Magnetic Field Effects on Tritium Release from Neutron-Irradiated Beryllium Pebbles

The effects of temperature, magnetic field (MF), and ionizing radiation on the release of tritium from the Be pebbles irradiated in the BERYLLIUM experiment in 1994 in Petten, The Netherlands (irradiation neutron fluence 1.24 × 10²⁵ m^-2, irradiation temperature 780 K, and ³H content 7 appm) were investigated in this study. Simultaneous action of these factors corresponds to the real operating conditions of the blanket of a fusion reactor. The total amount of tritium in a separate pebble, the chemical forms of localized tritium (T⁰, T₂, and T⁺), and the tritium distribution in the pebble volume were determined by a lyomethod (dissolution). Thermoannealing experiments were performed at a constant temperature of 1123 K for 2 h under the following conditions: separately both in MF (1.7 T) and under fast electron radiation (E = 5 MeV; P = 14 MGyh^-1) as well as under the action of all three factors. Tritium in the Be pebbles is localized for the most part as T₂ (85 to 94%). The abundances of T⁺ (4 to 5%) and T⁰ (5 to 10%) are little. The tritium distribution in a pebble is not uniform; most of the tritium is localized in the inner part of a pebble. An MF of 1.7 T decreases slightly the fractional release of tritium under the given conditions of thermoannealing (from 30 to 25%), the fast electron radiation increases it (from 30 to 40%), but the simultaneous action of the MF and radiation increases it (from 30 to 54%). The effects observed are explained that the MF and radiation affect the concentration of main diffusing particles T⁰ in a beryllium matrix.