Investigation for evaluating containment source term of BWR4/Mark-I plant considering iodine chemistry in suppression pool

Ishikawa, Jun ; Moriyama, Kiyofumi

At the late phase of severe accident (SA), there is a possibility that gaseous iodine species which dissolved in the pool water at the early phase of accident are released to the containment (CV) atmosphere due to radiation chemical reactions. In order to evaluate the influence on the CV source terms considering iodine chemistry, a coupling analysis method of SA analysis code THALES2 and iodine chemistry analysis code Kiche was developed. The evaluation of thermal-hydraulics conditions and source term in the CV at the late phase of severe accident were conducted for 4 accident scenarios of BWR4/Mark-I by using this coupling method. As for the re-vaporization of iodine to the CV atmosphere, the influence of pH is larger than that of difference of accident sequences. Total release fractions of I to the CV atmosphere at 50 h for pH = 5, 7 and 9 were 10-10, 10 and 10 for the initial core inventory. The lower the pH was, the larger the release fraction of I was.