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Journal Articles

High-temperature gaseous reaction of cesium with siliceous thermal insulation; The Potential implication to the provenance of enigmatic Fukushima cesium-bearing material

Rizaal, M.; Nakajima, Kunihisa; Saito, Takumi*; Osaka, Masahiko; Okamoto, Koji*

ACS Omega (Internet), 7(33), p.29326 - 29336, 2022/08

 Times Cited Count:0 Percentile:16.24(Chemistry, Multidisciplinary)

Journal Articles

Revaporization behavior of cesium and iodine compounds from their deposits in the steam-boron atmosphere

Rizaal, M.; Miwa, Shuhei; Suzuki, Eriko; Imoto, Jumpei; Osaka, Masahiko; Gou$"e$llo, M.*

ACS Omega (Internet), 6(48), p.32695 - 32708, 2021/12

 Times Cited Count:1 Percentile:7.13(Chemistry, Multidisciplinary)

Journal Articles

Investigation of high-temperature chemical interaction of calcium silicate insulation and cesium hydroxide

Rizaal, M.; Nakajima, Kunihisa; Saito, Takumi*; Osaka, Masahiko; Okamoto, Koji*

Journal of Nuclear Science and Technology, 57(9), p.1062 - 1073, 2020/09

 Times Cited Count:7 Percentile:67.5(Nuclear Science & Technology)

The interaction of cesium hydroxide and a calcium silicate insulation material was experimentally investigated at high temperature conditions. A thermogravimetry equipped with differential thermal analysis was used to analyze thermal events in the samples of mixed calcium silicate and cesium hydroxide under Ar-5%H$$_{2}$$ and Ar-4%H$$_{2}$$-20%H$$_{2}$$0 with maximum temperature of 1100$$^{circ}$$C. Prior being mixed with cesium hydroxide, a part of calcium silicate was pretreated at high temperature to evaluate the effect of possible structural changes of this material due to a preceding thermal history and also the sake of thermodynamic evaluation to those available ones. Based upon the initial condition (preliminary heat treatment) of calcium silicate, it was found that if the original material consisted of xonotlite (Ca$$_{6}$$Si$$_{6}$$0$$_{17}$$(0H)$$_{2}$$), the endothermic reaction with cesium hydroxide occurred over the temperature range 575-730$$^{circ}$$C meanwhile if the crystal phase of original material was changed to wollastonite (CaSi0$$_{3}$$), the interaction occurred over temperature range 700-1100$$^{circ}$$C. Furthermore, the X-ray diffraction analyses have indicated on both type of pretreated calsils that regardless of Ar-5%H$$_{2}$$ and Ar-4%H$$_{2}$$-20%H$$_{2}$$0 atmosphere, cesium aluminum silicate, CsAlSi0$$_{4}$$ was formed with aluminum in the samples as an impurity or adduct.

Journal Articles

Room-temperature adsorption behavior of cesium onto calcium silicate insulation

Rizaal, M.; Saito, Takumi*; Okamoto, Koji*; Erkan, N.*; Nakajima, Kunihisa; Osaka, Masahiko

Mechanical Engineering Journal (Internet), 7(3), p.19-00563_1 - 19-00563_10, 2020/06

The adsorption of cesium (Cs) on calcium silicate insulation of primary piping system is postulated to contribute in high dose rate of surrounding pedestal area in Fukushima Daiichi NPP unit 2. In this study, room-temperature experiment of Cs adsorption on calcium silicate has been studied as an initial approach of Cs adsorption behavior toward higher temperature condition. As the result of analyzing of Cs adsorption kinetics, it was expected that the underlying adsorption mechanism is chemisorption. Furthermore, analysis of adsorption isotherm suggested unrestricted monolayer formation followed by multilayer formation.

Oral presentation

Thermochemical investigation of calcium silicate insulation with cesium hydroxide

Rizaal, M.; Nakajima, Kunihisa; Osaka, Masahiko; Saito, Takumi*; Erkan, N.*; Okamoto, Koji*

no journal, , 

Experimental study using thermogravimetry and X-ray diffractometry was conducted to investigate chemical interaction between calcium silicate insulation and cesium hydroxide under steam and hydrogen atmospheres. This interaction might be one of the causes for the high dose rate reading outside the pedestal in 1F, Unit2. Our results suggested that some chemical interaction occurred in temperature range of 575-730$$^{circ}$$C regardless of atmospheres.

Oral presentation

High-temperature gas-solid interaction of calcium silicate insulation with cesium hydroxide

Rizaal, M.; Nakajima, Kunihisa; Osaka, Masahiko; Saito, Takumi*; Okamoto, Koji*

no journal, , 

Oral presentation

Study on revaporization of deposited CsI from stainless steel 304 surface in high-temperature steam atmosphere

Rizaal, M.; Miwa, Shuhei; Suzuki, Eriko; Imoto, Jumpei; Osaka, Masahiko; Gou$"e$llo, M.*

no journal, , 

Oral presentation

Investigation of effect by the late-phase release of boron containing atmosphere on CsI deposit formed on reactor structural material SUS304L

Rizaal, M.; Miwa, Shuhei; Suzuki, Eriko; Imoto, Jumpei; Osaka, Masahiko; Gou$"e$llo, M.*

no journal, , 

Oral presentation

Evaluation of FP behavior models in SAs, 5; Evaluation of a chemical reaction model for Cs-I-B-H-O system in SA codes

Karasawa, Hidetoshi; Rizaal, M.; Miwa, Shuhei; Kino, Chiaki*

no journal, , 

In SA analysis, the importance of chemical reactions related to FP behavior has been pointed out. For this reason, the amount of gaseous iodine produced was evaluated by a gaseous chemical reaction model using the ECUME database in the previous CsI-TeRRa experiment. In this study, we investigated the gas phase chemical reaction model for the CsI-B$$_{2}$$O$$_{3}$$-TeRRa experiment, which evaluated the influence of B on CsI behavior. In the experiment, the addition of B$$_{2}$$O$$_{3}$$ increased the production of gaseous iodine by about 10 times. To explain this behavior, we set up a Cs-I-B-H-O reaction mechanism in which HBO$$_{2}$$ generated from B$$_{2}$$O$$_{3}$$ is reacted with CsI and CsOH to produce gaseous iodine. Calculations of the chemical reaction model using chemical reaction rates in the ECUME database confirmed an increase in gaseous iodine (about 26 times at 1,273 K) due to the addition of B$$_{2}$$O$$_{3}$$. The results showed that gaseous iodine was sufficiently produced at high temperatures, indicating the possibility of reproducing the TeRRa experiment by calculating chemical reactions during the transition of decreasing temperature.

Oral presentation

Study on FP chemistry for improvement of LWR source term

Rizaal, M.; Nakajima, Kunihisa; Karasawa, Hidetoshi; Luu, V. N.; Miwa, Shuhei

no journal, , 

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