Evaluation of chemical speciation of iodine and cesium considering fission product chemistry in reactor coolant system

Ishikawa, Jun ; Zheng, X. ; Shiotsu, Hiroyuki  ; Sugiyama, Tomoyuki ; Maruyama, Yu 

Japan Atomic Energy Agency is pursuing the development and application of the methodologies on fission product (FP) chemistry for source term analysis by using integrated severe accident analysis code THALES2/KICHE. Generally, specific chemical forms of iodine and cesium such as cesium iodide (CsI) and cesium hydroxide (CsOH) were assumed in the source term analysis for light water reactors using an integrated severe accident analysis code. The accident at the Fukushima Dai-ichi Nuclear Power Station leads possible chemical effects of BC control materials and atmosphere on chemical speciation of iodine and cesium such as cesium metaborate (CsBO) and hydrogen iodide (HI). The difference of chemical speciation affects not only the FP behavior in the reactor coolant system (RCS) and transport to containment but also pH value of the suppression pool water in the containment. The pH value is one of the influential factors on the release of gaseous iodine (I and organic iodine) from containment liquid phase. In the present study, the improvement of the THALES2/KICHE code in terms of FP chemistry in RCS was performed and applied to source term analysis for severe accidents at a boil water reactor with Mark-I containment vessel. This paper discusses the chemical speciation of iodine and cesium, and FP behavior and transport to containment.