Westinghouse and Toshiba did not disclose the terms of the agreement, scheduled to close Oct. 11.
"This acquisition will better enable Westinghouse to provide engineering support and project management services in the very important French market," said Nick Liparulo, Westinghouse vice president of engineering, in the statement provided by the Japanese electronics maker.
The deal should further help Westinghouse prepare for expected growth in the industry around the globe, the statement also quoted Liparulo as saying.
Astare, which is headquartered near Paris and has offices in Marseille and Lyon, will continue to operate as Astare, and the company's approximately 100 employees will be retained, Liparulo said.
Tokyo-based Toshiba holds a 77 percent stake in Monroeville, Pennsylvania-based Westinghouse, which it bought from the U.K.'s British Nuclear Fuels PLC last year for US$4.2 billion (EUR 3.0 billion).