The Energy Commissioner, Günther Oettinger, has revealed that "nearly all" of the EU's 145 nuclear reactors need improvements to help them withstand natural disasters.
He said that the results of tests carried out in the wake of the Fukushima disaster showed that the power plants were merely "satisfactory".
Speaking during the unveiling of the results on 4 October 2012, Mr Oettinger said no reactors needed to be shut down immediately, but that "major potential for improvements" was needed "almost everywhere".
He warned that the cost of improving nuclear safety could reach 25bn.
He was particularly critical that some improvements recommended following the 1979 Three Mile Island and the 1986 Chernobyl nuclear incidents had not been carried out.
Four reactors in two unnamed countries would have less than an hour to restore safety functions if electrical power was lost, the results show.
In France - Europe's largest nuclear power producer which relies on 58 nuclear reactors for 80% of its electricity, specific failings were found in all 58 nuclear reactors.
The European Commission ordered stress tests to be carried out following the meltdown at the Fukushima plant in Japan, following the earthquake and tsunami.
The tests were designed to establish how the EU's nuclear facilities could withstand earthquake and floods.
Mr Oettinger said that as a result of the tests, he would bring forward a review of the EU's Nuclear Safety Directive, to ensure that technical standards throughout the EU could be raised "to the highest possible level in a uniform manner".
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