulic conductivity, infiltration rates in the fill must be less than the saturated vertical hydraulic conductivity.
Soil types on the Maine Yankee site are representative of those assumed in the soil screening model. These soil types include: silt loams derived from glaciomarine sediments, fine sandy loams derived from glacial till, and fill that has a wide textural variation. However, the primary fill in the immediate plant area is a sand or loamy sand. The silt loams are most typical over the undisturbed portions of the site. The exceptions are in the knoll and ridge areas where bedrock is exposed or shallow where the fine sandy loams predominate. Fill areas surrounding the plant buildings are sand or loamy sand. Fill areas north of the 345 KV yard tend to have a silt loam surface covering. The most likely foundation fill material will be bank run sand.
(See Section 6.6.1d.)
: 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.
 
MYAPC License Termination Plan                                                                  Page 6-29 Revision 3 October 15, 2002 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 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., 28,500 m3, for the purpose of conservatively determining the    l 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 actual remaining volume of deep soil with any significant contamination will be a very small fraction of 28,500 m3.                      l
 
MYAPC License Termination Plan                                                                  Page 6-30 Revision 3 October 15, 2002
: 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 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 Contaminated Zone site specific hydraulic conductivity        32          m/y Contaminated Zone site specific b factor                    4.05 Site Specific Effective Porosity                            0.01 Unsaturated. Zone Site Specific Hydraulic Conductivity      1000          m/y Co                        335.0        cm3/g        l Sr                        152.0        cm3/g        l Site Specific Soil Kds:
Cs                        1200.0        cm3/g        l Ni                        274.0        cm3/g        l
 
MYAPC License Termination Plan                                                                                          Page 6-31 Revision 3 October 15, 2002 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.
Table 6-9 Deep Soil Unitized Dose Factors Key Parameters Porosity          0.3                  Yearly Drinking Water            478        L/y        Surface Soil Depth        0.15    m Bulk Density      1.6      g/cm3      Irrigation Rate                  0.274      L/m2-d DOSE CALCULATION FACTORS                                Source Term                          DEEP SOIL ANNUAL DOSE NUREG-1727    FGR 11      Microshield  Deep Soil    Derived Water      Water      Drinking  Irrigation  Direct    Total Nuclide    mrem/y per  mrem/pCi      mrem/y per  Inventory  Conversion Units  Inventory  Water Dose      Dose      Dose      Dose pCi/g                      pCi/g        pCi/g    pCi/L per pCi/g    pCi/L      mrem/y      mrem/y    mrem/y    mrem/y Cs-137      2.27E+00    5.00E-05      4.00E-01    1.00E+00      9.02E-03      9.02E-03    2.16E-04    8.53E-06  4.00E-01  4.00E-01 Co-60      6.58E+00    2.69E-05      2.40E+00    1.00E+00      2.24E-02      2.24E-02    2.88E-04    6.15E-05  2.40E+00 2.40E+00 H-3      2.27E-01    6.40E-08      0.00E+00    1.00E+00      6.69E+03      6.69E+03    2.05E-01    6.33E-01  0.00E+00 8.37E-01 Ni-63      1.19E-02    5.77E-07      0.00E+00    1.00E+00      6.01E-01      6.01E-01    1.66E-04    2.98E-06  0.00E+00 1.69E-04 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 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
 
MYAPC License Termination Plan                                                                Page 6-32 Revision 3 October 15, 2002 these samples have exceeded the MDC level of about 2500 pCi/l. (Additional                l sampling and analyses of site groundwater conducted in 2002, including the                l containment foundation sump, are discussed in Section 2.5.3.d and reported to the          l NRC in references noted in that section. The additional sampling confirmed the            l nuclide fraction and conservatism of the H-3 activity level assumed in the dose            l assessment.)                                                                              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.
As discussed in Section 2.5.3.d, additional routine sampling of the containment            l foundation sump and PAB test pit will be conducted routinely until final status survey    l has commenced in these two plant areas. The samples will be taken on an                    l approximate monthly basis and will be analyzed by gamma spectroscopy and for H-3.          l Sample analysis results will be evaluated regarding: (1) the need for additional          l assessment (such as, additional sampling or hard to detect analyses) and (2) any        l impact to the dose assessment.                                                            l 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.
 
MYAPC License Termination Plan                                                                  Page 6-33 Revision 3 October 15, 2002 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, 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
: 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 buried in open land, not pipe embedded in concrete basements, which were described in Section 6.6.3. A list of the buried piping that current plans call to remain after decommissioning is provided in Attachment 6-10. The buried piping is expected to contain very limited levels of contamination, if any. The radionuclide mixture is assumed to be the same as for contaminated materials.
 
MYAPC License Termination Plan                                                                  Page 6-34 Revision 3 October 15, 2002 The conceptual dose model for the buried piping 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. 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 DCGLs will be limited to ensure that the projected soil concentrations are below the surface soil DCGLs. This additional measure of conservatism was also applied to deep soil to account for hypothetical future excavation of the buried contamination.
: b.      Unitized Dose Factors for Buried Piping The total surface area and total volume were calculated for all of the buried piping 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 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, 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 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
 
MYAPC License Termination Plan                                                                                      Page 6-35 Revision 3 October 15, 2002 and Buried Piping 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 are provided in Table 6-10.
Table 6-10 Buried Piping Unitized Dose Factors Key Parameters Porosity                                  0.3                                      Yearly Drinking Water          478    L/y Bulk Density                              1.6    g/cm3                            Irrigation Rate              0.274    L/m2-d Buried Pipe Conversion Factor          2.59E-04  pCi/g per dpm/100 cm2            Surface Soil Depth            0.15    m Dose Calculation Factors                              Source Term                            Buried Piping Annual Dose FGR 11    NUREG-1727    Microshield      Water          Pipe Surface      Soil      Drinking    Irrigation    Direct    Total Nuclide  mrem/pCi    mrem/y per    mrem/y per      Inventory        Inventory    Inventory    Water Dose    Dose        Dose      Dose pCi/g        pCi/g      pCi/L per pCi/g    dpm/100cm2        pCi/g      mrem/y      mrem/y    mrem/y  mrem/y Sr-90    1.42E-04    1.47E+01      0.00E+00        2.15E-02          1.00E+00      2.59E-04    3.77E-07    3.41E-08  0.00E+00  4.12E-07 Cs-134    7.33E-05    4.39E+00      2.21E-05        2.25E-05          1.00E+00      2.59E-04    2.04E-10    1.07E-11  5.72E-09  5.94E-09 Cs-137    5.00E-05    2.27E+00      3.97E-06        3.27E-04          1.00E+00      2.59E-04    2.02E-09    8.01E-11  1.03E-09  3.13E-09 Co-60    2.69E-05    6.58E+00      2.53E-04        8.14E-04          1.00E+00      2.59E-04    2.71E-09    5.78E-10  6.55E-08  6.88E-08 Co-57    1.18E-06    1.67E-01      9.44E-09        1.15E-04          1.00E+00      2.59E-04    1.68E-11    2.07E-12  2.45E-12  2.13E-11 Fe-55    6.07E-07    2.50E-03      0.00E+00        4.30E-05          1.00E+00      2.59E-04    3.23E-12    1.16E-14  0.00E+00  3.24E-12 H-3      6.40E-08    2.27E-01      0.00E+00      1.98E+02          1.00E+00      2.59E-04    1.57E-06    4.85E-06  0.00E+00  6.42E-06 Ni-63    5.77E-07    1.19E-02      0.00E+00        2.09E-02          1.00E+00      2.59E-04    1.49E-09    2.68E-11  0.00E+00  1.52E-09 6.6.9    Forebay and Diffuser                                                                                    l
: a.        Forebay Source Term                                                                          l l
Forebay Physical Description                                                                            l l
The forebay is a basin approximately 400 feet long by 160 feet wide at the                              l top with a granite (ledge) floor, rock/soil walls on two sides, and small                              l concrete walls at each end. The depth is approximately 20 feet. The volume                              l is (64,000 ft2 bottom + 10,150 ft2 top incline area) x (20 feet deep) = 1.48E6                          l ft3 or 42,000 m3. The surface area of the bottom plus sides (assuming flat                              l sides) is 7435 m2. If the rip-rap surface is calculated, the surface area is                            l 2337 m2. (This assumes the number of circles of 2 foot diameter contained                              l within the forebay wall area then converting those to a half sphere area of 1                          l
 
MYAPC License Termination Plan                                                                  Page 6-36 Revision 3 October 15, 2002 foot radius.) The rip-rap volume is estimated at 478 m3. The total surface        l area when the forebay is backfilled is 7435 m2.                                    l l
There are four potentially contaminated media associated with the forebay:        l ledge, rip-rap, sediment, and soil. Each of these will be examined separately      l to determine the dose contribution of each medium. It should be noted that        l pre-remediation studies conducted to date indicate that the activity in the        l forebay sediment is very insoluble (i.e., no activity is given up to water nor    l is there detectable activity in a water filtrate). Most of the activity is        l contained within the organic layer of sediment or the organic film deposited      l on the rip-rap of the forebay. Based on solubility, pH, and water chemistry,      l the conditions for the maximum release of activity from sediment or surface        l film are occurring now. In spite of these ideal release conditions, no            l detectable activity is found in the standing water of the forebay.                l Furthermore, the infiltration water that enters the forebay through pathways      l in the dikes is brackish which makes the drinking or irrigation pathways          l doubtful. None the less, drinking and irrigation were evaluated.                  l l
Characterization Data                                                              l l
A detailed discussion of forebay / diffuser characterization is provided in        l Attachment 2H. Table 6-10A (below) provides estimated total activity,              l where appropriate, for each principal contaminated media. No current              l contamination data are available for the forebay granite ledge floor; but          l given its low permeability, the ledge is expected to be clean following            l remediation. This will be verified. The rip-rap activity is based on the          l average surface activity of the rip-rap times the entire rip-rap surface area. l l
 
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Table 6-10A                                                l Estimated Media Activity                                          ll Media                            Total Activity                    l Ledge                  To be remediated. (See also Table 2H-5 in          l Attachment 2H.)                                    l Rip-Rap                10.5 uCi Co-60                                      l Marine Sediment To be remediated. (See also Table 2H-5 in                  l Attachment 2H.)                                    l Soil                  1.85E4 uCi Co-60                                    l 1.52E3 uCi Cs-137                                  l l
Drinking Water and Irrigation Dose                                                l l
The drinking water and irrigation water dose was modeled using the same          l approach as that used for the basement fill model. The forebay surface area        l to volume ratio was calculated as 0.177 m2/m3, or using the rip-rap surface,      l as 0.06 m2 /m3. The surface area of 435 m2 for the source term was                l calculated by multiplying the surface area to volume ratio by the volume          l associated with the annual water usage (738m3) for the soil porosity 0.3.        l The source term for the drinking water was then calculated assuming a              l contamination level equal to the concrete structure DCGL of 18,000                l dpm/100cm2. Thus, the dose contribution from the forebay surface area              l source term was calculated as 0.002 mrem from drinking water and 0.0004            l mrem from irrigation water. These dose contributions are well below and            l are bounded by the dose contributions from the drinking water and irrigation      l water sources to the resident farmer from the building basements.                  l Therefore, these dose contributions are considered separate from the resident      l farmer dose modeling scenario. Furthermore, since this dose is so                l insignificant and the probability is so low that an individual would be able to  l successfully place a viable well within the forebay, survey measurements of        l the forebay surfaces including rip-rap will be limited.                            l l
Rock (Rip-Rap) Dose                                                                l l
The exposed surface area of the rip-rap is 2337 m2. The surface activity is        l spread over the exposed surface area at 0.1 pCi/g (based on diffuser surface      l sample and rip-rap sample levels) or 45 pCi/100 cm2 Co-60. When                  l deposited over the exposed surface area, this level of Co-60 contamination        l results in a total activity from rip-rap of 10.5 uCi. This activity is assumed    l
 
MYAPC License Termination Plan                                                                Page 6-38 Revision 3 October 15, 2002 to be instantaneously released and mixed within the forebay soil backfill        l volume. This results in a soil concentration of 1.56E-4 pCi/g Co-60.            l l
Sediment Dose                                                                    l l
Several large pockets of sediment were identified on the floor of the forebay    l during diving inspections. There are also small deposits lying between the      l rip-rap and also behind the weir (in the seal pit). The activity of the          l underwater marine sediment averages 19 pCi/g Co-60 and 2 pCi/g Cs-137.          l (One small area of very high activity was discovered which had Co-60 levels      l as high as 445 pCi/g.) The sediment within the forebay is all slated for        l removal by washing, settling, filtering and dewatering. The dewatered            l sediment will be disposed of as radwaste and will not contribute                l significantly to dose. Any residual activity remaining following sediment        l removal would be included in the ledge dose for 18,000 dpm/100 cm2              l surface contamination and the shallow pockets of contaminated sediment          l which might remain have previously been analyzed and found not to                l contribute a significant dose (EC 004-01).                                      l l
Direct Dose Excavated Forebay Soil                                              l l
Coastal zoning or land use restrictions may prohibit or severely limit          l excavation or construction activities in the area of the former forebay given    l its closeness to the shoreline. None the less, the dose from these activities    l has been evaluated as discussed in this section. Contaminated soil has been      l detected in approximately a two foot deep band behind the rip-rap. The          l nuclide fraction is assumed to be the same as the sediment since it originates  l from the same effluent releases. (See Section 2.5.3 and Attachment 2H for        l additional discussion of the nuclide fraction and supporting characterization    l data.) The average activity levels detected were 7.3 pCi/g Co-60 and 0.6        l pCi/g Cs-137; maximum levels were 21.3 pCi/g Co-60 and 1.35 pCi/g Cs-            l 137. No Sb-125 was detected in the soil samples. A two foot thick band of        l contaminated soil 35 feet high by 400 feet long (the forebay wall                l dimensions) for two dike walls is 1586 m3 of contaminated soil.                  l l
The excavation of two different sized homes are evaluated to determine the      l volume of soil which must be excavated assuming the worst case volumetric        l capture of contaminated soil within the excavation volume. An excavation        l for a 2000 square foot house results in a factor of 11 associated with the      l worst case capture of contaminated soil with clean soil. An excavation of a      l 1000 square foot house results in a factor of 7.9 associated with the worst      l case capture of contaminated soil with clean soil. In neither case, is credit    l taken for any additional clean soil which would be generated if the              l
 
MYAPC License Termination Plan                                                                    Page 6-39 Revision 3 October 15, 2002 excavation was sloped for safety concerns. In both cases, the contaminated            l soil is assumed to begin at the surface with no cover material, even though          l the as-left elevation of the forebay will be a few feet above the contaminated        l zone which exists in the inter tidal zone of the forebay. Therefore, a                l conservative dilution factor of 7 may be applied to determine acceptable              l levels of radioactive materials of forebay soil in the two feet immediately          l behind the rip rap.                                                                  l l
The dose to a person from the excavation of the contaminated soil is shown          l in Table 6-10B below, assuming the dilution factors described above and the          l annual outdoor exposure time for soil at the average activity values and for          l soil at the 3 pCi/g equivalent activity. The dose reduction due to shielding          l by a 6" concrete basement floor for the average soil activity is also shown in        l Table 6-10B.                                                                          l l
Table 6-10B                                                    l Excavated Soil Direct Dose                                            ll Initial Dose Rate (mrem/h)                          Dose at Average        Dose at        ll Soil Concentration  3 pCi/g Equivalent ll Average                            Dilution                                            ll 3 pCi/g  Hrs/y                    (mrem/y)          (mrem/y)
Concentration                            Factor                                              l Large House      1.30E-02          3.0E-03    964        11            1.14                0.26          l Small House        7.90E-03        1.80E-03    964      7.88            0.97                0.22          l Basement          6.70E-04            ---    5756        ---            3.9                ---          l l
The excavation scenario dose rates are less than the soil dose rate to the            l resident farmer, therefore, this scenario is presented as a separate and dose-        l bounded scenario to the resident farmer.                                              l l
: b.      Diffuser Source Term                                                        l l
The source term for the diffuser is the sediment entrained within the diffuser        l pipes. The sediment activity initially came from plant liquid effluent                l releases via the forebay and later via the movement of benthic silt back into        l the diffuser pipes by tidal action. These liquid effluent releases were made          l in accordance with licensed effluent controls and were routinely reported to          l the NRC. The effluent reports contained dose assessments which                      l demonstrated compliance with 10 CFR 20 limits. The diffuser consists of 2            l pipes 9 feet in diameter and 516 feet long. These two pipes are fed by trunk          l lines originating at the forebay. The portions of the trunks that are                l submerged and can contain sediment are 1421.5 feet in length. The volume              l
 
MYAPC License Termination Plan                                                                  Page 6-40 Revision 3 October 15, 2002 occupied by the diffusers is 1860 m3 and the volume of the trunk lines is        l 2562 m3. This conservatively results in a potential sediment-filled source of    l 4422 m3. For a circumference of 28.3 ft. and a length of 2543.5 ft, the pipe      l interior would have a surface area of 71,981 ft2. Converting this area in ft2    l to 100 cm2 areas results in a value of 6.68E5 100 cm2 areas.                      l l
Coupons of the diffuser pipe were removed and analyzed for surface                l contamination. The nuclides detected were Co-60 and Cs-137 at nearly              l equal activity. The combined activities of both nuclides were approximately      l 0.28 pCi/g. This specific activity multiplied by the sample mass of 125g          l results in approximately 35 pCi per sample. The samples represent about          l 100 cm2. The activity was present as a tightly-adhered, thin film of organic      l material. Based on the total interior surface area of the diffuser, if all of the l activity on the interior surface of the pipes is relocated to the sediment, the  l additional activity would be 30 uCi.                                              l l
Sediment samples taken from inside the diffuser and analyzed by gamma            l spectroscopy gave the following average activity values.                          l l
Co-60      1.1 pCi/g                                              l Cs-137    0.15 pCi/g                                            l l
The sediment nuclide activity was determined by multiplying the activity          l values by the sediment volumes as shown for Co-60 and Cs-137 for a total          l activity of 8315 uCi.                                                            l l
Water Activity                                                                    l l
The sediment activity is assumed to be instantaneously released non-              l mechanistically into the waters of Montsweag Bay. (It is likely that the          l sediment will remain in the diffuser pipes for years to come and the              l radioactivity slowly be reduced by decay.) Since the Bay is an estuary, the      l water is considered non-drinkable. The volume of water into which the            l activity is released was determined by consulting MYC-2035 which                  l discussed the former condenser cooling water mixing zone. The mixing            l zone was established for thermal mixing assuming cooling water is released        l at a rate of 950 cfs. With the cooling water pumps no longer operable, such      l flow rates are not feasible. However, using the area in which forced mixing      l of the diffuser water occurred would result in a reasonable estimate for a        l mixing area for the potential sediment activity released at a much lower flow    l rate. (Churchill (1980) stated that the same flow model applies to both          l radionuclide dispersion and hot water dispersion from the plant.)                l l
 
MYAPC License Termination Plan                                                                  Page 6-41 Revision 3 October 15, 2002 Using this mixing zone and the activities given above for sediment with        l HTDs included, the water concentrations for each nuclide were calculated.        l This activity level is assumed to exist for a year, when in fact, it would be    l dissipated within 56 hours by tidal flushing of the bay. Assuming dilution,      l the water concentration would be reduced by 6.4E-3 (56 h dilution                l time/8760 h per year) and the total annual dose would be on the order of          l 0.005 mrem/y for fish and 0.002 mrem/y for shell fish.                            l l
The annual dose rate to the individual who consumes seafood from this            l contaminated water source was derived by multiplying the water activity by        l the seafood bioaccumulation factors given in NUREG-5512 by the FGR-11            l dose conversion factor for each nuclide times the consumption rate taken          l from NUREG-5512. Based on a comparison to local marine organism                  l nuclide levels, the NUREG-5512 values are considered to be conservative.          l l
The total dose from eating seafood (fish plus shell fish) grown in the              l contaminated water is 0.007 mrem/y. The consumption of this food source            l would actually replace other food sources included in the dose model. If the        l dose from eating this seafood were simply added to the annual dose to the          l resident farmer, it would represent a negligible increase compared to the          l farmers total annual dose. Therefore, since the dose increase is negligible,      l this dose has not been added to Table 6-11. Furthermore, since the dose is          l negligible and the activity would likely be contained in the diffuser for          l sufficient time for substantial decay of dose significant nuclides, any further    l survey measurements of the diffuser will be limited.                                l l
Sediment Dose                                                                      l l
A person could be exposed from direct radiation originating from the                l contaminated sediment if it were deposited upon a shoreline or mud flat.            l This portion of the calculation assumes that the total sediment activity is        l suspended within the area outlined by the mixing zone and is then non-            l mechanistically dewatered to the condition of a mud flat. The area is              l approximately 52,500 m2 compared to the entire mud flat of Bailey Cove              l (130,000 m2). An area ratio of 0.404 describes that portion of the entire          l Bailey Cove mud flat that could be covered intact by the postulated release.        l l
The NRC (RG 1.109) adjusts the annual dose from shoreline deposits for the            l amount of time spent on the shore and for the geometry of the shoreline              l (shoreline width factor). For tidal basins like Montsweag Bay, the width              l factor is 1. For river shorelines, like the Back River, the factor is 0.2. For        l conservatism, a factor of 1 was used. The NRC time for shoreline recreation          l is 47 hours per year, however, Maine Yankee recognizes (ODCM) the                    l
 
MYAPC License Termination Plan                                                                Page 6-42 Revision 3 October 15, 2002 presence of the commercial worm digger on the mud flats for 325 hours per        l year.                                                                            l l
The sediment dose rate (mrem/hr) is the product of the sediment activity        l divided by the mud flat area factor times the dose rate at 1 m from the          l resulting activity deposited (from RG 1.109). For Co-60 the dose rate would      l be: 7315 uCi/5.25E4 m2 x width factor of 1 x 1E6 pCi/uCi x 1.7E-8                l mrem/hr/pCi/m2 x 0.404 = 9.6E-4 mrem/hr. (Note that Reg. Guide 1.109 does        l not provide values for Sb-125. The dose rate was estimated at half the Cs-137    l value based on the dose rate for soil.)                                          l l
The total whole body dose rate is 1.01E-3 mrem/h from contaminated mud          l flats. Using the worm digger exposure time of 325 hr/y x 1.01E-3 mrem/hr =      l 0.327 mrem/y. If the DandD outdoor time fraction (964 hr/y) is used, the        l annual dose would be 0.97 mrem/y.                                                l 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 6-43 Revision 3 October 15, 2002 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). 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
 
MYAPC License Termination Plan                                                                Page 6-44 Revision 3 October 15, 2002 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 special areas differs from the rest of the          l basement surfaces. Therefore, a separate DCGL was selected and a separate dose calculation was performed for the special areas. (See Attachment 2F for a discussion of special          l areas.)                                                                                        l 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 6-45 Revision 3 October 15, 2002 Table 6-11 Contaminated Material DCGL Basement Contaminated Concrete (gross beta dpm/100 cm2):                        18,000 Special Area Contaminated Concrete (gross beta dpm/100 cm2)                      9,500              l Basement Activated Concrete (pCi/g):                                                  1.00 Surface Soil (Cs-137 pCi/g):                                                          3.20          l Deep Soil (Cs-137 pCi/g):                                                              3.20          l BOP Embedded Piping [Limit: 100K], (gross beta dpm/100 cm2):                  100,000                l Spray Building Pump Piping [Limit: 800K], (gross beta dpm/100 cm2):            800,000                l Ground Water (H-3, pCi/L):                                                        6,812 Surface Water (H-3, pCi/L):                                                        960 Buried Piping, Conduit and Cable, (gross beta dpm/100 cm2):                      9,800 Contaminated Material Annual Dose Drinking    Direct, Inhalation        Total Material                      Water          & Ingestion        Annual Dose (mrem/y)          (mrem/y)            (mrem/y)
Contaminated Concrete                          2.70E-01          3.08E-02          3.01E-01          l Activated Concrete                            1.05E-02          3.02E-02          4.08E-02          l Surface Soil                                  0.00E+00          7.52E+00            7.52E+00          l Deep Soil                                      3.97E-02        1.48E+00            1.52E+00          l BOP Embedded Piping                            4.59E-02          5.23E-03          5.11E-02          l Spray Building Pump Embedded Piping            7.60E-02          8.67E-03          8.47E-02          l 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                6.33E-04          1.89E-03          2.52E-03          l ll Total                                        0.68 mrem/y      9.08 mrem/y        9.76 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 transport. A more realistic and less conservative environmental pathway analysis would consider these effects.
 
MYAPC License Termination Plan                                                                Page 6-46 Revision 3 October 15, 2002 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 2-11 The DCGL for areas outside the RA is 4.2 pCi/g. This DCGL can be            l calculated most directly by the ratio to the 3.2 pCi/g Cs-137 DCGL provided in LTP Table        l 6-11, recognizing that the dose from 3.2 pCi/g is 7.52 mrem/yr. This calculation is provided    l below:                                                                                          l l
4.2 pCi/g = (3.2 pCi/g) (10.00 mrem/yr)                                                l (7.52 mrem/yr)                                                l 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 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
 
MYAPC License Termination Plan                                                                Page 6-47 Revision 3 October 15, 2002 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 special areas differs from the other the l basement surfaces (see Table 2-8). Therefore, a separate mixture is applied to the dose assessment for the special areas, resulting in a different DCGL for the special l areas. The DCGL selected for the special areas resulted in a lower dose than that    l 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 special areas mixture.                        l
 
MYAPC License Termination Plan                                                                Page 6-48 Revision 3 October 15, 2002 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.
During final survey, and in the final site dose assessment, the non-gamma emitting radionuclides (HTD nuclides) will be accounted for using Cs-137 as a surrogate as      l described in Equation 17 (from NUREG-1505, Page 11-2, Equation 11-4). The              l contribution from soil HTD radionuclides will be calculated using the radionuclide      l fractions listed in Table 2-11. Cs-137 was selected as the surrogate since it is the    l predominant radionuclide in soil (i.e., 89%) and since many of the soil samples will    l not result in positively detected Co-60. As seen of page 5 of Attachment 6-13, the      l dose contribution from the HTD radionuclides in soil (Ni-63 and H-3) is less than 1%    l of the Cs-137 dose. Therefore, the effect of the surrogate calculation on the Cs-137 DCGLw value will be minimal.
To calculate the surrogate Cs-137 DCGL, the following equation is used:                l
 
MYAPC License Termination Plan                                                                Page 6-49 Revision 3 October 15, 2002 1
CS  137 s =
1 R2 R3          R
                                                +    +    + ...+ n D1 D2 D3          Dn                              (17)      l Where:Cs-137s is the surrogate Cs-137 DCGLw;                              l D1 is the DCGL for Cs-137;                                          l Rn is the ratio of the HTD radionuclide mixture fraction to the Cs- l 137 mixture fraction; and                                          l Dn is the DCGLw of the HTD radionuclide corresponding to 10        l mrem/yr. The DCGLs are calculated by inverting the Unitized        l Dose Factors Listed in the LTP, Table 6-7, and multiplying by 10. l 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 in NUREG-1505, Chapter          l
: 11.                                                                                      l Before applying the unity rule, the DCGLs, for areas inside the RA, will be adjusted      l to represent the Table 6-11 total surface soil dose, as opposed to 10 mrem/yr. As seen    l in Table 6-11, the dose from surface soil is limited because of the additional dose      l from the other contaminated materials on the site. The unity rule calculation will limit  l the surface soil dose by multiplying the Cs-137S and Co-60 DCGLs corresponding to        l 10 mrem/yr by a factor equal to the Table 6-11 total surface soil dose value divided by  l 10 mrem/yr. If the dose contribution from surface soil changes in the future, the        l multiplication factor will change accordingly.                                            l l
In order to demonstrate compliance with the surface soil DCGL, the gamma                  l spectroscopy results for each soil sample will be converted to a unity rule equivalent    l using the Table 6-11 surface soil DCGLs in the following equation. After this            l conversion, the DCGL becomes a unitless value of 1.0 that is equivalent to the total      l surface soil dose shown in Table 6-11. If the dose contribution from surface soil        l changes in the future, the dose corresponding to a unity rule equivalent of 1.0 will      l change accordingly. The unity rule equivalent is calculated per the following            l equation:                                                                                l
 
MYAPC License Termination Plan                                                                  Page 6-50 Revision 3 October 15, 2002 Cs -137          Co  60              RN Unity Rule Equivalent  1 =                      +              + ...+
DCGL(Cs-137S ) DCGL(Co 60A )        DCGL(N A )
Where: Cs-137 and Co-60 are the gamma spec results,                          l DCGL(Cs137S ) is the surrogate Cs-137S DCGL,                        l adjusted to represent the Table 6-11 total surface  l soil dose, as applicable (inside RA)                  l DCGL(Co60A )  is the Co-60 DCGL adjusted to                        l represent the Table 6-11 total surface soil dose, as l applicable (inside RA)                                l l
RN is any other identified gamma emitting radionuclides, and          l DCGL(N A ) is the adjusted DCGL for radionuclide N.                  l l
Absent sample-specific information from the final survey, using the radionuclide          l 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.
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.
 
MYAPC License Termination Plan                                                                  Page 6-51 Revision 3 October 15, 2002 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.
Buried Piping The buried piping 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.
Embedded Piping                                                                          l l
The embedded piping planned to remain after decommissioning has a total internal        l surface area of 154.3 m2. The Spray Building contains 26.5 m2 of embedded                l containment spray pump piping surface area with the remaining 127.8 m2 located in        l the Containment, Spray Building PAB, and Fuel buildings.                                l l
Remediation performed to date on the Spray Building embedded piping has been            l extensive. Numerous sections of Ric-Wil piping (pipes within a pipe), most less that 5  l feet long, that were contained in the concrete walls of the Spray building have been    l removed. Additionally, two Containment Spray Supply lines were removed by                l cutting 24- inch diameter cores through five feet of concrete. The cost was              l approximately $30,000.                                                                  l l
The longest run of Spray building piping that remains is approximately 70 linear feet    l of 16 inch diameter, stainless steel Containment Spray Pump lines (CS-M-91, 92).        l The two pipes, which are 15 feet apart and cross- connected, extend from the lower      l
 
MYAPC License Termination Plan                                                                  Page 6-52 Revision 3 October 15, 2002 level of the Spray building (at El.-14'9") to the safeguards sump (El.-4') in            l containment and are embedded in over 10 vertical feet and 16 horizontal feet of          l concrete.                                                                                l l
An extensive effort to chemically decontaminate the containment spray pump piping        l occurred in June 2002. A caustic chemical, which has been successfully used in other      l facilities, was applied to the piping in four separate applications over a total of 74    l hours. Although several sections of the vertical piping were decontaminated to            l relatively low levels, the majority of piping still contains residual contamination at an l average level of ranging from 1E+04 dpm/100 cm2 to about 1.5E+05 dpm/100 cm2.            l The maximum level encountered based on remediation surveys to date is about 4E+05        l dpm/100 cm2. The cost of this project was on the order of $200,000.                      l l
The decontamination factors (ratio of before and after contamination levels) were        l high initially (up to 104). However, the decontamination factors were low for the        l fourth chemical decontamination effort (as low as 1). Further chemical                    l decontamination is not expected to be effective. The only remaining alternative is        l removal and disposal as LLRW waste. Estimates to remove the spray building                l embedded piping range from about $200,00 to $285,000, excluding disposal costs            l which, for the large volume of concrete required to be removed, are approximately        l
                $150,000-175,000.                                                                        l l
Assuming that residual contamination were present at an average level of 8E+05            l dpm/100 cm2 in the 26.5 m2 of spray pump piping, the resident farmer dose                l contribution would be approximately 0.085 mrem/yr. The 8E+05 dpm/100 cm2 value            l was selected to represent the upper range of the average contamination level.            l l
Based on the total projected costs for removal and disposal of the spray pump piping      l of at least $350,000, the cost per person-rem would be over $4,000,000 per person-        l rem. This is far in excess of the NRC ALARA criteria of $2000 per person-rem listed      l in NUREG-1727. Therefore, additional decontamination is not justified.                    l l
Maine Yankee has evaluated the contamination potential of the embedded piping in          l the Containment, PAB, and Fuel building and does not believe the levels of                l contamination found in the spray pump piping will be encountered in these buildings.      l Therefore, two different DCGLs will be used for embedded piping. The DCGL for            l the spray pump piping will be 800,000 dpm/100 cm2 and the DCGL for the rest of the        l embedded piping in the Spray Building, Containment, PAB, and Fuel buildings will          l be 100,000 dpm/100 cm2.                                                                  l l
The inventory for the dose assessment was calculated assuming that the spray pump        l piping (26.5 m2) is contaminated at 800,000 dpm/100 cm2 and that the remaining            l
 
MYAPC License Termination Plan                                                              Page 6-53 Revision 3 October 15, 2002 embedded piping (127.8 m2) is contaminated at 100,000 dpm/100 cm2. The entire          l inventory of embedded piping from all buildings was summed and assumed to be          l instantaneously released. The dose under these assumptions was calculated to be        l 0.136 mrem/yr.                                                                        l l
The assumption of instantaneous release is conservative since the spray pump          l embedded piping will be filled with cement grout.                                      l l
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 6-54 Revision 3 October 15, 2002 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 DCGLw. 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 (AF) for Surface Soil and Deep Soil                                    l Survey Unit = 10,000 m2 Area m2            1      2        4      6      8      16      25      50    100 500 1,000  10,000 Co-137 (AF)      11.9  6.7    4.1      3.2    2.8    2.0      1.7    1.5    1.3 1.2  1.1    1.0    l Cs-60 (AF)        12.7  7.2    4.4      3.1    2.9    2.1      1.8    1.5    1.2 1.2  1.1    1.0    l MY Mix (AF)*      12.0  6.8    4.1      3.2    2.8    2.0      1.8    1.5    1.3 1.2  1.1    1.0    l
* Where MY mix is the surface and deep soil radionuclide mixture.                          l
 
MYAPC License Termination Plan                                                              Page 6-55 Revision 3 October 15, 2002 6.8.3  Embedded Piping Area Factors                                                  l l
Since the dose model for embedded piping is the same as the basement fill model, the  l same area factor equation would apply.                                                l l
50 m 2 AF =                                                                        l elevated area l
An evaluation of contamination potential and remediation effectiveness in embedded    l piping concluded that area factors can be limited to 2.0. Area factors larger than 2.0 l can readily be justified on a dose basis using the above equation. However, a          l conservative application of ALARA was applied to limit the embedded piping area        l factor to 2.0                                                                          l l
The number of elevated areas in embedded piping will be limited to ensure that the    l source term inventory (and annual dose) relative to the selected DCGL(s) is not        l exceeded.                                                                              l l
6.8.4  Buried Piping Area Factors                                                    l l
Buried piping contributes less than one-tenth of one percent of the total dose to the  l resident farmer. The volume of piping expected to remain on site is 142.0 m3. The      l radioactive contaminants associated with buried pipe are considered to be excavated    l to the soil surface uniformly mixed in the top 0.15 m of soil. Under these conditions  l area factors for soil would apply.                                                    l l
The following equation calculates an area factor that is ALARA and conserves the      l survey unit total inventory. As a measure of conservatism, a limit of 10 is placed on  l area factors for buried piping. The DCGLEMC (the DCGL used for the elevated            l measurement criteria) is calculated using the same equation.                          l l
Buried Piping SurveyUnit Size(m 2 )
Area Factor =                                                                l Buried Piping Elevated Area (m2 )
l 2                                  2 For example, a 20 m survey unit containing a 1.0 m elevated area and using the        l DCGL of 9.50E+03 dpm/100 cm2 would result in an area factor (AF) of 20:                l l
20 m 2 Area Factor = 20 =                                                            l
                                              . m2 10
 
MYAPC License Termination Plan                                                                Page 6-56 Revision 3 October 15, 2002 The AF would be limited to 10 as stated above so the allowable activity in the          l elevated area would be 9.50E+04 dpm/100 cm2. The DCGLEMC calculated by the              l equation would be 20 times the DCGL or 1.90E+05 dpm/100 cm2.                            l l
If the maximum concentration of the elevated area (i.e., 9.50E+04 dpm/100 cm2) were    l the only activity in the survey unit, the unity rule application would be as follows:  l l
dpm 9.50 E + 04 100 cm2 Unity Rule =
dpm
                                                              = 0.5 which is < 10
                                                                                .                      l
                                            . E + 05 190 100 cm2 l
6.8.5  Activated Concrete/Rebar Area Factors                                          l l
The activated concrete/rebar conceptual model is conservatively treated in the same    l manner as the basement contamination model. Activated concrete includes the source      l term in the entire volume of activated concrete (surface and subsurface). As in the    l basement fill model the activated radionuclide inventory is assumed to be              l instantaneously released; however, the release of radionuclides for the activated      l concrete is expected to be significantly slower (more conservative) than the release of l radionuclides from structures surface contamination. Since the dose models are        l identical, the area factor for the Basement Fill Model (Section 6.8.1, equation 19 of  l the LTP) will be used for activated concrete.                                          l l
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.
NUREG-1727, NMSS Decommissioning Standard Review Plan, Appendix C, describes the justification necessary to allow direct use of these screening values.
When using the screening approach licensees need to demonstrate that the particular site conditions (e.g., physical and source term conditions) are compatible and consistent with the DandD model assumptions.
 
MYAPC License Termination Plan                                                                Page 6-57 Revision 3 October 15, 2002 The following site conditions are specified for use of the Standing Building screening values:
: 1. The contamination on building surfaces (e.g., walls, floors, ceilings) should be surficial and non-volumetric (e.e., less than 0.4 in (10 mm)).
: 2. Contamination on surfaces is mostly fixed (not loose), with the fraction of loose contamination not to exceed 10 percent of the total surface activity.
: 3. The screening criteria are not applied to surfaces such as buried structures (e.g., drainage or sewer pipes) or mobile equipment within the building; such structures and buried surfaces will be treated on a case-by-case basis.
The above conditions are satisfied for the Maine Yankee site.
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.
 
MYAPC License Termination Plan                                                                Page 6-58 Revision 3 October 15, 2002 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) 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 6-59 Revision 3 October 15, 2002 Table 6-14 Area Factors (AF) for Standing Buildings                                l (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 Cs-137 (AF)      23.5    12.6      7.1    4.3    2.8      1.9    1.6      1.2  1.0 ll Co-60 (AF)      23.5    12.6      7.1    4.3    2.8      1.9    1.6      1.2  1.0  ll MY Mix (AF)      23.5    12.6      7.1    4.3    2.8      1.9    1.6      1.2  1.0  ll
* Where MY mix is the Contaminated Concrete radionuclide mixture.                          l 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.
6.10.6    Maine Yankee Engineering Calculation, Diffuser and Forebay Dose                          l Assessment, EC-041-01 (MY), Revision 0.                                                  l
 
MYAPC License Termination Plan                        Attachment 6-2 Revision 3                                            Page 1 of 12 October 15, 2002 Attachment 6-2 BNL Kd Report for Fill
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Attachment 6-6 MYAPC License Termination Plan                              Page 1 of 2 Revision 3 October 15, 2002 Attachment 6-6 Activated Concrete Inventory
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MYAPC License Termination Plan                              Attachment 6-8 Revision 3                                                  Page 1 of 5 October 15, 2002 Attachment 6-8 Deep Soil Microshield Output
 
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MYAPC License Termination Plan                        Attachment 6-9 Revision 3                                            Page 1 of 26 October 15, 2002 Attachment 6-9 Deep Soil RESRAD Output
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MYAPC License Termination Plan                                                Attachment 6-10 Revision 3                                                                    Page 1 of 4 October 15, 2002 Attachment 6-10 Buried Piping List and Projected Concentration Calculation
 
MYAPC License Termination Plan                            Attachment 6-11 Revision 3 Page 1 of 38 October 15, 2002 Attachment 6-11 Buried Piping RESRAD Output
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MYAPC License Termination Plan                                  Attachment 6-12 Revision 3                                                      Page 1 of 7 October 15, 2002 Attachment 6-12 Buried Piping Microshield Output
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Attachment 6-13 Page 2 of 12 Table 6-11 Contaminated Material DCGL Refer to Section 6 for Table 6-11
 
Attachment 6-13 Page 4 of 12 ACTIVATED CONCRETE Key Parameters:
Porosity                              0.30                        Concrete Density                          2.20      g/cm3 3
Bulk Density                          1.50    g/cm                Annual Total Well Water Vol              738.0      m3 Yearly Drinking Water                478.0      L/yr              Irrigation Rate                          0.274    L/m2-d Wall Surface Area                    4182.0      m2                Surface Soil Depth                        0.15        m Fill Volume                          2460.0      m3                Activated Concrete Total Inventory      3.30E+08  Total pCi per pCi/g Surface Area/Open Volume              1.70    m2/m3              Activated Concrete Total Conc.            1.00      pCi/g Concrete Volume                        4.18      m3 DOSE CALCULATION FACTORS                    SOURCE TERM                            Kd          WATER, FILL, CONCRETE CONCENTRATION                ACTIVATED CONCRETE ANNUAL DOSE NUREG-1727  FGR 11  Microshield                                          Kd            Kd                                                          Drinking  Irrigation  Direct    Total Nuclide    mrem/y per  mrem/pCi  mrem/y per Nuclide    Inventory    Inventory      Fill    Concrete  Adsorption    Water          Fill  Concrete Nuclide  Water Dose    Dose      Dose    Dose pCi/g                pCi/g  Fraction      pCi/g        pCi      cm3/gm        cm3/gm    Factor      pCi/L        pCi/g    pCi/g            mrem/y    mrem/y      mrem/y  mrem/y Cs-134      4.39E+00  7.33E-05  6.09E-05  8.40E-03    8.40E-03    2.77E+06    7.91E+01      3.00E+00  3.96E+02  9.47E-03      7.49E-04 2.84E-05  Cs-134    3.32E-04  1.85E-05  4.56E-08 3.50E-04 Co-60      6.58E+00  2.69E-05  6.30E-04  4.00E-02    4.00E-02    1.32E+07    1.28E+02      1.00E+02  6.40E+02  2.79E-02      3.56E-03 2.79E-03  Co-60    3.59E-04  8.16E-05  2.25E-06 4.43E-04 C-14      2.08E+00  2.09E-06  0.00E+00  5.80E-02    5.80E-02    1.91E+07    5.00E+00      1.00E+02  2.72E+01  9.52E-01      4.76E-03 9.52E-02    C-14    9.51E-04  8.80E-04  0.00E+00 1.83E-03 Eu-154      3.13E+00  9.55E-06  3.10E-04  9.00E-03    9.00E-03    2.97E+06    4.00E+02      5.00E+03  2.06E+03  1.95E-03      7.80E-04 9.75E-03  Eu-154    8.90E-06  2.71E-06  2.42E-07 1.19E-05 Fe-55      2.50E-03  6.07E-07  0.00E+00  1.24E-01    1.24E-01    4.09E+07    2.50E+01      1.00E+02  1.27E+02  4.36E-01      1.09E-02 4.36E-02  Fe-55    1.26E-04  4.84E-07  0.00E+00 1.27E-04 H-3      2.27E-01  6.40E-08  0.00E+00  6.47E-01    6.47E-01    2.14E+08    0.00E+00      0.00E+00  1.00E+00  2.89E+02    0.00E+00  0.00E+00      H-3  8.84E-03  2.91E-02  0.00E+00 3.80E-02 Eu-152      2.87E+00  6.48E-06  2.09E-04  1.11E-01    1.11E-01    3.66E+07    4.00E+02      5.00E+03  2.06E+03  2.41E-02      9.62E-03 1.20E-01  Eu-152    7.45E-05  3.07E-05  2.01E-06 1.07E-04 Ni-63      1.19E-02  5.77E-07  0.00E+00  7.00E-03    7.00E-03    2.31E+06    1.28E+02      1.00E+02  6.40E+02  4.88E-03      6.24E-04 4.88E-04    Ni-63  1.35E-06  2.58E-08  0.00E+00 1.37E-06 SUM    1.07E-02  3.02E-02  4.54E-06 4.08E-02
 
Attachment 6-13 Page 7 of 12 BOP EMBEDDED PIPE Key Parameters:
Porosity                              0.30                          Concrete Density                        2.20        g/cm3 3
Bulk Density                          1.50      g/cm                Surface Soil Depth                      0.15          m Yearly Drinking Water                478.0      l/yr                Irrigation Rate                        0.274      L/m2-d Wall Surface Area                    4182.0      m2                  Annual Total Well Water Vol              738          m3 3
Fill Volume                          2460.0      m                  Embedded Pipe Conversion Factor        5754.5    pCi per dpm/100 cm2 2  3 Surface Area/Open Volume              1.70      m /m                Gross Beta DCGL                      1.00E+05  dpm/100 cm2 3
Concrete Volume                        4.18      m                  Gross Beta Nuclide Fraction            0.616 Total Inventory                      1.62E+05  dpm/100 cm2 DOSE CALCULATION FACTORS                    SOURCE TERM                          Kd            WATER, FILL, CONCRETE CONCENTRATION                EMBEDDED PIPE ANNUAL DOSE NUREG-1727  FGR 11    Microshield                                          Kd          Kd                                                          Drinking  Irrigation    Direct    Total Nuclide    mrem/y per mrem/pCi  mrem/y per              Inventory    Inventory        Fill    Concrete Adsorption      Water        Fill  Concrete  Nuclide Water Dose    Dose        Dose    Dose pCi/g              pCi/g    Fraction  dpm/100 cm2      pCi        cm3/gm      cm3/gm    Factor        pCi/L      pCi/g    pCi/g            mrem/y    mrem/y      mrem/y  mrem/y Sr-90      1.47E+01  1.42E-04  0.00E+00  2.80E-03    4.55E+02    2.62E+06    6.02E+01    1.00E+00  3.01E+02    1.18E-02    7.07E-04 1.18E-05  Sr-90    7.98E-04  7.68E-05  0.00E+00  8.75E-04 Cs-134      4.39E+00  7.33E-05  6.09E-05  4.55E-03    7.38E+02    4.25E+06    7.91E+01    3.00E+00  3.96E+02    1.45E-02    1.15E-03 4.36E-05 Cs-134    5.09E-04  2.83E-05    6.99E-08 5.37E-04 Cs-137      2.27E+00  5.00E-05  1.20E-05  5.50E-01    8.93E+04    5.14E+08    7.91E+01    3.00E+00  3.96E+02    1.76E+00    1.39E-01 5.27E-03 Cs-137    4.20E-02  1.77E-03    1.67E-06 4.38E-02 Co-60      6.58E+00  2.69E-05  6.30E-04  5.84E-02    9.48E+03    5.46E+07    1.28E+02    1.00E+02  6.40E+02    1.15E-01    1.47E-02 1.15E-02 Co-60    1.48E-03  3.37E-04    9.29E-06 1.83E-03 Co-57      1.67E-01 1.18E-06  2.80E-08  3.06E-04    4.97E+01    2.86E+05    1.28E+02    1.00E+02  6.40E+02    6.05E-04    7.73E-05 6.05E-05 Co-57    3.41E-07  4.49E-08    2.16E-12 3.86E-07 Fe-55      2.50E-03 6.07E-07  0.00E+00  4.81E-03    7.82E+02    4.50E+06    2.50E+01    1.00E+02  1.27E+02    4.79E-02    1.20E-03 4.79E-03 Fe-55    1.39E-05  5.32E-08  0.00E+00  1.39E-05 H-3        2.27E-01 6.40E-08  0.00E+00  2.36E-02    3.82E+03    2.20E+07    0.00E+00    0.00E+00  1.00E+00    2.98E+01    0.00E+00 0.00E+00  H-3    9.10E-04  3.00E-03  0.00E+00  3.91E-03 Ni-63      1.19E-02 5.77E-07  0.00E+00  3.55E-01    5.77E+04    3.32E+08    1.28E+02    1.00E+02  6.40E+02    7.01E-01    8.96E-02 7.01E-02  Ni-63    1.93E-04  3.71E-06  0.00E+00  1.97E-04 SUM  4.59E-02  5.22E-03    1.10E-05 5.11E-02
 
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Latest revision as of 15:23, 16 January 2025

Maine Yankees License Termination Plan, Section 6, Table of Contents - Attachment 6-19
ML022970089
Person / Time
Site: Maine Yankee
Issue date: 10/15/2002
From:
Maine Yankee Atomic Power Co
To:
NRC/FSME
References
+sisprbs20060109, -nr, -RFPFR
Download: ML022970089 (302)
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