Retention and Release of Tritium in B4C Irradiated as Control Rod of Fast Breeder Reactor

Abstract

The release and retention of tritium generated in FBR control rods of B4C irradiated to high fluence were investigated for temperatures up to 800°C. The amounts of tritium generated in B4C specimens were released by reacting each specimen with a solid NaOH. Released tritium gas was introduced into water and then its radioactivity was measured with a liquid scintillation counter. The amounts of retention were expressed as a function of fluence, and the results agreed approximately with the theoretically calculated values. In addition, the amounts of tritium could be approximately evaluated by simply measuring the radioactivity of 54Mn using a germanium semiconductor detector, which is generated from Fe impurity in B4C. The temperature at which the tritium begins to be released from B4C was investigated by heating a specimen at a constant temperature increasing rate. It was found in this experiment that the tritium begins to be released from B4C at 400°C. From the results of this isochronal heating, diffusion coefficients of tritium in B4C were derived. Their temperature dependence was given using the following equation. The activation energy was expressed in J/mol and this result agreed approximately with results reported by other researchers.