TRITIUM RELEASE CHARACTERISTICS OF NEUTRON-IRRADIATED REFERENCE BERYLLIUM PEBBLES FOR THE HELIUM COOLED PEBBLE BED (HCPB) BLANKET

摘要

In this paper, we present results on tritium release from the beryllium pebbles irradiated for 294 full power days from 17 April 2003 to November 2004 to the neutron fluence of 1.5-2 × 10~(25) m~2 (E>1 MeV) at temperature 523-773 K in the pebble-bed assemblies (PBA) experiment in the high flux reactor (HFR) at Petten, the Netherlands. Stages of gradual and burst release are evident in the tritium release of the PBA Be pebbles at a temperature ramp of 2.3-4.8 K/min from room temperature to 1310-1520 K. These two stages may be related to the tritium release by atomic diffusion and bubble venting respectively. The main maximum of the tritium release rate of the PBA Be pebbles was found to be in the temperature ranges of 1178-1309 K and 1178-1350 K at the temperature ramps of 2.4 and 4.8 K/min respectively. The tritium inventory and abundance ratios of chemical forms of tritium localized in the pebbles were determined with dissolution methods. The total tritium inventory in the PBA Be pebbles was found to be 2-4 GBq/g.