Nuclear Fuel Selection:

A nuclear property of a material has be the first consideration within the selection of a suitable nuclear fuel.  Principle properties are those bearing on neutron economy:  absorption and fission cross sections, a reactions and products which result, neutron production, and the energy released. Those are properties of a specific nuclide, like as ²³²Th, and its product in during breeding, ²³³U. For assess these properties within the performance of the bulk fuel, a density value, or often of occurrence per unit volume, of the specific nuclide have to be used.

Once it has been established in which the desired nuclear reaction is feasible in a candidate fuel material, the effect of other material properties on reactor performance have to be considered.  To the reactor to perform its function of generating usable energy, the energy must be erased. It is desirable for thermal conductivity to be as high as possible by the temperature range of operations and working life of the reactor. High thermal conductivity permits high power density and high specific power without excessive fuel temperature gradients. A chosen of a ceramic fuel represents a compromise. Though it is known that thermal conductivities comparable to these of metals cannot be expected, chemical and dimensional stability at high temperature are acquire.

Since the thermal conductivity of a ceramic fuel is not high, it is essential to produce associatively high temperatures at the centers of ceramic fuel elements. A high melting point enables more energy to be removed, all other things being equivalent. Within all cases, the fuel must remain well below the melting point in normal operation, but a higher melting point consequence in a higher permissible operating temperature.