Delayed hydride cracking (DHC) of the reactor core zirconium items of light-water reactors and factors affecting this process (composition and structure state of alloy, hydrogenation level of zirconium item, direction of a defect evolution in it as well as conditions (temperature, stresses, irradiation) and regime (isothermal, thermal cycling) of operation were investigated. Influence of irradiation on DHC of zirconium items was studied. Possibility of evolution of the manufacturing defects (cracks) available in tubes of zirconium items in the process of their long storage under the effect of hydrogen available in tubes and residual stresses remained in them after fabrication was established. (c) 2005 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.