Development on the UO₂ fuel rod formation by a new type of extruder combined auger and press mechanism

As one of the economical processes to fabricate ceramic fuel, extrusion techniques was studied. It was intended that the process should be such that the obtained rods would be as highly dense and accurate in dimension as is usually claimed for fuel pellets. When the conditions of UO₂ powder, binder, lubricant and water content were properly selected, the kneaded mass was improved to have a moderate plasticity, a high green density and a high sinterability. The results of the preliminary experiment revealed the fact that neither of the auger type and press type extruder was satisfactory for obtaining the uniform rods. To overcome these difficulties, the vacuum extruder furnished auger and press mechanisms, was designed which had the advantages of both type. The rods extruded by this mechanism were enough uniform in quality and free from distortion. It was known that the extruded rods, thus prepared, were sintered to the density higher than 93% Th. D. at 1,700℃ for 2 hr in hydrogen with the diameter variation within ±2/100∼3/100 mm for the rods of about 10 mm in diameter, and with the camber values within ±5/100 mm for the rods about 200 mm long. Their chemical and physical properties were similar to those of cold compacted and sintered pellets. (author)