Niobium’s use in Nuclear Reactors
Niobium’s use in Nuclear Reactors
Niobium, with a chemical symbol of Nb, is the lustrous light gray ductile metallic element that resembles tantalum chemically, and proves to be an extremely essential yet fascinating transition element. With an atomic number of 41, niobium combines strength, a high melting point, resistance to chemical attack, and a low neutron absorption cross-section. All of this promotes its use in the nuclear industry, especially in control rods of nuclear reactors. The prices of niobium are reasonable too, at a mere $75/lb, and are maintained by the largest producer to avoid market perception of a monopoly situation (Winter). Thus, niobium acts as a key element in nuclear fission reactors, due to its enormous strength, high melting point, resistance to corrosive chemicals, and low neutron absorption.
Generally, niobium is incorporated into nuclear fission reactors due to its enormous strength and low density. It was discovered that the addition of 1% zirconium to niobium greatly improved the overall strength of the alloy over the soft pure metal. Thus the Nb-Zr alloy became the replacement for pure niobium in applications requiring the chemical resistance of niobium and a material with a high melting temperature. Because of the increasing need for better strengths and the advance of new technologies, Nb-Zr has been replaced by alloys such as C-103, which has greater strength and thus improved reliability, but still retains all the desirable characteristics of Nb-Zr. Although it is now outdated and isn’t used as much for its strength anymore, Nb-Zr still has several advantages over other alloys.
For example, it is much less expensive than the higher strength Carbon alloys, and can also be used in applications where a high-temperature material is needed with low loads, such as a load-free thermal shield in nuclear reactors. Furthermore, niobium possesses a moderate density, 8.57 gm/cc, which is considered moderate compared to a majority of other high melting point metals and similar to the density of alloyed steel (Li). This makes niobium lightweight, inexpensive, and easy to work with in its incorporation into nuclear fission plants (Dzhakishev).
The high melting points that niobium and its alloys possess are typically one of the most attractive features of this element. Therefore, this alloy has been closely associated with the nuclear industry, which requires specified elevated temperature strength in the range of 1800̊ F to 2200̊ F (Li). Niobium, however, can withstand temperatures of up to 4491̊ F without melting (Winter). Because of the tremendous heat generated by the nuclear fission reactions, this element can withstand these blistering temperatures without sacrificing much of its strength.
Niobium is a fairly stable element, and thus, will not react with other chemicals or substances. Niobium does not react with air under normal conditions, for the surface of niobium metal is protected by a thin oxide layer. This thin layer acts as a shield, protecting the malleable metal underneath from corrosion. Niobium, like other reactive metals, owes its corrosion resistance to this readily formed, adherent, passive oxide film. Niobium’s corrosion properties resemble those of tantalum, although it is slightly less resistant in aggressive media such as hot concentrated mineral acids (Li).
Niobium is resistant to water, most organic and mineral acids and bases at all concentrations below 100̊ C, except hydrofluoric acid, but does react with the halogens upon warming to form niobium(V) halides (Winter). Due to its relative stability and inability to be corroded by several substances, niobium can withstand a vast array of assorted chemicals and elements exposed to it during its exposure in the nuclear reactor. Furthermore, it isn’t corroded at all by uranium, one of the major components of a nuclear reactor. Because of this, and several other aspects, niobium is an excellent choice as an alloy in nuclear shields, control rods, and reactors.
Niobium’s final essential use in nuclear reactors is its low neutron absorption cross-section. It is used to make nuclear control rods, such as those found in nuclear submarines because of its moderate ability to absorb neutrons. In a nuclear chain reaction that are taken advantage of to generate power, the intention is to keep the chain reaction going at a slow, controlled rate to prevent the excessive build-up of heat and a possible meltdown of the reactor core. The fissile material, niobium, is kept mixed in with other atoms which do not support the chain reaction. It acts as a moderator in the control rods, slightly lowering the neutron absorption of the other constituent control rod elements. This allows the reaction to occur at a steady pace. Without this constituent in the control rods, the reaction would take either too slowly or too quickly, depending on the composition of the control rods. Niobium thus slows down and absorb the neutrons, preventing dangerous levels of heat-buildup and possible hazards (Williams).
Niobium, Nb, proves to be an extremely captivating and indispensable component of nuclear fission reactors, due to several of its fascinating properties. It combines strength, a high melting point, resistance to corrosive chemicals, and low neutron absorption cross-section, all of which contribute to its indispensable incorporation into these nuclear plants. What new developments can further lead to the incorporation of niobium into nuclear technology? How can these new technologies further benefit and edify out evolving society? As Alan Kay once stated, “The best way to predict the future is to invent it.” Thus, in today’s society, and for several decades to come, niobium proves to play an exceptionally integral role in its incorporation into nuclear fission reactors, due to its tremendous strength, high melting point, chemical resistance, and low neutron absorption.