= Solution
A useful fuel combines \b[neutronic suitability, heat removal, containment and dimensional stability]. A sufficient fissile inventory and acceptable <neutron> economy permit the intended power and exposure, while unnecessary parasitic absorption wastes <neutrons>. These requirements are reactor-specific rather than a recommendation for one universal composition.
A high melting margin and stable phases help preserve geometry. Good <thermal conductivity> reduces the centre-to-surface <temperature> rise and associated thermal <stress>; <heat capacity> helps moderate transient <temperature> changes. Chemical stability and compatibility with <reactor coolant> and <nuclear fuel cladding> reduce <corrosion> and reactions at the interface with <nuclear fuel cladding>. Oxygen chemistry and other composition variables can affect both transport and interface reactions.
Under irradiation the fuel should tolerate <displacement damage>, restructuring, <radiation-induced swelling> and <fission gas> accumulation without unacceptable cracking, gap closure or pressure. Retention of radionuclides and controlled release of <fission gas> support the <nuclear fuel cladding>'s containment function. Predictable <creep (deformation)> can relieve <stress>, but excessive deformation may compromise geometry. Fabrication reproducibility, inspectable <microstructure>, resource availability and the practicability of subsequent waste management also matter.
\b[<uranium dioxide> illustrates the compromises:] it is a chemically robust, high-melting ceramic fuel, but its relatively limited <thermal conductivity>, irradiation-dependent <microstructure> and gas behaviour require explicit thermal and mechanical design margins. A desirable individual property does not establish the performance of the coupled <nuclear fuel> and <nuclear fuel cladding> system.
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