The move comes as Westinghouse is exploring selling itself, with a deal likely valuing it at close to $4 billion, Reuters reported last week, quoting people familiar with the matter.
Private equity firms Blackstone Group and Apollo Global Management have teamed up to bid for Westinghouse, the sources said. And buyout firm Cerberus Capital Management is in talks with U.S. nuclear power plant component provider BWX Technologies about submitting a joint bid, the sources added.
A successful sale would reduce the financial hit to Toshiba caused by Westinghouse’s failure.
Kazakh uranium miner Kazatomprom, which bought the stake in 2007, has exercised a put option that allows it to sell it back to Toshiba, the troubled conglomerate said in a statement.
Toshiba said it would book an impairment charge of 15.3 billion yen that had already been included in the earnings estimates for the current financial year.
The stake buyback will take place on January 1, 2018, Toshiba said.
Westinghouse filed for bankruptcy early this year after being hit by billions of dollars of cost overruns at four nuclear reactors under construction in the U.S. Southeast.