Patent Number: 
Section: claims

1. A control rod for a nuclear reactor, comprising: a cladding tube closed hermetically at both ends thereof by means of a top and a bottom end plugs, respectively;  a neutron absorber loaded into said cladding tube and including a reduced-diameter portion having a smaller diameter than the other portion, said reduced-diameter portion being disposed at the bottom end plug side of said control rod, said other portion of said neutron absorber having a lower peripheral edge, said edge having an inwardly facing chamfer;  a hold-down spring for pressing said neutron absorber downwardly against said bottom end plug;  a sleeve being disposed within an annular space defined between an outer peripheral surface of said reduced-diameter portion of said neutron absorber and an inner peripheral surface of said cladding tube, said sleeve having an upper peripheral edge, said edge being chamfered on its inner side; and  said chamfered edges of said sleeve and said other portion of said neutron absorber being complementary to each other, said chamfered edge of said sleeve being positioned on said chamfered edge of said other portion of said neutron absorber. 2. A control rod according to  claim 1 , wherein said chamfered portion of said sleeve has an axial length not greater than ca. 20 mm. claim 1 3. A control rod according to  claim 2 , wherein said reduced-diameter portion has a diameter which is substantially equal to a value obtained by subtracting from the diameter of said other portion of said neutron absorber the sum of 0.13 mm and not more than about 0.7 mm. claim 2 4. A control rod according to  claim 3 , wherein said sleeve has an outer diameter which is substantially equal to the outer diameter of said other portion of said neutron absorber. claim 3