Development of fission product chemistry database ECUME for the LWR severe accident

Abstract

We extended the first version of fission product (FP) chemistry database named ECUME (Effective Chemistry database of fission products Under Multiphase rEaction). The extended ECUME consists of three kinds of datasets: CRK (dataset for Chemical Reaction Kinetics), EM (Elemental Model set) and TD (ThermoDynamic dataset). The present ECUME is equipped with the CRK for the reaction of Cs-I-B-Mo-O-H system and Ru-N-O-H system in gas phase, the EM for the Cs chemical reaction with stainless steel (SS) (Cs chemisorption onto SS) and the TD for CsBO₂ vapor species and solid Cs₂Si₄O₉ and CsFeSiO₄. A FP chemical reaction calculation in gas phase with the CRK of Cs-I-B-Mo-O-H system has shown the necessity of consideration of chemical reaction kinetics for more accurate estimation of Cs and I release amount into environment. The EM for Cs chemisorption has successfully achieved more accurate estimation of Cs distribution in a reactor by reproducing the effects of CsOH vapor concentration in gas phase and Si content in SS which were not considered by the existing model. The high quality vapor pressure data for CsBO₂ vapor were evaluated based on the result of a high temperature mass spectrometry. Cesium species at high temperature can be estimated by the thermodynamic data with high reliability. Thermodynamic data for solid Cs₂Si₄O₉ and CsFeSiO₄ were successfully evaluated by the experiment and ab-initio based methodology, respectively. These results have shown the validity and importance of the ECUME application for the more accurate evaluation of FP chemistry during transportation in a reactor under a LWR severe accident.