Rolls‑Royce SMR receives positive justification decision

By Ian Truman

27 Mar 2026 4 min read

The UK Government has confirmed that the Rolls‑Royce Small Modular Reactor (“RR SMR”) is justified in principle under the Justification of Practices Involving Ionising Radiation Regulations 2004.

The decision concludes that the benefits of the RR SMR outweigh the potential health, environmental and safety detriments associated with its deployment. Justification is a mandatory early step for new nuclear reactor technologies and must be satisfied before a reactor type can be introduced in the UK.

What does this decision do?

The goal of the radiation protection regime is to protect human health and the environment from the harmful effects of ionising radiation. The fundamental safety principles adopted by the International Atomic Energy Agency to achieve this fundamental safety objective includes the requirement for the ‘justification’ of facilities and activities that give rise to radiation risks, in other words a reasoned consideration of whether the benefit from such facilities or activities outweigh the associated radiation risks.

The justification applies to the following class or type of ‘practice’:

“The generation of power from nuclear energy using uranium dioxide fuel of low enrichment in fissile content in a light water cooled, light water moderated thermal reactor currently known as the RR SMR designed by Rolls-Royce SMR Limited"

In reaching its decision, the Government was satisfied that the RR SMR:

delivers significant climate change, energy security and socio‑economic benefits;
presents only a very limited radiological health detriment to workers and the public;
generates radioactive waste that can be safely managed and disposed of within existing UK policy frameworks; and
does not pose unacceptable safety, security or safeguarding risks.

The decision also confirms that there is no restriction on the number of SMR units that could be deployed on a single site, subject to compliance with applicable regulatory controls.

Why this matters:

This decision represents a critical regulatory milestone for the UK SMR programme. Without justification, a new reactor design cannot progress through the UK’s nuclear regulatory framework.

For developers, investors and the supply chain, the decision:

• removes a policy and regulatory barrier to RR SMR deployment;

• provides increased certainty for investment and project planning; and

• supports progression to subsequent regulatory, planning and commercial stages.

What happens next?

The justification decision must be given effect through secondary legislation approved by Parliament. Any future deployment of RR SMRs will then remain subject to the full suite of site‑specific approvals, including planning consent, environmental permitting and licensing by the Office for Nuclear Regulation.

The RR SMR is currently in stage 3 of the UK’s (non-mandatory) Generic Design Assessment process having completed the second step of the process in July 2024.

The justification decision is an important milestone in the consenting of the RR SMR as it allows a develop to proceed with an application for a site specific nuclear site licence. In practice a developer is likely to wait until the RR SMR has completed Step 3 of the Generic Design Assessment process.

Regulatory Justification and the Nuclear Regulatory Review

On the same date the Government announced the RR SMR justification decision it also published its response to the Nuclear Regulatory Review.

Recommendation 35 of the Nuclear Regulatory Review (streamlining regulatory justification) recommended that the Government:

Propose legislation that would deem the grant of a planning permission, the completion of Stage 2 of the GDA, or the grant of a nuclear site licence for a nuclear installation to be a justified practice.

The Secretary of State for Environment, Food and Rural Affairs should issue a Regulation 12 determination that ‘the use of ionising radiation for the generation of electricity from nuclear energy using uranium oxide fuel of low enrichment in fissile content in light water cooled, water moderated thermal reactors’ is justified. Given we are not persuaded that there is a legal impediment to this route, in the event this target is not met, Government should propose amending the regulations via primary legislation, deeming that light-water reactors are deemed to be justified. Propose legislation that would deem the grant of a planning permission, the completion of Stage 2 of the GDA, or the grant of a nuclear site licence for a nuclear installation to be a justified practice. The Secretary of State for Environment, Food and Rural Affairs should issue a Regulation 12 determination that ‘the use of ionising radiation for the generation of electricity from nuclear energy using uranium oxide fuel of low enrichment in fissile content in light water cooled, water moderated thermal reactors’ is justified. Given we are not persuaded that there is a legal impediment to this route, in the event this target is not met, Government should propose amending the regulations via primary legislation, deeming that light-water reactors are deemed to be justified.

The implementation plan published in Annex A of the Government’s response to the Nuclear Regulatory Review confirmed that the Government agreed with the intent of Recommendation 35 and would address the issue as soon as possible, working with GBE-N to submit a single regulatory justification application for all Light Water Reactors and then moving forward to simply the wider pathway for other reactor classes, to cut unnecessary duplication whilst preserving robust public protections. The Government response did not, however, rule out legislative change if the proposed improvements did not go far enough.

Written by Ian Truman and Ishbel McCormack