Mechanical performance of oxidized Zr-Nb-O nuclear cladding tubes

Abstract

Ring compression and tensile tests on oxidized Zr-Nb-O cladding tubes were performed, to examine the reliability of nuclear cladding tubes after oxidation. The oxidation rate was observed to be far greater at 700°C than 600°C, because of the increased volume fraction of less protective porous oxide. The tensile strength of oxidized Zr-1Nb cladding tubes at 600°C for 3 h increased, with no appreciable loss of ductility. After heat treatment at 600°C for 24 h and 700°C for 3 h, the yield strength and the initial flow stress increased, and the flow stress decreased rapidly with strain, resulting in decreased ductility. The increase of yield strength after heat treatment at 600°C in Zr-1Nb was associated with the presence of strong and protective oxide film. In compressive loading, for cladding tubes oxidized at 600°C for 24 h and 700°C for 3 h, a small drop of load, resulting from cracking of the surface oxide layer, was observed at the total displacement of 1.3 ∼ 1.5 mm. The catastrophic fracture that was observed at the total displacement of 5.7 mm in Zr-Nb-Sn-Fe did not occur in Zr-Nb-O. The absence of sudden drop and catastrophic fracture at the displacement of 5 ∼ 7 is thought to be associated with the softer matrix of annealed Zr-Nb-O.