" However the nuclear fleet in advanced economies is 35 years old on average and many plants are nearing the end of their designed lifetimes. Given their age, plants are beginning to close, with 25% of existing nuclear capacity in advanced economies expected to be shut down by 2025.
It is considerably cheaper to extend the life of a reactor than build a new plant, and costs of extensions are competitive with other clean energy options, including new solar PV and wind projects. Nevertheless they still represent a substantial capital investment. The estimated cost of extending the operational life of 1 GW of nuclear capacity for at least 10 years ranges from $500 million to just over $1 billion depending on the condition of the site."https://www.iea.org/reports/nuclear-power-in-a-clean-energy-system
Safe Enclosure ('Safstor') or deferred dismantling: This option postpones the final removal of controls for a longer period, usually in the order of 40 to 60 years. The facility is placed into a safe storage configuration until the eventual dismantling and decontamination activities occur after resudual radioactivity has decayed. There is a risk in this case of regulatory change which could increase costs unpredictably.
Entombment (or 'Entomb'): This option entails placing the facility into a condition that will allow the remaining on-site radioactive material to remain on-site without ever removing it totally. This option usually involves reducing the size of the area where the radioactive material is located and then encasing the facility in a long-lived structure such as concrete, that will last for a period of time to ensure the remaining radioactivity is no longer of concern.
EDF chose partial dismantling and postponed final dismantling and demolition for 50 years. As other reactors will continue to operate at those sites, monitoring and surveillance do not add to the cost.
Of the eight German units shut down in March 2011 for political reasons, most will be dismantled over about 15 years. The four operators had €38 billion set aside for decommissioning and waste disposal.
Duke’s Crystal River 3 (860 MWe) was expected to cost $1.18 billion (2013 dollars) to decommission via Safstor over 60 years, during which time the funds reserved for the purpose would accrue interest, thereby fully covering the cost, despite the fact that is was closed after only 35 years of operation. Immediate decommissioning (Decon) was then expected to cost $994 million, but the decommissioning fund would have had less time to grow sufficiently to cover it, and a $195 million impact on Florida ratepayers would have resulted.
Construction of an onsite dry cask storage facility commenced in 2016, and fuel transfer started in summer 2017 and completed in January 2018. The spent fuel is planned to remain at the onsite storage facility until 2036, when it would be moved to a federal facility. Safstor was expected to end with removal of the unit’s remaining components about 2070 and site restoration in 2074. In August 2020 the Florida Public Service commission approved Accelerated Decommissioning Partners completing demolition by 2027 and managing the ISFSI to 2038 for a fixed price of $540 million, fully covered by the existing trust funds of over $700 million (with balance plus any money recovered from suing the DOE returned to ratepayers). Duke will remain the owner to 2038, but Accelerated Decommissioning Partners became the licensed operator of the plant and ISFSI in October 2020.
