The Kyoto University Critical Assembly (KUCA) is a multi-core type critical assembly established in 1974 as a facility for the joint use study on reactor physics for researchers of all universities in Japan. It has three independent cores named A, B and C as shown in Figure. Solid moderators such as polyethylene and graphite are used in the A and B cores, whereas a light water moderator is used in the C core. In the KUCA, however, only a single core can attain the critical state at a time because the assembly is equipped with control mechanism.

  There are two types of 93% enriched uranium fuels; coupon type fuel plates of 2" square and 1/16" in thickness with thin plastic coating for the A and B cores, and plate type ones of 6×60cm and 1.5mm in thickness with aluminum (Al) cladding of 0.5mm in thickness for the C core. In addition, for the C core, there are two types of curved fuel plates of 65cm in length and 1.4mm in thickness with Al cladding of 0.45mm in thickness, which have 32 kinds of different curvatures and widths; one is of 93% enrichment and the other of 45%.
  In the first decade, it was mostly used for following subjects:

 (1) Experimental study of nuclear characteristics of the Kyoto University High Flux Reactor (KUHFR), coupled core,
 (2) Critical experiments in thorium loaded cores,
 (3) Critical experiments using medium enriched uranium fuel.

  In the second decade, it has been used for,

 (4) Critical safety experiment,
 (5) Reactor physics study for high conversion light water reactors.

Solid Moderated Core(A or B)

Light Water Moderated Core (C)


Control Room

First Critical

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Four Seasons

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