Comment on ‘Influence of metallurgical variables on delayed hydride cracking in Zr–Nb pressure tubes’ by P. Cirimello et al., J. Nucl. Mater. 350 (2006) 135–146

Reanalysis of the DHC initiation temperature, Tc and the crack propagation rate, Vp of CANDU and RBMK Zr–2.5Nb tubes, recently published by Cirimello et al., was conducted, using Kim’s DHC model. It is shown that a negative temperature dependency of Vp at above T(max Vp) for both Zr–2.5Nb tubes is due to a decreased hydrogen supersaturation below ΔCmin over which Vp becomes independent of hydrogen concentrations. When compared to more than 200 data of Vp for the same Zr–2.5Nb tubes collected through the IAEA round robin tests, it is concluded that the temperature dependencies of their Vp which the authors determined using a single specimens are faulty.