JRR3

JRR-3M Neutron Source

The former JRR-3, the first domestically designed and constructed reactor (10 MW) in Japan, had been utilized by many researchers since 1962. In 1985 modification of JRR-3 started because demands for higher performance of reactor utilization for various experiments had been increased with the progress of nuclear energy development. JRR-3M ( Japan Research Reactor No.3 Modified ) attained its first critically in March 1990 as a high-performance multi-purpose research reactor and started operation for use with maximum output of 20 MW in November of the year. JRR-3M is a pool type research reactor using low enriched aluminide fuels. For neutron beam experiments, the experimental building (guide hall) is located contiguous to the reactor building. Reactor core is installed at the bottom of the reactor pool of about 8.5 m in depth and about 4.5 m internal diameter with keyhole shaped horizontal cross section. Cylindrical reactor core of about 60 cm diameter and about 75 cm height is surrounded by a heavy water tank of about 200 cm outer diameter and about 160 cm height. Reactor core is composed of 26 standard-type fuel elements, 6 follower type control rods with fuel elements, beryllium reflectors and vertical irradiation holes. Cooling and moderation are done by light water circulation. Utilization facilities include irradiation facilities using vertical irradiation holes in the reactor core and heavy water tank, and beam experimental facilities using horizontal experimental holes furnished to heavy water tank. Horizontal experimental holes are tangentially set to the reactor core so that only thermal neutron can be extracted(cf. top figure on p.17). Cold neutrons can be utilized in addition to thermal neutrons for the beam experimental facilities (guide hall). The facility is designed to make thermal neutron penetrate in the liquid hydrogen with 20 K, and thereby become cold neutron with lowered speed(cf. bottom figure on p. 17). Neutrons are guided to the guide hall from the reactor by the neutron guide tubes which are made by rectangular glass tubes covered with vaporized natural nickel film. The size of neutron guide tubes are 20 cm in height and 2 cm in width for thermal neutron, and 12 cm in height and 2 cm in width for cold neutron. A lot of beam experimental equipments have become available to install on these neutron guide tubes.

thermal power	20 MW
max thermal flux in the core	2 x 10¹⁴ [cm^-2 s^-1]
reactor cycle	26 days
annual operating cycles	7 cycles / year
average consumption of 235U	20%