Still without a publicized name, Rolls-Royce's design is a pressurized water reactor in a close-coupled four-loop configuration. A team of about 150 people have been working on it for around two years. The first months were taken with major design decisions including the use of a light-water as coolant and moderator and to select the close-coupled arrangement of steam generators as opposed to integrating them into the reactor vessel, or adopting a more spread out design similar to today's large reactors. At 450 MWe the output is higher than other innovative designs, and actually outside the usual range considered to define the SMR market of up to 300 MWe.

They are trying to make a design that is cost competitive with natural gas.

Rolls-Royce believes its SMR design will:
• Provide 450 MW, depending on the configuration, that's the equivalent of up to 160 onshore wind turbines.
• Supply power to the grid in a timely manner at lower cost to the taxpayer and consumer, generating electricity that is at least as cheap (per MW) as power generated by today's large scale reactors – potentially even cheaper when SMRs go into volume production.
• Represent the lowest risk by using proven technology and best value by using a high degree of commercial or standardized off-the-shelf components.