Effect of high temperature annealings on swelling and helium release in boron carbide irradiated with neutrons

The investigation results of helium content, measurement of limar sizes and boron carbide microstructure after irradiation at 350 deg C up to burnup of 1.4 and 2.6 % of boron and annealings in the temperature range from 1000 to 1400 deg C are presented in the paper. High-temperature annealing of boron carbide samples is shown to lead to considerable volume changes caused by porosity development both on boundaries and in a grain body, as well as to helium yield. The changes depended grealty on the temperature and grew with the increase of boron burnup. Effect of grain boundaries on void generation and growth near and on the grain boundaries themselves is considered; estimations of helium diffusion coefficient are carried out; dependence of the coefficient on annealing conditions and on characteristics of helium bubbles formed during annealing is shown. 7 refs.; 3 figs.; 1 tab