Design Features | Advantages | Disadvantages | |
Neutron spectrum | Fast | · large fission to absorption ratio · minimize radioactive waste formation · burnup extension · sustainability (breeding) | · potential for disruptive power excursions · low margin to prompt criticality (Pu-239 compared to U-235) |
Thermal | · robust reactivity against fluctuations in physical parameters · safer margin to prompt criticality · long operational experience | · inefficient fuel exploitation · larger radioactive waste formation | |
Coolant | Sodium | · superior thermal hydraulic properties/heat transfer characteristics · excellent neutronic properties and economy · good compatibility with structural materials | · significant reactivity insertion issues (sodium boiling, large coolant temperature coefficient) · high chemical activity with water, steam, and air (explosion risk) · optical opacity |
Lead | · good natural circulation and heat transfer properties · superior neutronic characteristics and performance · chemically inactive · low cost (lead is abundant) | · high melting point (freezing potential) · erosion and corrosion potentials (need for coating) · Polonium-210 activity build up · optical opacity | |
Molten Salt (fluorides or chlorides) | · high density-specific heat product (large grace period) · high boiling temperatures (no void reactivity insertions) · chemically inactive · optical transparency | · high melting point (freezing potential) · neutronically challenging · small thermal conductivity limiting the power density · pumping constraints (large viscosity) | |
Inert Gas (e.g. Helium) [26] | · high breeding ratio · small void reactivity coefficient · chemically inactive (inert) · no corrosion/material challenges · optical transparency · potential for direct Brayton cycle (lower capital costs) | · high neutron leakage · relatively poor heat transfer characteristics · water ingress concerns (positive reactivity insertions) |