Takayuki Terai

Surface behaviour in deuterium permeation through erbium oxide coatings

Suppression of tritium permeation through structural materials is essential in order to mitigate fuel loss and radioactivity concerns. Ceramic coatings have been investigated for over three decades as tritium permeation barriers (TPBs); however, a very limited number of investigations on the mechanism of hydrogen-isotope permeation through the coatings have been reported. In this study, deuterium permeation behaviour of erbium oxide coatings fabricated by filtered arc deposition on reduced activation ferritic/martensitic steels has been investigated. The samples coated on both sides of the substrates showed remarkably lower permeability than those coated on one side, and the maximum reduction efficiency indicated a factor of 105 compared with the substrate. The different permeation behaviour between the coatings facing the high and low deuterium pressure sides has been found by the crystal structure analysis and the evaluation of the energy barriers. It is suggested that the permeation processes on the front and back surfaces are independent, and the TPB efficiency of the samples coated on both sides can be expressed by a multiplication of that of each side.

Modeling of Tritium Permeation Through Erbium Oxide Coatings

Abstract Tritium permeation through erbium oxide coatings has been modeled on the basis of experimental results. Permeation models were constructed step-by-step by the introduction of the following predominant parameters: surface coverage, grain size, and energy barrier. The surface-coverage model agreed with the imperfectly coated samples fabricated by filtered arc deposition as well as by metal-organic decomposition. The grain-boundary-diffusion model also agreed with the coatings fabricated by filtered arc deposition, though it was not applicable to the metal-organic decomposition coatings because of impurities and different layer structures. The energy-barrier model explains the contributions to the additional permeation reduction of the multilayer coatings. The discussion of permeation models provides new design concepts for the development of tritium permeation barriers.

THERMAL INFLUENCE ON ERBIUM OXIDE COATING FOR TRITIUM PERMEATION BARRIER

Er2O3 coating for tritium permeation barrier has been fabricated on steel substrates by a filtered arc deposition method at room temperature and 973 K. Thermal expansion of the oxide layer and the substrate induced peel-off of the coating. The non-crystalline layer is thought to play a role in forming a uniform surface coating. Five cycles of permeation measurements at 773-973 K resulted in no degradation of the coating. Different permeation behaviors are seen between degassing for 12 h at 873 K and at room temperature. Low hydrogen background following degassing at 873 K helps detect the transition to deuterium permeation. The permeation flux following different degassing conditions eventually approached comparable levels.

Tritium Monitoring for Liquid Lithium by Permeation Through Iron Window

Abstract Hydrogen permeation window is a candidate not only as the tritium recovery device from liquid lithium, but also as the hydrogen isotopes monitor for molten lithium because hydrogen permeation rate is dominated by hydrogen concentration. In this study, changing tritium concentration in lithium, tritium permeation through iron window contacting with tritium was quantified by ionization chambers. As a result, measurable amount of tritium permeated the window even though tritium concentration in lithium was in the order of wppb. The amount of tritium permeation increased as tritium concentration in lithium increased. Iron window is hopeful as tritium monitor for liquid lithium.

EFFECT OF OXYGEN ON CORROSION OF ERBIUM OXIDE IN LITHIUM

Abstract Er2O3 is one promising material for use as an insulating coating in a liquid lithium blanket system. In this study, corrosion of bulk Er2O3 in Li with high or low O concentrations was investigated at 600°C. The tests revealed that the corrosion reaction is accelerated under high O condition and suppressed in low O concentration. From these results we assumed the corrosion reaction and tested with more precise condition. The Er2O3 bulk specimen corroded significantly in Li with more than 300 ppm O. Control of O concentration is essential for a Li blanket system with an Er2O3 coating.