The nuclear stress tests were not due to be presented to EU leaders until their next summit in mid-October, but several news agencies acquired the report ahead of time on Monday.

"On the basis of the stress test results, practically all nuclear power plants need to undergo safety improvements," the report from the European Commission said. "Following the accidents at Three Mile Island and Chernobyl, urgent measures to protect nuclear plants were agreed. The stress tests demonstrated that even today, decades later, their implementation is still pending in some member states."

French nuclear reactors courted the most safety recommendations, perhaps unsurprisingly as France is Europe's most prolific producer of nuclear power.

Oettinger praised the overall situation, but said there was no room for complacency

"Generally, the situation is satisfactory, but there is no room for complacency," the EU's energy commissioner, Günther Oettinger of Germany, said in a statement. "We must work together to ensure that the highest safety standards are in force in every single nuclear power plant."

Following Fukushima

The stress tests were prompted by the meltdowns at the Japanese Fukushima power plant, triggered by damage from a magnitude 9.0 earthquake and subsequent tsunami on March 11 last year. They were designed to establish how European nuclear plants would cope with threats like earthquakes, flooding, cooling systems failures or power outages.

Two reactors, the Olkiluto site in Finland and Sweden's Forsmatk, were found not to have measures in place to restore safety functions within one hour in the event of an electricity blackout.

Many more plants were found lacking on issues like the on-site installation of seismic devices, or the provision of tools designed to help combat safety scares.

Germany's nine currently active power plants were found wanting when it came to equipment to help detect earthquakes, with early-warning systems either lacking or in need of improvement.

There are 145 reactors in the bloc, with 134 of them still active. The stress tests estimated the costs of the safety improvements to total between 10 and 25 billion euros ($13-32 billion) across the whole continent.

msh/sej (AFP, dapd, dpa)