The effect of helium generation and irradiation temperature on tritium release from neutron irradiated beryllium

The effect of neutron irradiation condition on tritium release from beryllium is described in this paper. Beryllium samples were irradiated in the SM reactor with neutron fluence (E>0.1 MeV) of (0.37–2.0) × 1022 cm−2 at 70–100 and 650–700 °C. Mass-spectrometry technique was used in out of pile tritium release experiments during stepped-temperature anneal within a temperature range from 250 to 1300 °C. The total amount of helium accumulated in irradiated beryllium samples varied from 521 to 3061 appm. The first signs of tritium release were detected at temperature of 406–553 °C. It was shown that irradiation temperature and helium generation level significantly affect the tritium release. A fraction of 44–74% of tritium content in samples irradiated at low temperature (70–100 °C) is released from beryllium at an annealing temperature below 800 °C, whereas for samples after high temperature irradiation (650–700 °C) tritium release did not exceed 14%. Majority of tritium (∼68%) is released within a temperature range from 800 to 920 °C. The increase of helium generation from 521 to 3061 appm results in lowering the temperature of maximal tritium release rate and the upper temperature of tritium release from beryllium by 100–130 and 200–240 °C, correspondingly. On the basis of data obtained, the diffusion coefficients of tritium in beryllium were calculated.