All 80,000 fuel rods at the plant near Hamburg will be examined from Friday because "it looks as if one or several of the rods in the reactor is defective," said Ernst Michael Zuefle, head of operator Vattenfall's nuclear arm.

Kruemmel, one of the oldest of Germany's 17 nuclear power stations, suffered an emergency shutdown on Saturday after a short circuit in one of its transformers and Vattenfall expects it to be offline for at least nine months. It was the second such incident in several days at the plant, which had only re-opened around a week earlier after two years of repairs following a failure in a transformer that had caused a fire and a shutdown.

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.

The situation at Kruemmel has attracted significant media attention in recent days, and political parties have jumped on it ahead of general elections on September 27 with nuclear power a rare divisive issue between the parties.

Germany decided in 2000 under Social Democrat (SPD) ex-chancellor Gerhard Schroeder to mothball its reactors by about 2020, when current premier Angela Merkel's CDU/CSU conservatives were in opposition.

Merkel's conservatives, now coalition partners to the SPD, want to extend the life of some of the nuclear plants, if -- as polls suggest -- they can form a majority with the liberal Free Democrats (FDP) in the September vote.

Nuclear power remains highly unpopular in Germany, but the desire to cut carbon emissions and reduce dependence on foreign oil and gas has led many to push for a re-think.