European Union leaders called for worldwide stress testing of nuclear plants on Friday and committed to putting their 143 reactors through the toughest security checks possible.
France, one of the nations most reliant on nuclear energy, with 58 reactors, said it would immediately close any plant if it failed a test.
At the end of a two-day summit, the EU nations agreed to submit their nuclear plants to tough safety tests by year-end and promised to heed the lessons from the accident at Japan's Fukushima Dai-ichi nuclear complex.
German Chancellor Angela Merkel said the 27 leaders agreed "on uniform euro stress tests and the highest possible safety standards."
"The experience of Japan has to be reflected in the new stress tests. This is not business as usual," she said.
Merkel's comments come two weeks since a magnitude-9 quake triggered a tsunami that knocked out the Fukushima reactor's cooling system. Japanese Prime Minister Naoto Kan said Friday the fight to stabilize the plant remains "very grave and serious," as officials said they suspected there was a breach in the core of a reactor that could mean more serious contamination.
The fallout has set off fears of the biggest radioactive contamination since the 1986 disaster at Ukraine's Chernobyl, which spewed radiation across a wide distance and continues to haunt Europeans.
"European stress tests will be prepared in a coordinated fashion," Merkel said after the summit. "The aim is the highest possible safety standard," she said, insisting the EU would press for other European nations to follow suit.
EU officials will follow up the nuclear issue during talks in Ukraine next month. Nuclear energy is key for Ukraine, a country of 46 million. Ukraine today operates 15 reactors at four power plants, which generate nearly half of all its electricity.
"Because the danger does not stop at our borders, we encourage and support neighboring countries to do similar stress-tests," said EU President Herman Van Rompuy. "A worldwide review of nuclear plants would be best."
There are currently 442 nuclear power reactors in operation around the globe, with 65 more under construction. Five are in long-term shutdown.
French President Nicolas Sarkozy said experts will have to work out the details of the tests.
"Independent nuclear authorities will proceed with the controls, will make them public and the EU Commission and nuclear regulators will say whether they suffice or not," Sarkozy said.
In France, Sarkozy said, "we decided to subject all our plants to a stress tests in the light of what happened in Japan. If any power plant fails the test, it will be shut down. That's clear."
The EU had its own small nuclear problem. Slovenia's only nuclear power plant that shut down automatically earlier this week due to what plant officials called a minor incident failed to restart because of technical problems.
There was no danger of radiation fallout during the stoppage or the attempted restart, Slovenian authorities said.
Japan's nuclear accident continued to have political impact beyond Europe.
In New Delhi, some 100 protesters marched to India's Parliament demanding that the government give up plans to build a large number of nuclear power plants because of safety issues underscored by Japan's nuclear crisis.
"The choice is clear _ no nuclear," chanted the protesters from the Anti-Nuclear Struggles Solidarity Forum, a coalition of more than a dozen groups.
Gabriele Steinhauser, Robert Wielaard and Don Melvin contributed from Brussels, Veronika Oleksyn from Vienna and Maria Danilova from Kiev contributed to this report.