Axially non-homogenous FBR type reactors

Purpose: To obtain a flat radial power distribution in a FBR type reactor over the entire life period of the reactor irrespective of the initial fueling and balanced cycles. Constitution: In an axially non-homogenous FBR type reactor in which a disc-like nuclear fuel fertile substance region extended in the radial direction with the peripheral area thereof being thinner than the central area thereof and disposed at the central portion in the axial direction of the reactor core surrounded at the upper, lower and peripheral portions thereof with the nuclear fuel substance region, the thickness of the disc-like fertile substance region in the inside of the reactor core is made thinner during the initial charging cycle than that during the balanced cycle, so that the power shearing rate at the central and the peripheral portions in the radial direction of the reactor core in the initial charging cycle where the nuclear fuel substance is not breeded at all in the disc-like fertile substance region can be made equal to that in the balanced cycle thereby enabling to flatten the radial power distribution also in the initial charging cycle. (Horiuchi, T.)