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Journal Articles

An Alpha imaging detector for on-site measurement of Plutonium and Neptunium

Morishita, Yuki; DiPrete, D. P.*; Deason, T.*; Nagaishi, Ryuji

Radiation Measurements, 181, p.107366_1 - 107366_8, 2025/02

 Times Cited Count:0 Percentile:0.00(Nuclear Science & Technology)

Nuclear fuel materials such as Plutonium (Pu) and Neptunium (Np) are produced as by-products of reprocessing operations, necessitating precise understanding of their contamination distribution within controlled areas for radiation protection. This study presents the development and application of an alpha particle imaging detector for on-site detection of Pu and Np contamination. The detector's performance was evaluated using various alpha sources, demonstrating promising energy resolution and spatial resolution. Subsequently, $$^{239}$$Pu and $$^{237}$$Np oxide samples were measured at the Savannah River National Laboratory, showing the detector's effectiveness in on-site applications. The detector enabled simultaneous measurement of radioactivity and energy spectrum of individual particles, facilitating rapid discrimination between $$^{239}$$Pu and $$^{237}$$Np. The imaging detector has potential for enhancing on-site detection of alpha nuclides in nuclear facilities, aiding in decontamination efforts and environmental monitoring.

Journal Articles

Study on the effect of radiation-resistant resin on water radiolysis

Ito, Tatsuya; Nagaishi, Ryuji; Kuwano, Ryo*; Godo, Masao*; Yoshida, Yoichi*

Radiation Physics and Chemistry, 226, p.112198_1 - 112198_5, 2025/01

 Times Cited Count:0 Percentile:0.00(Chemistry, Physical)

In recent years, the use of radiation-resistant resins of polyimide and polyether ether ketone becomes increasing as vessels for irradiation and unsealed radioisotope experiments. However, in our radiolysis experiments, the possibility of interaction between radiolysis products of water and the resin was found, suggesting concerns that the resin may affect reactions in water in radiation fields. To clarify the interaction, dichromate (Cr$$_{2}$$O$$_{7}$$$$^{2-}$$) reduction and hydrogen peroxide (H$$_{2}$$O$$_{2}$$) formation in $$gamma$$-radiolysis of water were compared with and without the resin. The Cr$$_{2}$$O$$_{7}$$$$^{2-}$$ reduction amount in aqueous solution with the resin became larger than that without the resin at the same dose, indicating the promotion of Cr$$_{2}$$O$$_{7}$$$$^{2-}$$ reduction by the resin. On the other hand, the H$$_{2}$$O$$_{2}$$ formation in pure water with and without an electron scavenger were almost independent of the presence of resin. These suggested the interaction between hydroxyl radical and the resin in contact with water in radiation fields.

Journal Articles

Numerical simulation on dispersion of hydrogen leaked in particle layers of glass beads and soil

Terada, Atsuhiko; Nagaishi, Ryuji

Nuclear Technology, 210(10), p.1871 - 1887, 2024/10

 Times Cited Count:0 Percentile:0.00(Nuclear Science & Technology)

In order to understand dispersion of H2 leaked in packed beds of non-porous/porous particles in a partially open space practically, the dispersion of H2 in the particle layers of glass beads and soil was analytically studied using a CFD code to be compared with the experiments and to elucidate the effects of particle layer. H2 flowed out from a single leak point in the particle layer of non-porous glass beads was affected by buoyancy around the leak point, and diffused directly above the leak point in an elliptical shape faster than in the horizontal direction. After that, when it reached the air layer in the head space above the particle layer, H2 spread horizontally, formed a large concentration gradient near the boundary between the particle layer and the air layer, and further diffused in the air layer until the H2 concentration became about 1/3 or less of the concentration near the surface of particle layer. The calculations largely reproduced the experimental concentration distributions. When the particle layer was porous decomposed granite soil, the diffusion behavior of H2 in the particle layer proceeded in the same manner as in the case of glass beads. However, a large concentration gradient was formed near the boundary between the particle layer and the air layer, and then H2 diffused in the air layer until the H2 concentration became below the lower combustion limit. It was suggested through sensitivity analysis that the air permeability coefficient had a large effect on the time course of H2 concentration distribution. Based on the above, we further simulated H2 behavior in the vessel containing the H2 leaked particle layer. By inserting multiple vent pipes without considering H2 generation distribution and particle properties in the particle layer, H2 accumulated from one pipe was discharged by buoyancy without depending on the H2 generation distribution and particle properties in the particle layer, and air flowed in from the other pipe.

Journal Articles

Analytical studies on effects of wind on dispersion of hydrogen leaked in a partially open space

Terada, Atsuhiko; Nagaishi, Ryuji

Journal of Nuclear Science and Technology, 61(8), p.1135 - 1154, 2024/08

 Times Cited Count:0 Percentile:0.00(Nuclear Science & Technology)

In order to elucidate ventilation and exhaust of hydrogen leaked in a partially open space practically, the effects of outer wind on them were studied analytically by using a CFD code in the room of experimental Half-size Hallway model, which has a H$$_{2}$$ release hole on the bottom, one vent on the roof and another vent on the side: external air flowed in the room from the Door vent and then H$$_{2}$$ was discharged outside from the Roof vent. The H$$_{2}$$ concentration distribution in the room was divided into two layers at the height of Door vent, with a high concentration layer above it and a low concentration layer below it, forming a stratified interface. When the wind speed blown into the room increased, the combination of the Realizable k-e; turbulence model and the turbulence Schmidt number of 1.0 improved the reproducibility of the analysis results of H$$_{2}$$ concentration distribution. The trial analysis suggested that the concern that wind would increase the indoor H$$_{2}$$ concentration could be reduced by using the plate with a simple structure in which two plates were crossed on the Roof vent.

Journal Articles

Retention of hydrogen bubbles generated from water radiolysis in carbonate slurry

Ito, Tatsuya; Nagaishi, Ryuji; Kuwano, Ryo*

Nuclear Technology, 210(8), p.1427 - 1443, 2024/08

 Times Cited Count:0 Percentile:0.00(Nuclear Science & Technology)

The retention of hydrogen (H$$_{2}$$) bubbles generated by water radiolysis was quantitatively studied in a high-viscous suspension of carbonate slurry consisting of a mixture of suspended solid (SS) of magnesium and calcium precipitates under strongly alkaline conditions, like the radioactive wastes discharged from the coagulation sedimentation (co-precipitation) process at the multinuclide removal equipment in the Fukushima Daiichi Nuclear Power Station. The H$$_{2}$$ retention properties were evaluated in two types of carbonate slurry with different hydrophilicity: the hydrophilic "current type" and the hydrophobic "return type". Then, their properties were compared with those in another suspension of clay suspension of bentonite. From the comparison between the amounts of chemical adsorption and H$$_{2}$$O in the slurry, it was confirmed that H$$_{2}$$O molecules must be shared among the SS particles, and this sharing formed the structural viscosity in the slurry, different from that in the clay suspension where electrostatic bonding between the fine clay minerals forms the viscosity. The retention of H$$_{2}$$ bubbles in (by) the slurry was evaluated from the difference in the amount of H$$_{2}$$ observed with and without stirring the slurry after $$^{60}$$Co $$gamma$$-irradiation. From the comparison of the retention properties of the hydrophilic slurry, the hydrophobic slurry, the clay suspension, and treated water, it was suggested that H2 bubbles were retained not only by the structural viscosity but also by the steric hindrance in the hydrophilic slurry.

Journal Articles

Adsorption behavior of platinum-group metals and Co-existing metal ions from simulated high-level liquid waste using HONTA and Crea impregnated adsorbent

Osawa, Naoki*; Kim, S.-Y.*; Kubota, Masahiko*; Wu, H.*; Watanabe, So; Ito, Tatsuya; Nagaishi, Ryuji

Nuclear Engineering and Technology, 56(3), p.812 - 818, 2024/03

 Times Cited Count:2 Percentile:57.00(Nuclear Science & Technology)

Journal Articles

The Effects of unburned-gas temperature and pressure on the unstable behavior of cellular-flame fronts generated by intrinsic instability in hydrogen-air lean premixed flames under adiabatic and non-adiabatic conditions; Numerical simulation based on the detailed chemical reaction model

Thwe Thwe, A.; Kadowaki, Satoshi; Nagaishi, Ryuji

Journal of Nuclear Science and Technology, 60(6), p.731 - 742, 2023/06

 Times Cited Count:0 Percentile:0.00(Nuclear Science & Technology)

In this study, we performed numerical calculations of unsteady reaction flow considering detailed chemical reactions, investigated the unstable behavior of hydrogen-air dilute premixed flame due to intrinsic instability, and clarified the effects of unburned gas temperature and pressure. I made it. The unstable behavior of the flame in a wide space was simulated, and the burning rate of the cellular flame was obtained. Then, the effects of heat loss and flame scale on flame unstable behavior were investigated. The burning velocity of a planar flame increases as the unburned-gas temperature increases and it decreases as the unburned-gas pressure and heat loss increase. The normalized burning velocity increases when the pressure increases and heat loss becomes large, and it decreases when the temperature increases. This is because the high unburned-gas pressure and heat loss promote the unstable behavior and instability of flame.

Journal Articles

Effects of vent size and wind on dispersion of hydrogen leaked in a partially open space; Studies by numerical analysis

Terada, Atsuhiko; Nagaishi, Ryuji

Nuclear Science and Engineering, 197(4), p.647 - 659, 2023/04

 Times Cited Count:3 Percentile:42.88(Nuclear Science & Technology)

In order to understand dispersion of hydrogen leaked in a partially open space practically, which can be considered as a basic model for all processes of transfer, treatment, storage and disposal of radioactive materials containing fuel debris in the decommissioning of nuclear facilities after a severe accident, by using a CFD code, the effects of vent size and outer wind on the H$$_{2}$$ dispersion were analytically studied by adopting the experimental Hallway model, which has H$$_{2}$$ release hole on the ceiling, one vent on the Roof vent and Door vent. Air flowed in the model from the Door vent, while H$$_{2}$$ was discharged outside from the Roof vent. The discharged amount of H$$_{2}$$ increased in conjunction with the air inflow when the size of Roof and or Door vents was increased. The effect of wind depended on the direction to the Door vent: wind from the same direction as the Door vent promoted the H$$_{2}$$ discharge, while wind from the opposite direction suppressed. The dispersion characteristics of indoor leaked H$$_{2}$$ was clarified for comparing model tests with the same Froude number and different scales. It was found from the analysis results of comparing model tests with the same Froude number and different scales that when the H$$_{2}$$ leaked into the room and diffused to the air, the flow generated by the buoyancy of mixed gas created the stack effect which caused the natural ventilation by drawing in the air from the outside through vent. In addition, it was speculated that the H$$_{2}$$ concentration decreased after its leak by quickly mixing with the air which flowed in from the vents and reached to the floor due to the Coanda effect, which is the effect of the free jet being drawn to a nearby wall.

Journal Articles

Simulation of the self-propagating hydrogen-air premixed flame in a closed-vessel by an open-source CFD code

Thwe Thwe, A.; Terada, Atsuhiko; Hino, Ryutaro; Nagaishi, Ryuji; Kadowaki, Satoshi

Journal of Nuclear Science and Technology, 59(5), p.573 - 579, 2022/05

 Times Cited Count:1 Percentile:0.00(Nuclear Science & Technology)

The simulations of the combustion of self-propagating hydrogen-air premixed flame are performed by an open-source CFD code. The flame propagation behavior, flame radius, temperature and pressure are analyzed by varying the initial laminar flame speed and grid size. When the initial laminar speed increases, the thermal expansion effects become strong which leads the increase of flame radius along with the increase of flame surface area, flame temperature and pressure. A new laminar flame speed model derived previously from the results of experiment is also introduced to the code and the obtained flame radii are compared with those from the experiments. The formation of cellular flame fronts is captured by simulation and the cell separation on the flame surface vividly appears when the gird resolution becomes sufficiently higher. The propagation behavior of cellular flame front and the flame radius obtained from the simulations have the reasonable agreement with the previous experiments.

Journal Articles

Extraction behavior of a novel functionalized ionic liquid for separation of platinum group metals from aqueous nitric acid solution

Ito, Tatsuya; Osugi, Haruka*; Osawa, Naoki*; Takahashi, Tadayuki*; Kim, S.-Y.*; Nagaishi, Ryuji

Analytical Sciences, 38(1), p.91 - 97, 2022/01

 Times Cited Count:3 Percentile:22.50(Chemistry, Analytical)

A novel ionic liquid (IL) functionalized with thiodiglycol amic acid containing a soft S donor was synthesized for the effective and efficient extraction of platinum group metals (Ru, Rh, and Pd) from aqueous nitric acid solutions, such as high-level radioactive liquid waste (HLLW). The IL allowed a rapid extraction of Pd(II) with an extraction ratio of approximately 100%. The extractions of Ru(III) and Rh(III) by the IL were slower than that of Pd(II), but the rates were accelerated by temperature elevation. The extractions of Ru(III) and Rh(III) at 50$$^{circ}$$C reached equilibrium within 4 and 8 h, respectively, with the extraction ratios of over 90% without assisting agents or other methods for the extraction system. Furthermore, the IL could extract more than 90% of Ru(III), Rh(III), and Pd(II) from the simulated HLLW within 2 h at 50$$^{circ}$$C.

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

Insights Concerning the Fukushima Daiichi Nuclear Accident, Vol.4; Endeavors by Scientists, p.37 - 45, 2021/10

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 zeolites was 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.

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:0.18MB

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:2 Percentile:17.88(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:9.90(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

BB2016-0884.pdf:1.24MB

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:4 Percentile:30.44(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

228 (Records 1-20 displayed on this page)