Quantitative evaluation of tritium transfer in the ground surface

本研究的目的是通过开展土壤氢同位素气体氧化实验和环境中氚迁移的测量，建立和验证氚在环境中迁移的数值模型。理论研究表明，氚沉积过程可以分为大气扩散、土壤内扩散和土壤微生物氧化三个基本过程，每个过程都建立了概念模型。利用水汽和二氧化碳通量观测数据，建立了一维多层数值模型并进行了验证，通过室内实验定量评价了氢同位素气体氧化速率对浓度、温度、土壤湿度和土壤类型的依赖关系。氧化速率在含水率为8~14w%、45℃时有极大值。氧化速率和米氏常数可用Arrhenium formul…表示此外，红壤和冲积土土壤类型之间的氧化速率没有太大差异。采用这些实验结果的数值模型用白垩河现场氚释放实验数据进行了验证。用该模型进行的数值实验表明，氚的沉积特征如下：1)高温的沉积主要受土壤中的扩散和氧化过程控制。2)在体积含水率约为0.1时，沉积速度趋于最大值，约为0.2~0.4 mm S^-1；3)虽然沉积速度在45℃左右有一个最大值，但对温度的依赖性相对较小。这些综合结果的汇编方式使其可以方便地用于安全分析。开发了一种单独确定设施气体流出物中氚的化学形态的方法。该方法被应用于现有的设施，以评估从乏燃料后处理厂的烟囱中排出的气体中氚氢与总氚的比率。为评价氚在农产品中的迁移，进行了一系列的水稻植株氚暴露实验。氚的转移特性，如收获时籽粒中的脱氢脱氧核糖核酸(OBD)在成熟早期暴露时表现出最高值，被发现较少。

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