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% |
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