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.