In December 1953, US President Dwight D. Eisenhower delivered his “Atoms for Peace” address at the United Nations General Assembly. The following year, the US tested the hydrogen bomb in Bikini Atoll creating a deadly nuclear fallout affecting Japan’s fishermen. These two events marked the beginning of the introduction of atomic energy in Japan. Sponsored by Hidetoshi Shibata, director of Nippon Television Network Corporation, "the Atomic Energy Peace Mission" led by John Jay Hopkins, president of General Dynamics Corporation visited Japan in May 1955. In spite of this American effort, it was the British built Calder Hall type reactor that was adopted as the first commercial reactor in Japan. This paper focuses on the role of nuclear reactors in Japan-UK relations during the Cold War Era.

In January 1946, the UK Atomic Energy Research Establishment Harwell was established to study atomic energy factories for not only for military use but also for peaceful use. Headed by the Nobel Prize physicist John Cockcroft, the institute developed a gas-cooled and graphite moderated reactor. Its construction of the Calder Hall nuclear power plant began in April 1953, in the early period of the Cold War.

Wishing to set up a nuclear power plant, Japan began to pay a close attention to the Calder Hall nuclear power plant under construction in the UK. In April 1956, Sir Christopher Hinton, Director of the UK Atomic Energy Authority visited Japan. With Sir Esler Dening, Ambassador to Japan, Hinton had talks with Matsutaro Shoriki, Chairman of Atomic Energy Commission, Shibata and Dr. Ryokichi Sagane on the Calder Hall type reactor. Shoriki had a good impression of this reactor. They reached an agreement on introducing to Japan a Calder Hall type commercial power plant from the UK.

However, the UK was still uneasy about the introduction of nuclear power plant to Japan: Given its frequent earthquakes, was it really possible to construct a nuclear power plant in Japan? Was it possible to reach an agreement on supplying uranium or plutonium to Japan on a commercial base? To negotiate the situation, Ichiro Ishikawa, Chairman of the Japan Business Federation, Shibata, Sagane and others visited the UK in October 1956. Finally, in 1965, the Calder Hall type reactor operated Tokai-mura Nuclear Power Plant for the first time. Introducing a commercial nuclear reactor from the UK within a short time after Hopkins’ visit to Japan was a big change for Japanese atomic energy strategy.