Favorable Effects of an Inner Lead Cavity on Neutronic Physics of a Lead-Cooled Fast Reactor

The paper considers the effects produced by arranging a lead cavity in the central part of a lead-cooled fast reactor core. It is shown that the most favorable effect from the presence of an inner lead cavity at the center of the core can be obtained when radiogenic lead with a dominant 208Pb isotope content is used as the material of the cavity, coolant, and neutron reflector. This is explained by the extremely low neutron absorption of 208Pb in a wide range of neutron energies. If the thickness of the 208Pb inner cavity is chosen properly, then a spectral region with the prevailing share of resonance, epithermal, and thermal neutrons is created in the cavity. This results in a sharp increase in the mean prompt neutron lifetime (by few orders of magnitude) and enhancement of the stabilizing Doppler effect. The neutron migration from the inner cavity to the reactor core is able to intensify the fission chain reaction (FCR) and contribute positively to reactor reactivity. In addition, the high flux of slowed neutrons in the inner 208Pb-cavity makes it possible to expect efficient transmutation of long-lived fission products.