The creation of the Rolls-Royce Small Modular Reactor (SMR) business was announced following a £195m cash injection from private firms and a £210m grant from the government.
It is hoped the new company could create up to 40,000 jobs by 2050.
However, critics say the focus should be on renewable power, not new nuclear.
Private investors and the UK government will help fund the firm’s development of small nuclear reactors.