[en] Delayed hydride cracking (DHC) velocity of Zr- 2.5Nb pressure tubes is one of the material testing items for pressure tube surveillance to be examined regularly. Thus, it is required to establish a model to accurately predict the DHC velocity with operating conditions. According to our new DHC model called Kim's model, the DHC velocity is governed by the supersaturated hydrogen concentration above the heating solvus or the terminal solid solubility for dissolution of hydrogen (TSSD) or ΔC at the test temperature. However, by arguing that the DHC velocity increased with increasing hydrogen concentration dissolved in the bulk, not the ΔC, Shek pointed out that Kim's model is invalid. The aim of this work is to show the validity of Kim's model by checking if the DHC velocity of the Zr-2.5Nb tube is governed either by total hydrogen concentration dissolved in the bulk as suggested by Shek or by the ΔC as shown in Kim's DHC model