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JAEA Reports

Preparation of carbonate slurry simulating chemical composition of slurry in overflowed high integrity container and evaluation of its characteristics

Horita, Takuma; Yamagishi, Isao; Nagaishi, Ryuji; Kashiwaya, Ryunosuke*

JAEA-Technology 2021-012, 34 Pages, 2021/07

JAEA-Technology-2021-012.pdf:2.1MB
JAEA-Technology-2021-012(errata).pdf:0.15MB

Waste mainly consisting of carbonate precipitates (carbonate slurry) from the Advanced Liquid Processing System (ALPS) and the improved ALPS at the Fukushima Daiichi Nuclear Power Station of Tokyo Electric Power Holdings, Inc. have been storing in the High Integrity Container (HIC). The supernatant solution of carbonate slurry contained in some of HICs were overflowed in April of 2015. The all of level of liquid in the HICs were investigated; however, almost of the HICs were under the level of overflow. The mechanism of overflow suggested to be depending on the difference of the properties of the carbonate slurry such as the retention/release characteristics of the bubbles. Therefore, in order to clarify the mechanism of leakage, the repeatability experiment was carried out by using simulated carbonate slurry. The simulated carbonate slurry was perpetrated by using the same cross-flow filter system of the actual ALPS. Moreover, the preparative conditions for the simulated carbonate slurry were the same as Mg/Ca concentration ratio in inlet water of the ALPS (raw water) and the ALPS operating conditions. The chemical characteristics of simulated carbonate slurries were revealed by ICP-AES, pH meter, etc. The density of the settled slurry layer tended to increase depending on the calcium concentration in the raw water. The bubble injection test was conducted in order to investigate the bubble retention/release behavior in the simulated carbonate slurry layer. The simulated carbonate slurry with high settling density, which was generated by high calcium concentration solution was revealed to retain the injected bubbles. Since the ratio of concentration calcium and magnesium during the carbonate slurry generation is assumed to affect the retention of bubbles in the slurry layer, the information on the composition of raw water is one of important factor for overflow of HICs.

Journal Articles

Evaluation of energy spectrum around structural materials in radiation environments

Matsumura, Taichi; Nagaishi, Ryuji; Katakura, Junichi*; Suzuki, Masahide*

Radiation Physics and Chemistry, 166, p.108493_1 - 108493_9, 2020/01

 Times Cited Count:0 Percentile:0.01(Chemistry, Physical)

In this work, when radiation sources of $$^{137}$$Cs, $$^{90}$$Sr and $$^{90}$$Y were assumed to be put in the front of a plain SUS304 plate as a typical material submerged in water, energy spectra of secondary photons and electrons at the front and back sides of plate were simulated with changing the thickness of plate, and spacing between the source and plate by using a Monte Carlo calculation code of PHITS. In the case of $$^{137}$$Cs gamma-ray (monochromatic 662 keV), the energy spectra at the front side was smaller than those at the back side due to the existence of plate. Then the dependence of spectra on the plate thickness was observed more clearly at the back side than at the front side. It was clearly shown how the energy spectra of photons and electrons varied with the incident radiation type, the spacing, and the thickness.

Journal Articles

Analytical studies of three-dimensional evaluation of radionuclide distribution in zeolite wastes through gamma scanning of adsorption vessels

Matsumura, Taichi; Nagaishi, Ryuji; Katakura, Junichi*; Suzuki, Masahide*

Nuclear Science and Engineering, 192(1), p.70 - 79, 2018/10

 Times Cited Count:1 Percentile:17.98(Nuclear Science & Technology)

The gamma-scanning of SDS (submerged demineralizer system) vessel used as a typical vessel for decontamination of radioactive water at Three Mile Island Unit 2 (TMI-2) accident was simulated in the axial and radial directions of real and cylindrical-shaped vessels by using a Monte Carlo calculation code (PHITS) on the basis of the geometrical and compositional information of vessel and gamma-scanning available in the previous reports at the accident. In the axial simulation, the true distribution of radioactive $$^{137}$$Cs in the zeolite packed bed of vessel was successfully evaluated when a correction function derived from a virtual constant distribution of $$^{137}$$Cs was applied to the reported gamma-scanning profile. In the radial simulation, the virtual disk-formed and shell-formed sources of $$^{137}$$Cs displaced in the packed bed were clearly observed from the top and bottom views of vessel. This new radial gamma-scanning indicates that the radial localization of $$^{137}$$Cs could be well observed by measuring gamma-ray from the top view of vessel during storage. We further examined the radial gamma-scanning from the side view whether the radial localization of $$^{137}$$Cs can be confirmed in the normally existing gamma-scanning room or not.

Journal Articles

Gas retention behavior of carbonate slurry under $$gamma$$-ray irradiation

Motooka, Takafumi; Nagaishi, Ryuji; Yamagishi, Isao

QST-M-2; QST Takasaki Annual Report 2015, P. 95, 2017/03

We conducted $$gamma$$ ray irradiation test using simulated carbonate slurry to investigate the cause of stagnant water over the high integrity container (HIC). This test was performed at Co-60 irradiation facility in Takasaki Advanced Radiation Research Institute. We observed a rise in water level, air bubbles in the slurry, a supernatant when the carbonate slurry with 95 g/L density was irradiated by $$gamma$$ ray at a dose rate of 8.5 kGy/h. The cause of the rise in water level was regarded as the volume expansion by the gas retention of the carbonate slurry. It was suggested that the cause of stagnant water over the high integrity container might be the volume expansion by the gas retention.

Journal Articles

Irradiation experiments of simulated wastes of carbonate slurry

Nagaishi, Ryuji; Motooka, Takafumi; Yamagishi, Isao

Proceedings of 2016 EFCOG Nuclear & Facility Safety Workshop (Internet), 6 Pages, 2016/09

Overflow of water from waste storage tanks of High Integrity Containers (HIC) in the multi-nuclide removal equipment (ALPS) was discovered at Fukushima Daiichi NPS in April of last year. The mechanism of overflow was not understood very much at that time. To elucidate that for chemical safety in the waste storage, irradiation experiments of simulated carbonate slurry by Co-60 $$gamma$$-rays have been conducted in CLADS, JAEA in cooperation with TEPCO, TOSHIBA and KURITA. Hydrogen molecule was the main radiolytic gas product in the slurry, and its amount was enhanced by dissolved species of not only halide ions as seawater components but also carbonate ion as an additive for co-precipitation at a basic condition. The bubbles of molecules were further formed and almost held in the slurry without stirred. These sequentially led to the expansion of slurry, and then to its separation into the shrunk one and supernatant water, which was little accumulated without irradiated.

Journal Articles

Hydrogen generation by water radiolysis with immersion of oxidation products of zircaloy-4

Matsumoto, Yoshinobu*; Do, Thi-Mai-Dung*; Inoue, Masao; Nagaishi, Ryuji; Ogawa, Toru

Journal of Nuclear Science and Technology, 52(10), p.1303 - 1307, 2015/10

 Times Cited Count:3 Percentile:32.14(Nuclear Science & Technology)

Effects of zirconium oxides and oxidation products of zircaloy-4 on water radiolysis were investigated to predict the hydrogen generation from the water-immersed debris after a severe accident of a nuclear power plant. Observed yields of hydrogen in water containing the oxides were measured as a function of their weight fractions. Assuming that energies of Co-60 $$gamma$$-ray deposited to water and the oxides brought about the water radiolysis to generate hydrogen independently, the radiolysis showed an additional term of hydrogen generation due to the energy deposition to the oxides. This term seemed to be dependent on the specific surface area or particle size of oxides, but not on the crystal structure of oxides in our experimental results. The oxides in distilled water gave the strong enhancement of term. The enhancement tended to saturate with increasing the weight fraction of oxides and was not apparent in the seawater.

Journal Articles

Development of new type passive autocatalytic recombiner, 1; Characterization of monolithic catalyst

Kamiji, Yu; Taniguchi, Masashi*; Nishihata, Yasuo; Nagaishi, Ryuji; Tanaka, Hirohisa*; Hirata, Shingo*; Hara, Mikiya; Hino, Ryutaro

E-Journal of Advanced Maintenance (Internet), 7(1), p.84 - 89, 2015/05

For hydrogen mitigation, a new type passive autocatalytic recombiner is under developing. This new recombiner has been developed from automotive monolithic catalyst in order to reduce weight and to improve hydrogen treating capacity, environmental resistance and product quality. In this study, activation energy of hydrogen-oxygen recombination reaction was examined to clarify the basic characteristics of the catalyst. In addition, the degradation of the catalyst by $$gamma$$-ray irradiation simulating the environmental condition in nuclear power plants was also examined. As a result, the activation energy was experimentally estimated at 5.75 kJ/mol. Besides, no significant differences were observed in compositional distribution from the EPMA results. On the other hand, specific surface area of the catalyst and surface area of the precious metals were increased. Moreover, catalyst performance test showed that $$gamma$$-ray irradiation up to 1.0 MGy can increase activity of catalyst.

Journal Articles

Nuclear engineering and radiation effect; Radiation effects in reprocessing and geological disposal

Nagaishi, Ryuji

Genshiryoku, Ryoshi, Kakuyugo Jiten, 4, p.106 - 107, 2014/12

no abstracts in English

Journal Articles

Development of new type passive autocatalytic recombiner, 1; Characterization of monolithic catalyst

Kamiji, Yu; Taniguchi, Masashi*; Nishihata, Yasuo; Nagaishi, Ryuji; Tanaka, Hirohisa*; Hirata, Shingo*; Hara, Mikiya; Hino, Ryutaro

Proceedings of 2nd International Conference on Maintenance Science and Technology (ICMST-Kobe 2014), p.87 - 88, 2014/11

For hydrogen mitigation, a new type passive autocatalytic recombiner is under development. In this study, the activation energy of hydrogen-oxygen recombination reaction was examined to clarify the basic characteristics of the catalyst. In addition, the degradation of the catalyst by $$gamma$$-ray irradiation simulating the environmental condition in nuclear power plants was also examined. As a result, the activation energy was experimentally estimated at 5.75 kJ/mol. Besides, no significant differences were observed in the compositional distribution from the EPMA results between the non-irradiated and the irradiated catalyst. However, the irradiated catalyst showed much more activity because of larger specific surface area of the catalyst and surface area of the precious metals. It showed that $$gamma$$-ray irradiation up to 1.0 MGy can increase activity of the catalyst.

Journal Articles

Revaluation of hydrogen generation by water radiolysis in SDS vessels at TMI-2 accident

Nagaishi, Ryuji; Morita, Keisuke; Yamagishi, Isao; Hino, Ryutaro; Ogawa, Toru

Proceedings of 2014 Nuclear Plant Chemistry Conference (NPC 2014) (USB Flash Drive), 9 Pages, 2014/10

BB2014-1745.pdf:0.92MB

Two years after Three Mile Island Unit 2 (TMI-2) loss-of-coolant accident, radioactive contaminated water has been processed by Submerged Demineralizer System (SDS) with two types of zeolite adsorbents to remove radioactive nuclides. During and after the process, adsorption amount and distribution of nuclides on the zeolites, residual water content and thermal conductivity in the SDS vessels have been measured or estimated for verification of safety in the process, subsequent transportation and disposal. Hydrogen generation has been also evaluated mainly by direct monitoring in the large-scale of vessel after the process. In this work, the revaluation of hydrogen generation was demonstrated on the basis of the open information of vessel, and the latest experimental data obtained in adsorption and radiolysis occurring in small-scale of zeolite-water mixtures. As a result, the evaluated data was found to be comparable with the reported data obtained in the large-scale of real vessel.

Journal Articles

Consideration of radiolytic behavior in diluted and concentrated systems of seawater for computational simulation of hydrogen generation

Nagaishi, Ryuji; Inoue, Masao; Hino, Ryutaro; Ogawa, Toru

Proceedings of 2014 Nuclear Plant Chemistry Conference (NPC 2014) (USB Flash Drive), 9 Pages, 2014/10

Since seawater has been used as a coolant for reactors and spent fuel pools in broken reactor buildings at Fukushima Daiichi NPS accident, radioactive contaminated water emitted following the accident has contained salt content of seawater at high concentrations, different from that at TMI-2 accident. Radiolysis of seawater leading to hydrogen generation and corrosion has been simulated and reported by several groups. However, the proposed radiolysis models cannot be always applied to water radiolysis at the wide range of salt concentrations present in the NPS, mainly because primary yields of radiolysis products of water and radiation-induced reactions are dependent on the salt concentration. In this study, the radiolytic behavior in diluted and concentrated systems of seawater was considered on the basis of results in steady state and pulse radiolysis experiments, in which the above salt effects were demonstrated from the obtained results.

Journal Articles

Characterization and storage of radioactive zeolite waste

Yamagishi, Isao; Nagaishi, Ryuji; Kato, Chiaki; Morita, Keisuke; Terada, Atsuhiko; Kamiji, Yu; Hino, Ryutaro; Sato, Hiroyuki; Nishihara, Kenji; Tsubata, Yasuhiro; et al.

Journal of Nuclear Science and Technology, 51(7-8), p.1044 - 1053, 2014/07

 Times Cited Count:9 Percentile:65.28(Nuclear Science & Technology)

For safe storage of zeolite wastes generated by treatment of radioactive saline water at the Fukushima Daiichi Nuclear Power Station, properties of the Herschelite adsorbent were studied and its adsorption vessel was evaluated for hydrogen production and corrosion. Hydrogen production depends on its water level and dissolved species because hydrogen is oxidized by radicals in water. It is possible to evaluate hydrogen production rate in Herschelite submerged in seawater or pure water by taking into account of the depth effect of the water. The reference vessel of decay heat 504 W with or without residual pure water was evaluated for the hydrogen concentration by thermal hydraulic analysis using obtained fundamental properties. Maximum hydrogen concentration was below the lower explosive limit (4 %). The steady-state corrosion potential of a stainless steel 316L increased with absorbed dose rate but its increase was repressed by the presence of Herschelite. At 750 Gy/h and $$<$$60$$^{circ}$$C which were values evaluated at the bottom of the vessel of 504 W, the localized corrosion of SUS316L contacted with Herschelite would not immediately occur under 20,000 ppm of Cl$$^{-}$$ concentration.

Journal Articles

Hydrogen production in $$gamma$$ radiolysis of the mixture of mordenite and seawater

Kumagai, Yuta; Kimura, Atsushi; Taguchi, Mitsumasa; Nagaishi, Ryuji; Yamagishi, Isao; Kimura, Takaumi

Journal of Nuclear Science and Technology, 50(2), p.130 - 138, 2013/02

AA2012-0798.pdf:0.36MB

 Times Cited Count:26 Percentile:92.04(Nuclear Science & Technology)

Journal Articles

Safe storage of zeolite adsorbents used for treatment of accident-generated water at Fukushima Daiichi Power Station

Yamagishi, Isao; Nagaishi, Ryuji; Terada, Atsuhiko; Kamiji, Yu; Kato, Chiaki; Morita, Keisuke; Nishihara, Kenji; Tsubata, Yasuhiro; Ji, W.*; Fukushima, Hisashi*; et al.

IAEA-CN-211 (Internet), 5 Pages, 2013/01

Since the accident at Fukushima Daiichi Nuclear Power Station, a large amount of radioactive contaminated water has been generated to cool damaged reactor cores. Adsorption of cesium with zeolite-like media was employed for treatment of this contaminated saline water. As spent zeolite media are highly radioactive, their safe storage is a pressing issue. Japan Atomic Energy Agency has extensively conducted R&D on the management of secondary wastes produced by the operation of the treatment system. Subjects on the safe storage of spent zeolites include the analysis of their characteristics and the evaluation of effectiveness of the present safety measures in consideration of decay heat emission and hydrogen generation by water radiolysis as well as durability of vessels exposed to saline. Preliminary results obtained are described in the present paper.

Journal Articles

Surface speciation of Eu$$^{3+}$$ adsorbed on kaolinite by time-resolved laser fluorescence spectroscopy (TRLFS) and parallel factor analysis (PARAFAC)

Ishida, Keisuke*; Saito, Takumi*; Aoyagi, Noboru; Kimura, Takaumi; Nagaishi, Ryuji; Nagasaki, Shinya*; Tanaka, Satoru*

Journal of Colloid and Interface Science, 374(1), p.258 - 266, 2012/05

 Times Cited Count:24 Percentile:55.15(Chemistry, Physical)

Journal Articles

Measurement and evaluation of hydrogen production from mixtures of seawater and zeolite in decontamination of radioactive water

Kumagai, Yuta; Nagaishi, Ryuji; Kimura, Atsushi; Taguchi, Mitsumasa; Nishihara, Kenji; Yamagishi, Isao; Ogawa, Toru

Nihon Genshiryoku Gakkai Wabun Rombunshi, 10(4), p.235 - 239, 2011/12

Zeolite adsorbents are to be used for decontamination of radioactive water in Fukushima Dai-ichi Nuclear Power Station. Evaluation of hydrogen production by water radiolysis during decontamination is important for safe operation. Thus hydrogen production from the mixture of zeolite adsorbents and seawater was studied because seawater was urgently used as a coolant for the fuels. The hydrogen yield from the mixture decreased at a high weight fraction of zeolites. However, the measured yield was higher than the yield expected from the direct radiolysis of seawater in the mixture, which would decrease proportional to the weight fraction of seawater. The result suggests that the radiation energy deposited to zeolite is involved in the hydrogen formation. From the results, the hydrogen production rate was evaluated to be 3.6 mL/h per ton of radioactive water before decontamination. After the process, it was evaluated to be 1.5 L/h per ton of waste adsorbents due to the high dose rate.

Journal Articles

Studies on radiation effects in decomtamination of radioactive water by using zeolites as absorbents for radioactive nuclides

Nagaishi, Ryuji

Hoshasen Kagaku (Internet), (92), p.15 - 21, 2011/09

AA2011-0467.pdf:0.57MB

Radioactive water has been emitted following incidents at the Fukushima Dai-ichi Nuclear Power Station, and needed to be quickly decontaminated by the adsorption and/or the coagulation sedimentation of radioactive nuclides, where hydrogen molecules are produced by water radiolysis. The decontamination process with zeolites as absorbents of radioactive cesium was assumed, the observed yields of hydrogen production were determined in mixtures of seawater and zeolite, and then the production rates were estimated for the safety operation of process before the operation started.

Journal Articles

Effect of alumina on the enhancement of hydrogen production and the reduction of hydrogen peroxide in the $$gamma$$-radiolysis of pure water and 0.4M H$$_{2}$$SO$$_{4}$$ aqueous solution

Yamada, Reiji; Kumagai, Yuta; Nagaishi, Ryuji

International Journal of Hydrogen Energy, 36(18), p.11646 - 11653, 2011/09

 Times Cited Count:7 Percentile:22.28(Chemistry, Physical)

The H$$_{2}$$ and H$$_{2}$$O$$_{2}$$ produced by $$^{60}$$Co $$gamma$$-radiation at room temperature were measured in pure water and 0.4M H$$_{2}$$SO$$_{4}$$ aqueous solution with alumina powder. By increasing the addition of alumina powder, a strong reduction of H$$_{2}$$O$$_{2}$$ concentrations in the solutions was obtained, and the final product H$$_{2}$$ yields were correspondingly enhanced. These enhancement and reduction effects were diminished in the subsequent $$gamma$$-radiation when irradiated alumina powder was used. The effects were reversibly restored by washing the irradiated powder with purified water. In 0.4M H$$_{2}$$SO$$_{4}$$ solution with alumina powder, the H$$_{2}$$ yields increased by increasing the absorbed dose rate in the region of 1-5 kGy/hr. The radiation-enhanced H$$_{2}$$ production correlated with the reduction of H$$_{2}$$O$$_{2}$$ concentration could be brought about by the reduction of H$$_{2}$$O$$_{2}$$ molecules and OH radicals in the solutions due to alumina powder.

Journal Articles

Thermochromic properties of low-melting ionic uranyl isothiocyanate complexes

Aoyagi, Noboru; Shimojo, Kojiro; Brooks, N. R.*; Nagaishi, Ryuji; Naganawa, Hirochika; Van Hecke, K.*; Van Meervelt, L.*; Binnemans, K.*; Kimura, Takaumi

Chemical Communications, 47(15), p.4490 - 4492, 2011/04

 Times Cited Count:39 Percentile:72.35(Chemistry, Multidisciplinary)

201 (Records 1-20 displayed on this page)