Quantitative evaluation of tritium transfer in the ground surface

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The purpose of this study is to develop and validate a numerical model of tritium transfer in the environment by carrying out laboratory experiments of hydrogen isotopic gas oxidation by soil and measurements of tritium transfer in the environment.Theoretical study showed that the tritium deposition process can be divided into three elemental processes of the atmospheric diffusion, the in-soil diffusion and the oxidation by microorganisms in soil, for each of which a conceptual model was developed. A one-dimensional multi-layer numerical model was developed and validated by using observation data on water vapor and carbon dioxide fluxes.Dependency of hydrogen isotopic gas oxidation rate on concentration, temperature, soil moisture and soil type was quantitatively evaluated by laboratory experiments. The oxidation rate had the maximum value at the water content of 8 to 14 w % and 45 ℃. It was also found that the oxidation rate and the Michaelis constant can be expressed Arrhenium formul … More a well and the oxidation rate did not largely differ between soil types of andosol and alluvial soil.The numerical model with these experimental results adopted was validated with the experimental data from Chalk River field tritium release experiment. Numerical experiments with this model illustrated the following characteristics of tritium deposition; 1) The HT deposition is mainly controlled by the diffusion and oxidation processes in soil. 2) The deposition velocity tends to have maximum values of about 0.2 to 0.4 mm s^<-1> at the volumetric water content of about 0.1. 3) Although the deposition velocity has a maximum value at around 45 ℃, the dependency on temperature is relatively small. These comprehensive results were compiled in such a way that they can easily be utilized in safety analyses.A method was developed to determine chemical forms of tritium in gaseous effluent from a facility separately. This method was applied to a existing facility to evaluate the ratio of tritiated hydrogen to total tritium in gaseous effluent from a stack of a spent fuel reprocessing plant. A series of experiments of rice plant exposure to deuterated water were carried out to evaluate tritium transfer to agricultural products. Deuterium transfer characteristics, such as that OBD in grain at harvest showed the highest value when the exposure was in the early stage of the ripening period, were found Less