The 'Horizon Nuclear Project' looked to develop nuclear reactors at Wylfa in North Wales and Oldbury-on-Severn in Gloucestershire.
The Welsh Government said: "This is disappointing news. The First Minister made it clear that Anglesey remains the best option for a nuclear development and has asked for the full support of the UK Government as we work with Horizon to deliver this investment and secure jobs for workers at Wylfa."
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