The speed with which Constellation Energy’s fate was sealed took most people by surprise, but none more so than Pierre Gadonneix, chief executive of Électricité de France.

He was still hoping on Thursday to be able to win his board’s backing for a roughly $500m cash injection into the utility that he hopes will be his bridgehead into the US civil nuclear power market. It was a hard sell to directors already becoming impatient with the French group’s protracted efforts to acquire British Energy in the UK for an estimated £12.4bn ($22.5bn).