Patent Number: 040642046
Section: description

The following examples further illustrate various features of the present invention but are intended to in no way limit the scope of the invention which is defined in the appended claims. EXAMPLE I Six hundred gm batches of a graphite flour-pitch matrix and additive blend were prepared. The batches contained 342 gm of pitch, 240 gm of graphite flour having a particle size of less than about 0.04 and 18 gm of an additive. A control batch was prepared wherein the additive was replaced with an additional 18 gm of pitch. For each batch the pitch was heated to a temperature of 200.degree. C, the additive was blended with the heated pitch and the graphite flour was then added. The mixture was then blended for thirty minutes in a sigma blade mixer at a temperature of 200.degree. C and at a mixing rate of 100 rpm. After the batch was cooled, the batch was ground to provide a matrix and additive blend having a particle size in the range of 0.6 to 0.9 mm. The viscosity of the batches was then measured at 175.degree. C and a capillary viscometer. Each of the batches was non-Newtonian showing a decrease in apparent viscosity with increasing shear rate. At a wall shear rate of 100 sec.sup.-1 the apparent viscosities of the batches, with various additives were as set forth below in Table I. About 7 grams of the matrix and additive blend was mixed with about 20 grams of a nuclear fuel material consisting of coated ThC.sub.2 particles and having a particle size in the range of 0.6 to 0.9 mm. Each of the batches was then used to prepare nuclear fuel rods by placing the 27 gram batch (20 grams fuel particles, 7 grams matrix) into a steel mold and compressing the batch at a temperature of 190.degree. C and a pressure of 120 psig. After the nuclear fuel rod was formed the wall shear stress necessary to push each of four consecutive rods out of the same mold cavity with no cleaning of the molds between rods was measured. The average wall shear stress value obtained for each of the additives is indicated below in Table II. Fuel rods fabricated as described above using matrix without additives and fuel rods fabricated using matrix with additives were heat treated to 1800.degree. C in graphite sleeves about 12 inches long, about 0.625 inches inside diameter, and about 0.975 inches outside a diameter with both ends plugged with graphite. It was found that the fuel rods fabricated using matrix without additives adhered to the graphite sleeve, while those fabricated using matrix with additive did not. Table I ______________________________________ Viscosity, Additive Poise ______________________________________ None 2350 Petrolatum (avg. molecular weight-approx. 500) 610 1-Octodecanol 600 Paraffin wax (avg. molecular weight-approx. 700) 770 Oleic acid 920 Stearic acid 660 1-Hexadecanol 800 Stearic acid + paraffin (50:50) 660 Stearic acid + 1-Octadecanol (50:50) 660 1-Octadecylamine 800 ______________________________________ Table II ______________________________________ Additive Shear Stress, PSI ______________________________________ None 1900 Petrolatum 8.71 1-Octadecanol 0.61 Paraffin wax (avg. molecular weight-approx. 31.28 700) Oleic acid 2.11 Stearic acid 0.73 1-Hexadecanol 3.56 Stearic acid + paraffin (50:50) 1.21 Stearic acid + 1-Octadecanol (50:50) 0.95 ______________________________________ EXAMPLE II Further batches of a graphite flour, pitch and additive matrix were prepared having the formulation set forth below in Table III. The apparent viscosity of each of the batches was determined. Each of the matrix batches was then used to prepare fuel rods by the injection method. In this method, about 20 grams of ThC.sub.2 nuclear fuel particles having a particle size in the range of 0.6 to 0.9 mm, were placed in a 15.9 mm diameter cylindrical steel mold. About 7 grams of coarsely ground matrix having a particle size of about 0.6 mm were placed on top of the fuel particles in the mold. The mold was then heated to a temperature of 200.degree. C and a piston was used to force the matrix through the fuel particles to form fuel rods having a length of 61 mm. The average shear stress required to remove four fuel rods from the mold was measured and is reported below in Table III. Table III ______________________________________ Apparent Graph- Viscosity at Average ite Addi- 175.degree. C and Shear Flour- Pitch.sup.1 - tive Additive 100 sec.sup.-1 - Stress- grams grams grams Type poise psig ______________________________________ 180.sup.2 402 18 1-Octadecanol 410 12.6 180.sup.2 384 36 " 420 14.5 198.sup.2 384 18 " 460 14.5 198.sup.2 384 60 " 270 10.6 240.sup.3 324 36 " 380 14.8 240.sup.4 324 36 " 260 2.0 ______________________________________ .sup.1 Obtained from Ashland Oil Co. and identified as A-240 .sup.2 Obtained from Asbury Graphite Corp. and identified as grade 6353 .sup.3 Obtained from Great Lakes Carbon Co. and identified as grade 1089 .sup.4 Obtained from Lonza Ltd. and identified as grade KS-44. By the present invention, a matrix composition with reduced viscosity is provided for the manufacture of nuclear fuel rods intended for use in gas cooled nuclear reactors. The invention also provides a matrix composition that reduces the adhesion of the fuel rods to graphite fuel elements after heating the fuel rods in the fuel element.