Japanese electronics giant Hitachi is set to buy the UK nuclear project Horizon, which was put up for sale by German-owned E.ON and RWE in March.
The Horizon project to covers the building of new reactors at Wylfa and Oldbury in Gloucestershire.
The deal to build six gigawatts of nuclear capacity should be completed by the end of November, Hitachi said, without disclosing how much it is paying.
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The firm plans to build two to three plants on the current sites, with the first unit becoming operational in the first half of the 2020s.
Hitachi said it anticipates creating between 5,000 and 6,000 direct jobs at each site during the construction phase.
A further 1,000 permanent staff will be employed on each site when they become operational.
Babcock International and Rolls-Royce have signed preliminary contracts with Hitachi to plan and deliver the new nuclear reactors.
Under the Memorandum of Understanding Babcock said it will discuss "how its skills and capabilities can be best used to support the delivery of Hitachi's nuclear new build programme in the UK".
Rolls Royce said it would "explore how it can support Hitachi in the deployment of Advanced Boiling Water Reactor technology in the UK and internationally, through the provision of high value added manufacturing, engineering and technical services".
The firm will also focus on the development of instrumentation and control opportunities both in the UK and overseas.
Both companies hailed the deal, calling Hitachi "a recognised leader in the global nuclear market".
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