Abstract
It is important to evaluate sorption ability of cementitious materials to enclose radionuclides therein in waste repository. The cementitious material will be neutralized by interaction with CO2 in air and HCO3 in groundwater and this neutralization is supposed to have an effect on the sorption ability of the materials. Therefore, it is necessary to clarify this effect of degraded cement by neutralization.
The behaviors of 239Pu(IV) and 237Np(V) in a highly alkaline groundwater solution contacting with cement and also their sorption on degraded neutralized cement paste were studied by batch method.
It was found that Kd values of 237Np(V) or 239Pu(IV) on non-neutralized cement were as large as over 105 ml/g. The values gradually decreased with decreasing pH of the solution following neutralization of the cement paste. At pH 10, the Kd values of 239Pu(IV) and 237Np(V) remained in the order of 104 and 103 ml/g, respectively, and chemical barrier ability was still large. Chemical behaviors of 237Np(V) were also studied by spectroscopic method and particle size measurement. A shift of absorption peak was found and colloidal 237Np(V) was observed to be formed in solution contacting with cement. Colloidal 237Np(V) would be filtrated by cementitious materials in a repository.
For the performance assessment of artificial barriers, it is necessary to take into account that chemical atmosphere in near field is affected by neutralization of cementitious materials, which will occur over a very long period.
