Research and development on the thermochemical water-splitting cycle using iodine and sulfur, a potential large-scale hydrogen production method, is reviewed. Feasibility of the closed-cycle ...continuous water splitting has been demonstrated by coupling the Bunsen reaction, thermal decomposition of hydrogen iodide and that of sulfuric acid. Studies are in progress to realize efficient hydrogen production. Also, development of chemical reactors made of industrial materials has been carried out, especially those used in the corrosive process environment of sulfuric acid vaporization and decomposition.
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IJS, KILJ, NUK, UL, UM, UPUK
In this study, it was evaluated the long-term catalytic effect and catalyst poisoning effect of gamma-ray irradiation on zirconium molybdate hydrate in the presence of three-way catalysts. The ...results indicated that the three-way catalyst was effective in suppressing the increase in hydrogen concentration due to radiolysis without being affected by poisoning. In addition, hydrogen diffusion analysis of the compressed hull and endpiece waste shows that hydrogen flows well through the waste and is suppressed by a three-way catalyst located in the center of the waste headspace.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
In order to elucidate ventilation and exhaust of hydrogen (H
2
) leaked in a partially open space (room) practically, the effects of outer wind (forced external flow) on them were studied ...analytically by using a CFD (computational fluid dynamics) code in the room of experimental 'Half-size Hallway model (1/2 Hallway model),' which has a H
2
release hole on the bottom, one vent on the roof (Roof vent) and another vent on the side (Door vent): 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-ε 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.
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To understand the dispersion of hydrogen (H
2
) 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, this paper uses a computational fluid dynamics code to study analytically the effects of vent size and outer wind on H
2
dispersion. The paper adopts the experimental Hallway model, which has a H
2
release hole on the ceiling, one vent on the roof (Roof vent), and one vent on the side (Door vent). Air flows in the model (room) from the Door vent while H
2
is discharged outside from the Roof vent. The discharged (outflow) amount of H
2
increases in conjunction with the air inflow when the size of the Roof and/or Door vents is increased, and then vice versa. The effect of wind depends on the direction to the Door vent: Wind from the same direction as the Door vent promotes H
2
discharge while wind from the opposite direction suppresses it. The dispersion behavior characteristics of indoor leaked H
2
are clarified for comparing model tests with the same Froude number and different scales. It is found from the analysis results of comparing model tests with the same Froude number and different scales that when H
2
leaks into the room and diffuses to the air, the flow generated by the buoyancy of mixed gas creates the stack effect, which causes natural ventilation by drawing in air from the outside through the vent. In addition, it is speculated that the H
2
concentration decreases after its leak by quickly mixing with air that flows in from the vents and reaches the floor due to the Coanda effect, which is the effect of the free jet being drawn to a nearby wall.
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For the safe storage of zeolite wastes generated by the treatment of radioactive saline water at the Fukushima Daiichi Nuclear Power Station, this study investigated the fundamental properties of ...herschelite adsorbent and evaluated its adsorption vessel for hydrogen production and corrosion. The hydrogen produced by the herschelite sample is oxidized by radicals as it diffuses to the water surface and thus depends on the sample's water level and dissolved species. The hydrogen production rate of herschelite submerged in seawater or pure water may be evaluated by accounting for the water depth. From the obtained fundamental properties, the hydrogen concentration of a reference vessel (decay heat = 504 W) with or without residual pure water was evaluated by thermal-hydraulic analysis. The maximum hydrogen concentration was below the lower explosive limit (4%). The steady-state corrosion potential of a stainless steel 316L increased with the absorbed dose rate, but the increase was repressed in the presence of herschelite. The temperature and absorbed dose at the bottom of the 504 W vessel were determined as 60 °C and 750 Gy/h, respectively. Under these conditions, localized corrosion of a herschelite-contacted 316L vessel would not immediately occur at Cl
−
concentrations of 20,000 ppm.
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In the design of MW-class spallation target system, using mercury to produce practical neutron applications, keeping the highest level of safety is vitally important. To establish the safety of ...spallation target system, it is essential to understand the thermal hydraulic properties of mercury. Through thermal hydraulic experiments using a mercury experimental loop, which flows at the rate of 1.2 m
3
/hr maximum, the following facts were experimentally confirmed. The wall friction factor was relatively larger than the Blasius correlation due to the effects of wall roughness. The heat transfer coefficients agreed well with the Subbotin correlation. Furthermore, for validation of the design analysis code, thermal hydraulic analyses were conducted by using the STAR-CD code under the same conditions as the experiments. Analytical results showed good agreement with the experimental results, using optimized turbulent Prandtl number and mesh size.
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A district heating system for household heating and road snow melting utilizing waste heat from Gas Turbine High-Temperature Reactors of 300 MW (GTHTR300s), a high-temperature gas-cooled reactor ...design, was analyzed. The application area was set in Sapporo and Ishikari, cities with heavy snowfall in northern Japan. The heat transport analyses were performed by modeling heat-transfer components in the system to estimate the system's overall heat supply profile. These components included the pipelines of the secondary water loops between the GTHTR300s and the heat-application area; heat exchangers to transfer the heat from the secondary loops to the tertiary water loops of the district-heating pipes; and the district-heating pipes of the tertiary loops between the heat exchangers and houses and roads. Single- and double-pipes for the secondary loops were compared. Although the double-pipes were advantageous for having less heat loss and a smaller excavation area, these advantages did not compensate for the higher construction cost of the pipes. To satisfy the heat demand of the application area in the month of maximum requirement, 520-529 MW of heat were supplied by 3 GTHTR300s and delivered by 6 secondary loops, 3,450 heat exchangers about 90 m long, and 3,450 tertiary loops. More efficient designs for the heat exchangers and improvements to the tertiary loops applying branched flow networks are desired to reduce the number of heat exchangers and tertiary loops and to make the heat exchangers smaller. Heat lost to the ground from the tertiary loops comprised 80%-90% of the heat loss. Applications of the larger pipe or loops using the branched flow network or double-pipe are required for more efficient heat utilization. More than 90% of the construction cost went into thermal insulators. The thickness and properties of the insulator must be reevaluated for economical heat delivery.
Japan Atomic Energy Agency (JAEA) has been conducting a study on a thermochemical IS process for hydrogen production. A pilot test of IS process is under planning that covers four R&D subjects: (1) ...construction of a pilot test plant made of industrial materials and completion of a hydrogen production test using electrically-heated helium gas as the process heat supplier, (2) development of an analytical code system, (3) component tests to assist the hydrogen production test and also to improve the process performance for the commercial plant, (4) a design study of HTTR-IS system. Development of innovative chemical reactors is in progress, which are equipped with a ceramic heat exchanger. In the design of the IS plant, it is important to establish the system for "design by analysis". Therefore, we have developed a multiphase flow analysis code that can analyze systems in which chemical reactions occur.
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Research and development (R&D) of hydrogen production systems using high-temperature gas-cooled reactors (HTGR) are being conducted by the Japan Atomic Research Institute (JAERI). To develop the ...systems, superior hydrogen production methods are essential. The thermochemical hydrogen production cycle, the IS (iodine–sulfur) process, is a prospective candidate, in which heat supplied by HTGR can be consumed for the thermal driving load. With this attractive feature, JAERI will conduct pilot-scale tests, aiming to establish technical bases for practical plant designs using HTGR. The hydrogen will be produced at a maximum rate of 30
m
3/h, continuously using high-temperature helium gas supplied by a helium gas loop, with an electric heater of about 400
kW. The plant will employ an advanced hydroiodic acid-processing device for efficient hydrogen production, and the usefulness of the device was confirmed from mass and heat balance analysis. Through design works and the hydrogen production tests, valuable data for construction and operation will be acquired to evaluate detailed process performance for practical systems. After completing the pilot-scale tests, JAERI will move onto the next R&D step, which will be demonstrations of the IS process to which heat is supplied from a high-temperature engineering test reactor (HTTR).
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