Due to the high atomic mass of lead (among the heaviest elements on earth), neutrons are very poorly moderated in the coolant, thereby remaining in the high-energy range. Energetic neutrons are then able to both significantly generate new fissile fuel (remarkably, plutonium – Pu) and to effectively transmute the long-term-radioactive component of the waste being generated (the so called Minor Actinides – MA).
The breeding of new plutonium permits first of all to extend the residence time of fuel elements in the core, achieving higher burnups that is: extracting more energy from the given amount of fuel.
Also, a reactor capable to breed is also a reactor able to reuse its spent fuel, once made up with a fraction of new elements to replace the amount that has been fissioned to generate energy. Associating this with the effectiveness in transmuting the Minor Actinides, and leveraging on the extreme safety of Lead Fast Reactors, an unparalleled flexibility is gained to fulfill any aimed fuel and waste management policy. Focusing on plutonium (as the fissile part of the fuel) and Minor Actinides (as the long-term fraction of the waste), the four operating modes shown in figure can be easily set and, within each, an optimal operation point achieved.