Hafnium, HAF nee uhm, a chemical element, is a silver-colored metal. It absorbs neutrons better than most metals and is resistant to corrosion. For these reasons, rods made of hafnium are used to control the rate of reactions in nuclear reactors of nuclear submarines. When the reaction rate is too high, the rods are pushed into the reactor to absorb some of the neutrons. When the rate is low, the rods are withdrawn. Hafnium is also used in some gas-filled and incandescent lamps.