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Title: Tritium release from SS316 under vacuum condition

Abstract

The plasma facing surface of the ITER vacuum vessel, partly made of low carbon austenitic stainless steel type 316L, will incorporate tritium during machine operation. In this paper the kinetics of tritium release from stainless steel type 316 into vacuum and into a noble gas stream are compared and modelled. Type 316 stainless steel specimens loaded with tritium either by exposure to 1.2 kPa HT at 573 K or submersion into liquid HTO at 298 K showed characteristic thin surface layers trapping tritium in concentrations far higher than those determined in the bulk. The evolution of the tritium depth profile in the bulk during heating under vacuum was non-discernible from that of tritium liberated into a stream of argon. Only the relative amount of the two released tritium-species, i.e. HT or HTO, was different. Temperature-dependent depth profiles could be predicted with a one-dimensional diffusion model. Diffusion coefficients derived from fitting of the tritium release into an evacuated vessel or a stream of argon were found to be (1.4 ± 1.0)*10{sup -7} and (1.3 ± 0.9)*10{sup -9} cm{sup 2}/s at 573 and 423 K, respectively. Polished surfaces on type SS316 stainless steel inhibit considerably the thermal release rate of tritium.

Authors:
;  [1]
  1. Hydrogen Isotope Research Center, University of Toyama, Toyama (Japan)
Publication Date:
OSTI Identifier:
22429780
Resource Type:
Journal Article
Resource Relation:
Journal Name: Fusion Science and Technology; Journal Volume: 67; Journal Issue: 3; Conference: TRITIUM 2013: 10. International Conference on Tritium Science and Technology, Nice Acropolis (France), 21-25 Oct 2013; Other Information: Country of input: France; 13 refs.
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ARGON; AUSTENITIC STEELS; DIFFUSION; FIRST WALL; ITER TOKAMAK; ONE-DIMENSIONAL CALCULATIONS; STAINLESS STEELS; TEMPERATURE DEPENDENCE; TEMPERATURE RANGE 0400-1000 K; TRITIUM; TRITIUM OXIDES

Citation Formats

Torikai, Y., and Penzhorn, R.D.. Tritium release from SS316 under vacuum condition. United States: N. p., 2015. Web. doi:10.13182/FST14-T93.
Torikai, Y., & Penzhorn, R.D.. Tritium release from SS316 under vacuum condition. United States. doi:10.13182/FST14-T93.
Torikai, Y., and Penzhorn, R.D.. Sun . "Tritium release from SS316 under vacuum condition". United States. doi:10.13182/FST14-T93.
@article{osti_22429780,
title = {Tritium release from SS316 under vacuum condition},
author = {Torikai, Y. and Penzhorn, R.D.},
abstractNote = {The plasma facing surface of the ITER vacuum vessel, partly made of low carbon austenitic stainless steel type 316L, will incorporate tritium during machine operation. In this paper the kinetics of tritium release from stainless steel type 316 into vacuum and into a noble gas stream are compared and modelled. Type 316 stainless steel specimens loaded with tritium either by exposure to 1.2 kPa HT at 573 K or submersion into liquid HTO at 298 K showed characteristic thin surface layers trapping tritium in concentrations far higher than those determined in the bulk. The evolution of the tritium depth profile in the bulk during heating under vacuum was non-discernible from that of tritium liberated into a stream of argon. Only the relative amount of the two released tritium-species, i.e. HT or HTO, was different. Temperature-dependent depth profiles could be predicted with a one-dimensional diffusion model. Diffusion coefficients derived from fitting of the tritium release into an evacuated vessel or a stream of argon were found to be (1.4 ± 1.0)*10{sup -7} and (1.3 ± 0.9)*10{sup -9} cm{sup 2}/s at 573 and 423 K, respectively. Polished surfaces on type SS316 stainless steel inhibit considerably the thermal release rate of tritium.},
doi = {10.13182/FST14-T93},
journal = {Fusion Science and Technology},
number = 3,
volume = 67,
place = {United States},
year = {Sun Mar 15 00:00:00 EDT 2015},
month = {Sun Mar 15 00:00:00 EDT 2015}
}
  • One conceivable option for the disposal of tritium-contaminated stainless steel consists in its storage at ambient temperature in a purged containment. To assess this option several stainless steel 316 specimens, previously loaded at elevated temperatures with 0.8-8.5 MBq of tritium, were flushed continuously with dry argon (water partial pressure 0.073 Pa) for extended periods of time. The released tritium (more than 99 % in the form of tritiated water (HTO)) was collected in bubblers and monitored periodically by liquid scintillation counting. After an initial fast liberation a fairly constant rate of the order of 0.2 % per day established. Tritiummore » depth profile in the SS specimens could be simulated by a diffusion limited desorption model. The rate determining step for tritium release appears to be bulk diffusion.« less
  • Tritium concentration measurements have been made of the tritium recovery from the JT-60U after high power neutral beam injected discharges. This work has been done to study tritium release characteristics and to assess the tritium inventory in the vacuum vessel. Cleanup operations by hydrogen divertor discharges and helium glow discharge cleanings were performed to deplete the tritium inside the wall prior to in-vessel maintenances. After the beginning of the divertor discharges the tritium release from walls increases gradually. The release rate depends on the surface temperature of divertor plates and it is enhanced by high-power neutral beam heated divertor dischargesmore » combined with high-temperature vessel baking. Helium glow discharges, furthermore, give strong release characteristics compared with divertor discharges in spite of their short duration within {approximately}1 hr. After the deuterium discharges and cleanup operations from July 1991 to July 1994, it is estimated that 70{approximately} 80% of the total tritium of 39 GBq generated in the plasma is retained inside the graphite first wall.« less
  • The behavior of tritium release from the vacuum vessel of JT-60U during air exposure phase at controlled water vapor concentration and gas purging in the wall conditioning phase has been investigated. For the air exposure with varying water vapor concentrations of 40ppm, 300ppm, 680ppm and 3400ppm, tritium concentration in the vacuum vessel of JT-60U was measured. At each water vapor concentration, tritium concentration initially increased with time and then became steady finally. The steady tritium concentration increased with water vapor concentration. The total amount of tritium released from the vacuum vessel was 13MBq for 3400ppm. This amount is almost themore » same as that removed by 5 hours' H{sub 2}-GDC, which has been the most effective method for tritium removal from JT-60U. This suggests that tritium in the vacuum vessel of JT-60U can be easily removed by water vapor. Tritium released into exhaust gas during gas purging was also measured for varying gases (H{sub 2}, He and Ar), at different pressures and temperatures of the vacuum vessel. Tritium concentration of the exhaust gas was about 0.1Bq/cm{sup 3} at room temperature and was independent of gas species within the pressure from 0.05 to 0.3 Pa. This result indicates that isotope exchange of tritium with hydrogen molecules was not so active under these purge conditions.« less
  • The 2:1 mixture of LiF and BeF{sub 2} (Flibe) is a potential liquid tritium breeding material for fusion reactors, because of low electric conductivity, high chemical stability in air, etc. We have been studying tritium release behavior from Flibe by in-pile tritium release experiment in the fast neutron source reactor `YAYOI` of the University of Tokyo. About 100g of Flibe was utilized for neutron irradiation to produce tritium, and the tritium released from the specimen was swept by making purge gas flowing over the specimen. Tritium release rate increased with elapsed time after the start of irradiation and a steadymore » state was attained in about four hours at 873K in case of H{sub 2} purge gas. Released chemical forms of tritium were HT and TF, and their proportions depended not on the kind of container and tubing materials, but on the chemical composition of purge gas and the dehumidification time of specimen at high temperatures. Tritium generated as T{sup +} in Flibe was released by way of two routes; (1) direct release to purge gas as TF and (2) release to purge gas after converted to HT by the isotopic exchange reaction with H{sub 2}. The reaction rate was controlled by the H{sub 2} concentration and F{sup -} potential in the system. In case of high hydrogen concentration and low F{sup -} potential in the system, tritium was released as HT with a relatively high rate. In case of high F{sup -} potential in the system, on the other hand, tritium was released as TF with a low rate. 5 refs., 7 figs., 1 tab.« less
  • Experimental data on x-ray-induced gas adsorption and gas release from surfaces are reviewed with results for stainless steel and Al/sub 2/O/sub 3/ surfaces. CO/sub 2/ and O/sub 2/ are the major species which desorb from such surfaces under x-ray irradiation. Mean quantum yields are given for these systems. Results from experiments using photons of lower (e.g., visible or uv range, synchrotron radiation) or higher (..gamma..-ray) energy help to interpret the data obtained with photons in the x-ray range. X-ray-induced photodesorption needs to be considered in attaining high vacuum in plasma containment devices.