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Justification is an early regulatory step required for the operation of a new nuclear technology in the country. It determines whether or not a new reactor design is justified under The Justification of Practices Involving Ionising Radiation Regulations 2004.

The Nuclear Industry Association (NIA) applied in July 2024 to the Department for Environment, Food and Rural Affairs (DEFRA) for a justification decision for the Rolls-Royce SMR, marking the first ever application for justification of a UK reactor design. In October last year, the deparment, DEFRA, opened a public consultation on the NIA's application, which closed on 1 December. It said it was seeking views on: whether the proposed practice belongs to a new, or to an existing class or type of practice; whether the proposed practice was a suitably defined class or type of practice for a justification decision; and whether the information in the application and supplementary information is suitable for DEFRA to make an appropriate assessment of the balance of benefits and detriments of the proposed practice.

The Secretary of State for Environment, Food and Rural Affairs has now decided that the Rolls-Royce SMR is justified. 

"The decision takes into account responses to the Consultation on the Application for the Rolls-Royce SMR designed by Rolls-Royce SMR Limited, open from 6 October to 1 December 2025, and the views of statutory consultees," DEFRA said. "Secondary legislation giving effect to the justification decision will need to be approved by a resolution of each House of Parliament."

Helena Perry, Safety and Regulatory Affairs Director for Rolls-Royce SMR, said: "We welcome the decision by the Secretary of State for Environment, Food and Rural Affairs, providing regulatory justification for our power station - a key step in our regulatory journey to deploying the UK's first small modular reactors and in our mission to provide clean, affordable energy for all."

The NIA, as the representative body of the UK civil nuclear industry, often makes justification applications, because justification is a generic decision that can be relied upon by anyone and are not personal to individual reactor vendors or project developers. The NIA has previously applied for justifications for Hitachi's Advanced Boiling Water Reactor, Westinghouse's AP1000 and Framatome's EPR.

The Rolls-Royce SMR is a 470 MWe design based on a small pressurised water reactor. It will provide consistent baseload generation for at least 60 years. Ninety percent of the SMR - measuring about 16 metres by 4 metres - will be built in factory conditions, limiting activity on-site primarily to assembly of pre-fabricated, pre-tested, modules which significantly reduces project risk and has the potential to drastically shorten build schedules.

In June last year, Rolls-Royce SMR was selected as the UK government's preferred technology for the country's first SMR project. A final investment decision is expected to be taken in 2029.

In November, the government announced that Wylfa on the island of Anglesey, North Wales, will host three Rolls-Royce small modular reactors. It said the site - where a Magnox plant is being decommissioned - could potentially host up to eight SMRs.