The malfunction was the second such incident in several days at the plant in northern Germany, which had only just re-opened after two years of repairs following a malfunction in a transformer that had caused a fire and a shutdown.

Vattenfall, the power plant's operator, has since said it failed to install an important safety sensor, and that all of Kruemmel's 80,000 fuel rods had to be checked after some appeared to be defective.

Tuomo Hatakka, head of Vattenfall Europe, said the problems at Kruemmel, which has been operating for over 25 years, "posed no risk to the population."

"The safety systems worked at Kruemmel and there is no reason to question them," he told a news conference in Berlin.

"Tug of war" needs to end

But Vattenfall's failure to act according to established safety rules as well as regulators' inability to uncover such breaches before an accident occurs prompted German Environment Minister Sigmar Gabriel to call for a single oversight body for the country's nuclear power plants.

"This tug of war between the states and the federal government doesn't exist anywhere else in the world," Gabriel said.

Currently, the federal government is responsible for dealing with all radioactive material - including its production, use and disposal. But the Federal Office for Radiation Protection delegates the task of fulfilling its regulations to authorities in Germany's 16 states.

A similar set of rules applies to the operation of Germany's 17 nuclear power plants. The states watch the plant operators and the federal government watches the states. But each level of government oversight relies on separate sets of consultants and expert panels, which are largely chosen by the political party in power at the state or federal level regulation of nuclear power plants is often a major bone of political contention.

Greens want stricter inspections

The Greens chancellor candidate, Renate Kuenast, said state agencies needed to be more stringent in their tests of nuclear plant operators' practices, adding that it was "completely irresponsible" for state authorities to allow Kruemmel to be reopened with a safety sensor missing.

"You can't get a registration sticker for your car before an inspector has seen that problems had been taken care of," she told the Tagesspiegel am Sonntag newpaper.

One of the issues where Germany's two largest parties are diametrically opposed, the use, oversight and future of nuclear power seems certain to become a major issue as German politicians begin a summer of campaigning for September's general election.

Frank-Walter Steinmeier, the current foreign minister and Social Democratic chancellor candidate, has the Kruemmel incident shook his faith in the safety of nuclear power and called for the plant to be permanently closed.

Chancellor Angela Merkel, who also heads the Christian Democratic Union, has said the current regulations have proven to work.

But it's not politicians who are best suited to decide on the fate of nuclear power, Baden-Wuerttemberg's Premier Guenther Oettinger told the Bild am Sonntag newspaper.

"Whether and for how long nuclear power plants run should be decided by engineers, technicians and regulators but not by candidates for the chancellery," he said.

sms/AFP/dpa/AP

Editor: Neil King