EDF Energy "betrayed the public" after safety fears led to the closure of both reactors at Dungeness B nuclear power station in Kent, campaigners have said.
They were taken offline for two months last May while extra sea defences were installed after a review into Japan's Fukushima disaster highlighted risks.
Barrie Botley, of Kent Against a Radioactive Environment, said not enough details were given at the time.
EDF said it had ensured that everyone knew about what was happening.
A massive earthquake and tsunami which led to the nuclear meltdown at Japan's Fukushima reactor in 2011 prompted new research into the flood risk at Dungeness.
The review concluded that there was "a theoretical but plausible scenario in an extremely rare case where water could have got on to the site, potentially up to waist height", the BBC understands.
EDF issued a statement last May saying Unit 21 was offline for "planned refuelling" and Unit 22 for "improvements to flood defences for extreme events".
It said both units were expected to be returned to service that month.
Mr Botley said that did not make clear that both reactors were completely out of action,
"They betrayed us all and I think it's absolutely disgusting. They're supposed to be very open nowadays and they're not," he said.
But Martin Pearson, station director at Dungeness B, said: "The language we've used is language we've used for 30 years.
"If there's more of an interest from the public, and that is seen as a very positive move, then we'll need to review some of the language that we use."
Flood defence wall
EDF stressed the site was never unsafe and was now protected against the kind of extreme weather expected to happen "only once in 10,000 years".
A flood defence wall between 5ft 2in (1.6m) and 6ft 6in (2m) high has been constructed all the way around the plant at a cost of £2.3m.
It is part of a £5m investment in flood protection including work inside the station, such as sealing trenches, installing dam boards and raising equipment height.
Both Dungeness B reactors automatically shut down during the St Jude's Day storm on 28 October, when electricity to the site was cut off.
EDF said that during the recent floods and storms it had operated normally.