Toshiba drops 15% after flagging multi-billion-dollar nuclear writedown

Toshiba is facing an impairment charge of several billion US dollars after its nuclear project completion costs will far surpass original estimates due to "increases in key project parameters," says the company in a news release.

The news sent Toshiba tumbling 15% on the Tokyo Exchange.

Westinghouse, a Toshiba subsidiary, acquired CB&I Stone & Webster in December 2015. CB&I is one of the largest providers of commercial nuclear plant maintenance services.

Toshiba says the impairment is still an estimate and it will revise its financials when it fully values the impact.

The Japanese conglomerate, which has been dogged by past nuclear write-downs and accounting scandals was looking to its nuclear and semiconductor business to boost growth.