Hafnium is used in tungsten alloys in filaments and electrodes . It is also used as a neutron absorber in control rods in nuclear power plants . Hafnium 's large neutron capture cross-section makes hafnium a good material for neutron absorption in control rods in nuclear power plants , but at the same time requires that it be removed from the neutron-transparent corrosion-resistant zirconium alloys used in nuclear reactors .