Nuclear Fuel Cycle

Unirradiated fuel contains uranium isotopes that are alpha emitters with low-energy, low-abundance gamma rays. Combined with the self-shielding properties of the dense fuel material, the external radiation hazard from fresh (non-recycled) fuel is very small — typically around ~20 $\mu$Sv/h surface dose rate.

For routine worker-dose estimates from a fuel pellet, can or assembly the source can usually be treated as a point source and the dose rate at distance $r$ scales as

$\dot{D}(r) = \dot{D}(r_0)\left(\frac{r_0}{r}\right)^2$

i.e. the familiar inverse-square law. This is used throughout the tutorial questions for fresh-fuel handling. (For extended sources such as a contaminated floor, the dose rate falls off more slowly than $1/r^2$ — the extended-area-source formula developed in Chapter 6 §6.14.)

However, recycled fuels and MOX fuels present significantly higher radiological hazards (see Sections 3.7 and 3.8).