The Carborundum Company

Kennecott Corporation

Dean P Owens

Robert G Naum

Carl H McMurtry

Michael T Hortman

Irving B Ruppel, Jr

George I Dooher

Silicon carbide sintered bodies having controlled porosity in the range of about 3-25 vol % are prepared from raw batches containing a multimodal distribution of silicon carbide particles and comprised of at least a first set of particles having one average grain size and a second set of particles having another average grain size larger than the first set of particles. The resulting pores are 3-5 microns in the largest dimension, with an aspect ratio between about 1/1 and about 3/1 . The porous bodies, e.g., in the form of mechanical seal members, exhibit good tribological properties.

Porous silicon carbide

A neutron absorbing article, preferably in long, thin, flat form, suitable for but not necessarily limited to use in storage racks for spent nuclear fuel at locations between volumes of such stored fuel to absorb neutrons from said spent fuel and prevent uncontrolled nuclear reaction of the spent fuel material, is composed of finely divided boron carbide particles and a solid, irreversibly cured phenolic polymer forming a continuous matrix about the boron carbide particles, in such proportions that at least 6% of B.sup.10 from the boron carbide content is present therein. The described structures possess a multiplicity of desirable properties for the use mentioned, including withstanding thermal cycling from repeated spent fuel insertions and removals, withstanding radiation from said spent nuclear fuel over long periods of time without losing desirable neutron absorbing and physical properties, being sufficiently chemically inert to water so as to retain neutron absorbing properties if brought into contact with it, not being galvanically corroding and being sufficiently flexible so as to withstand operational basis earthquake and safe shutdown earthquake seismic events without loss of neutron absorbing capability and other desirable properties when installed in storage racks for spent nuclear fuel. In preferred embodiments of the invention the phenolic polymer is a phenol formaldehyde type polymer, such as a trimethylol phenol formaldehyde type polymer, the boron carbide contains at least 12% of B.sup.10, the plate contains from 8.0 to 11.5% thereof, the plate density is 1.6 to 2.1 g./cc. and the proportions of boron carbide (which may be accompanied by limited amounts of certain impurities) and phenol formaldehyde type polymer (preferably free of halogens, mercury, lead and sulfur) are from 20 to 35% of the former and 65 to 80% of the latter. The invention also relates to a plurality of such neutron absorbing articles in a storage rack for spent nuclear fuel and to a method for the manufacture of the articles. In the manufacturing method a portion of the phenol formaldehyde type resin, in liquid state, is mixed with the boron carbide particles, compacted and cured, after which the cured article is impregnated with additional phenol formaldehyde type resin, which is then cured to make the final product.

Method for manufacturing neutron absorbing article

A neutron absorbing article, preferably in long, thin, flat form, suitable for but not necessarily limited to use in storage racks for spent nuclear fuel at locations between volumes of such stored fuel, to absorb neutrons from said spent fuel and prevent uncontrolled nuclear reaction of the spent fuel material, is composed of finely divided boron carbide particles and a solid, irreversibly cured phenolic polymer, forming a continuous matrix about the boron carbide particles, in such proportions that at least 6% of B.sup.10 from the boron carbide content is present therein. The described articles withstand thermal cycling from repeated spent fuel insertions and removals, withstand radiation from said spent nuclear fuel over long periods of time without losing desirable neutron absorbing and physical properties, are sufficiently chemically inert to water so as to retain neutron absorbing properties if brought into contact with it, are not galvanically corrodible and are sufficiently flexible so as to withstand operational basis earthquake and safe shutdown earthquake seismic events, without loss of neutron absorbing capability and other desirable properties, when installed in storage racks for spent nuclear fuel. The disclosure also relates to a plurality of such neutron absorbing articles in a storage rack for spent nuclear fuel and to a method for the manufacture of the articles.

Neutron absorbing article and method for manufacture of such article

Neutron absorbing articles, such as those in plate form suitable for use in a storage rack for spent nuclear fuel and having such properties as to make them useful in such application for long periods of time, are made by an improved one-step curing method in which a mixture of boron carbide particles, powdered phenolic resin and a minor proportion of a liquid medium which boils at a temperature below 200.degree. C., preferably water, is compacted to desired article form and is cured at an elevated temperature, without simultaneous imposition of pressure in compacting or pressing means, so as to cause bonding of the irreversibly cured phenolic polymer resulting to the boron carbide particles and production of the neutron absorber in desired form. In preferred aspects of the invention the proportions of boron carbide particles, resin and water are respectively, 60 to 80, 20 to 40 and 2 to 8, the resin is a phenol formaldehyde two-stage resin containing hexamethylenetetramine in sufficient quantity to provide formaldehyde to cure it, the resin is of a molecular weight in the range of 1,200 to 10,000, e.g., 6,500, the resin and the irreversibly cured polymer resulting are substantially free of halogens, lead, mercury, sulfur, filler, plasticizer and solvent and the boron carbide particles contain no more than 2% of iron and no more than 0.5% of B.sub.2 O.sub.3. The described method is also employable when a proportion of the boron carbide particles, e.g., 1/10 to 9/10, is replaced by a diluent compound, such as silicon carbide, alumina, silica, graphite, amorphous carbon or mixtures thereof.

Method for manufacture of neutron absorbing articles

A neutron absorbing article, preferably in flat plate form and suitable for use in a storage rack for spent nuclear fuel, includes boron carbide particles, diluent particles and a solid, irreversibly cured phenolic polymer cured to a continuous matrix binding the boron carbide and diluent particles. The total content of boron carbide and diluent particles is a major proportion of the article and the content of cured phenolic polymer present is a minor proportion. By regulation of the ratio of boron carbide particles to diluent particles, normally within the range of 1:9 and 9:1 and preferably within the range of 1:5 to 5:1, the neutron absorbing activity of the product may be controlled, which facilitates the manufacture of articles of particular absorbing activities best suitable for specific applications.

Growing community of inventors

Tonawanda, NY, United States of America

Dean P Owens