Shigeru O'hira

Tritium behavior in the Caisson, a simulated fusion reactor room

Abstract In order to confirm tritium confinement ability in the deuterium–tritium (DT) fusion reactor, intentional tritium release experiments have been started in a specially fabricated test stand called ‘Caisson’, at Tritium Process Laboratory in Japan Atomic Energy Research Institute. The Caisson is a stainless steel leak–tight vessel of 12 m3, simulating a reactor room or a tritium handling room. In the first stage experiments, about 260 MBq of pure tritium was put into the Caisson under simulated constant ventilation of four times air exchanges per h. The tritium mixing and migration in the Caisson was investigated with tritium contamination measurement and detritiation behavior measurement. The experimental tritium migration and removal behavior was almost perfectly reproduced and could almost be simulated by a three-dimensional flow analysis code.

On-line Tritium Process Gas Analysis by Laser Raman Spectroscopy at TSTA

Laser Raman spectroscopy has been applied to the on-line analysis of the operation of the cryogenic Isotope Separation System (ISS) at the Tritium Systems Test Assembly (TSTA). A flow-through cell was employed to permit near real-time observation of the dynamic response of the 3-column ISS. Accurate analysis of hydrogen isotopic mixtures may be made in less than 2 minutes. Full response to a change in the sampling point is achieved in approximately one minute. In this paper, response measurements are shown as well as static column profiles and dynamic response to induced parameter changes. Cross check of analysis was performed with radio-gas chromatography.

Tritium contamination and decontamination study on materials for ITER remote handling equipment

Abstract Several materials, lenses, dry bearings and cables were exposed to a tritiated moisture environment to study the behavior of tritium contamination on candidate materials for ITER remote handling equipment. To optimize the tritium removal procedure, decontamination experiments using a gas purge with three different moisture concentrations were also performed. The surface tritium concentrations of CeO 2 containing alkaline barium glass (NB), CeO 2 containing lead glass (LX) and synthetic quartz (Quartz) after the exposure experiments were 7.80, 10.94 and 0.67 Bq/cm 2 , respectively. It was found that the tritium concentration was influenced by the compositions of the materials. The concentrations of tritium on type 831 (solid lubrication material: graphite) and type 237 (solid lubrication material: tungsten disulfate) dry bearings after the exposure experiments were 89.80 and 31.78 Bq/cm 2 , respectively. The tritium concentration in an electric cable tested was 5014 Bq/g after HTO moisture exposure. The tritium concentrations of lenses, LX, as typical experimental results, decreased to 2.72, 4.42 and 3.89 Bq/cm 2 by purging with the moist air, dry air and dry N 2 , respectively. The tritium concentrations of dry bearing, type 831 dropped to 6.61, 9.42 and 10.16 Bq/cm 2 by the same three decontamination treatments, respectively. A large decontamination factor of 13.6 was achieved in the case of type 831 dry bearing with a moist air purge. The tritium concentration in the electric cable was 3236 Bq/g after a moist air purge, and the decontamination factor was as low as 1.6. Therefore, decontamination with a moist air purge is not so effective for the electric cable.

Behavior of tritium in the TSTA test cell combined with operation of the Experimental Tritium Cleanup (ETC) system

Abstract Tritium and deuterium are expected to be the fuel for the first fusion power reactors. Being radioactive, tritium is a health, safety and environment concern. Room air tritium clean systems can be used to handle tritium that has been lost to the room from primary or secondary containment. Such a system called the Experimental Tritium Cleanup (ETC) systems is installed at the Tritium Systems Test Assembly (TSTA) at Los Alamos National Laboratory. The ETC consists of (1) two compressors which draw air from the room, (2) a catalyst bed for conversion of tritium to tritiated water, and (3) molecular sieve beds for collection of the water. The exhaust from this system can be returned to the room or vented to the stack. As part of the US–Japan fusion collaboration, on two separate occasions, tritium was released into the 3000 m3 TSTA test cell, and the ETC was used to handle these releases. Each release consisted of about one Curie of tritium. Tritium concentrations in the room were monitored at numerous locations. Also recorded were the HT and HTO concentrations at the inlet and outlet of the catalyst bed. Tritium surface concentrations in the test cell were measured before and at a series of times after the releases. Surfaces included normal test cell equipment as well as idealized test specimens. The results showed that the tritium became well-mixed in the test cell after about 45 min. When the ETC was turned on, the tritium in the TSTA test cell decreased exponentially as was expected. The test cell air tritium concentration was reduced to below one DAC (derived air concentration) in about 260 min. For the catalyst bed, at startup when the bed was at ambient temperature, there was little conversion of tritium to HTO. However, once the bed warmed to about 420 K, all of the tritium that entered the bed was converted to HTO. Immediately after the experiment, surfaces in the room initially showed moderately elevated tritium concentrations. However, with normal ventilation, these concentrations soon returned to routine levels. The data collected and reported here should be useful for planning for the operation of existing and future tritium facilities.

Tritium decontamination of TFTR carbon tiles employing ultra violet light

Tritium decontamination on the surface of Tokamak Fusion Test Reactor (TFTR) bumper limiter tiles used during the Deuterium-Deuterium (D-D) phase of TFTR operations was investigated employing an ultra violet light source with a mean wavelength of 172 nm and a maximum radiant intensity of 50 mW/cm 2 . The partial pressures of H 2 , HD, C and CO 2 during the UV exposure were enhanced more than twice, compared to the partial pressures before UV exposure. In comparison, the amount of O 2 decreased during the UV exposure and the production of a small amount of O 3 was observed when the UV light was turned on. Unlike the decontamination method of baking in air or oxygen, the UV exposure removed hydrogen isotopes from the tile to vacuum predominantly in forms of gases of hydrogen isotopes. The tritium surface contamination on the tile in the area exposed to the UV light was reduced after the UV exposure. The results show that the UV light with a wavelength of 172 nm can remove hydrogen isotopes from carbon-based tiles at the very surface.

Tritium Decontamination of TFTR D-T Plasma Facing Components Using an Ultra Violet Laser

ABSTRACT Tritium decontamination of the surface of plasma facing components used during the deuterium-tritium (D-T) phase of the Tokamak Fusion Test Reactor (TFTR) was investigated using an ultra violet (UV) laser with a wavelength of 193 nm, a pulse energy of 200 mJ, a pulse duration of 25 ns and a beam size of 2.3 cm by 0.7 cm. Tritium was released immediately after the samples were irradiated by the UV laser. An initial spike of tritium release was observed within 40 seconds for each of three types of TFTR D-T plasma facing components. Most of the decrease in surface tritium concentration occurred in the first minute of UV laser irradiation. In a second experiment, the UV laser was focused to irradiate the deposited layers on JT-60 graphite tile that had experienced hydrogen plasma operation. The effective absorption coefficient and the ablation threshold for the JT-60 codeposits irradiated by the UV laser were determined to be 1.9 µm−1 and 1.0 J/cm2, respectively. An erosion rate of 1.1 µm/pulse was reached at a laser energy density of 7.6 J/cm2.

Beta induced reaction study on T2-CO system

Abstract To identify the reaction products and process in the reaction of T 2 –CO 1:1 mixed system, infrared adsorption spectroscopy was applied. From the results of spectral measurements of the reaction products, aldehydes (RCTO), alcohol (ROT) and carboxylic acids (RCOOT) were found in solid phase and tritiated water and methane in gas phase. From rapid resume of absorption band intensities of CO and CO 2 following intentional extraction of the sample gas, it was revealed that ‘quasi-equilibrium states’ existed by balancing consumption and reproduction of CO and CO 2 . The ratio −ΔCO/+ΔCO 2 was much higher than that reported for the CO transformation by α irradiation and in proportion to tritium concentration in the gas phase. Tritium was accumulated in the condensed reaction products and estimated to move into the condensed phase from the gas phase about 5% per day without any hygroscopic substance. The solid products of this system, which remained for a long time, would be carboxylic acids.

Beta-decay induced reaction studies of tritium by laser Raman spectroscopy : T2CO system

The dynamic measurement of the reaction in T{sub 2}-CO 1:1 mixed gas was carried out using laser Raman spectroscopy. A catastrophic change was observed in the Raman spectra due to appearance of fine particles floating in the quartz Raman cell at about 100 min after mixing. Assignment of the new peaks on the spectra due to appearance of the particles was not successful. An attempt to specify the solid reaction product by mass spectroscopic analysis of the gas phase constituent showed the elemental formula of the product was about C{sub 1.4}:T{sub 3.0}:O{sub 1.0}. 18 refs., 3 figs., 2 tabs.

Interaction of tritium gas with Li2O crystals and dissolution processes

Interactions of T2, HT and H2 with crystalline Li2O powders as well as with single crystals were studied with emphasis on the dissolution processes. The solubility was measured with an equilibrium-quenching method at pressures from 0.02 to 70 kPa in the temperature range between 473 and 973 K. Although the amount of tritium dissolved in Li2O crystals increased as the square root of the equilibrium pressure, a discontinuity was observed at a pressure around 1–5 kPa. The heat of dissolution was 16.5 ± 2.0 kJ/mol at 0.3 kPa and 24.3 ± 0.9 kJ/mol at 67 kPa. The result suggested that chemical reactions, such as Li2O(s)+H2(g) → LiOH(s) + LiH(s), are involved in the dissolution process at pressures above 5 kPa. On the other hand, a dissociative adsorption step was suggested to play a dominant role in the course of dissolution in the low pressure range.

Tritium Decontamination from Co-deposited Layer on Tungsten Substrate by Ultra Violet Lamp and Laser

Tritium decontamination using ultra violet (UV) lamp and laser was performed. Simulated co-deposited layer on tungsten substrate was deposited by C2H2 or C2D2 glow discharge. The co-deposited layer was irradiated to UV lights from a xenon excimer lamp (172 nm) or ArF excimer laser (193 nm) and the in-situ decontamination behavior was evaluated by a mass spectrometer. After the UV irradiation, the hydrogen concentration in the co-deposited layer was evaluated by elastic recoil detection analysis (ERDA) and the depth profile was analyzed by secondary ion mass spectrometry (SIMS). For the co-deposited layer formed by C2D2 glow discharge, it was found that M/e 3 (HD) gas was released mainly during the UV lamp irradiation while both M/e 3 (HD) and M/e 4 (D2) gases were detected during the UV laser irradiation. Though the co-deposited layer was not removed by UV lamp irradiation, almost all the co-deposited layer was removed by UV laser irradiation within 1 min. The ratio of hydrogen against carbon in the co-deposited layer was estimated to be 0.53 by ERDA and the number of photon needed for removing 1 fim thick co-deposited layer was calculated to be 3.7×1018 cm-2 for the UV laser by SIMS measurement. It is concluded that C-H (C-D) bond on the co-deposited layer were dissociated by irradiation of UV lamp while the co-deposited layer itself was removed by the UV laser irradiation.