Influence of chemical speciation in reactor cooling system on pH of suppression pool during BWR severe accident

Shiotsu, Hiroyuki  ; Ishikawa, Jun ; Sugiyama, Tomoyuki ; Maruyama, Yu 

The influences of chemical speciation for Cs-I-Te-Mo-Sn-B-C-O-H system, simulating a state in the reactor cooling system (RCS) of BWR, on pH of the suppression chamber (S/C) water pool were analytically investigated with PHREEQC code. Major conditions were chosen on the basis of the outputs from a BWR severe accident analysis by THALES2 code and chemical thermodynamic analysis with VICTORIA2.0 code. The chemical thermodynamic analysis showed that the chemical speciation of important volatile FPs, Cs and I, was strongly influenced by Mo and BC control material. As a consequence, pH of the S/C water pool was predicted to range from approximately 6 to 10, depending on the fraction of volatile FPs transported from the RCS to the S/C water pool and the H/HO ratio associated with the oxygen potential. It was implied that the formation of volatile I species such as I in the S/C water pool was larger by 3 orders at the lowest pH than that at the highest pH.