Tritium release behavior of beryllium pebbles after neutron irradiation between 523 and 823 K

Post-irradiation tritium release from the Pebble Bed Assembly (PBA) neutron-irradiated beryllium (Be) pebbles (∅ ≈ 1 mm; the total tritium inventory 2–4 GBq/g) was investigated on annealing in He + 0.1% H2. Temperature ramps of 2.3 K/min followed by annealing for 1 h at 1310–1320 K resulted in complete detritiation of the PBA Be pebbles. The tritium burst release occurred after a time lag of 1–6.5 h during constant temperature anneals at 1089–1180 K, with the release time measured after reaching the annealing temperature. Tritium burst release was also observed to occur during cool down. Anneals at 1089 K for 8 h and at 1045 K for 23 h caused detritiation of the PBA Be pebbles by ⩾75%. Effective values of the tritium diffusivity were estimated for the PBA Be pebbles as 2.6 × 10−13 m2/s for 1045 K; 4.7–5.1 × 10−13 m2/s for 1089 K