4. METHODS
KICHE simulates such chemical behavior of iodine under irradiation by mechanistic model. The system is dominated by reactions specific to an irradiated environment, in which chemical effects by water radiolysis products (radicals) prevail. Thus the primary reaction field is the aqueous phase. In a so-called mechanistic model, the generation and interactions of water radiolysis products, their reactions with iodine species, and some non-chemical processes such as adsorption and interface mass transfer are handled. Those reactions and transfer laws are converted into a set of ordinary differential equations and solved numerically. Each reaction and rate constant is given by referring a database constructed with knowledge from fundamental researches. On the other hand, a semi-empirical model uses a more simplified overall reaction set (especially, water radiolysis is not treated directly) with rate constants tuned on experimental data. While the mechanistic model has a large number of reactions and needs more computer resource than the semi-empirical model, the advantage is its versatility and the availability as a tool for examination of mechanisms. Also, recent PCs and usage of an implicit scheme on the time integration make the mechanistic model practical enough.
The system to be simulated has its attributes described in the input file such as aqueous and gaseous volumes, wall surface areas, gas-liquid interface area, temperature, dose rate and so on. The system volume is called "cell". At present KICHE handles one cell only. Extension to more cells is possible, working on the code.
