During World War II, Japan had several programs exploring the use of nuclear fission for military technology, including nuclear reactors and nuclear weapons. Like the similar wartime programs in Nazi Germany, it was relatively small, suffered from an array of problems brought on by lack of resources and wartime disarray, and was ultimately unable to progress beyond the laboratory stage during the war.
The Institute of Physical and Chemical Research building in Taisho period
The third director of the RIKEN Institute Masatoshi Okochi submitted a report on "Possibility of Uranium Bomb Manufacturing" in May 1941.
Dr. Yoshio Nishina completed this "small" cyclotron in 1937, the first cyclotron constructed outside the United States (and the second in the world).
The second RIKEN cyclotron, completed in 1943
Prior to the 2011 Tōhoku earthquake and tsunami, Japan had generated 30% of its electrical power from nuclear reactors and planned to increase that share to 40%. Nuclear power energy was a national strategic priority in Japan.
As of March 2020, of the 54 nuclear reactors in Japan, there were 42 operable reactors but only 9 reactors in 5 power plants were actually operating. A total of 24 reactors are scheduled for decommissioning or are in the process of being decommissioned. Others are in the process of being reactivated, or are undergoing modifications aimed to improve resiliency against natural disasters; Japan's 2030 energy goals posit that at least 33 will be reactivated by a later date.
The Onagawa Nuclear Power Plant, a 3-unit BWR site typical of Japan's nuclear plants.
The Kashiwazaki-Kariwa Nuclear Power Plant, a nuclear plant with seven units, the largest single nuclear power station in the world, was completely shut down for 21 months following an earthquake in 2007.
The 2011 Fukushima Daiichi nuclear disaster, the world's worst nuclear accident since the 1986 Chernobyl disaster, displaced 50,000 households after radioactivity leaked into the air, soil, and sea. Radiation checks led to bans on some shipments of vegetables and fish.
The Ikata Nuclear Power Plant.