CONTROL ROD FOR BOILING WATER TYPE REACTOR

PURPOSE: To prevent crevice corrosion cracking by winding a protective sheath water-tightly round a flat member constituted of tubular members having square cross-section, containing a neutron-absorptive poisonous substance on the inside, and arranged in parallel state. CONSTITUTION: A protective sheath 70 is so installed as to directly cover the outer faces of flat members S1, S2, S3, S4 constituted of tubular members T having regular square cross-section shape, containing a neutronabsorptive poisonous substance in the insides, and constituting a control rod. The sheath 70 is joined to a cross-shaped member 50 along the center of a control rod and joined to flat parts V1 -V4 of a velocity limiting apparatus in the lower ends and at the same time joined to a handle H in the upper ends. Then the sheath 70 is wound loosely round the outsides of the flat members S1 -S4 . Consequently, water for a nuclear reactor is prevented from being brought into contact with the tubular members T and crevice corrosion cracking can be prevented.