Implementation of a NPP decommissioning project begins from its final shutdown.
The preparatory stage lasting 3 - 5 years starts. During this period the reactor is brought into the nuclear-safe condition.
Nuclear fuel is taken out of the core and removed from the power unit. RW produced in the course of operation is also removed; the equipment undergoes scheduled decontamination;
a number of other relevant activities is carried out.
In accordance with the requirements of regulatory bodies this period is not included into the decommissioning stage. The NPP power unit is still listed as being in service, its maintenance is performed in accordance with appropriate procedures.
The preparatory period can take several years (or indefinite time) depending on the availability of the regional or federal SNF and RW storage/repository for the certain reactor type.
A decision can be taken to keep the spent fuel on the NPP site and transfer it from the
cooling pools to the dry storage in special containers.
Reactors can be dismantled after several years of idleness. Large equipment can be dismantled and transported without cutting.
Big components can serve as containers (barriers for contained radionuclides).
It is expedient to employ the NPP operators in the decommissioning activities. Storage
facilities for the decommissioning waste are built on the plant site on a certain level,
which depends on the NPP geographic position.
The importance of decision about the decommissioning timing should be mentioned
separately. After a certain period following the reactor shutdown short-lived radionuclides
decay, only long-lived ones staying in the contaminated equipment continue to be noxious. This way the amount of radioactive waste decreases. After 10-30 years this process of "activity self-liquidation” slows down. The self-liquidation of some environmentally hazardous radioniclides, e.g. 60^Co, can last 70 years and more.