Migration analysis of Ra with distribution model

Yoshida, Yasushi*; Yoshikawa, Hideki

Distribution model were established to estimate an effect of substitution reaction of Ra in calcite. To apply this model, number of reactive layers is required. It was reported to be 21 based on an experimental results. In the present study, distribution coefficient for substitution reaction (Kcp) for pore water of H-12 were estimated and release rate of 4n+2 series nuclide was calculated. Values of Kcp for types of pore water were estimated with mole amount of Ca in solid phase and solution and partition coefficient. Estimated Kcp are smaller than Kd of Ra in bentonite. Kd is empirical parameter shows all distribution reactions, including the effect of Kcp. Therefore, Kd Kcp is reasonable. It was assumed that Kd included an effect of substitution reaction. As a result, similar trend of Th was shown for Ra. Half life of Ra (T1/2=1600 years) is significantly short and therefore behavior of it depends on radiation equilibrium with Th (T1/2=770000 years).