Utilities Vattenfall, Uniper and Fortum, which operate the reactors, warned this month that the CLAB storage facility would soon be full and Sweden's six reactors at three nuclear power plants would have to shut down as a result.

Nuclear power plants produce around 35% of Sweden's electricity.

"The government decided today to allow an expansion of capacity at CLAB," news agency TT reported Environment Minister Per Bolund saying.

Sweden has still to decide on long-term storage of nuclear waste, which remains dangerous for more than 100,000 years. Bolund said this could take several months more.

In 1980, Swedes voted to phase out nuclear power.

But increased demand for energy and the need to address climate change led to a change of tack and in 2010 parliament agreed to the continued operation of existing reactors as well as their eventual replacement.

The cost of new reactors and lack of public subsidies means it is unlikely any will be built.

(Reporting by Simon Johnson; editing by Jason Neely)