= Solution
\b[A <reactor coolant> must remove heat reliably while remaining compatible with the core.] Desirable properties include adequate <heat capacity> and heat transfer, manageable viscosity and pumping demand, stability over the operating range, limited <corrosion> of fuel and structures, acceptable <neutron> absorption and activation, and a tolerable leakage or chemical-reaction hazard. \b[<water>] is a standard example in light-water reactors: it transfers heat well and also moderates, but pressure, boiling behaviour, <corrosion> chemistry and loss of inventory must be managed. No single <reactor coolant> is best independently of reactor design.
\b[A control-rod material must absorb <neutrons> effectively and retain mechanical and chemical integrity.] It needs a suitable absorption cross section over the relevant spectrum, adequate absorber inventory over life, manageable capture heating and transmutation products, and compatibility with its sheath and <reactor coolant>. \b[<boron carbide>] is an example. Depletion, gas generation, <radiation-induced swelling> and cracking must be allowed for; a large initial cross section alone does not establish lifetime performance.
\b[A <neutron moderator> must slow <neutrons> efficiently while absorbing relatively few.] Light nuclei provide effective energy transfer per collision, but absorption, <density>, radiation stability, purity and temperature-dependent properties determine the usable moderation. \b[<heavy water>] is an example combining effective slowing with low parasitic absorption; <graphite> is another possible material in different designs. Heat removal and compatibility remain necessary even though moderation is its principal neutronic role.
\b[<nuclear fuel cladding> must retain fuel and <fission products> while transferring heat and carrying load.] Desirable properties include <corrosion> resistance, low <neutron> absorption, adequate <thermal conductivity>, strength and <ductility>, resistance to <irradiation growth>, <void swelling> and <creep (deformation)>, and compatibility with fuel and <reactor coolant>. \b[A <zirconium alloy> such as <Zircaloy>] is a light-water-reactor example. Hydrogen uptake, <corrosion> and irradiation response constrain service; the low absorption benefit does not eliminate these materials problems.
Back to article page
