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Hafnium and zirconium are both used in nuclear reactors, including those that power nuclear submarines. In this application, each must be pure and free from the other. The manufacture of nuclear-grade zirconium therefore produces hafnium as a by-product and, conversely, the manufacture of nuclear-grade hafnium produces zirconium as a by-product. Nuclear power plant applications account for a large proportion of hafnium metal. Hafnium has three properties that make it useful in control rods used in nuclear reactors: a high-thermal neutron absorption cross section (almost 600 times that of zirconium), strength and corrosion resistance. Hafnium and its alloys are used for control rods in nuclear reactors and nuclear submarines because hafnium is excellent at absorbing neutrons and it has a very high melting point and is corrosion resistant.
One of the difficult problems in building a nuclear power plant is selecting the right materials. Many metals capture neutrons that pass through them. The neutrons become part of the metal atoms and are no longer available to make fission reactions occur. An engineer needs to use materials in a power plant that are transparent to neutrons—that is, that allow neutrons to pass through them.
Zirconium is one of the best of these metals. Zirconium is a commercially available refractory metal with excellent corrosion resistance, good mechanical properties, very low thermal neutron cross section, and can be manufactured using standard fabrication techniques. It is transparent to neutrons and if it is used to make the parts in a nuclear power plant, it will not remove neutrons from the fission reaction going on inside the plant.
It is therefore, nuclear energy applications such as in the cladding (outer layer) of fuel rods through which it is important that neutrons can travel easily.
Tungsten is one of the candidate armor materials for the plasma facing components of the International Thermonuclear Experimental Reactor (ITER), due to its favorable thermal and mechanical properties, and its low sputtering yield. For the present reference design, tungsten has been selected as armor for the divertor upper vertical target, dome, cassette liner, and for lower baffle because of its unique resistance to ion and charge-exchange particle erosion in comparison with other materials.
