Development on coprecipitation model of Ra for radionuclide migration analysis

Yoshida, Yasushi*; Yoshikawa, Hideki

A concentration of Ra limited by coprecipitation with calcite used to be estimated by a model of distribution assuming that constant mol ratio of Ra/Ca is preserved in solid and liquid phase. According to experiments, it has been revealed that mol ratio of Ra/Ca in solid differs from that in liquid. This difference was evaluated by a partition coefficient(D). In this study, a partition model was established to evaluate an effect of coprecipitation of Ra in calcite with D. In the model, D was converted to a distribution coefficient(Kcp) and the effect of incorporation of Ra was examined. As an example, this model was adopted under a condition of FRHP porewater and a converted Kcp was conducted. Release rates of 4n+2 series nuclides from engineered barrier with this model were also calculated. As a result of calculation, release rate of Ra was largest in their series on an outer surface of engineered barrier. This release rate was more than one order magnitude lower than that of Cs.