Rolls-Royce, UKNNL, and JAEA: This new partnership between Japan and the United Kingdom builds on an extensive history of nuclear collaboration. According to UKNNL, it first established an advanced reactor partnership with JAEA in 2001. In more recent years, starting in 2022, the U.K.’s Department for Energy Security and Net Zero (DESNZ) selected both UKNNL and JAEA as contractors and partners for its AMR and AMR fuel development programs—specifically focusing on HTGRs.
At the time, the U.K. government said that, together, both agencies would “leverage a proven HTGR baseline from Japan and adopt an innovative approach in its design, build, construction and operation.” While Japan does not currently commercially operate any HTGRs, it has conducted extensive research and development activities relating to HTGR designs and has operated its High Temperature Engineering Test Reactor since 1998.
The language of the statement detailing the countries’ HTGR collaborations from 2022 and this week fall along similar lines, and memorandums have been signed to speed deployment. But the question remains: What is actually different about this newest set of agreements?
The answer is that, in February, the DESNZ launched a new Advanced Nuclear Framework, a 45-page document that aims to create a pipeline of credible U.K. nuclear projects. That pipeline is expected to attract private investment in projects and ultimately accelerate new deployment.
JAEA explained that, since then, “Rolls-Royce has expressed its intention to develop and deploy HTGRs in the U.K. using this framework and has requested collaboration with JAEA and UKNNL in order to utilize the outcomes of existing collaborations between the parties.”
While this week’s announcements do not list any specifics about Rolls-Royce’s reactor design, the company’s website states that the Rolls-Royce AMR has a power output of up to 25 MWe, will use coated particle fuel, and will be factory built.
TerraPower news: In another advanced reactor development, TerraPower announced that it has formally begun the first step in the United Kingdom’s generic design assessment process. In April 2025, the company sent its first letter to the DESNZ expressing interest in building Natrium units in the country, which was followed by a GDA application in October.
Along with this GDA news, TerraPower announced the formation of TerraPower UK, a new subsidiary that will be the company’s “operational base for all U.K. activities, including GDA engagement.” This new office is the company’s first outside of the United States. More broadly, this is TerraPower’s first time working to deploy Natrium internationally. Back across the Atlantic, the company continues to progress on its flagship project in Kemmerer, Wyo.
_70610.jpg)
