Diffusion Coefficient Of Tritium Research Articles

Hydrogen Diffusion and Solubility in Silicon Carbide

Tritium diffusion coefficients and deuterium solubilities were measured for silicon carbide. At 500° to 1300° C, measured tritium diffusion coefficients were much lower than the recorded values for metals, whereas the activation energies for diffusion were much higher (30 to 75 kcal/mol). The solubility of deuterium in silicon carbide decreased as temperature increased and exhibited a pressure dependence of ∼P1l2.

Tritium Diffusion in A12O3 and BeO

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.

Abstract: Tritium diffusion in ceramic materials for thermonuclear reactors

Tritium diffusion coefficients have been measured in ceramic materials of potential interest as insulator or wall materials in controlled thermonuclear reactors. Tritium was recoil injected into samples to about 2×1014 atoms/cm2 through thermal‐neutron transmutation of a surface blanket of 6Li‐enriched Li2CO3 in the NCSU Pulstar research reactor. Diffusion coefficients were determined from measurement of the tritium release rate during postirradiation isothermal annealing. Released tritium was detected either with an internal‐flow proportional counter using P‐10 sweep gas or with an ion chamber using a 90% helium–10% hydrogen gas mixture. The total amount of tritium in a sample was determined by heating to successively higher temperatures until no further tritium was released.Tritium release fractions were linear with t1/2 for short times as predicted by classical solutions for recoil‐injected specimens.1 Diffusion coefficients were calculated from the release curves employing calculated values for the tr...

Surface effects on tritium diffusion in niobium, zirconium and stainless steel

Tritium diffusion in niobium, Zircaloy-2 and stainless steel has been studied by measurement of both tritium concentration profiles and surface tritium release rates. Concentration profiles show buildup of tritium in the surface layers of a specimen with classical diffusion behavior at depths greater than about 5 μm from the surface. Application of a two-region diffusion model to the experimental data gives tritium diffusion coefficients in the surface films which are lower than the bulk diffusion coefficients by two orders of magnitude in stainless steel and eight to ten orders of magnitude in niobium and Zircaloy over a temperature range of interest for fission and fusion reactor systems. The surface effect appears to be a consequence of oxide film formation and is not due to the helium injected into specimens along with the tritium.

Untersuchungen zur Diffusion von Tritium in Übergangsmetallen

Investigations of the diffusion of tritium in transition metals have been carried out by using "time-lag" methods. The β-radiation, originating from tritium decay within a thin layer near the external surface of the metal, was taken as the signal to follow the change of tritium concentration with time in this layer. No passage of tritium atoms through the phase boundary is necessary for this method; the influence of energy barriers, which might retard this passage, can therefore not interfere. Measurements with palladium at temperatures between 16.5 °C and 50 °C and vanishing hydrogen content in the Pd yielded: D0 T = (10.5 ± 3.0) • 10-3 • exp{- (6350 ± 300)/RT} cm2 s-1, (R T in cal/mole). The observed isotope effects in the diffusion of H, D and T in palladium are discussed. At 25 °C diffusion coefficients of tritium in Pd/Ag-alloys of different compositions (0 - 70 atom-% Ag) were determined. They first decrease slowly with rising silver content up to 30% and then drop sharply to very low values at higher Ag-contents. Measurements with tantalum at 25 °C yielded: DT = (0.50 ±0.25) • 10-6 cm2 s-1

On the solubility and diffusion coefficient of tritium in single crystals of silicon

The solubility and the diffusion coefficient of tritium in silicon were measured. The samples were of p-typesilicon, with a resistivity of 150Ωcm and with dimensions of 10 × 5 × 2 ∼ 0.5 mm. The samples were put into fused silica ampoules and tritium, under 100 mm Hg and at 20°C, was introduced into them. The ampoules were then heated at 900 ∼ 1200°C for an hour. The samples thus prepared were placed in another ampoule connected to the gas ionization chamber and heated at 1000°C and the total amount of tritium evolved from the silicon was estimated. The solubility was expressed by: S = 1·6 × 10 20 exp (−34000/ RT) atoms cm −3 under 1 atm of tritium. The diffusion coefficient, D, was also estimated from the out-diffusion of tritium at 400 ∼ 500°C: it is given by: D = 4·2 × 10 −5 exp (−13000/ RT) cm 2 sec −1.

The diffusion of tritium from irradiated beryllium oxide powders

The release of tritium from irradiated beryllium oxide powders has been studied by the method of post-irradiation anneal. Over the temperature range 400–660° C, the release is a diffusion controlled process with an activation energy of 24 kcal. The diffusion coefficient of tritium in the two powders studied is given by D UOX = 6.6 × 10 −13 exp − 24 500 RT D MINOX = 7.6 × 10 −13 exp − 24 000 RT . The precautions necessary to obtain reliable results are described.