On Tuesday Chancellor Angela Merkel ordered by decree the closure for at least three months of seven nuclear plants, all of which began operating before 1980, so that they could undergo safety checks following Japan's nuclear crisis.
Environment Minister Norbert Roettgen discussed with coalition partners on Friday a ministry paper, offering "preliminary thoughts" on possible standards that few of Germany's 17 nuclear plants currently fulfil, sources said.
"It is right to put such proposals onto the table," the sources quoted Roettgen as saying.
The costs of implementing them would make even the more modern reactors not viable commercially, experts say.
A ministry spokeswoman said no decisions had yet been made in the coalition of conservatives and the liberal Free Democrats.
"It is a listing of that which is theoretically possible, but it is not an official paper," she said. "These reflections have not been concluded yet."