Migration of fissiogenic Sm in fractures at the natural fission reactor site of Bangombé and effects of neutron capture on remote samples

Abstract

The Sm isotopic composition of samples from fractures below the reactor zone (RZ) Bangombé is investigated by thermal ionization mass spectrometry to shed light on neutron capture effects and migration of fission products. A well-defined mixing line from normal to fissiogenic Sm isotopic composition, which reveals that migration of normal and fissiogenic Sm at the reactor site of Bangombé is more significant than that at other RZs, is found.A small shift in the Sm isotopic composition in one fracture, which was 3m below the RZ Bangombé, shows neutron capture effects in situ. The shift indicates a neutron fluence of about 4×1015neutron/cm2. The neutron fluence originates from the fission reaction and is consistent with a macroscopic neutron capture cross-section.