Reducing the Uranium-Plutonium Loading of a Fast Reactor Due to the Use of a Low Neutron Capturing Core Coolant Consisted of Enriched Lead-208

Long-term scenarios of nuclear energy evolution over the world scale predict deployment of fast reactors (FRs) from 2020–2030 and achievement near 2050 the world installed capacity equal to 1500 GW_e with essential increasing the FRs number. For several countries (i.e. Russia, Japan) which policies are based on a sharp increase of nuclear production, at the stage near 2030–2040 when plutonium, Pu, from PWR spent nuclear fuel is consumed, the Pu lack will stimulate minimizing its loading in FRs. The period of Pu deficiency will be prolonged till the years when Breeding Gain (BG) equal to 0.2–0.3 in 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 with 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 mean cross-section <σ _{n, γ}> of radiation neutron capture by the lead isotope ²⁰⁸Pb averaged upon an Accelerator Driven System (ADS) core neutron spectra is by ∼3.7 – 4.5 times less than the corresponding mean cross-section for a natural mix of lead isotopes ^natPb. This circumstance allows minimizing the load of a lead fast reactor (LFR) core for achievement its criticality as well as the load of the ADS subcritical core — for achievement its small subcriticality. In using ²⁰⁸Pb instead of ^natPb in the ADS blanket the multiplication factor of the subcritical core, K_eff, could be increased from the initial value K_eff = 0.953 up to the value K_eff = 0.970. To achieve this higher value of K_eff in the same core cooled by ^natPb an additional amount, about 20–30%, of U-Pu fuel will be needed. The isotope ²⁰⁸Pb content in the mix of lead isotopes, ^natPb, is high enough, above 52%, and its separation in large amounts (several tons) is expensive but really solvable technical task. In the ISTC #2573 project developed in 2005 with author 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, less than $200/kg.