US-based nuclear operator Exelon Generation has announced the start of negotiations with French utility EDF on the full takeover of three nuclear power stations – the single-unit Ginna, and the two-unit Nine Mile Point and Calvert Cliffs.Exelon said in a statement that EDF, which owns a 49.99% stake in the three stations, has decided to exercise a put option allowing it to sell its share to the US utility.