Control rods in nuclear reactors

Hafnium is obtained as a by-product of the production of hafnium-free nuclear-grade 2irconium (see Nuclear reactors Zirconiumand zirconium compounds). Hafnium s primary use is as a minor strengthening agent in high temperature nickel-base superakoys. Additionally, hafnium is used as a neutron-absorber material, primarily in the form of control rods in nuclear reactors. 

An alloy containing 80% Ag, 15% In, and 5% Cd is used in control rods in nuclear reactors because it has a high neutron cross-section and good mechanical strength (see Nuclearreactors). 

The silvery, shiny, ductile metal is passivated with an oxide layer. Chemically very similar to and always found with zirconium (like chemical twins, with almost identical ionic radii) the two are difficult to separate. Used in control rods in nuclear reactors (e.g. in nuclear submarines), as it absorbs electrons more effectively than any other element. Also used in special lamps and flash devices. Alloys with niobium and tantalum are used in the construction of chemical plants. Hafnium dioxide is a better insulator than Si02. Hafnium carbide (HfC) has the highest melting point of all solid substances (3890 °C record ). 

Naturally occurring boron consists of approximately 20% of 10B and 80% of UB, leading to an average atomic mass of 10.8 amu. Because 10B has a relatively large cross-section for absorption of slow (thermal) neutrons, it is used in control rods in nuclear reactors and in protective shields. In order to obtain a material that can be fabricated into appropriate shapes, boron carbide is combined with aluminum. 

Cadmium is a neutron absorber, making it useful as control rods in nuclear reactors. The rods are raised to activate the reactor and then lowered into the reactor to absorb neutrons that halt the fission reaction. 

Several rare-earth elements are used as control rods in nuclear reactors because of their ability to absorb neutrons. 

There are few uses for terbium. However, terbium can be used as an activator for green phosphor in TV tubes, and some of its compounds are used to produce laser lights. It is also used to dope (coat) some forms of solid-state instruments, as a stabilizer in fuel cells so that they can operate at high temperatures, and as a metal for control rods in nuclear reactors. 

Uses/Sources. Obtained in mining and purification of the metal used in control rods in nuclear reactors and in manufacture of... 

Hafnium dioxide is a high temperature refractory material. It is used for control rods in nuclear reactors. It has high stability and high thermal neutron absorption values. It also is used in special optical glasses and glazes. 

One of its two stable isotopes, 10B, is such a good absorber of neutrons that it is used in control rods in nuclear reactors. This property also makes it useful for construction of neutron detectors. Boron is used to make windows that are transparent to infrared radiation, for high-temperature semiconductors, and for electric generators of a thermoelectric type. 

Because Cd strongly absorbs neutrons, it is also used in the control rods in nuclear reactors. 

Because europium, gadolinium (Gd), and dysprosium (Dy) are good absorbers of neutrons, they are used in control rods in nuclear reactors. Promethium (Pm) is the only synthetic element in the lanthanide series. 

Properties Hard bik. cryst. insol. in water m.w. 55.26 dens. 2.510 m.p. 2350 C b.p. > 3500 C hardness (Mohs) 9.3 resist, to chem. attack dec. by molten alkalis at red heat does not burn in oxygen flame Toxicology Harmful dust avoid inhalation of dust or particles TSCA listed Uses Raw material for paint mfg. alloying agent mfg. of chem.-resist. ceramics grinding wheel abrasive neutron absorber reinforcing agent in composites for military aircraft control rods in nuclear reactors pol-... 

Boron forms a range of compounds with elements that are less electronegative than itself, called BORIDES. Natural boron consists of two isotopes, B (18.83%), used in steel alloys for control rods in nuclear reactors, and B (81.17%). These percentages are sufficiently high for their detection by splitting of infrared absorption or by nuclear magnetic resonance spectroscopy. 

Dark, gray, brittle sohd, the most refractory binary material known. Used in control rods in nuclear reactors and in crucibles for melting HfOj and other oxides. Corrosion-resistant to hquid metals such as Nb, Ta, Mo, and W. Severe oxidation in air above 1100-1400 °C, but stable up to 2000 °C in helium. Hafnium monocarbide... 

Dysprosium (Dy) Owing to its important thermal neutron cross section, dysprosium is used to produce control rods in nuclear reactors and also as a neutron flux measurement. The alloy Tb Dy Fe, is used as a magnetostrictive material. The alloy Nd-Fe-B is a permanent magnet. Finally, dysprosium is also used as phosphors, catalysts, and garnet microwave devices. 

Europium (Eu) Owing to its important thermal neutron cross section, europium serves to produce control rods in nuclear reactors. Europium compounds are also used as phosphors for television screens. 

Gadolinium is a silvery white metal, malleable and ductile, with a white oxide and colorless salts. It is relatively stable in dry air but tarnishes in moist air and reacts slowly with water. Gadolinium has the highest thermal neutron capture cross-section of any element and is used as a component of control rods in nuclear reactors. It is ferromagnetic and used in equipment for magnetic cooling. 

Boron consists of two isotopes, B and B. The former, which accounts for 20% of natural boron, is a very strong neutron absorber and for that reason is used for the control rods in nuclear reactors and as a shield for nuclear radiation. A1 cm thick layer of boron enriched in the isotope B gives the same shielding action against neutrons as 20 cm of lead or 5 m of concrete (an alternative to boron is gadolinium). The pure boron isotope is however very expensive. In many applications natural boron is... 

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