Patent Number: 054835631
Section: description

DETAILED DESCRIPTION OF THE INVENTION The processing steps necessary for ice blasting zirconium and zirconium alloy components are shown in FIG. 2. After ice blasting a drying step is necessary to remove any moisture before assembling the components into a billet. The end joints on the billet are then electron beam welded in a vacuum to seal the annulus. The welded billet is then heated to 550.degree.-750.degree. C. and extruded into tubing which is suitable for further cold working into nuclear fuel cladding. Ultrasonic testing on extruded tubing shows that metallic components cleaned by ice blasting have a defect-free bondline. Destructive testing on cross sectional samples cut from the tubes revealed no bondzone voids that escaped detection by ultrasonic testing. The samples were analyzed using optical microscopy. Given these attributes, metallic components cleaned with ice blasting represent a significant improvement in the bonding integrity of multi-layered tubing. EXAMPLE 1 Zirconium alloy components used to produce external liner tubing were ice blasted prior to billet assembly. A surface quality monitor confirmed the cleaning ability of ice blasting during fabrication. The surface quality monitor is able to detect a clean or contaminated surface based on the number of electrons returning from a surface when exposed to ultraviolet light. A low reading on the surface quality monitor corresponds to a contaminated surface while a high reading corresponds to a clean surface. Although the test values of the surface quality monitor are unitless, the values provide a quantitative test for determining the cleanliness of surfaces. The surface test produced readings of approximately 30 on the as-machined component before ice blasting and approximately 200 after ice blasting. Surface readings of hydrofluoric acid pickled components are approximately 165. EXAMPLE 2 Four sets of zirconium alloy components described in EXAMPLE 1 were ice blasted and assembled into billets. The annulus of the billet was sealed by electron beam welding in vacuum. The billets were heated to 550.degree.-750.degree. C. and extruded to 63.5 mm OD.times.10.9 mm WT.times.L. Evaluation of the bond integrity was performed by ultrasonic and destructive testing techniques. Both test methods failed to discover any bondline voids at the interface of the multi-layered tube. FIG. 3 shows a photomicrograph of the defect-free bondline that was manufacture by ice blasting. This invention has been described with respect to the preferred practice thereof known to the inventor. Alterations can be made in the particle size and temperature and pressure and composition of the propellant gas, and the duration of the cleaning cycle, to achieve the results desired without undue experimentation. The scope of the invention is therefore to be defined by the appended claims interpreted in light of the pertinent prior art.