Problems encountered during design, fabrication and construction of JRR-3

JRR-3, (natural uranium-heavy water moderated and cooled research reactor) went critical on Sep. 12 in 1962, and at present measurements are being made of its characteristics at low power. The measured data will be compared in detail with design calculations, and the full power of 10 MW thermal is expected to be attained during 1964. Preliminary design study for JRR-3 started in 1954, when for the first time in Japan budgetary appropriation was made for research and development in atomic energy. Since 1956, work on JRR-3 has been under the charge of JAERI. Detailed design began in April 1957 with the cooperation of Japanese industrial companies. Construction work started in the beginning of 1959. Some problems encountered during these 6 years are described in this paper. (author)