The Japan Atomic Energy Agency and two Japanese companies signed an agreement on Wednesday with TerraPower LLC on a fast reactor the U.S. nuclear power firm plans to build with financial assistance from the U.S. Energy Department.

The two sides will discuss nuclear technology cooperation, the memorandum of understanding said, with the discussions likely to focus on the use of sodium as a coolant and information exchange regarding Japan's experience of operating the Monju prototype fast-breeder reactor.

The two Japanese companies are Mitsubishi Heavy Industries Ltd. and Mitsubishi FBR Systems Inc.