Application of Radiogenic Lead with Dominant Content of ²⁰⁸Pb for Long Prompt Neutron Lifetime in Fast Reactor

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 small neutron radiative capture cross section ([approximately]0.23 mb for thermal neutrons, i.e., less than that for graphite and deuterium) and highest albedo of thermal neutrons.

The use of radiogenic lead to make it possible to slow down the chain fission reaction on prompt neutrons in a fast reactor is evaluated. This can improve the safety of a fast reactor.

It is noteworthy that radiogenic lead with high ²⁰⁸Pb content may be recovered from thorium (as well as thorium-uranium) ores without isotope separation. This has been confirmed experimentally by the investigations performed at the University of São Paulo in Brazil.