Thermodynamic evaluation on chemical reaction between UO and SiC in LWR conditions

軽水炉におけるUOとSiCの反応の熱力学的評価

白数 訓子  ; 倉田 正輝 

Shirasu, Noriko; Kurata, Masaki

福島第一原子力発電所の過酷事故をうけ、事故耐性の高い燃料の開発が進められている。SiCは、その化学的安定性や照射耐性から、有力な事故耐性被覆管の候補材となっている。水蒸気との反応性も、ジルカロイより低く、発生する熱や水素量の大きな減少も期待できる。軽水炉の通常運転時や過酷事故時における、燃料とSiCの間で生じる化学反応や懸念される事象を、熱力学平衡計算により評価した。SiCは、酸化によりSiOになるが、水蒸気の存在下では、SiOガスの生成割合が増加することがわかった。

After Fukushima Daiichi nuclear accident in 2011, enhancing the accident tolerance of light water reactor fuels became a very important issue and currently the development of accident-tolerant fuel (ATF) are in progress. SiC is an attractive candidate of ATF cladding material because of its high chemical stability, high radiation resistance and low neutron absorption. SiC reacts much less than Zircaloy with steam, the generation of heat and hydrogen gas would be extremely suppressed. Thermodynamic evaluation on chemical interactions between UO and SiC were performed on various possible conditions of oxygen potential and temperature in severe accident. SiC is converted to SiO by reaction with O. SiC is also converted to SiO by reaction with HO. However, the fraction of the sub-reaction for forming SiO increases than in the case of reaction with O when comparing the results at the same temperatures and the same oxygen potentials.