Uncertainty analysis of solubility for selenium and neptunium by Monte Carlo simulation of geochemical modeling code

Takeda, Seiji ; Kimura, Hideo

Solubility of radioactive element in waste glass is a key parameter for safety assessment of geologic disposal of radioactive waste. JAEA has developed the probabilistic analysis code of uncertainty of solubility limit for radioactive substances in a geological disposal (PA-SOL) to estimate the uncertainty of solubility associated with the uncertainties in both groundwater chemistry and thermodynamic data. The selenium and neptunium solubilities are calculated for the uncertainty of groundwater chemistry in repository environment, based on previous data of pore water chemistry in buffer materials, using the representative thermodynamic database, EQ3/6-TDB and JNC-TDB. The results of uncertainty analyses show that the highly effective parameters of groundwater chemistry are identified as the Eh-pH condition and iron concentration for selenium and the Eh-pH condition and carbonate concentration for neptunium.