Education and science minister Hiroshi Hase said the Japan Atomic Energy Agency estimates it will cost around ¥300 billion to scrap the Monju fast-breeder reactor over 30 years.
The estimate was made by the agency in 2012 but had never been disclosed to the public.
The ministry has been in the middle of discussions about how to ensure safe operations of the trouble-prone experimental reactor in Tsuruga, Fukui Prefecture, after getting a warning from the Nuclear Regulation Authority last November.