Abstract
Study of tritium and helium release from beryllium pebbles with diameters of 0.5 and 1mm after high-dose neutron irradiation at temperatures of 686–968K was performed. The release rate always has a single peak, and the peak temperatures at heating rates of 0.017K/s and 0.117K/s lie in the range of 1100–1350K for both tritium and helium release. The total tritium release from 1mm pebbles decreases considerably by increasing the irradiation temperature. The total tritium release from 0.5mm pebbles is less than that from 1mm pebbles and remains constant regardless of the irradiation temperature. At high irradiation temperatures, open channels are formed which contribute to the enhanced tritium release.
Highlights
Beryllium is considered to be used as a neutron multiplier material in a form of pebbles with a diameter of 1 mm in the helium cooled pebble bed (HCPB) breeding blanket of ITER and DEMO
Tritium and helium release tests of beryllium pebbles irradiated in the High Flux Reactor (HFR), Petten, the Netherlands, were chosen as a mandatory step of post-irradiation examinations (PIE)
This increase means a permanent helium accumulation in beryllium with increasing neutron fluence because according to the capsule design [4,5], the higher irradiation temperature of the pebbles in the capsule corresponds to the higher neutron fluence. From this point it can be concluded that helium produced under irradiation in beryllium remains in the pebble what completely differs from tritium, which can leave the pebble during irradiation at increasing irradiation temperatures
Summary
Beryllium is considered to be used as a neutron multiplier material in a form of pebbles with a diameter of 1 mm in the helium cooled pebble bed (HCPB) breeding blanket of ITER and DEMO [1,2]. The beryllium pebbles will be irradiated by high fluxes of fusion neutrons resulting in the production of significant amounts of tritium and helium atoms. Helium plays a key role in mechanisms of radiation damage of beryllium under neutron irradiation, in particular, in the tritium retention. Tritium and helium release tests of beryllium pebbles irradiated in the HFR, Petten, the Netherlands, were chosen as a mandatory step of post-irradiation examinations (PIE). The objective of this study is to establish regularities of tritium and helium release behavior in neutron-irradiated beryllium in connection with radiation-induced changes in the microstructure
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