Nuclear fuel

A material that supplies energy through a nuclear reaction, usually nuclear fission in a power nuclear reactor. Its usable performance depends on its thermal and mechanical response as well as its nuclear composition.

The coupled thermal, mechanical, chemical and irradiation response determining whether fuel retains its intended function and containment during service.

Gaseous fission-product constituents, notably xenon and krypton. Retention, bubble formation and release can change fuel void swelling and internal pressure.

The center-to-center spacing of neighboring rods or other repeating elements in a specified fuel lattice. Changing pitch at fixed rod dimensions changes the coolant-to-fuel volume ratio; its effect on core size additionally depends on rod count and layout.

Energy released per initial heavy-metal mass, commonly $\mathrm{MW}\mathrm{d}{\mathrm{t}}^{-1}$. For thermal energy production $E$ and burnup $B$, the corresponding initial fuel mass is $M=E/B$.

The burnup accumulated by a fuel batch when it is removed from its specified irradiation service. Its residence can span more than one operating cycle, so it is not generally the increment of burnup accumulated in a single cycle.

The mass of heavy fuel elements, excluding oxygen, cladding and other structural materials. burnup and fuel-cycle prices must use a stated heavy-metal reference basis.

A fuel-and-cladding system designed for improved performance under specified accident conditions while maintaining acceptable normal-operation behavior. Improvements to pellet and cladding materials address different parts of the system's response.

TRISO fuel uses coated nuclear fuel particles, each with a fuel kernel surrounded by four layers: a porous carbon buffer, an inner dense pyrolytic carbon layer, a silicon carbide layer and an outer pyrolytic carbon layer. The name abbreviates tristructural isotropic: the four layers use three coating material forms.^[ref]

The layers perform complementary functions. The porous carbon buffer accommodates released fission gas; the pyrolytic carbon supports the particle mechanically; and the silicon carbide supplies a strong barrier to fission products. Coated particles can be embedded in a graphite matrix. Their retention performance depends on coating integrity, material behaviour under irradiation, and the conditions experienced in service. The architecture makes a small particle itself part of the containment system, linking nuclear engineering closely to materials science.^[ref]

A uranium–nitrogen compound investigated as nuclear fuel. High uranium loading and thermal conductivity are attractive, while chemical and irradiation compatibility constrain applications.

A uranium–silicon compound considered in nuclear-fuel applications, including ${\mathrm{U}}_3\mathrm{S}{\mathrm{i}}_2$. High uranium loading and thermal conductivity motivate study; chemical compatibility and irradiation behavior remain essential qualifications.

The structural layer enclosing nuclear fuel, retaining fuel and fission products while transferring heat to a coolant. Its pressure loading, chemical compatibility and irradiation response must remain consistent with its required geometry and integrity.

Alloys based on zirconium, widely used for water-reactor nuclear fuel cladding because of their useful combination of low neutron absorption and material properties. Corrosion, hydrogen uptake, creep and irradiation-induced dimensional changes limit performance.

Mechanical contact and load transfer between expanding or cracking fuel pellets and their enclosing nuclear fuel cladding. Local stress depends on clearance, fuel deformation and the cladding's evolving material properties.

Nuclear fuel based on metal oxides. Chemical composition and the oxygen-to-metal ratio affect transport, stability and compatibility with surrounding materials.

A plutonium oxide, $\mathrm{Pu}{\mathrm{O}}_2$, used as a component of mixed oxide nuclear fuel. Its use requires attention to decay heat, chemical compatibility and the distribution of fissile material; no fabrication recipe is specified.

The number ratio of oxygen atoms to metal atoms in an oxide. Departures from a reference stoichiometry change defect populations, oxidation states and chemical potentials; these can influence transport and compatibility.

Oxide nuclear fuel containing more than one metal oxide; in the usual power-reactor context it refers to uranium–plutonium oxide fuel. Its initial averaged composition does not preclude local variations or actinide redistribution in oxide fuel during service.

Spatial changes in actinide composition during service. Temperature gradients, chemical potentials, oxygen chemistry and transport through the solid or across pores can contribute. A temperature gradient alone does not determine a unique plutonium migration direction.

A ceramic uranium oxide used as nuclear fuel. Its thermal conductivity, gas retention and microstructure evolve with temperature and irradiation.

Uranium-dioxide fuel modified by controlled dopant additions to influence properties such as grain structure and deformation. Irradiated behavior must be assessed for the actual modified material.