A nuclear power plant produces and accumulates a certain quantity of radioactive products which, normally, remain in the fuel rods. Other radioactive products are found in the cooling liquid together with the products of corrosion/activation.
The fuel most commonly used to produce energy in a nuclear plant is uranium.
The radioactivity in irradiated fuel is mainly generated in two ways:
- by the fission process, in which lighter, more unstable and therefore radioactive fragments are produced. In a time varying from just a few seconds to hundreds of years, these fragments decay and become stable again, thereby ending their radioactivity. All fission reactions produce radioactive isotopes.
- by neutron capture reactions; by neutron capture reactions; for example the formation of unstable actinides, following consecutive neutron capture by heavy nuclei (U, Pu). Such elements are characterised by high radioactivity.