The ageing plant, one of four in Switzerland, has long been the target of critics who have argued it should be shut down for safety reasons.
But operator BKW Energy said it planned to invest 200 million francs ($220 million) in the plant’s operation and maintenance over the next six years before disconnecting it from the grid.
“The decision not to invest in the plant’s long-term operation significantly reduces the business risk and will facilitate stronger hydro and wind power expansion in Switzerland and abroad,” the company said in a statement.
It will also boost “investments in new innovative products and services,” BKW said.
The money to be invested in the nuclear plant includes around 15 million francs for “extraordinary upgrade measures” that include steps to improve the cooling water supply and the cooling system for the fuel element storage pool.
Last year, a lower court ruled that Mühleberg, which first went into operation in 1972, would have to be shut down because of security reasons.
The court cited concerns with the plant’s lack of earthquake proofing.
However, the ruling was overturned by the Supreme Court in March.
Switzerland currently relies on nuclear plants for around 40 percent of its electricity.
But the federal government has decided to phase out nuclear energy by 2034 while scrubbing plans to build new plants in the face of public opposition following Japan’s Fukishima disaster in 2011.
BKW’s decision changes a previous plan to continue operating Mühleberg for a longer period.
Because the plant’s operating plant is shorter than expected, the utility said the value of its plant assets would have to be adjusted.
“An extraordinary impairment . . . is likely to be in the double-digit millions range.”
BKW is controlled by the canton of Bern, which holds 52.4 percent of the share capital, with other investors including Groupe E and E.ON Energie.
Environmental group WWF, meanwhile, said it was scandalous that the Mühleberg plant would continue operating for six more years.
The group said that the plant should be shut down immediately because of the risks it poses.