Control rod for nuclear reactor

Hafnium metal plates constituting neutron absorbers are opposed at a gap kept by spot spacers, and the gap between the metal plate and the inner surface of a sheath is kept by ring spacers. With such a constitution, a moderator flow channel can be ensured with no contact between the hafnium metal plates with each other or between the hafnium metal plate and the inner surface of the sheath. Further, since the contact between the hafnium metal plate and the inner surface of the sheath at a narrow gap and over a large area can be completely prevented, both of them are kept from corrosion. Further, even when the hafnium metal plate is used in a reactor water containing a great amount of dissolved hydrogen, dimensional change caused by the formation of hydrides due to hydrogen absorption can be prevented completely since the hafnium metal plate has protective oxide membranes. Further, the control rod is divided axially and laterally, and neutron absorbing elements are charged in accordance with the neutron irradiation dose so that each of the elements reaches nuclear lifetime simultaneously, causing no loss upon waste processing. (N.H.)