2. Fuels for the different sectors

At the beginning of 2008, the world's fleet of nuclear power reactors in service was as shown in the table 1 .

In most reactor systems, fuel is made up of circular cylindrical elements called rods or needles. The only exceptions are UNGG (natural uranium graphite-gas) and HTR (High Temperature Reactor) fuels.

The rod is therefore generally the elementary fuel element (fissile material + cladding). It consists of a stack of UO ₂ pellets, a tube (cladding), and end plugs. The rods are bundled together to form a fuel assembly. On the one hand, this grouping enables fissile material fractionation, necessary for neutron reasons (appropriate moderation ratio) and for cooling reasons at high power density (high surface-to-volume ratio). It...