The logo of Toshiba Corp is seen behind cherry blossoms at the company's headquarters in Tokyo, Japan April 11, 2017. REUTERS/Toru Hanai

TOKYO (Reuters) - Japan's Toshiba Corp 6502.T said on Thursday it is buying back a 10 percent stake in Westinghouse Electric Co from minority shareholder Kazatomprom for 59 billion yen ($522 million), taking full ownership of the bankrupt U.S. unit.

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 BX.N and Apollo Global Management APO.N 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 BWXT.N 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.