Prediction of the effects of boron release kinetics on the vapor species of cesium and iodine fission products

Cesium (Cs) and iodine (I) vapor species formed just after release from degraded fuels were predicted by means of the chemical equilibrium calculation with focuses on the effects of boron (B) release kinetics. Modified equations for the release kinetics of Cs, I and molybdenum (Mo) were utilized for evaluation of atmospheric dependences of their releases fractions. The B release kinetics was evaluated considering the formation of iron (Fe)-B-O-H compounds. The release of B was enhanced above approximately 2250 K with the vapor species of CsBO2 under steam atmosphere, while the formation of CsBO2 was limited under steam-starvation atmosphere due to the much lower release of B by the formation of low volatile Fe-B compounds. This limitation on CsBO2 formation under steam-starvation atmosphere would have resulted in a lesser formation of gaseous hydrogen iodine, HI, and of high volatile atomic I.