Yoshinori Kawamura

Extraction of Hydrogen from Water Vapor by Hydrogen Pump Using Ceramic Protonic Conductor

Abstract A blanket tritium recovery system that uses an electrochemical hydrogen pump with a protonic conductor membrane is proposed. One of the advantages of this system is the potential for processing the blanket sweep gas without fractionation of hydrogen isotopes and water vapor. In this work, hydrogen in a water molecule is extracted by a hydrogen pump using a Perovskite-type ceramic such as SrCe0.95Yb0.05O3-α. The threshold, which corresponds to the energy of H2O decomposition, for hydrogen extraction from the water molecule is 500 to 600 mV at 873 K. The threshold becomes smaller with increases of the partial pressure of the water vapor. In the case of pumping of the H2-H2O mixture gas, transportation of H2 precedes H2O decomposition below the threshold (H2O decomposition voltage), and the threshold becomes larger. In order to process the blanket sweep gas without fractionation of hydrogen isotope and water vapor, comparatively high applied voltage is required.

Tritium mass balance in the piping system of a fusion reactor

This paper discusses the behavior of tritium on the surface of various piping materials considering the various mass transfer steps. It is observed in this study that the isotope exchange reaction between gaseous hydrogen in gas stream and surface water and transfer of hydrogen isotopes and water through surface layer formed on materials or pores are most effective when an oxide film layer is formed on a material surface such as stainless steel. The amount of tritium sorbed on the stainless steel is correlated and compared with that observed for copper or quartz. The memory effect observed for an ionization chamber having stainless steel electrodes is also compared with that having copper electrodes.

R&D of a Li2TiO3 pebble bed for a test blanket module in JAEA

At JAEA, a test blanket module (TBM) with a water-cooled solid breeder is being developed. This paper presents recent achievements of research activities for the TBM, particularly addressing the pebble bed of the tritium breeder materials and tritium behaviour. For the breeder material, the chemical stability of Li2TiO3 was improved using Li2O additives. To analyse the pebble bed behaviour, thermomechanical properties of the Li2TiO3 pebble bed were assessed experimentally. To verify the pebble beds nuclear properties, the activation foil method was proposed and a preliminary experiment was conducted. To reduce the tritium permeation, the chemical densified coating method was developed and the coating was attached to F82H steel. For tritium behaviour, the tritium recovery system was modified in consideration of the design change of the TBM.

OPERATIONAL RESULTS OF THE SAFETY SYSTEMS OF THE TRITIUM PROCESS LABORATORY OF THE JAPAN ATOMIC ENERGY AGENCY

Abstract The building and safety systems of the TPL (Tritium Process Laboratory) were constructed in 1984 and 1985. The safety systems in the TPL have operated with tritium since March 1988. The amount of tritium held in the TPL was 13 PBq in March 2007. The average tritium concentration in a stream from a stack of the TPL to the environment was 6.0 x 10-3 Bq/cm3 and is 1/100 smaller than that of the regulatory value for the concentration of HTO in the air in Japan. Safe operation with tritium has been demonstrated. A set of failure data for several main components of the TPL was also obtained as valuable data for a fusion tritium facility.

Adsorption isotherms for tritium on various adsorbents at liquid nitrogen temperature

Abstract The cryosorption method is useful for extracting hydrogen isotopes from a helium gas stream with a small amount of hydrogen isotopes. Therefore, in fusion reactors, this method is expected to be applied for the helium glow discharge exhaust gas processing system and the blanket tritium recovery system. To design these systems, adsorption isotherms for each hydrogen isotope are needed, making it possible to estimate the amount of adsorption in a wide pressure range. The amount of tritium adsorption on molecular sieve 5A, molecular sieve 4A, and activated carbon, which are potential adsorbents in the cryosorption bed, at liquid nitrogen temperature were quantified using the volumetric method. It was found that adsorption isotherms of tritium were also expressed with the two-site Langmuir model and that the obtained isotherms were close to the reported isotherms, the Langmuir coefficients for which were estimated using a reduced mass of hydrogen isotopes.

Research and development of the tritium recovery system for the blanket of the fusion reactor in JAEA

A water-cooling solid breeder blanket is a prime candidate for the blanket of the fusion reactor in Japan. In this case, the blanket tritium recovery system will be composed of three processes: tritium recovery from helium sweep gas as hydrogen, that as water vapour and tritium recovery from coolant water. The authors have proposed a set of advanced systems. For tritium recovery as hydrogen, an electrochemical hydrogen pump with a ceramic proton conductor has been proposed. The correlation between the proton concentration in the ceramic and the hydrogen gas pressure has been investigated to describe the pumping performance specifically. A ceramic electrolysis cell has been proposed to process the tritiated water vapour. The authors have developed a new electrode containing cerium oxide, and it has shown fairly good electrolysis efficiency. For tritium recovery from coolant water, reduction in the processing water by tritium concentration is necessary. The authors have proposed to apply the fixed-bed adsorption process of synthetic zeolite, and have developed new zeolite. It showed unique characteristics for water adsorption and desorption. The authors have determined the potential of these systems for the blanket of the fusion DEMO reactor.

Interlinked Test Results for Fusion Fuel Processing and Blanket Tritium Recovery Systems Using Cryogenic Molecular Sieve Bed

A simulated fuel processing (cryogenic distillation columns and a palladium diffuser) and CMSB (cryogenic molecular sieve bed) systems were linked together, and were operated. The validity of the CMSB was discussed through this experiment as an integrated system for the recovery of blanket tritium. A gas stream of hydrogen isotopes and He was supplied to the CMSB as the He sweep gas in blanket of a fusion reactor. After the breakthrough of tritium was observed, regeneration of the CMSB was carried out by evacuating and heating. The hydrogen isotopes were finally recovered by the diffuser. At first, only He gas was sent by the evacuating. The hydrogen isotopes gas was then rapidly released by the heating. The system worked well against the above drastic change of conditions. The amount of hydrogen isotopes gas finally recovered by the diffuser was in good agreement with that adsorbed by the CMSB. The dynamic behaviors (breakthrough and regeneration) of the system were explained well by a set of basic codes.

Recovery of tritium by cryogenic molecular sieve bed in breeding blanket interface condition

Experiments were performed to obtain detailed adsorption and desorption characteristics of tritium (HT) by Cryogenic Molecular Sieve Bed (CMSB) in liquid nitrogen temperature under the simulated Breeding Blanket Interface (BBI) condition. Computer simulation analyses gave the values of separation factor and mass transfer coefficient of HT in H{sub 2}, which are very important basic parameters for the optimum design of CMSB process in BBI.

ADSORPTION OF HYDROGEN ISOTOPES ON VARIOUS ADSORBENTS AT CRYOGENIC TEMPERATURE

Cryogenic adsorption is effective for the separative recovery of hydrogen isotopes of small concentrations from the bulk helium gas. The authors performed a screening test to find candidate adsorbents for the recovery of hydrogen isotopes from the bulk helium gas at liquid nitrogen temperature. The screening test indicates that a natural mordenite adsorbent has a quite high adsorption capacity for hydrogen under the helium atmosphere. The effect of the ion exchange for the natural mordenite on the adsorption capacity of hydrogen was also investigated using protium and silver as well. With regard to the adsorbent examined in the screening test, the adsorption characteristics of deuterium were also investigated. For the adsorption of deuterium, it was found that the natural mordenite adsorbent have a high adsorption capacity. The isotope effect on the adsorption of hydrogen isotopes on the natural mordenite adsorbent is not large compared with the MS5A adsorbent.

Conceptual design of the blanket tritium recovery system for the prototype fusion reactor

ABSTRACT In this design work, a combination of the hydrogen pumps in charge of the function of hydrogen isotopes recovery and the oxygen pump was adopted to the blanket tritium recovery system for the prototype fusion reactor designed by Japan Atomic Energy Research Institute (JAERI). The main functions of this system are described below. 1) Transport of tritium with helium purge gas: tritium released from ceramic breeding material in the blanket is transported to the tritium recovery system by the helium purge gas which contains a small amount of hydrogen gas. 2) Steam electrolysis and removal of oxygen gas: the oxygen pump with electrolyte of oxygen ionic conductors electrolyzes the steam (H2O and HTO) contained in the purge gas into hydrogen isotopes and oxygen, and simultaneously removes impurity of oxygen by electrical membrane permeation. 3) Recovery of hydrogen isotopes: the hydrogen pump with electrolyte of protonic conductors electrically recovers the pure hydrogen isotopes (HT and H2) from the purge gas. Based on the experimental data obtained by feasibility study and the present design effort, it was revealed that the simple and continuous tritium recovery system for gaseous stream is possible and attractive for fusion power reactors.