Study on the distribution coefficient for evaluation of neptunium migration in loess media. Cooperative research program on field migration test between CIRP and JAERI

We have performed adsorption experiments of 237Np onto the loess by a batch system, migration experiments of 237Np through the loess media by a column system, and migration tests of 237Np through natural loess media in the field test site of CIRP, Shanxi, China. The valid distribution coefficient (Kd) value was determined on the basis of the 237Np concentration in both the static batch and the dynamic column experiments. An adsorption ratio corresponding to the 237Np concentration at the peak position of the 237Np migration through the column was calculated the adsorption isotherm. The apparent Kd calculated was in well agreement with the Kd value estimated from the migration behavior of 237Np in the migration system. The valid Kd value of 237Np, of which specific activity is very low due to a long half-life, can be determined in the batch and column systems. Applicability of the Kd determined by the batch system in to the evaluation of radionuclide migration was confirmed through analyses of the result obtained from the 237Np migration test in natural loess media. (author)