Patent Number: 044514280
Section: summary

BACKGROUND OF THE INVENTION This invention relates to control rods and method of producing same, and more particularly it is concerned with a control rod having a prolonged service life and a method for producing such control rod. A control rod has the function of controlling the number of neutrons concerned in a chain reaction of nuclear fission involving 235U in the fuel rods disposed in the core of a nuclear reactor, by virtue of the presence of materials of large neutron absorption cross section in the control rod. Thus control rods are used for controlling the power of a nuclear reactor. Control rods used in a boiling-water nuclear reactor will be described. A control rod includes blades in the form of a cross in transverse cross section having arranged therein a plurality of sealed poison tubes each containing powder of boron carbide (hereinafter B.sub.4 C) serving as a neutron absorber. The blade has a sheath enclosing the plurality of poison tubes. SUMMARY OF THE INVENTION This invention has as its object the provision of a control rod of prolonged service life which is capable of flattening a neutron flux distribution in the vicinity of the forward end portion of the control rod being inserted in the reactor core. The outstanding characteristic of the invention is that in a control rod comprising first neutron absorber causing an (n, .alpha.) reaction to take place and a second neutron absorber causing an (n, .UPSILON.) reaction to take place, the second neutron absorber is disposed in an end portion of the control rod at which the control rod is inserted in the core and formed of an alloy containing a material of large neutron absorption cross section and a material of small neutron absorption cross section.