An evaluation of volatile iodine in a pool under sever accident condition

Iodine is potentially one of the most hazardous fission products that can be released from the fuel of nuclear reactors during a severe accident. They undergo physical and chemical processes that govern their behavior in the containment, which play an important role in determining the amount of volatile iodine emitted to the containment environment. Thus, iodine retention in solution was evaluated based on models in SPARC and BUSCA code to analyze chemical kinetics relevant to iodine volatilization in the containment vessel of light water reactors (LWRs) during a severe accident. The generation rates of radiolysis products are mainly determined by the dose rate. The dose rate depends on the total amount of fission products and other radionuclides dissolved in water. Dose rates in water would depend on the type of reactor, accident scenario, and time. Typical dose rate under the severe accident condition would be in the range of 1 to 20 kGy/hr and it is possible that the total iodine concentration in wet scrubber and suppression chamber of a boiling water reactor could increase up to 10^-3 M during the severe accident. Molecular iodine concentrations and partition coefficients of the gaseous iodine in various pH solutions were evaluated to find volatility of iodine in solution with / without radiation. The results of analysis shown that the higher the pH the higher the amount of molecular iodine captured in the solution, the gas/water phase partition coefficients and DF factors (capture capacity of solutions) increase as the pH increases, by 10 to 100 times in the non-irradiated solution. However, these coefficients decreased by about 10 times under the influence of gamma radiation. In order to achieve the best effect of capturing molecular iodine in the solution, it becomes important to maintain the alkaline condition (pH > 8) in the solution. (author)