Japanese firm Toshiba has sold a 10% stake in its majority-owned nuclear firm Westinghouse to uranium maker Kazatomprom for $540m (£268m).
Nuclear energy is seeing a resurgence
The Kazakh firm hopes the investment will help it to expand. Toshiba aims to gain access to key uranium sources.
Toshiba bought 77% of Westinghouse, the US power plant arm of British Nuclear Fuels (BNFL), for $5.4bn in 2006.
Interest in nuclear energy has grown as an alternative to oil. Japan gets 25% of its energy from nuclear sources.
"By welcoming Kazatomprom - a global leader in resource exploitation - as a Westinghouse investor, Toshiba will strengthen the global development of its atomic energy business," said the Japanese conglomerate.
When Toshiba invested in Westinghouse, the final stake it bought was far larger than originally planned after another investor pulled out.
Since buying its share, the firm has been trying to spread the cost by including other investors.
The latest deal needs to be given the go-ahead by US and Japanese regulators.
Kazatomprom, which holds 10% of the global uranium market, aims to increase that stake to 40% over the next decade or so.
The firm hopes to boost uranium production three-fold to 17,500 tonnes a year by 2015.
The combination of higher oil prices and the need to reduce greenhouse gas emissions has prompted countries to seek an alternative to fossil fuels, including nuclear fuel.