NuGen aims to develop a new nuclear power station with a capacity of up to 3.6GW in West Cumbria, north-west England.
The companies have secured an option to develop the power plant in October last year.
In October 2010, the UK government confirmed that the site for the nuclear power station is suitable, and the NuGen consortium now intends to prepare detailed plans for developing the site, with the aim of a final investment decision being taken around 2015.
Iberdrola and GDF Suez hold a 37.5% stake each in the JV, while SSE owns the remaining stake.
The utilities entered into a partnership in February 2009 to jointly participate in the development of new nuclear power stations in the UK.
