The European Commission vowed Monday there would be "no complacency" when it comes to nuclear safety in Europe despite "hundreds of defects" revealed by stress tests especially in France.

"Our stress test was strict, serious and transparent," European Union Energy Commissioner Guenther Oettinger said in a statement, after German daily Die Welt published what it said were figures from a report Oettinger will present on Wednesday to the EU executive board.

The testing regime "reveals bluntly and objectively what we are good at and where there is a need to improve," the German official said. "Generally the situation is satisfactory, but there is no room for complacency."

The German newspaper said Oettinger's report puts the bill for improving the safety of Europe's nuclear power plants at 25 billion euros ($32 billion), after identifying "hundreds of defects".

It said the faults lay mainly in French reactors -- France has 58 of Europe's 145 nuclear reactors.

Oettinger did not comment on the report, but his spokeswoman Marlene Holzner said his conclusions were still being "finalised."

The commissioner wants the executive to sign off on final conclusions in time for the next EU summit on October 18-19.

He said the stress tests involved assessment by nuclear operators, then by the national authorities and finally spot-checks by international expert teams.

The tests simulated safety and robustness in case of floods, earthquakes and airplane crashes where "normal safety and cooling functions" are shut down.

The call for stress tests originated in last year's Japan earthquake, and gathered fresh momentum after two Belgian plants were closed for safety precautions.

The head of Belgium's federal agency for nuclear safety AFCN, Willy de Roovere, said last month tests had suggested there could be "thousands" of possible fissures inside a giant multi-cylindrical structure that serves as a protective vessel for the Doel 3 reactor.