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Decommissioning is the final phase in the lifecycle of a nuclear installation. It 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. Although the final phase, decommissioning needs to be taken into account in all lifecycle phases, starting with facility planning and design.

Decommissioning 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 radionuclides in the materials and facilities on the site, so that they can be safely recycled, reused, or disposed of as exempt waste and as radioactive waste.

IAEA has identified two possible options for decommissioning strategies which have been adopted or are being considered for nuclear facilities across the world, including in the UK:

  • Immediate dismantling - Decommissioning actions begin shortly after operation finally ceases. Equipment and structures, systems and components of a facility containing radioactive material are removed and/or decontaminated to a level that permits the facility to be released from regulatory control for unrestricted use or released with restrictions on its future use.
  • Deferred dismantling - After removal of the nuclear fuel from the facility (for nuclear installations), all or part of a facility containing radioactive material is either processed or placed in such a condition that it can be put into a state of safe storage (typically referred to as “care and maintenance” in the UK). The facility is maintained in a safe state for a period of time, followed by subsequent decontamination and/or dismantling. Deferred dismantling may involve early dismantling of some parts of the facility and early processing and removal of some radioactive material, as preparatory steps for safe storage of the remaining parts.

The IAEA does not consider that entombment (in which all or part of a facility is encased in a structurally long-lived material) is a decommissioning strategy and is not an option for planned permanent shutdown.

Licence Condition 35 is a specific condition of every site licence that requires licensees to have arrangements and programmes for decommissioning. Each licensee is expected to develop a decommissioning strategy for the site and facility specific plans to implement the strategy. These should be developed during the design phase to demonstrate the facility can be safely decommissioned at the end of its life, and be kept updated during the operational phase.

Typically we will agree a concise set of high-level key decommissioning milestones, which are included in the licensees’ programme and against which we monitor progress, including the use of hold points where necessary. The milestones normally represent the achievement of significant hazard reduction steps in the programme to deliver the overarching decommissioning strategy. Licensees are expected to review and update the decommissioning strategy and plans periodically. We engage with licensees to review the strategy and plans, using a graded approach and in consultation with the relevant environment agency.

We ensure that the licensee adequately controls decommissioning activities by means of routine inspections and the permissioning of higher hazard projects, where proportionate.

Decommissioning progressively reduces residual hazards and risks on a site, but we recognise that sometimes risks may increase temporarily to achieve this. In such circumstances the licensee should justify its overall approach and ensure that risks are reduced to as low as reasonably practicable (ALARP) across all stages.

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

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