Convention on Supplementary Compensation for Nuclear Damage: UK Accession

I am writing to inform the House of the UK’s accession to a further international nuclear third-party liability (NTPL) treaty, the convention on supplementary compensation for nuclear damage (CSC). On 3 October 2025, the UK deposited its instrument of accession with the Director General of the International Atomic Energy Agency. Under the provisions of the convention, the CSC will enter into force 90 days following the deposit of the instrument, on 1 January 2026.

The domestic implementing legislation for the CSC is set out in the Energy Act 2023, which amends the Nuclear Installations Act 1965. Minor technical changes were made by the Nuclear Installations (Compensation for Nuclear Damage) (Amendment) Regulations 2025. The CSC was laid before Parliament on 30 June 2025, under cover of Miscellaneous Series No. 4 (2025), and completed scrutiny on 10 September 2025.

Nuclear power is a reliable and low-carbon source of electricity. It is an essential part of this Government’s mission to protect family finances and replace the UK’s dependency on fossil fuel markets with home-grown power that we control. NTPL treaties bring benefits to the nuclear sector and potential victims as they establish minimum compensation thresholds which operators have financial security to cover, assign liability exclusively to the operator of the nuclear installation, and channel claims to the jurisdiction where the incident occurs.

The UK will remain party to the Paris convention on third-party liability in the field of nuclear energy and the Brussels convention supplementary to the Paris convention on third-party liability in the field of nuclear energy—or the Brussels supplementary convention. Accession to the CSC will enhance the UK’s NTPL regime by establishing NTPL treaty relations with the 11 contracting parties to the CSC, thus further removing potential barriers to investment and supporting UK exports.

The CSC establishes a shared international fund of supplementary compensation for victims of a nuclear incident, which is made up of contributions from contracting parties to the convention based on their installed nuclear capacity and UN rate of assessment. At present, assuming UK membership of the convention, the shared international fund would be valued at approximately £120 million, with the UK’s contribution at approximately £6.6 million. This would create a contingent liability on HM Government that could crystallise in the event of a nuclear incident in a contracting party to the convention. In the unlikely event of an incident in another contracting party, said contracting party could call on the UK to make its contribution of £6.6 million to the shared international fund once that party’s national minimum compensation amount has been exhausted.

Additionally, should an incident occur in the UK, HM Government may be required to compensate victims up to the value of the shared international fund of approximately £120 million. However, in the event of a civil incident, the UK would be able to call on the shared international fund for the contributions from the other contracting parties to the convention, thus significantly offsetting the value of the contingent liability to the value of the UK’s contribution to the shared international fund—i.e. approximately £6.6 million. To date, there have been no calls on this fund. Further details are available in the departmental minute also submitted to the house.