Surging sea levels due to climate change could mean new power station Sizewell C is cut off by the water within decades, a top scientist has warned.
Sue Roaf, emeritus professor of architectural engineering at Heriot Watt University, said it was madness to build a new power station near flood risk sites.
She warned the proposals on the Suffolk coast risked lives and could transform parts of the area into a "toxic wasteland".
"It's ridiculous the government is even considering another power station on the coast," Prof Roaf said.
"You can downplay the future risk, but even by conservative estimates sea levels will have risen by a metre by 2100, potentially making Sizewell a nuclear island during storm surges."
EDF Energy, which operates Sizewell B and is expected to submit final plans for Sizewell C in the coming months, said its assessments of flood risk already took into account extreme high tides and sea-level rises.
A spokesman said EDF had considered climate change using the "worst case, but plausible sea-level rise" forecasts - and its sea defences could adapt, if needed.
"As part of its marine studies, EDF has also drawn on advice from an independent 'expert panel' of climate change advisors," the spokesman added.
EDF and the Government also said nuclear power would address climate change by providing clean energy.
But some forecasts show how rising sea levels could pose problems for nuclear plants, which are mainly based on the coast to use seawater for cooling.
US-based Climate Central recently produced a map showing swathes of Suffolk's coast and estuaries below the annual flood level by 2050, based on predictions that sea levels will rise 10cm a decade.
Although the modelling does not consider the effect of flood defence strategies, it shows towns such as Aldeburgh, Lowestoft, Orford and Southwold to be at risk.
Sizewell itself is shown above the flood level - but almost surrounded by flooded sites.
The Environment Agency's map already shows much of the land around Sizewell to be at medium or high risk of flooding.
Government analysis of nuclear sites, obtained by the Guardian, found Sizewell had been deemed at high risk of flooding in 2010.
Prof Roaf said Suffolk already faced "chronic environmental risk" in protecting Sizewell A and B, as well as their spent fuel, from the sea - and claimed adding Sizewell C would increase the risks.
Nick Scarr, who lives in Aldeburgh and owns an international engineering consultancy, has also written reports highlighting concerns about how spent fuel from Sizewell will be dealt with amid rising sea levels.
Mr Scarr said Suffolk was set to become a "nuclear waste storage facility for at least 200 years" and communities deserved to know more about how it would be safeguarded.
He said current proposals failed to consider the risk of extreme sea events, which according to the International Panel on Climate Change, were likely to happen every year by 2050. Mr Scarr said it was "extraordinary" the government was seemingly oblivious to these warnings and progressing with new nuclear sites on the coast.
Together Against Sizewell C (TASC) raised similar concerns at the Nuclear Free Local Authorities seminar in Colchester last year. TASC's Pete Wilkinson said as Sizewell was predicted to be an island within a century, or sooner, any new nuclear plant at the site was "irresponsible".
Paul Dorfman of UCL's Energy Institute warned during a debate on nuclear power that sites such as Sizewell may need considerable investment to protect against rising sea levels or "even abandonment in the long term".
The Department for Business, Energy and Industrial Strategy said nuclear safety and environmental protection were of "paramount importance" and kept under regular review. "The UK has a strong regulatory system and companies involved in the civil nuclear industry are required to meet robust requirements overseen by an independent regulator - the Office for Nuclear Regulation", it said. "This includes ensuring plants remain safe against the effects of climate change."
EDF said monitoring would continue throughout the life of the station, as is done for Sizewell B, not just during planning. "We continue to work with Lowestoft based marine experts Cefas to gather important information in this area," it added.
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