Minimization of an initial fast reactor uranium–plutonium load by using enriched lead-208 as a coolant

Long-term scenarios of nuclear energy evolution over the world scale predict deployment of fast reactors (FRs) from 2020 to 2030 and achievement on 2050 the world installed capacity equal to 1500 GWe with essential increasing the FRs number. For several countries (i.e. Russia, Japan) whose policies are based on a sharp increase of nuclear production, at the stage near 2030–2040 when plutonium, Pu, from the PWR spent nuclear fuel is consumed, the Pu lack will stimulate minimization of its load in FRs. The period of Pu deficiency will be prolonged till the years when breeding gain (BG) equal to 0.2–0.3 in fast breeding reactors (FBRs) is obtained which corresponds to Pu inventory doubling time of 44–24 years.In this paper one of opportunities to minimize fuel loading is considered: it is related to using a low neutron capturing lead isotope, 208Pb, as a FR coolant. It is known, that natural lead, natPb, contains a stable lead isotope, 208Pb, having a small cross-section of neutron capture via (n, γ) reaction. In the paper it is shown that the macroscopic cross-sections 〈σn,γ〉 of radiation neutron capture by the lead isotope 208Pb averaged on the ADS core neutron spectra are by ∼3.7–4.5 times less than the corresponding macroscopic cross-sections for a natural mix of lead isotopes natPb. This circumstance allows minimizing load of a lead fast reactor (LFR) core for achievement its criticality, as well as the load of an accelerator-driven system (ADS) subcritical core—for achievement of its small subcriticality. In using 208Pb instead of natPb in the ADS blanket, the multiplication factor of the subsritical core, Keff, could be increased from the initial value Keff = 0.953 up to the value of Keff = 0.970. To achieve this higher value of Keff in the same core cooled by natPb an additional amount of 20–30% of U–Pu fuel will be needed.The isotope 208Pb content in the natural mix of isotopes, natPb, is high enough, above 52%, and its separation in large amounts (several tens’ and hundreds’ of tonnes) is expensive but really solvable technical task. In the project (ISTC #2573, 2005), developed with authors’ participation, it is shown that a new laser photochemical technique of lead isotope separation, being developed in future, permits to obtain large quantities of 208Pb under its acceptable price, of close to $200 kg−1.