Measurement of tritium in tungsten deposition layer by imaging plate technique after exposure to gaseous tritium

It is important to understand tritium desorption behavior from plasma-facing materials of a fusion reactor in order to discuss effective tritium recovery method from in-vessel components. However, basic behavior of hydrogen isotopes in W deposition layer is not understood completely. In this study, characterized tungsten deposition layer formed by hydrogen plasma sputtering was exposed to gaseous tritium at 300 °C or 500 °C and tritium desorption behavior by vacuum heating was investigated by the imaging plate technique. For comparison, bare tungsten substrates were exposed to gaseous tritium in the same condition. Initial tritium activity in the deposition layer was much higher than that in the bare substrate. Tritium desorption behavior from tungsten deposition layer was different by the temperature of the layer during tritium exposure process. By heating at 500 °C for 1 h, 97.5% of tritium was desorbed from the layer exposed to tritium at 300 °C. On the other hand, by heating at 500 °C for 2 h, only 44.6% of tritium was desorbed from the layer exposed to tritium at 500 °C. To recover most tritium from W deposition layer and W substrate, heating at above 700 °C is required.