Database development of glass dissolution and radionuclide migration for performance analysis of HLW repository in Japan

Japan Nuclear Cycle Development Institute (JNC, the successor of Power Reactor and Nuclear Fuel Development Corporation (PNC)) has published the second progress report for high-level radioactive waste (HLW) disposal in Japan (H12 report) in November, 1999. This report is important to obtain the confidence of HLW disposal system and to establish the implementation body in 2000. JNC has developed databases of glass dissolution and radionuclide migration for performance analysis of the engineered barrier system (EBS) and the geosphere for H12 report. The databases developed for H12 report are of dissolution rates of high-level radioactive vitrified waste, thermochemical data of radioactive elements (JNC-TDB), sorption/diffusion data in the EBS and the geosphere. The database development has been focused on the repository conditions; reducing conditions and compacted/intact system, e.g., actinide (IV)/(III), derivation of sorption coefficients from diffusion experiments rather than batch sorption experiments. The JNC-TDB and sorption database have been developed under the auspices of international experts. The quality of these databases has been checked through independent individual experiments; glass leaching, solubility, batch sorption, diffusion experiments and through coupled leaching experiments by using the fully high-level radioactive glass and plutonium-doped glass which were sandwiched between compacted bentonite saturated with water. The maximum concentration of insoluble elements dissolved from the glass has also been investigated to check the quality of the JNC-TDB by comparison with solubility prediction. Based on these studies, JNC has determined the transport parameters for H12 report; dissolution rate of glass for a soluble radioactive element (Cs), solubility for insoluble radioactive elements (e.g., actinides, Tc), distribution coefficients and effective diffusion coefficients in the EBS and the geosphere.