Control rods for nuclear reactors

Purpose: To prevent cobalt-60 production and to improve the impact shock strength of control rods from the viewpoint of material composition. Constitution: A guide roller is supported by a retaining pin in the aperture of an upper handle and a limiter roller is rotatably provided by a retaining pin in the recess of a lower handle of a control rod blade. Both of the rollers are made with a nickel base alloy containing 0.08% or less of carbon, 14 - 17% of chromium, 5 - 9% of iron, 0.7 - 1% of niobium, 2.25 - 2.75% of titanium, 0.4 - 1% of aluminium (by weight ratio). Both of the retaining pins are made with a cold worked iron base alloy containing 0.1% or less of carbon, 16 - 26% of chromium, 5.5 - 15% of nickel, 0.4 - 5% of silicon, 5.5 - 15% of manganese, 0.05 - 0.6% of nitrogen (by weight ratio). (Horiuchi, T.)