By David Stamp and Annika Breidthardt
BERLIN (Reuters) - Chancellor Angela Merkel said on Thursday she aimed to accelerate Germany's move away from nuclear energy after Japan's crisis, and dismissed accusations that she may have closed seven atomic plants illegally.
Merkel, who this week backtracked on an unpopular decision last year to extend the life of aging nuclear stations, said nuclear technology remained a transitional source of affordable power while renewable energy sources were developed further.
Under a "moratorium," the government ordered by decree on Tuesday the closure of all nuclear plants which began operating before 1980 for at least three months, so that they could undergo safety checks.
"We will use the moratorium period, which we deliberately set to be short and ambitious, to drive the change in energy policy and accelerate it wherever possible, as we want to reach the age of renewable energy as quickly as possible," she told a rowdy session of parliament.
Imposing the moratorium, Merkel suspended a government decision taken only last autumn to prolong the life of Germany's 17 nuclear power plants beyond their original closure dates.
The opposition Social Democrats accused her of merely trying to avoid defeat in regional elections later this month.
But the sudden suspension of her nuclear policy provoked a political row even within her own ranks. Speaker of parliament Norbert Lammert, a member of Merkel's conservative CDU party, questioned why the Bundestag had not been consulted.
Facing heckling from the opposition, Merkel said repeatedly that the catastrophe in Japan, where an earthquake and tsunami provoked a crisis at the Fukushima nuclear complex, meant Germany faced a new situation.
Everything had been done legally, she said. "The nuclear law provides precisely for this: shutting down a plant temporarily until the authorities have achieved clarity about a new situation," she said.
While business pushed for the seven plants to be reopened if they pass the safety tests, the Social Democrats have called for an emergency law to close them permanently.
Bavaria's Isar 1 reactor is due to go offline on Thursday, its operator E.ON said. E.ON was complying with the government's closure plans even though it saw no safety-related reason to do so, chief executive Johannes Teyssen said.
Teyssen told reporters he regarded the closures as purely political and he warned against an uncoordinated approach to nuclear policy after the Japanese crisis.
Isar 1 is likely to be followed by EnBW's Neckarwestheim 1, a target of anti-nuclear protests which is in the state of Baden-Wuerttemberg, where Merkel's conservatives face a struggle to hold on to power in a March 27 election.
Defeat in Baden-Wuerttemberg would deliver a psychological blow to Merkel and weaken her coalition which has already lost its majority in parliament's upper house, where representation depends on the relative strength of parties in state assemblies.
(Additional reporting by Stephen Brown, Tom Kaeckenhoff and Vera Eckert; Editing by Jon Hemming)