3B-O2-1520 PDF
原子力機構における最近の高温質量分析研究：気体CsBO2の熱力学研究
Cesium is one of the main fission products having long-term radiation and heat sources, and knowledge on its chemical behavior is indispensable for reactor safety analysis. While a large amount of boron is used as neutron absorber by dissolving boric acid into cooling water in PWR or used as B4C control rod in BWR such as Fukushima-Daiichi nuclear power plant. Though the thermodynamic calculations indicate the principal chemical form of cesium in gaseous phase severe accidents is CsBO2(g), the quality of thermodynamic data of CsBO2(g) used in this calculation is regarded as poor. Therefore, Knudsen effusion mass spectrometric measurement of CsBO2 was carried out to obtain the reliable thermodynamic data of CsBO2(g). As the result, the determined vapor pressures surprisingly agree well with the values estimated from the existing thermodynamic data. The Gibbs energy function of CsBO2(g) was derived from newly obtained molecular constants. The determined ΔfH298º(CsBO2,g) by the second and third law treatments were found to be -700.7±10.7 kJ/mol and -697.0±10.6 kJ/mol. The agreement of these two values within the errors demonstrates the reliability of our results. Further, it was found that the existing ΔfH298º(CsBO2,g), -696.8 kJ/mol, agreed with our data and was reliable.