Office for Nuclear Regulation


Decommissioning is defined by the International Atomic Energy Agency (IAEA) as the administrative and technical actions taken to allow the removal of some or all of the regulatory controls from a facility. It is the final phase in the lifecycle of a nuclear installation and typically includes dismantling redundant nuclear facilities that have finally ceased operating and removing any associated radioactive waste for safe storage or disposal. However, a facility could be decommissioned without dismantling and the existing structures subsequently put to another use.

The objective of decommissioning is to ensure long-term protection of the public and the environment, and typically includes reducing the levels of residual radionuclides in the materials and facilities on the site, so that they can be safely recycled, reused, or disposed of as exempt waste or as radioactive waste. 

Decommissioning is usually divided into stages, these are typically as follows:

There is a specific condition of every site licence (Licence Condition 35) that requires sites to have arrangements, plans and programmes to undertake facility decommissioning through defined stages. Typically, we will agree a set of key decommissioning milestones with the licensee and these are included in its programme and progress with decommissioning is monitored though meeting these milestones. The milestones normally represent a point of significant hazard reduction e.g. spent fuel pond emptied and cleaned up; Intermediate Level Waste retrieved and put into safe storage etc. Throughout the decommissioning activities we ensure through routine inspection, and assessment of higher hazard projects, that the licensee is adequately controlling its work to progressively reduce the residual hazards and risks on a site. As the hazard and risk on the sites gradually diminish, so concomitantly do our regulatory activities.

The Nuclear Reactors (Environmental Impact Assessment of Decommissioning) Regulations (EIADR)

Prior to commencing decommissioning of shutdown nuclear reactors, there is a requirement to assess the potential environmental impact of decommissioning these facilities. Work can’t start until ONR issues its Consent under EIADR.