Isotopic dilution model for 36Cl in the French landscape

Chlorine-36 is one of the most critical radionuclides to consider in intermediate- and high-level nuclear waste management. Special attributes are long half-life, high mobility, biologically essential element, and massive isotopic dilution in the geosphere and biosphere. A model was developed to predict the radiological consequences of 36Cl to human dose receptors. The approach had three parts, a literature and benchmarking review of other 36Cl models and programs, the development of a 36Cl model suitable for ANDRA applications within Aquabios, and the measurement of stable Cl concentrations and parameter values in the relevant landscape. A major issue was to resolve the degree to which specific activity relationships were useful. Soil-to-plant and aquatic food pathways were modeled using specific activity relationships. For subsequent transfers, the model used more traditional transfer factors. The use of the partial specific activity model simplified the problem and made the model and parameters more general. This is especially relevant for transfers of 36Cl because the concentrations of stable Cl in the environment can vary substantially as a result of oceanic effects and local mineralizations. The preliminary field study confirmed some of the key parameters to add confidence to the chosen parameter values and their ranges.