Tritium Diffusion in A1₂O₃ and BeO

Abstract

Tritium diffusion in aluminum and beryllium oxides was studied by recoiling tritium into specimens and measuring the time rate of tritium release during postirradiation heating. Results were consistent with classical diffusion solutions and gave single values for the diffusion activation energy over the temperature range of measurement for single‐crystal, sintered, and powdered specimens. Varying amounts of tritium were released as tritiated water even after attempts to remove most of the water absorbed by the specimens. Condensable amounts of tritium ranged from <20% for single‐crystal specimens to as high as 90% for some powders. Alumina containing 0.2% MgO gave tritium diffusion coefficients 4 to 5 orders of magnitude higher than those for undoped A12O3, implying a significant impurity effect on tritium diffusion. Measured diffusion coefficients were many orders of magnitude lower than hydrogen diffusion coefficients in metals. When a simple equilibrium permeation model was used which neglected tritium partition effects at interfaces and enhanced diffusion along grain boundaries, it was shown that thin coatings of beryllium or aluminum oxides on metal substrates could markedly reduce tritium permeation rates through metals. The present results may be applied in the future to fusion reactors where tritium inventories will be high and tritium diffusion within the blanket region undesirable.

Verification and validation of TMAP4

“…However, the effects of trapping are dearly evident because the breakthrough time in the absence of trapping would have been 0.0506 seconds for the same parameters otherwise. In Figure 5 note that the permeation turns on much more abruptly than in Figure 4, and it agrees quite well with the breakthrough time of 500 seconds calculated by Equation (11). There is some diffusive permeation before the theoretical breakthrough time and it takes a while Time (s) Figure 5.…”

Hydrogen Permeation Estimated by HMT in Carbon Steel Exposed to Gaseous Hydrogen

“…It is reported that the diffusion coefficient of hydrogen in the carbon steels ranges from 4:2 Â 10 À9 $1:0 Â 10 À8 m 2 /s, 14,18) while that in the Al 2 O 3 ranges from 3:4 Â 10 À46 $2:6 Â 10 À29 m 2 /s. 19) Thus, it is assumed that the low diffusivity of hydrogen in the Al 2 O 3 is closely related to the HMT result obtained in this study, in which silver particles were not visible directly on the Al 2 O 3 inclusions. Otsuka reported 20) on the basis of tritium autoradiography (TAR) that tritium was trapped on the interface between matrix phases and Al 2 O 3 inclusions in steel.…”

Corrosion Behavior of Pure Ti under a Solid NaCl Deposit in a Wet Oxygen Flow at 600 °C

“…Thus, we can conclude that the composition and the crystal structure of the oxide scale are even, and the difference between the two layers is just their compactness. At high temperature, H 2 O tends to dissociate at the defects on TiO 2 /(110) planes into free H atoms and OH groups [21][22][23]. The generated hydrogen atoms are more prone to diffuse into TiO 2 through the crystal channels in the c-axis direction, along which the diffusion rate is at least one order of magnitude larger than that in the direction perpendicular to c-axis [21,22].…”

“…At high temperature, H 2 O tends to dissociate at the defects on TiO 2 /(110) planes into free H atoms and OH groups [21][22][23]. The generated hydrogen atoms are more prone to diffuse into TiO 2 through the crystal channels in the c-axis direction, along which the diffusion rate is at least one order of magnitude larger than that in the direction perpendicular to c-axis [21,22]. This dissolution of hydrogen in TiO 2 can increase the concentration of crystal defects by forming hydrogen defects, thereby increasing the diffusion outward of Ti ions [23].…”