Shutting down Switzerland's five nuclear power stations will cost about 20.7 billion Swiss francs (16.8 billion euros, $22.5 billion) and take about 20 years, Swiss authorities said on Thursday.

A study published by the Federal Office of Energy said that the cost had risen by 10.0 percent compared with a 2006 estimate.

The most expensive part of the process will be the long-term management of radioactive waste, it said.

The Swiss parliament approved a phased exit from nuclear energy at the end of September, six months after the Fukushima plant catastrophe in Japan.

Strong public opposition to nuclear led to a recommendation that SWitzerland's five reactors not be replaced when they come to the end of their operation in 2034.

A huge earthquake and tsunami on March 11 knocked out cooling systems at Fukushima, sending reactors into meltdown and leaking radiation in what was the world's worst nuclear accident since Chernobyl in 1986.