Neutron absorbers boron carbide

Hydrochloric acid Succinic acid neutralizer, preboiler system Methoxypropylamine neutralizer, urea-formaldehyde resins Ammonium biborate neutron absorber Boron carbide Samarium oxide neutron absorber, laser crystals Samarium... 

Control of the nuclear chain reaction in a reactor is maintained by the insertion of rods containing neutron absorbing materials such as boron, boron carbide, or borated steel. In state-of-the-art high temperature reactor designs, such as the Gas... 

Control rods. These are usually made of boron steel or boron carbide (p. 149), but other good neutron absorbers which can be used are Cd and Hf. 

It is used in antiseptics and medicines, as a flux in smelting, soldering and welding operations, as a deoxidizer in nonferrous metals, as a neutron absorber for atomic energy shields, in rocket fuels, and as extremely hard abrasive boron carbide (harder than corundum). See also Boron. 

Tlte control element assembly, shown in Fig. 15. consists of 0.8-inch (2-ceiuimeler) outside diameter Inconel tubes containing boron carbide pellets as the neutron absorbing material. A gas plenum is provided in order to limit the maximum stress due to generation of internal gas pressure. 

Naturally occurring boron consists of two isotopes 10B, which comprises about 20%, and nB, which makes up the remaining 80%. This results in the average atomic mass being 10.8 amu. 10B has the ability to absorb slow neutrons to a great extent. Therefore, it finds application in reactors as control rods and protective shields. However, because boron itself is very brittle (and, therefore, nonmalleable), it must be combined or alloyed with a more workable material. Boron carbide is often mixed with aluminum and then processed into the desired shape. 

The fuel is transported from the reactor pools to Sellafield in MEBs contained within heavily shielded, high integrity, transport flasks. The MEBs are cylindrical stainless steel vessels containing stainless steel clad "Boral" or boronated stainless steel dividers between the fuel assemblies to prevent criticality. "Boral" consists of boron carbide particles in an aluminimn matrix clad with pure aluminimn and is widely used as a neutron absorber. MEB s are used to contain mobile contamination from crud or spalling smface layers of the fuel pins. 

Boron carbide is a relatively inexpensive hard material, which is used for its mechanical properties of strength and extreme hardness in armor-plates for body protection, in sandblast nozzles, and as an abrasive for grinding and cutoff wheels. In nuclear plants, boron carbide is used as the neutron absorbing material of the control rods. 

Use of europium oxide as a neutron absorber in the control rods avoids gas generation under irradiation and gives a slower loss of reactivity with neutron exposure than boron carbide (10%). The main problems are obtaining adequate critical nuclear... 

Boron has been included as a neutron absorber in various materials in addition to concrete. For example, borated graphite, a mixture of elemental boron and graphite, has been used in fast-reactor shields. Boral, consisting of boron carbide (B4C) and aluminum, and epoxy resins and resin-impregnated wood laminates incorporating boron have been used for local shielding purposes. Boron has also been added to steel for shield structures to reduce secondary gamma-ray production. In special situations, where a shield has consisted of a heavy metal and water, it has been beneficial to add a soluble boron compound to the water. 

In the short review by Beauvy et al. (2002) on nuclear boron compounds being used or under investigation, it was reported on the helium gas migration and release mechanisms for the boron carbide neutron absorber under the neutron irradiation. 

Metal borides and boron carbides of different compositions were used as neutron absorber materials—see patents (Hortman and Naum 1981 Lipp et al. 1981 McMurtry et al. 1981, 1982 Naum et al 1979 Owens 1980 Storm 1980 Wieczorek 1988)—and in the control rods of power reactors as well—see patents (Andrews 1987 Dixon et al. 1990). 

Hafnium-like boron is known to be a neutron absorber or neutron moderator element, and, therefore, composites of boron carbide, B4C, and hafnium diboride, HfB2, can be considered as nuclear materials. These boron compounds after sintering and °B/"B isotopic ratio adapting are found to be heterogeneous polyphone cermets useful for nuclear applications (Beauvy et al. 1999). Boron acid obtained from the °B enriched boron trifluoride also was used in nuclear reactors (Shalamberidze et al. 2005). Amorphous boron powders enriched both in °B and "B, boron carbide, and zirconium diboride (ZrB2) powders and pallets labeled with °B isotope And applications in nuclear engineering too. The °B enriched Fe-B and Ni-B alloys are useful for the production of casks for spent nuclear fuel transfer and storage. 

Lipp, A., K. Reinmuth, and D. von Struensee. 1981. Neutron absorber based on boron carbide and carbon and aprocess for their production. U.S. Patent 4252691. 

Storm, R. S. 1980. One-step curing method for manufacture of neutron absorbing plates. U.S. Patent 4198322. Stoto, T., L. Zuppiroli, and J. Pelissier. 1985. Absence of defect clusters in electron irradiated boron carbide. Radiat. Effects 90 161-170. 

In 1998, the plan is to include into the Handbook the results of experiments to determine the effectiveness of heterogeneous neutron absorbers of various types and sizes (e.g., boron carbide and cadmium in the form of separate rods and groups of rods). Experiments with regular cylinders filled with uranium dioxide and located in the moderator in the form of usual and heavy water mixture will also be put in the Handbook. These results are at the review stage. 

Neutron-Absorbing Capability Boron carbide is a neutron-absorbing material used to... 

Due to its neutron-absorbing efficiency, boron carbide is attractive as a neutron absorber material, and is used both in powdered and solid forms to control the rate of fission in nuclear reactors (Figure 4.19b)[530j. B4C mixed with other materials, such as aluminum metal or polyethylene plastic, is applied to protect it against oxidation in the reactor environment. AI-B4C metal-matrix composite plates (e.g., Boral, Bortec) have wide applications as isolators in spent fuel element racks, in the inner sections of reactor shields as shutdown control rods and neutron curtains, as shutters for thermal columns, and as shipping containers. 

The design of the reactor internals has not been addressed yet, but they likely will be made of graphite or carbon composites to accommodate the high-core outlet temperature required by the NGNP (1000°C). It is possible that carbon-insulated metallic alloy will be used for the core support structure, although this has not been evaluated yet. Control rods will be required to provide for reactor startup, normal operation, and shutdown. The munber and placement of control rods has not been evaluated yet, but the rods will be constructed from carbon composites for the drive shafts and absorber casing and boron carbide or other high-temperature absorber for the neutron absorber. The control rod drive mechanisms will be located above the reactor enclosure head. 

Control rod neutron absorber material boron carbide... 

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