The behavior of tritium at removal from graphite material for a fusion reactor is discussed. The mass transfer coefficient representing the isotope exchange reaction between hydrogen isotopes in the gas stream and tritium existing on graphite surfaces and that between water vapor in the gas stream and tritium on the surface are quantified. It was found that the reaction rate between hydrogen isotopes in the gas stream and tritium on the surface is much slower than that between water vapor in the gas stream and tritium on the surface. And, the release behavior of tritium from a graphite particle to the gas phase is calculated with the reaction rates obtained in this study using the solubility and the diffusion coefficient of hydrogen isotopes in graphite that have been presented in the previous report by the authors. A way to remove tritium from a graphite surface applying the isotope exchange reaction between water vapor in the gas stream and tritium on the surface turns out to be effective at the room temperature, although a temperature >1000K is needed to release tritium from the bulk of a 10-μm graphite particle.
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