Fundamentals for the development of a low-activation lead coolant with isotopic enrichment for advanced nuclear power facilities

The purpose of this paper is to study the prospects of new coolants for fast reactors and accelerator driven systems. The main focus is on their improvement using the isotopic tailoring technique to reduce post-irradiation activity. Calculations using the FISPACT-3 code show that irradiating natural lead (Pb-nat) for 30 years leads to the accumulation of long-lived toxic radionuclides, 207Bi, 208Bi and 210Pb, which extends the cooling down period to the clearance level. This time can be shortened by using the lead isotope 206Pb instead of Pb-nat. This substantially decreases the concentration of the most toxic polonium isotope, 210Po. Calculations for lead activation in the hard proton-neutron ADS spectrum were performed using the CASCADE/SNT code. The time-dependent activity of the 207Bi produced in Pb-nat and 206Pb after irradiation for one year with a proton beam having an energy of 0.8 GeV and a current of 30 mA is given. The activity of 207Bi is decreased by four orders of magnitude when 206Pb is used instead of natural lead as a coolant for ADS targets. The production of such radiotoxic nuclides as 210Po is also substantially diminished. (author)