IRRADIATION EFFECTS ON MASSIVE URANIUM MONO-CARBIDE

The results of examinations of UC compounds having nominal compositions of uranium-4.6, -4.8, and 5.0 wt. % carbon after irradiation to burnups of from 400 to 15,000 Mwd/t of uranium are given. Density changes were small. varying from a minimum of 0.3% to a maximum of about 2.5%. Cracking occurred in all specimens; however. it can probably be largely attributed to thermal stresses and to oxidation. after decapsulation. of NaK entrapped in microcracks. Depletion of carbon appears to be occurring in the specimens having the nominal uranium-5 wt.% carbon composition. Metallographic examination shows that the UC/sub 2/ phase disappears at high temperature and high burnup. The fission-gas-retention properties of the compounds appear quite good. In all cases. the amount of fission gas released was comparable with the calculated amount released by recoil. (auth

AN EVALUATION OF DATA ON NUCLEAR CARBIDES

Data on the properties, constitution, compatibility, radiation behavior, fabrication, preparation, storage, and handling of uranium, thorium, and plutonium carbides are reviewed. 187 references. (C.J.G.

PROGRESS ON THE DEVELOPMENT OF URANIUM CARBIDE-TYPE FUELS

It has been corfirmed that uranium monocarbide can be prepared by reacting uranium metal powder with methane at about 650 C, and that sintered carbides of greater than 90% of theoretical density can be made. The cast density of carbides has been found to vary from 13.56 g/cm/sup 3/ for UC to 11.7 g/cm/sup 3/ for UC/sub 2/. The electrical resistivity of cast carbides has been found to vary from about 40 microhm-cm for UC to about 90 microhm-cm for UC/sub 2/ . About 500 ppm of iron or silicon has been found to decrease the quality of arc- melted castings of uranium monocarbide. Oxygen reacts with molten carbide to produce metal and carbon monoride. Nitrogen seems to react with molten carbide to displace carbon from the monocarbide and produce some dicarbide. Diffusion rates in the carbides have been found to be appreciable at 1600 C (D = 3.6 x 10/sup -8/ cm/sup 2//sec) and very rapid at 1980 C (D = 2.2 x 10/sup -6/ cm/ sup 2/sec). The activation energy for diffusion in this system is very high (92,000 cal/mole). Additional studies are in progress to determine suitable chemical methods of preparing carbides from available raw materials, to develop techniques for making highdensity compacts of carbide powder, to cast large shapes of carbide by melting techniques, to measure the mechanical and physical properties of cast uranium carbide and its alloys, to determine the chemical compatibility of carbides with various metals and reactor coolants, and to obtain information on the mechanism by which carbide-type compounds are damaged by fission fragments during neutron irradiation. (auth

THE PROPERTIES OF URANIUM CONTAINING MINOR ADDITIONS OF ALUMINUM OR ZIRCONIUM

The tensile properties, hot hardness, and heattreatment characteristics of urarnium alloys containing up to 2.9 at.% aluminum or 4.0 at.% zirconium are described. The data shown that zirconium has a favorable effect upon the grain size, hardness, and tensile strength of uranium without materially affecting ductility. Additions of 3.8 at. % zirconium raised the tensile strength of uranium at room temperature fiom about 100,000 psi to about 200,000 psi, while the elongation in 2 in. increased from 14 to 22% and the grain size decreased from about 0.20 mm to less than O.01 mm. The data show that aluminum raises the yield strength, that it has very little effect on either the grain size, hardness, or tensile strength of uranium, and that it decreases ductility. The addition of 2.6 at.% aluminum decreased ihe roomtemperature ductility of ur-anium from l4 to 4%. (auth