Why Liquid Sodium? Unlike light water (${}^{1}\text{H}_2\text{O}$), sodium ($^{23}\text{Na}$) has a low neutron-capture cross section and a high atomic mass relative to hydrogen. Neutrons retain mean kinetic energies of 100–300 keV instead of slowing to thermal velocities ($0.025\text{ eV}$). Fast neutrons cause non-fissile $^{238}\text{U}$ to capture neutrons and transmutate through beta decay into fissile $^{239}\text{Pu}$ at a breeding ratio exceeding 1.0.
3-Loop Heat Transport: 1,750 tonnes of radioactive primary liquid sodium transfers heat to intermediate non-radioactive sodium loops. The intermediate sodium then boils water in the steam generators, creating an absolute physical barrier preventing dangerous sodium-water reactions in the core.