The United Kingdom deposited its instrument of accession to the Convention on Supplementary Compensation for Nuclear Damage (CSC) on 3 October 2025, strengthening the global nuclear liability regime and enhancing the capacity of nuclear power to support climate change mitigation, economic development and energy security. The CSC will enter into force for the UK on 1 January 2026, by which time the UK will become the 12th Contracting Party to the Convention. 

I congratulate the UK ???? in joining the Convention on Supplementary Compensation for Nuclear Damage. As the first Party to the Paris Convention to do so, its membership – effective 1 January 2026 – represents an important step on the road to achieving a global nuclear liability… pic.twitter.com/YCbLlrAjv2

— Rafael Mariano Grossi (@rafaelmgrossi) October 10, 2025

For over a decade, the General Conference of the IAEA has called upon Member States to consider joining the international nuclear liability instruments and to work towards establishing a global nuclear liability regime, to ensure prompt, adequate and non-discriminatory compensation for damage to people, property and the environment due to a nuclear accident or incident. 

Adopted under the auspices of the IAEA on 12 September 1997 and entering into force on 15 April 2015, the CSC is a key multilateral treaty in the field of nuclear liability. It serves as an ‘umbrella’ instrument open to all States — including Parties to the 1963 and 1997 Vienna Conventions on Civil Liability for Nuclear Damage, the Paris Convention on Third Party Liability in the Field of Nuclear Energy, and States that are not party to any of these conventions but whose national legislation conforms to the provisions of the Annex to the CSC. The CSC also aims at increasing the amount of compensation available in the event of a nuclear incident through supplementary funds to be provided by its Contracting Parties. 

“As the first Party to the Paris Convention to join the CSC, the UK’s accession establishes – for the first time - treaty relations based on the CSC across both the Paris and Vienna regimes and States belonging to neither,” said IAEA Director General Rafael Mariano Grossi, noting this represented “an important step towards achieving a truly global nuclear liability regime.” 

The CSC is the single existing international nuclear liability convention covering the greatest number of nuclear power reactors in operation worldwide. When the UK becomes a Contracting Party, the CSC will cover approximately 190, or around 45 per cent, of such operational reactors. 

The CSC currently has 11 Parties (Argentina, Benin, Canada, Ghana, India, Japan, Montenegro, Morocco, Romania, United Arab Emirates and United States of America) and 11 Signatories (Australia, Czech Republic, Indonesia, Italy, Lebanon, Lithuania, Mauritius, Peru, Philippines, Senegal and Ukraine). The IAEA’s online CSC calculator enables countries to run scenarios of potential contributions to the CSC’s contingent supplementary international fund. The CSC Parties and Signatories hold annual meetings, with the Fifth Meeting being held on 23-26 June 2025.