2025 Volume 32 Issue 1 Pages 10-22
In nuclide migration analyses for the safety assessments of geological disposal, when there is not necessarily sufficient confidence knowledge and data required for modeling phenomena, analyses are conducted using sufficiently conservative depending on the reliability of the technical basis, such as selecting data settings and modeling that yield severe results. There is a high level of uncertainty for setting a parameter value of dispersion length used for the nuclide migration analysis, due to the difficulty in measuring field scale data. However, the effects of fluctuation of dispersion length on maximum nuclide release rate has not yet been fully understood. In this study, the effect of fluctuation of dispersion length on maximum nuclide release rate was investigated. Specifically, a series of the sensitivity analysis focusing on not only the effect of fluctuation of dispersion length but also the effect of parameters related to the retardation effect such as distribution coefficient and half-life of nuclides was performed for fracture medium. As a result, it was suggested the maximum nuclide release rate may increase due to the shortened nuclide transit time as the dispersion length increases. When peak of the nuclide release rate is less than the half-life of the nuclide, the increase of the maximum release rate due to an increase in the dispersion length remains limited to a few times. On the other hand, in case of exceeding half-life, the maximum nuclide release rate increases ten times or more as the maximum release rate occurrence time of the release rate decreases. These findings would contribute to setting the conservative value of dispersion length taking the uncertainty into consideration.
