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東京電力福島第一発電所事故におけるセシウムの化学的挙動に関する検討,2; Csのステンレス鋼への化学吸着挙動の実験的評価

Investigation of in-reactor cesium chemical behavior in TEPCO's Fukushima Daiichi Nuclear Power Station accident, 2; Experimental investigation of Cs chemisorption behavior onto stainless steel

中島 邦久  ; 鈴木 恵理子   ; 西岡 俊一郎; 逢坂 正彦  

Nakajima, Kunihisa; Suzuki, Eriko; Nishioka, Shunichiro; Osaka, Masahiko

福島第一原子力発電所(1F)廃炉に際して重要となる炉内のCs分布評価へ資するため、Csと鋼材との化学反応や反応生成物の化学特性を考慮した化学吸着モデルの構築を目的として、化学吸着挙動の実験的評価や反応生成物の化学特性の評価を進めている。最初のステップとして、現状のSAMPSON等のシビアアクシデント(SA)解析コードに組み込まれているモデルの再現試験による検証を行った。その結果、反応速度定数は、Ar-H$$_{2}$$還元雰囲気では既存モデルのように温度と共に単調増加せず、800$$^{circ}$$Cよりも1000$$^{circ}$$Cで吸着量が低下した。一方、水蒸気を含んだAr-H$$_{2}$$-H$$_{2}$$O雰囲気下では1Fで想定される高い気相中のCs濃度の条件下では低下傾向を示したことから、雰囲気や気相中のCs濃度の影響も考慮できる化学吸着モデルが必要であることが分かった。

Information on the Cs distribution inside the reactors at Fukushima Daiichi Nuclear Power Station (1F) is important to proceed the decommissioning. For contribution to analysis of the Cs distribution, Cs chemisorption behaviors and chemical characteristics of the chemisorbed products have been investigated to establish a chemisorption model considering influences of the chemical reaction and the chemical characteristics of reaction products. As a first step, reproducibility tests were carried out to validate the existing model incorporated into sever accident analysis codes such as SAMPSON. As a result, reaction rate constants under an argon and hydrogen gas atmosphere do not increase with temperature as expected by the existing model and the chemisorbed amounts at 1000$$^{circ}$$C become lower than those at 800$$^{circ}$$C. On the other hand, in the case of steam-containing argon hydrogen gas atmosphere, the reaction rate constants in such a high concentration Cs gas as expected in 1F tend to become lower than those derived from the existing model. Therefore, it was found that a chemisorption model considering difference of reducing and oxidizing atmospheres and dependence of Cs concentration in gas phase was necessary.

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