The end of the life-cycle of a nuclear power plant when it reaches the end of its operating period, or due to any other circumstances that makes its operation technically or economically unfeasible, does not imply the end of the activities to be carried out in it but marks the start of the so-called decommissioning phase.

The decommissioning of a nuclear power plant can be defined as the set of technical and administrative actions and processes which, after its definitive withdrawal from service, progressively eliminate the remaining radioactivity from the areas affected by its former operation. Only when the residual risks of the power plant and its former site have been completely eliminated or have been reduced to an acceptable minimum can we refer to its declassification as a nuclear facility and its decommissioning.

Once decommissioned, the nuclear power plant is no longer subject to regulatory control. The final objective of decommissioning any nuclear power plant is to ensure that any future use of its site does not involve unacceptable radiation risks to the population or to the environment overall. In the case of a nuclear power plant, the decommissioning activities are more complex than those of other industrial facilities in which risks remain after they cease their operations.

Two important elements are involved in the dismantling and decommissioning of nuclear power plants that play a decisive role in the planning of all the activities involved: the work environment in the presence of ionising radiations and the final management of the waste materials generated.