Rie Kurata

Trapping behaviour of deuterium ions implanted into tungsten simultaneously with carbon ions

The trapping behaviour of deuterium ions implanted into tungsten simultaneously with carbon ions was investigated by thermal desorption spectroscopy (TDS) and x-ray photoelectron spectroscopy (XPS). The D2 TDS spectrum consisted of three desorption stages, namely desorption of deuterium trapped by intrinsic defects, ion-induced defects and carbon with the formation of the C–D bond. Although the deuterium retention trapped by intrinsic defects was almost constant, that by ion-induced defects increased as the ion fluence increased. The retention of deuterium with the formation of the C–D bond was saturated at an ion fluence of 0.5×1022 D+ m–2, where the major process was changed from the sputtering of tungsten with the formation of a W–C mixture to the formation of a C–C layer, and deuterium retention as the C–D bond decreased. It was concluded that the C–C layer would enhance the chemical sputtering of carbon with deuterium with the formation of CDx and the chemical state of carbon would control the deuterium retention in tungsten under C+–D2+ implantation.

Correlation between deuterium retention and microstructure change for tungsten under triple ion implantation

Triple ion (C+, D2+ and He+) implantation onto a tungsten substrate was performed to investigate the hydrogen isotope and microstructure behavior under fusion conditions. The results are compared to the ones from dual ion (C+ and D2+) implanted tungsten. It was found that the TDS spectrum for the triple ion implanted sample is quite different from that for the dual ion implanted sample and the deuterium retention decreased when He+ was added to the incident beam indicating that the helium prevented deuterium trapping. TEM images show that dislocations and dislocation loops were introduced in tungsten in both the dual and triple ion irradiation experiments and helium bubbles were formed on the triple ion implanted tungsten. After heating up to 1173 K, not only the dislocations and dislocation loops but also helium bubbles remained on the triple ion implanted sample, but the dislocations and dislocation loops were moved and/or annihilated on the dual ion implanted sample. The formation of a WC layer was inhibited in the triple ion implanted sample.

Operational Experience of Tritium Handling Facilities in the Japan Atomic Energy Agency’s Tritium Process Laboratory

Abstract Tritium Process Laboratory (TPL) in Japan is operated by the Japan Atomic Energy Agency (JAEA) and was established as the only facility to handle over one gram of tritium in Japan in 1985. Since March 1988, the TPL has been operated safely with tritium, and no tritium release accidents have been occurred. The maximum tritium concentration of a three-month average in a stream from a stack of TPL to environment was 350 Bq/m3, and is about 14 times smaller than that of the legal release limit in Japan. The failure data have been analyzed for several main components of the safety systems such as pumps and monitors. The tritium waste data has also been accumulated as liquid and solid waste from TPL. Through this operating experience, a significant database for the safety systems of the TPL has been accumulated. This data can provide a source of reliability information for a future fusion facilities.

Recent Progress on Tritium Technology Research and Development for a Fusion Reactor in Japan Atomic Energy Agency

Abstract JAEA has two tritium handling laboratories, such as Tritium Processing Laboratory (TPL) in Tokai and DEMO R&D building in Rokkasho. Specially, TPL has been accumulated a gram level tritium safety handling experiences without any accidental tritium release to the environment for more than 25years. At the Grate East Japan Earthquake 2011, TPL received many effects, such as building surface crack etc., however, tritium confinement function was successfully maintained with adequate safety interlock actions and almost all safety related effects will be recovered within March 2014. Recently, our activities have been focused to the 1) ITER Detritiation system R&D task; 2) DEMO R&D tasks in Broader Approach (BA) activities, such as a) tritium accountancy, b) tritium interactions with various materials, and c) tritium durability; and 3) Recovery works from the Grate East Japan Earthquake 2011.

Dynamic Behaviors of Deuterium Retained in SS-316 Oxidized at Various Temperatures

Abstract The trapping and release mechanisms of hydrogen isotopes for the stainless steel (SS) oxidized at various temperatures were investigated. The oxide layer was mainly consisted of iron oxides (FexOy) and its decomposition temperature was almost consistent with the release temperature of deuterium, where major chemical form was a molecular deuterium (D2). The deuterium retention was increased as the oxidation temperature increased. It was considered that the thickness of oxide layer would make a large influence on the retention of hydrogen isotopes. On the other hand, the amount of released deuterium as heavy water (D2O) was independent with oxidation temperature. It was considered that the formation of hydrogen isotope as water form was depended on the amount of FexOy on the top most surface layer of SS.

Impurity Effects on Hydrogen Isotope Retention in Carbon-Oxygen Containing Boron Films

Abstract Impurity effects on chemical behavior of energetic deuterium implanted into the carbon-oxygen containing boron films were investigated as a function of impurity concentrations by means of XPS and TDS. This study was carried out for about 40% impurities-containing boron films. It was found that a major chemical state of carbon was C-B bond and that of oxygen was free oxygen for the carbon-oxygen containing boron films. Most of deuterium was trapped by the C-B bond to form a B-C-D bond. On the other hand, free oxygen formed heavy water (D2O) and released as D2O during deuterium implantation. The amount of deuterium trapped by carbon was increased as the carbon concentration increased. However, the deuterium retention for the carbon-oxygen containing boron film with less than 20% carbon was almost twice as high as that for the only about 20% carbon-containing boron films. It was also indicated that the formation of free carbon was refrained due to the existence of free oxygen which induce the increase of C-B bond in about 40% impurities-containing boron films. These results indicate that hydrogen isotopes were trapped as B-C-D bond, which released deuterium at 900 K, in lower carbon concentration as oxygen coexists with carbon in the boron films. It was concluded that impurity concentration should be kept as low as possible to prevent tritium retention in the boron film deposited on the first wall in future fusion devices.

Retention and Desorption Behaviors of Hydrogen Isotopes in Gamma-Ray Irradiated Li 2 TiO 3

Abstract Annihilation behaviors of irradiation defect and, correlation of these behaviors with deuterium trapping and desorption in gamma-ray irradiated Li2TiO3, which is one of the candidates for tritium breeding material, were studied by means of an ESR(Electron Spin Resonance) method and TDS (Thermal Desorption Spectroscopy). From the ESR spectra, gamma-ray irradiation induced irradiation defects such as E’-centers, oxygen-hole centers which were expected to be tritium trapping sites. These irradiation defects were annihilated in the temperature range of 500-650 K. From the TDS spectra for Li2TiO3 exposed to D2 gas, the deuterium desorption behavior was found to consist of four stages, corresponding retention as the surface, in E’-center and as hydroxides bound with Ti or Li. In addition, most of deuterium was released as water form around 400, 550 and 650K. By comparison of the amounts of the deuterium retentions with or without the gamma-ray irradiation, the retention of deuterium trapped with the irradiation defects was increased by gamma-ray irradiation, indicating that the irradiation defects like E’-centers induced by gamma-ray irradiation would be one of the tritium trapping sites in tritium breeding materials. The activation energy of hydrogen isotope desorption from the E’-center was estimated to be 0.63 eV for gamma-ray irradiated Li2TiO3, showing good agreement with that of the recombination reaction between the E’-center and the oxygen-hole center. These results indicated that the tritium desorption was governed by the annihilation of the E’-centers.