The aim is to build and operate new nuclear power stations on the site, which will create at least six gigawatts of energy for the UK.
Between them, the companies currently hole stakes in 20 nuclear power stations around the globe.
Andrew Duff, chief executive of RWE npower, said the investment can help the UK to "replace aging coal and nuclear plants" and help create a "low carbon economy".
He added: "New nuclear build is a key part of RWE npower's commitment to meet the UK's energy needs and to reduce carbon dioxide intensity."
Energy Secretary Ed Miliband recently told BBC Radio 4's Today programme that the dispute between Russia and Ukraine will not affect the UK's gas supply.
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