Patent Number: 051006081
Section: claims

1. A fast breeder reactor having a core, a control rod assembly positioned therein, and a first guide tube above said core, said control rod assembly having a control rod means with dash rams arranged for vertical movement therein along a plurality of second guide tubes having dashpots located at the bottom portion of said core, said fast breeder reactor comprising a neutron flux measuring unit arranged on one of said dash rams of said control rod assembly at a predetermined location substantially within at least one of said second guide tubes of said control rod means, said neutron flux measuring unit being pulled upward in said first guide tube during reactor operation and being located at the center of said core while said dashpots remain at the bottom portion of said core to thereby directly and precisely measure neutron flux in said reactor core, and to thereby preclude hampering the dropping of said control rod means during emergency reactor shutdown when said dash rams fall and are received by said dashpots. 2. The fast breeder reactor according to claim 1, wherein said control rod assembly is a backup shut-down rod. 3. The fast breeder reactor according to claim 1, further comprising an instrumentation cable for said neutron flux measuring unit which is passed through a central portion of the control rod assembly and lead out to an upper portion of the core.