The Office for Nuclear Regulation (ONR) is the United Kingdom's independent nuclear regulator. Its self-stated mission is "to protect society by securing safe nuclear operations".

Mandate and statutory basis

ONR was established as a non-departmental public body under the Energy Act 2013 (commenced 2014), taking over functions previously performed by the Health and Safety Executive's Nuclear Directorate and the Department for Transport. ONR sponsors are the Department for Work and Pensions for safety, and the Department for Energy Security and Net Zero for civil nuclear security and safeguards.

The regulator covers three areas:

  • Safety — conventional and nuclear safety on licensed nuclear sites under the Nuclear Installations Act 1965.
  • Security — under the Nuclear Industries Security Regulations 2003.
  • Safeguards — under the Nuclear Safeguards Act 2018 and the Nuclear Safeguards (EU Exit) Regulations.

Licensed sites

ONR licenses around 36 civil nuclear sites in Great Britain, including operating power reactors at Heysham 1-2, Hartlepool, Sizewell B, Torness; the Sellafield reprocessing and storage complex; the Capenhurst enrichment plant; Springfields fuel fabrication; and research sites at Culham, Harwell and Dounreay. Northern Ireland nuclear matters are handled separately.

Regulatory approach

ONR uses a goal-setting, rather than prescriptive, regulatory style: licensees must demonstrate that risks are reduced "so far as is reasonably practicable" (SFAIRP) and that doses are As Low As Reasonably Practicable (ALARP). The principal vehicle is the 36 Licence Conditions attached to a Nuclear Site Licence, supplemented by Safety Assessment Principles (SAPs) and Technical Assessment Guides (TAGs).

Recent published work includes the Nuclear Industry Safety Culture Inventory (NISCI), expert-panel reports on natural hazards, the Chief Nuclear Inspector's Independent Advisory Panel, and exploratory work on regulatory sandboxing for AI and on blockchain in the nuclear sector.

Generic Design Assessment

ONR's pre-licensing Generic Design Assessment (GDA), run jointly with the Environment Agency and the Natural Resources Wales, evaluates new reactor designs before any site-specific application. Completed assessments include the UK EPR (now built at Hinkley Point C and Sizewell C); the AP1000; and ongoing work on Rolls-Royce SMR, Hitachi-GE BWRX-300 and other small-reactor concepts. In 2025 ONR began publishing new joint frameworks with international partners aiming to streamline cross-border reactor assessment.

International cooperation

ONR participates in IAEA IRRS missions, in WENRA reference-level harmonisation, in the NEA committee structure, and in bilateral cooperation arrangements with the US NRC and other major regulators.