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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 Cs
CO 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：4 パーセンタイル：78.52(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.
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.
Luu, V. N.; 中島 邦久
no journal, ,
This study investigated the possibility of chemical interaction between concrete/aggregate and cesium hydroxide at high temperatures. CsOH interaction with CaCO in concrete forms water-soluble CsCO(HO) even at room temperature, whereas CsOH interaction with aluminosilicate minerals in aggregate forms water-insoluble CsAlSiO just above 100C, according to TG/DTA and XRD analyses on the mixture of CsOH and pulverized concrete/aggregate. The results suggest that the formation of CsCO(HO) would be one of the main trapping mechanisms at shield plugs because CaCO is commonly formed on concrete surfaces and reacts with CsOH at room temperature.
CLuu, V. N.; 中島 邦久
no journal, ,
Chemisorption tests of CsOH onto concrete and aggregate were carried out at 200C in both dry and humid conditions to investigate the source of high dose rates at the concrete shield plugs of Units 2 and 3 at 1F. Post-test analyses using XRD, Raman, and SEM revealed that water-insoluble Cs-bearing deposits formed different morphologies under dry and humid conditions. Namely, uniform and large Cs deposits were formed under humid conditions, while heterogenous growth and smaller size Cs deposits were observed under dry conditions.
Rizaal, M.; 中島 邦久; 唐澤 英年; Luu, V. N.; 三輪 周平
no journal, ,
Our research focused on, but is not limited to, cesium (Cs) and iodine (I) chemistry due to their high impact on the overall source term. The retention or release of both elements is largely affected by chemical interaction with materials that are present in the reactor. To understand their chemistry during transport in the event of a nuclear severe accident (SA), we studied the interaction phenomena taking place from high- to low-temperature conditions. We have succeeded in elucidating these phenomena (particularly Cs) and summarized them in a fission product (FP) chemistry database ECUME. This database not only could deepen our understanding of the mechanism of Cs and I chemistry in an SA, but could also improve source term analysis. Improvement in the reaction between Cs vapor and stainless steel was shown by the use of the ECUME database in SA analysis code SAMPSON. Better reproducibility of Cs retention at high temperatures of the large-scale experiment was obtained, in contrast to using the MELCOR Cs interaction model (i.e. widely used model in SA code) that was worse in reproducing such phenomenon. Taking into consideration of near-term implementation of Accident Tolerant Fuel (ATF) materials such as chromium (Cr)-coated Zircaloy, further study on the interaction with FP would be important to ensure the material impact on source term because the reaction between Cs and Cr can be thermodynamically expected.
at temperature range 170 - 290 CLuu, V. N.; 中島 邦久
no journal, ,
A recent field survey revealed extremely high radioactivity on the concrete shield plugs, exceeding 20 PBq for Cs-137 at units 2, 3 of 1F. This leads to significant interest in the retention of Cs on concrete during severe accident. Despite this, the interaction of Cs vapors and/or aerosols in the gas phase with concrete surfaces at high temperatures remains inadequately explored. In this work, we investigated the deposition behavior of CsOH on CaCO, as a primary phase on the concrete surface, under humid atmosphere. As a result, the chemical reaction enhanced deposition rate, and increased linearly with CsOH concentration.
