Metallographic examination of a CANDU fuel bundle heated under severe accident conditions.

Abstract

Post-test metallographic examination of bundle cross sections of a 19-element modified CANDU fuel bundle was carried out. The bundle, HTBS-004, had been subjected to a severe temperature excursion to 1900 degrees C in superheated steam. For this study, quantitative image analysis, Auger analysis and SEM-EDX techniques were applied. A significantly large quantity of molten (Zr, U, 0) alloy was relocated in the bundle section 50 mm from the upstream end, whereas the 377-mm section showed little relocated material except at the inner element junctions. These variations in the molten material generation and relocation have been correlated with the corresponding axial and radial variations in the heatup rates.