Patent Number: 
Section: abstract

A control rod for a nuclear reactor has a structure which is capable of suppressing expansion of a reduced-diameter portion of a neutron absorber in a radial direction under shocks applied upon every stepwise driving of a control rod cluster and which can ensure integrity of a cladding tube over an extended period. The control rod includes a cladding tube closed hermetically at both ends thereof by a top end plug and a bottom end plug, respectively, a neutron absorber loaded into the cladding tube and includes a reduced-diameter portion having a smaller diameter than the other portion, the reduced-diameter portion being disposed at the bottom end plug side of the control rod, and a hold-down spring for pressing the neutron absorber downwardly against the bottom end plug. A sleeve is disposed within an annular space defined between an outer peripheral surface of the reduced-diameter portion and an inner peripheral surface of the cladding tube.