Development of a Biosphere Dose Model (BDOSE) for Waste Incidental-to- Reprocessing and Non-High-Level Waste Determination Consultations J.W. Mancillas, A.A. Simpkins, L.D. Howard, P.A. LaPlante, O. Pensado (Center for Nuclear Waste Regulatory Analyses, San Antonio, Texas); A. Turner Gray (U.S. Nuclear Regulatory Commission, Washington, DC) ABSTRACT: A radiological dose model has been developed in the GoldSim (registered trademark of GoldSim Technology Group, LLC ) modeling environment to be used as a tool for U.S. Nuclear Regulatory Commission (NRC) and the Center for Nuclear Waste Regulatory Analyses (CNWRA) staffs to review U.S. Department of Energy (DOE) non-high-level waste determinations for compliance with the appropriate performance objectives. The model uses a groundwater source to probabilistically evaluate radionuclide partitioning into intake pathways and evaluates dose histories for multiple receptor groups. Exposure pathways include direct exposure, inhalation, and ingestion. This model was constructed using basic GoldSim elements and elements of the Contaminant Transport (CT) module. Model development was funded by the NRC to support the requirement of the Ronald W. Reagan National Defense Authorization Act (NDAA) for Fiscal Year 2005 that the NRC consult on non-high-level waste determinations prepared by the DOE for sites in South Carolina and Idaho. Leaching constant Erosion constant PR = Precipitation rate [m/m 2 -yr ] IR = Irrigation Rate [m/m 2 -yr ] ER = Evapotranspiration rate [ m/m 2 -yr ] Θ = Volumetric water content of soil [Unitless] ρ = Soil density [Kg/m 3 ] d = Soil depth [m] Kd i = Soil-liquid partition coefficient of RN i [m 3 /Kg] ELR= Erosion rate [Kg/m 2 -yr] C gw,I = Concentration of RN i in groundwater [g/m 3 ] Pathways Resident Farmer Resident GardenerRecreationist Acute Intruder Chronic Intruder Ingestion Ingestion of Drinking WaterXX X Ingestion of VegetablesXX X Ingestion of MilkX X Ingestion of BeefX X Ingestion of GameX X Ingestion of FishXXX X Ingestion of SoilXXXXX InhalationXXXXX External SurfaceXXXXX Submersion in AirXXXXX Submersion in Water X Introduction: The Ronald W. Reagan National Defense Authorization Act (NDAA) for Fiscal Year 2005 provides for the US Nuclear Regulatory Commission (NRC) to consult on non-high-level waste determinations prepared by the US Department of Energy (DOE) for cleanup of facilities in Idaho and South Carolina The purpose of these consultations is to ensure performance objectives established in 10 CFR Part 61, Subpart C (dose-based performance objectives) are met. To understand key uncertainties and to evaluate whether these performance objectives are met, NRC staff may choose to perform limited confirmatory calculations using probabilistic performance assessment analyses developed in the GoldSim modeling environment. Because it is expected that the NRC will be involved in the evaluation of multiple site locations, such as those with unique source terms, ground water transport characteristics, and exposure environment and populations, the NRC is seeking ways to improve staff efficiency in the model development and review process. To aid the NRC in meeting the requirements of NDAA, CNWRA staff have developed a compact biosphere module which can be readily inserted into a performance assessment model to probabilistically evaluate dose consequences to resident receptors based on groundwater radionuclide (RN) concentrations and potential intruder scenarios. The development and use of a reusable robust biosphere module provides multiple benefits: (1) Reduces the time required for model development by allowing model developers to focus attention on site specific data rather than repeatedly develop biosphere models for individual performance assessment models; (2) Use of generic model components developed under approved quality assurance procedures, including documented validation testing, increases the confidence in the total performance assessment analysis; (3) The use of a single, well-documented biosphere module increases model transparency, thereby increasing consistency of reviews and reducing review time for model developers, site regulators, and affected stakeholders. BDOSE: BDOSE is a compact biosphere model developed for use as either a standalone module or use in performance models to stochastically evaluate dose consequences from radionuclides introduced into a biosphere via groundwater transport. BDOSE currently evaluates dose consequences for 49 radionuclides for multiple receptor groups. Receptors: BDOSE evaluates dose consequences for several site specific receptors. Three receptors types are defined within BDOSE: residents, either farmer or gardener, recreationists, and intruders, chronic and acute. Doses to respective receptors are evaluated for inhalation, ingestion and direct exposure pathways with considerations of receptor consumption rates, inhalation rates and exposure times. Within BDOSE individual receptor pathways are established by selecting to include or exclude possible pathways in a defined Pathway vector that defines a receptor. This selection is a simple operation of either selecting 1 or 0 within the vector. Potential pathway doses are stochastically evaluated for each receptor type and pathway based on user defined ingestion, inhalation rates and exposure time distributions. Each of these calculations generates a result that is stored in the DOSE_PATHWAYS matrix, which is defined as a [Species, Pathways] matrix. The dose to a receptor is evaluated by a simple matrix vector operation, where a receptor dose is the vector sum of the DOSE_PATHWAYS matrix multiplied by the receptor vector and an individual radionuclide dose from a specific pathway is evaluated by the multiplication of the DOSE_PATHWAYS matrix by the pathway vector and a defined RN vector. This type of data management and use of vector definitions for the receptors provides a robust and flexible means to evaluate dose consequences for receptors whose pathway definitions may change from site to site. The use of alternative dose coefficients (ICRP72 or FG11) for internal radionuclide dose calculations. The time for loss of institutional controls. Controls for manually defined sources (decay/no decay within source). The model use to evaluate soil concentrations. The exposure to various sources of contaminated water (ponds, streams, and groundwater). The receptor pathway definitions. Results: Using result elements, BDOSE generates graphical results for each receptor type. These results include time history statistical evaluations of multiple realizations and the mean dose for each radionuclide. In addition to these basic results, total receptor doses by pathway and receptor radionuclide doses by pathway are provided. In addition to dose histories, BDOSE provides time history results for sources, groundwater concentration, soil concentration, and air concentrations. Biosphere -- Soil: BDOSE is supplied with seven soil models that can be used to evaluate radionuclide buildup in the soil from irrigation with contaminated groundwater. These multiple models provide various considerations for deposition processes (irrigation and ingrowth) and removal processes (decay, soil erosion, and leaching into deep soil). Simple soil: (soil concentration = IR* C gw i ) no buildup, decay, ingrowth, erosion or leaching. Annual soil: Model includes partitioning of RN from groundwater to soil, soil erosion, deep leaching and RN decay. But only applied for the given year, with no ingrowth. Annual soil equilibrium: Model includes partitioning of RN from groundwater to soil, soil erosion, deep leaching, and RN decay. Annual soil buildup: Model includes partitioning of RN from groundwater to soil, soil erosion, deep leaching and RN decay. In this model, the soil evaluates RN buildup based on the continued irrigation of the soil with the contaminated groundwater to the equilibrium value. Physical soil: Model uses the physical descriptions of the soil environment (soil KD, soil density, water content of soil, plow depth, erosion rate, irrigation rate, precipitation rate, and evaporation rate) to evaluate the buildup of radionuclides in the soil (grams per square meter) using a GoldSim cell element. Analytic soil: Similar to the physical soil model, except that each RN is partitioned into a single GoldSim cell for decay, ingrowth, leaching, and erosion evaluation. User defined: Soil concentration can be set to a fixed concentration. Biosphere -- Animal Products: BDOSE evaluates radionuclide concentrations for several animal products including: Beef, Milk, Poultry, Eggs, Fish and Game. These concentrations are based on animal-specific-grain contamination and consumption rates, water contamination and consumption rates, soil concentration and consumptions rates and RN transfer coefficients. RN concentrations in animal products are evaluated for both the resident scenario, in which the biosphere contamination is from contaminated groundwater, and the intruder scenario in which soil and crops have been contaminated by direct deposition of radioactive waste from materials excavated by a site intruder. Biosphere -- Vegetation: BDOSE evaluates RN concentrations for multiple vegetation types, including those used for human consumption (Vegetables, Leafy Green Vegetables, Fruits and Grains), and those used for animal feed( animal specific grains and fodders). These concentrations are based on soil contamination levels and irrigation water contamination levels and vegetation specific irrigation rates, growth rates and durations, vegetation yields (kg/m 2 ), root uptake coefficients, fractions of uptake from air deposition, translocation factors, and transfer factors. Radionuclide concentrations in vegetation are evaluated for both the resident scenario, in which the biosphere contamination is from contaminated groundwater, and the intruder scenario in which soil and crops have been contaminated by direct deposition of radioactive waste from materials excavated by a site intruder. Grain Module Statistical Analysis of Dose Results Dose Results by Radionuclide Receptor Pathway Definitions H3 C14 Co60 Ni59 Ni63 Se79 Sr90 Y90 Nb94 Tc99 I129 Cs137 Ba137m Eu152 Eu154 Eu155 Pb210 Ra226 Ra228 Ac227 Th228 Th229 Th230 Th232 Pa231 U232 U233 U234 U235 U236 U238 Np237 Pu238 Pu239 Pu240 Pu241 Pu242 Pu244 Am241 Am242m Am243 Cm242 Cm243 Cm244 Cm245 Cm246 Cm247 Cm248 Cf249 Radionuclide List Biosphere Radionuclide transport diagram Biosphere Module This poster was prepared to document work performed by the CNWRA for NRC under Contract No. NRC–02–02–012. The activities reported here were performed on behalf of the Office of Federal and State Materials and Environmental Management Programs. This poster is an independent product of CNWRA and does not necessarily reflect the views of NRC. Groundwater Source Module Decay constant Pathway Module Pathway Vector This centralization of controls facilitates easier model manipulation, while minimizing inadvertent alteration of other model components Controls: Key biosphere model settings within BODSE are controlled by switch elements that are centrally located in a single Controls module. Switches and data elements were included to allow the user to control: Crops Module Livestock Module