Development of database system for performance assessment (III)

Ueta, Shinzo*; Kato, Hiroyasu*; Kurosawa, Susumu*; Nakazawa, Toshiyuki*

JNC is preparing the second Performance Assessment Report for high level waste disposal. This research was carried out to prepare the database and assessment model for nuclide migration analysis for the report. The main results are as follows. (1)Quality assurance of nuclide migration database. Thermodynamic database for formation and complexation of 21 elements was developed. International researchers reviewed the database. The review comments, for example the analogousness of actinide elements, were reflected on the database. (2)Modeling study for bentonite porewater chemistry. The porewater chemistry was modeled with ion exchange reaction and surface complexation reaction. The predicted chemistry was compared with the empirical data. (3)Modeling study for nuclide sorption. The sorptivity of Cs, Ra/Sr, Pb, Ni, Am was modeled with ion exchange reaction and surface complexation reaction. The predicted sorptivity was compared with the empirical data and showed the good agreements. (4)Data acquisition for reliable assessment. Hydraulic tests and colloid transport tests with altered bentonite, nuclide diffusion experiments with bentonite and sorption experiments with rocks and bentonite were carried out. The hydraulic conductivity of the altered bentonite was 1.35.110m/s, the apparent diffusivities of the actinide elements were in the range of 1010m/s, and distribution coefficients of Sm were approximately 6 m/kg. (5)Evaluation of colloidal effect on nuclide migration. An evaluation of validity of analytical model for nuclide migration under existence of colloids (Hwang's model), and an analysis of nuclide migration including colloids filtration effect were carried out. As a result, it was indicated that a concept of the Hwang's model were appropriate, and it was suggested that nuclide migration was retarded by colloids filtration.