Development and evaluation of spire pulse for AlSi lead-dip canning

In the AlSi process, the I&E fuel element is assembled in a two-piece aluminum container consisting of an outer cylindrical shell and an inner tube containing an integrally impacted cap wafer which forms the top end and cap during canning. Both autoclave failures and reactor failures have been attributed to porosity in the AlSi and non-wetting of the aluminum wafer with AlSi. Porosity and non-wetting in the area of the cap closure provides a pathway for water to penetrate through to the uranium from small defects in the weld which are not detected by visual weld inspection or radiography. These quality deficiencies are caused from two apparent fuel problems, (1) the disparity in mass between the spire and cap wafer which results in uneven pre-heating rates for spire and cap wafer and freezing of gas bubbles under the cap wafer, and (2) the heavyoxide and lubricant contamination on the underside and side of the wafer which causes non-wetting and outgassing. In December, 1958, an additional cleaning step was introduced in the 313 Manufacturing process to improve cap wetting. This change involved degreasing followed by a caustic etch to remove imbedded lubricants in the cap wafer. It was effective in reducingmore » cap wetting, although it did not completely resolve the problem.« less