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 Reac tor and Nuclear Fuel Development Corporation (PNC)) has published the secon d progress report for high-level radioactive waste (HLW) disposal in Japan (H12 report) in November, 1999. This report is important to obtain the conf idence of HLW disposal system and to establish the implementation body in 2 000. JNC has developed databases of glass dissolution and radionuclide migr ation for performance analysis of the engineered barrier system (EBS) and t he 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 reposi tory conditions, reducing conditions and compacted/intact system, e.g., act inide (IV)/(III), derivation of sorption coefficients from diffusion experi ments rather than batch sorption experiments. The JNC-TDB and sorption data base have been developed under the auspices of international experts. The q uality of these databases has been checked through independent individual e xperiments, glass leaching, solubility, batch sorption, diffusion experimen ts and through coupled leaching experiments by using the fully high-level r adioactive glass and plutonium-doped glass which were sandwiched between co mpacted bentonite saturated with water. The maximum concentration of insolu ble elements dissolved from the glass has also been investigated to check t he quality of the JNC-TDB by comparison with solubility prediction. Based o n these studies. JNC has determined the transport parameters for H12 report : dissolution rate of glass for a soluble radioactive element (Cs). solubil ity for insoluble radioactive elements (e.g., actinides. Tc), distribution coefficients and effective diffusion coefficients in the EBS and the geosph ere. (C) 2001 Elsevier Science B.V. All rights reserved.