Decommissioning is the set of administrative and technical actions taken to allow the removal of some or all of the regulatory controls from a nuclear facility, while ensuring the long-term protection of people and the environment. It begins legally when the operator declares permanent shutdown and ends with licence termination or unrestricted release of the site.

Strategies

The IAEA distinguishes three strategies (GSR Part 6):

  • Immediate dismantling — dismantling activities begin shortly after permanent shutdown (within months to years). Preferred where waste routes exist and financial provision is adequate.
  • Deferred dismantling — facility is placed in a safe enclosure (SAFSTOR in US terms) for decades while short-lived radionuclides decay. Reduces worker dose but requires institutional control during the dormancy period.
  • Entombment — radioactive material left in place under a long-lived engineered structure. Generally not accepted internationally as a primary strategy; treated as an emergency option (Chornobyl shelter) or for very limited inventories.

Many programmes are hybrid — for example, early removal of fuel and most-radioactive components, followed by a few decades of dormancy, followed by full dismantling and site release.

Decommissioning plan

Most modern regulatory frameworks require an Initial Decommissioning Plan at licensing and a Final Decommissioning Plan ahead of permanent shutdown. The plan covers:

  • End state — clearance levels, restricted vs unrestricted release, planned final use of the site.
  • Sequence of operations, planned dose budget for workers and public.
  • Waste arisings by category, conditioning, route to disposal or storage.
  • Environmental monitoring during and after dismantling.
  • Cost estimate and financing arrangements.
  • Stakeholder engagement and site characterisation programme.

Clearance and release

Clearance is the regulatory determination that material or a site can leave regulatory control. The reference levels are typically taken from IAEA RS-G-1.7 / GSR Part 3 and from the Council Directive 2013/59/Euratom (BSSD): exemption and clearance levels in becquerels per gram for individual radionuclides.

Free release of the site (unrestricted use) requires demonstration that the residual dose to a representative future user is below a national reference dose, typically 10 µSv/year or similar. Restricted release leaves the site for an industrial or controlled use with documented institutional control.

Financial assurance

Polluter-pays principle requires the operator to set aside funds for decommissioning during operation. National financing mechanisms include:

  • Trust funds with state oversight (US — under NRC's Decommissioning Trust Fund framework).
  • State-owned funds — e.g. the Swedish Kärnavfallsfonden, fed by levies on electricity generation, managed by SKB and supervised by SSM.
  • Producer pools — German KENFO (Kommission zur Lagerung hoch radioaktiver Abfallstoffe).
  • Direct producer accruals with state inspection (France — EDF/Orano provisions reported in regulated accounts).

Decommissioning experience to date

Several power reactors have completed dismantling and unrestricted site release:

  • Maine Yankee, Connecticut Yankee, Yankee Rowe (US, 2005-2007).
  • Würgassen (DE).
  • Niederaichbach, KKR Rheinsberg (DE).
  • JPDR (JP, first commercial reactor fully dismantled in Japan).

Major programmes in progress or pending include the German fleet (Energiewende), the UK Magnox programme led by the NDA (Sellafield, Magnox stations), the French first-generation gas-cooled reactors at Bugey-1 / Saint-Laurent / Chinon, and the Spanish José Cabrera and Vandellós I.