Development of a temperature-dependent chemical simulation code based on PHITS for water radiolysis from 0 to 350C

PHITSに基づく0350Cにおける水の放射線分解温度依存化学シミュレーションコードの開発

松谷 悠佑  ; 吉井 勇治*; 楠本 多聞*; Wang, Y.*; 小川 達彦   ; 佐藤 達彦   ; 甲斐 健師   

Matsuya, Yusuke; Yoshii, Yuji*; Kusumoto, Tamon*; Wang, Y.*; Ogawa, Tatsuhiko; Sato, Tatsuhiko; Kai, Takeshi

水の放射線分解は、人体におけるDNA損傷や原子炉における腐食など、材料に対する放射線影響に重要な役割を果たす。従来の化学コードは主に室温付近に限定されており、原子炉環境の温度条件とは大きく異なる。本研究では、汎用モンテカルロコードParticle and Heavy Ion Transport code System (PHITS)に基づき、0350Cの温度範囲に適用可能な化学コード(PHITS-Chem)を開発した。拡散係数および反応速度定数の温度依存性を考慮し、低LET(0.2keV/m)、中LET(11.9keV/m)、高LET(63.4keV/m)放射線に対する既報の実験および理論G値と比較することで検証した。本コードにより、広い温度範囲での放射線分解生成種の反応動力学を高精度に評価でき、炉内材料劣化やシビアアクシデント対策の検討への応用が期待される。

Water radiolysis plays an important role in radiation effects on materials, such as DNA damage in the human body and corrosion processes in nuclear reactors. Conventional chemical simulation codes are generally limited to around room temperature, which differs significantly from the temperature conditions encountered in reactor environments. In this study, we developed a chemical simulation code (PHITS-Chem) based on the general-purpose Monte Carlo code, the Particle and Heavy Ion Transport code System (PHITS), applicable over a temperature range 0 to 350C. The code explicitly considers the temperature dependence of diffusion coefficients and reaction rate constants, and its performance was validated by comparing the calculated G-values with previously reported experimental and theoretical data for low-LET (0.2 keV/m), medium-LET (11.9 keV/m), and high-LET (63.4 keV/m) radiation. The developed code enables high-precision evaluation of the reaction kinetics of radiolytic species over a wide temperature range and is expected to be useful for assessing in-core material degradation and for studies related to severe accident mitigation in nuclear reactors.