EXPERIMENTAL-EVIDENCE OF LITHIUM MIGRATION OUT OF AN IRRADIATED BORON-CARBIDE MATERIAL

The nuclear microprobe technique has been used to measure the B-10 and Li-7 profiles after thermal neutron irradiation of a boron carbide ab sorber. This technique allowed to obtain the B-10, B-11 and Li-7 conce ntrations along the radius of the absorbing pellet. The B-10 measured distribution is used to calculate the spatial distribution of Li-7 if no migration out of the sample is expected. This result is compared to the Li-7 measured distribution. This comparison suggests that Li-7 at oms have migrated out of the sample with a loss of about 40% in the pe llet. Some assumptions have been investigated in order to explain the main cause of the Li-7 migration. This Lithium migration may increase significantly the boron carbide brittleness and may be important for t he understanding of the boron carbide destruction mechanism under neut ron irradiation.