Radiogenic lead with dominant content of 208PB: New coolant, neutron moderator and reflector for innovative nuclear facilities. Application of Stable Lead Isotope Pb-208 in Nuclear Power Engineering and its Acquisition Techniques February 2013, Pages 4

As a rule materials of small atomic weight (light and heavy water, graphite and so on) are used as neutron moderators and reflectors. A new very heavy atomic weight moderator is proposed - radiogenic lead consisting mainly of isotope 208Pb. It is characterized by extremely low neutron radiative capture cross-section (~0.5 mbarn for thermal neutrons, i.e. less than that for graphite and deuterium) and highest albedo of thermal neutrons. It is evaluated that the use of radiogenic lead makes it possible to slow down the chain fission reaction on prompt neutrons in a fast reactor. This can improve safety of fast reactor and reduce as well requirements pertaining to the fuel fabrication technology. Radiogenic lead with high 208Pb content as a liquid-metal coolant of fast reactors helps to achieve a favorable (negative) coolant temperature reactivity coefficient. It is proposed to use the isotope Pb-208 as the main structural material of an ADS blanket for fast and effective transmutation of fission products and curium fraction from minor actinides, which are characterized by relatively small cross-sections of neutron absorption and fission. Model evaluation showed that in blanket containing of lead-208 (in contrast to natural lead and graphite) the value of thermal neutron flux is several orders higher and relaxes slowly up to a distance of several meters from the target. It is noteworthy that radiogenic lead with high 208Pb content may be extracted from thorium (as well as thorium-uranium) ores without isotope separation. This has been confirmed experimentally by the investigations performed at San Paulu University, Brazil.