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CLuu, V. N.; 中島 邦久
Mechanical Engineering Journal (Internet), 11(2), p.23-00446_1 - 23-00446_11, 2024/01
Cesium distribution is crucial for decommissioning Fukushima Daiichi Nuclear Power Station (1F). Several experimental studies confirmed Cs retention on stainless steels by performing chemical reactions at high temperatures (typically above 800C)), but the Cs retention on concrete, used in large quantities in light water reactors, is not fully understood. This study demonstrated that Cs might have been deposited and retained on the concrete structures where the temperature was not so high during the 1F accident. Results showed that the CsOH/concrete interaction at around 200C occurred in water-insoluble Cs-(Al,Fe)-Si-O deposits and water-soluble phases, i.e., cesium carbonate hydrate and possibly cesium silicate if Al and Fe are not present. CsOH might be trapped on concrete by chemical reaction with CaCO
to form Cs
CO hydrate, and with aluminosilicate and SiO(quartz) to form Cs-Al-Si-O and Cs-Si-O deposits, respectively. This output could help elucidate the trapping mechanism that caused extremely high radioactivity on concrete shield plugs at 1F and develop an effective decommissioning practice for concrete structures.
CLuu, V. N.; 中島 邦久
Proceedings of 30th International Conference on Nuclear Engineering (ICONE30) (Internet), 9 Pages, 2023/05
Information of Cs distribution is important for decommissioning of the Fukushima Daiichi Nuclear Power Station (1F). Several experimental studies confirmed the Cs retention on stainless steels by chemical reaction at very high temperatures (commonly above 800C), but the Cs retention on non-metallic materials, such as concrete and thermal insulators, was not fully understood though they are used with large quantity in light water reactors. This study demonstrated that Cs might be deposited and retained on the concrete structure where the temperature was not so high during the 1F accident. It was revealed that the CsOH/concrete interaction at around 200C resulted in the formation of water-insoluble Cs-(Al,Fe)-Si-O deposits and water-soluble phases, i.e., cesium carbonate hydrate and possibly cesium silicate, if Al and Fe are not present. CsOH might be trapped on concrete by chemical reaction with CaCO to form CsCO hydrate, and with aluminosilicate and SiO(quartz) to form Cs-Al-Si-O and Cs-Si-O deposits, respectively. This output will be useful for elucidating the trapping mechanism that caused an extremely high radioactivity on concrete shield plugs at 1F, and for developing an effective decommissioning practice for concrete structure.
Luu, V. N.; 中島 邦久
Journal of Nuclear Science and Technology, 60(2), p.153 - 164, 2023/02
被引用回数：6 パーセンタイル：67.31(Nuclear Science & Technology)Recently, extremely high dose rates were detected in the three-layer concrete plugs of Units 2 and 3 at the Fukushima Daiichi Nuclear Power Plant. The high dose rates suggest that there are some trapping effects of radioactive materials on shield plugs when gas species and aerosols (e.g., CsOH, CsI) are released from reactor through the plug layers. To determine the trapping mechanism, concrete and commonly used aggregate and minerals are pulverized and mixed with CsOH, followed by heating at different temperatures to clarify the chemical interaction. The results showed that interactions of CsOH and CaCO in concrete occurred even at room temperature to form CsCO(HO). The interaction with aggregates occurred above 100C and resulted in the formation of CsAlSiO
. Additionally, amorphous and crystalline SiO interacted with CsOH, forming a glass-like product above 200C. These results suggest that formation of CsCO(HO) would be one of the main trapping mechanism at shield plugs because CaCO is commonly formed on concrete surface and reacts with CsOH at room temperature.
Rizaal, M.; 中島 邦久; 斉藤 拓巳*; 逢坂 正彦; 岡本 孝司*
ACS Omega (Internet), 7(33), p.29326 - 29336, 2022/08
被引用回数：5 パーセンタイル：35.08(Chemistry, Multidisciplinary)Here we report an investigation of the gas-solid reaction between cesium hydroxide (CsOH) and siliceous (calcium silicate) thermal insulation at high temperature, which was postulated as the origin for the formation mechanism of cesium-bearing material emitted from the Fukushima Daiichi Nuclear Power Plant. A developed reaction furnace consisting of two heating compartments was used to study the reaction at temperatures of 873, 973, and 1073 K. Under the influence of hydrogen-steam atmospheric conditions (H/HO = 0.2), the reaction between cesium hydroxide vapor and solid thermal insulation was confirmed to occur at temperatures of 973 and 1073 K with the formation of dicalcium silicate (CaSiO) and cesium aluminum silicate (CsAlSiO). Water-dissolution analyses of the reaction products have demonstrated their stability, in particular, the CsAlSiO. Constituents similarity of the field-observed cesium-bearing materials near the Fukushima Daiichi Nuclear Power Plants with CsAlSiO suggests for the first time that gaseous reaction between CsOH with calcium silicate thermal insulation could be one of the original formation mechanisms of the cesium-bearing materials.
Rizaal, M.; 中島 邦久; 斉藤 拓巳*; 逢坂 正彦; 岡本 孝司*
Journal of Nuclear Science and Technology, 57(9), p.1062 - 1073, 2020/09
被引用回数：9 パーセンタイル：64.46(Nuclear Science & Technology)福島第一原子力発電所2号機においてペデスタル内よりもペデスタル外で線量が高くなっている現象が見つかっている。この線量の上昇については、原子炉格納容器内の配管に使用されている保温材(ケイ酸カルシウム)がガス状あるいは粒子状となって沈着したセシウム(Cs)と化学反応を起こして固着するとともに破損してペデスタル外に堆積することで線量が上昇した可能性があると考えている。そこで、本研究では、化学反応の有無を調べるため、反応温度等を調べることのできる熱重量示差熱分析装置(TG-DTA)を用いて、水素-水蒸気含有雰囲気下、最高1100Cまで温度を上昇させて、主なセシウム化合物の一つである水酸化セシウムと保温材との混合物に対して分析を行った。その結果、575-730Cの範囲で反応が起こり、試験後試料のX線回折パターンや元素分析機能付き走査型電子顕微鏡(SEM/EDS)による試料表面の元素分布の結果から、保温材の構成物質であるケイ素(Si)に加え、不純物として含まれるアルミニウム(Al)と安定な化合物(CsAlSiO)を形成することが分かった。したがって、ペデスタル外で見つかった高線量の原因として、保温材が関係する可能性があることが分かった。
Luu, V. N.; 中島 邦久
no journal, ,
To investigate the source of high dose rates at the concrete shield plugs of Unit 2 and 3 at 1F, high temperature tests on the mixture of CsOH and pulverized concrete/main components were conducted. Results showed that both water-soluble and -insoluble phases were formed below 300C. Namely, CsCO(HO) was formed due to chemical reaction with CaCO at room temperature. The authors will discuss the possibility that this might be one of the main trapping mechanisms on shield plugs.
