And just to be explicit, because I see people lie about this very often: this decision was made by the conservative party (CDU) while the Greens were not part of the government.
When the conservatives got back into power a decade later, they started to roll back the nuclear exit. But during the panic after the Japan tsunami this policy became unpopular so the conservatives reversed course and stuck with the disastrous Green policy.
But make no mistake, if the Greens did not make it into government, the Atomausstieg would never have happened.
Subjects to read for details:
* “Atomkonsens” 2000 and “Novellierung des Atomgesetzes” 2002, Kabinett Schröder,
* “Laufzeitverlängerung deutscher Kernkraftwerke”, 2010, Kabinett Merkel II
* “13. Gesetz zur Änderung des Atomgesetzes“ 2011 post-Fukushima, taking back the 2010 extensions