This paper reports the details of a test method that uses elements of elastic-plastic fracture mechanics to assess fracture resistance of zirconium (Zr)-2.5 wt.% niobium (Nb) pressure tubes for a pressurized heavy water reactor. The fracture properties were evaluated on curved specimens, and the effect of certain trace elements on the fracture properties was determined. Significant reduction of trace impurities, produced by using four-stage melting practices rather than the conventional two-stage process, was observed to cause considerable improvement in the fracture resistance of the alloy. Scanning electron microscopy (SEM) of the fracture surfaces of the test specimens confirmed this observation. © ASM International.