Development of the mechanistic sorption and diffusion model/database for safety assessment of geological disposal; Prototype model/database for bentonite systems

Tachi, Yukio  ; Yotsuji, Kenji; Suyama, Tadahiro; Ochs, M.*; Yui, Mikazu

This report presents the prototype model/database for integrated sorption and diffusion (ISD2009) in bentonite systems as basis for performance assessment (PA) of geological disposal. The sorption model is based on a relatively simple 1-site surface complexation/diffuse layer model in combination with 1-site ion exchange model. The model parameters for surface chemistry/sorption are evaluated based on existing datasets for Na-montmorillonite, which covers key geochemical conditions, in consistent way. The diffusion model based on homogeneous pore structure and electrical double layer theory was developed and coupled with batch-based sorption model, then was validated by using data in compacted montmorillonite. The sorption and diffusion models were also tested by applying data in bentonite systems. The model and related parameters developed for key radionuclides such as Cs, Np(V), Ni, Am, etc. are integrated to ISD2009 database, which could be useful in future PA exercise.