An NPP will cease to be operational if a decision is taken to retire it from service, at the end of its licensed operating life or earlier. Several causes may dictate the earlier termination of an operating NPP, for example a decision by the licensee for economic or other reasons, the cancellation of the operating license by the RB, or the impossibility of recovery from an accident. The licensee should formally communicate to the RB about such a decision and the proposed arrangements for safekeeping of the facility pending its decommissioning.

The RB will review the proposal and appropriately modify the operating license. This includes changes in the technical specifications for operation and other licensing conditions, like those related to requirements of operat­ing staff, in-service inspection, and surveillance and operability of equip­ment to maintain the facility in a safe state. However, as long as nuclear fuel is present in the reactor core, the NPP is considered operable and the complete operational discipline should remain in force. After the reactor core is completely defuelled, the operating license may be terminated. However, the facility will still remain under regulatory control, with appro­priate safety requirements specified, as long as radioactive material is present at the site, pending its final decommissioning.

Most RBs have enacted regulations on decommissioning commercial nuclear power plants, with these regulations covering the time from termi­nation of operation to when the site is declared fit for unrestricted use. In any case, the licensee declares that the reactor has been shut down perma­nently and that they are ready to request a decommissioning license. The licensee keeps its prime responsibility as long as there is fuel on the reactor premises, either in the reactor core or in the spent fuel decay pool. After removing the fuel, responsibility for the site can be transferred to the agency conducting the dismantling.

The operator performing the dismantling should submit a safety analysis report to the RB describing the decommissioning activities to be conducted and the safety provisions that have been made to comply with the existing regulations. Attention is given to decontamination activities, to radiological protection of workers and the environment, and to the management of radioactive waste. The RB evaluates the information received and prepares an SER with the proposed limits and conditions to be complied with during the process, these mostly being the acceptable residual radioactivity level remaining on the site for it to be released for unrestricted use, the reports to be submitted on the conduct of operations, and hold points for inspec­tion. At the end of the process, a radiological survey of the site is generally conducted before releasing and declaring that decommissioning has ended.