Patent Number: 042186226
Section: summary

This invention relates to a neutron absorbing article. More particularly, it relates to a composite, neutron absorbing, coated article wherein boron carbide particles are utilized as the neutron absorber. The invention also relates to the manufacture of such articles and to uses thereof. Neutron absorbing articles are known in which boron carbide particles (or the B.sup.10 content thereof) are the primary active neutron absorbing materials. U.S. Pat. Nos. 2,942,116 and 3,133,887 describe boron carbide and other boron compounds in polymeric matrices for the manufacture of products which are useful as neutron absorbers. U.S. patent applications Ser. No. 854,966 of McMurtry, Naum, Owens and Hortman, for Neutron Absorbing Article and Method for Manufacture of Such Article, filed Nov. 25, 1977; Ser. No. 856,378 of Roger S. Storm, entitled One-Step Curing Method for Manufacture of Neutron Absorbing Plates, filed Dec. 1, 1977; Ser. No. 866,102 of Owens for Method for Manufacture of Neutron Absorbing Articles, filed Dec. 30, 1977; and Ser. No. 866,101 of Naum, Owens and Dooher for Neutron Absorbing Article, filed Dec. 30, 1977 all relate to neutron absorbing articles, specifically plates, wherein boron carbide particles are dispersed in a phenolic polymer matrix. Such applications are hereby incorporated by reference for their disclosures of boron carbide particles and characteristics thereof, phenolic resins and polymers, other materials, methods and uses and other disclosures therein. Additionally, U.S. Pat. Nos. 2,796,411; 2,796,529; 2,858,451; 2,928,948; 2,991,368; 3,016,463; and 3,061,491 all relate to sheets or laminates including neutron absorbing materials such as boron compounds, e.g., boron carbide, in polymeric matrices. However, none of such patents describes the highly preferred products and processes of this invention and none is for products and processes possessing the distinct advantages of those described in this application. Thus, U.S. Pat. No. 2,796,411 is for a methyl methacrylate shield containing boron carbide. U.S. Pat. No. 2,796,529 describes a radiation shield in which a boron or calcium borofluoride powder is mixed with synthetic resin and sheets of the resin mix may be laminated with other materials. U.S. Pat. No. 2,858,451 relates to a laminated ray shielding material comprising three sheets, one of which is a heavy metal, another of which is a metallic reflector and the third of which is a resin bonding the first two together. U.S. Pat. No. 2,928,948 is also for a laminate which may include metals and fibrous materials, among which glass fabric or fibers are mentioned, and it is recited that boron compounds may be utilized. However, in such products a layer of boron in a binder is held to a lead sheet by a resin layer. U.S. Pat. No. 2,991,368 also describes laminates wherein resin impregnated paper film is used to bond a layer of boric oxide and a thin layer of phenolic resin. In such case the powdered loading material, e.g., boric oxide, is poured over an adhesive surface which readily captures it as a single layer. U.S. Pat. No. 3,016,463 is for a vessel having a neutron absorbing layer in the wall thereof, which layer may be composed of boron carbide powder. Finally, U.S. Pat. No. 3,061,491 teaches impregnation of a fabric substrate with a prime plastisol coat which may be laminated. The plastisol coat may include neutron absorbing materials such as heavy metals, e.g., lead. None of such patents describes the present invention. In accordance with the present invention a composite, neutron absorbing, coated article comprises a backing member, a synthetic organic polymeric coating or a plurality of such coatings on said backing member and boron carbide particles held to said backing member by said coating or plurality of said coatings. Preferably, the backing member is a woven fiberglass cloth and the synthetic organic polymeric coating is a cured and essentially or completely cross-linked phenolic polymer, such as a thermoset trimethylolphenol formaldehyde or phenol formaldehyde polymer. Also within the invention is a method for the manufacture of such neutron absorbing coated articles and an apparatus in which such articles may be installed so as to act as neutron shields or "poison plates" about nuclear materials, such as spent nuclear fuel. The various advantages of the products of the present invention and the method for their manufacture will be evident from the present specification but a few will be specifically mentioned now. The coated articles of this invention may be made to have a comparatively high B.sup.10 content and neutron absorbing capability and yet be desirably thin and light in weight. They may be produced more efficiently and economically and are easily cut, stamped, machined or shaped to desired condition or form. The product manufactured is of desirable tensile strength and various other physical properties and additionally, can be distorted or bent without harmful deterioration. Thus, while the coated article may crack when bent too far it will often still be in one piece without losing power as a neutron absorber and can still be used successfully. In such latter respects it differs greatly from neutron absorbing plates of greater thicknesses. Also, the present product lends itself to easier and quicker processing. Furthermore, the invented article is producible in higher concentrations of B.sub.4 C than articles made only from B.sub.4 C particlespolymer mixes laminated with backing or base members and are of reproducible neutron absorbing capability and such capability may be increased or decreased, as desired, with relatively minor changes in article composition and manufacturing procedures.