Strength: The material must be able to withstand the high temperatures and pressures inside the reactor. Steel is a good choice for this factor because it is strong and durable.
Durability: The material must be able to resist corrosion and erosion from the radioactive materials inside the reactor. Graphite is a good choice for this factor because it is corrosion-resistant and has a long lifespan.
Heat conductivity: The material must be able to efficiently transfer heat from the reactor core to the heat exchangers. Stainless steel is a good choice for this factor because it is a good conductor of heat.
Radiation shielding: The material must be able to protect the environment and personnel from harmful radiation. Lead is a good choice for this factor because it is a good absorber of radiation.
Cost: The material must be affordable and readily available. Concrete is a good choice for this factor because it is relatively inexpensive and can be found in most parts of the world.