The reasons for hydrogen saturation of Zr workpieces of reactor core zones and factors which influence this process are considered. The regularities of the hydrogen saturation effect on fracture toughness of the thin-walled workpieces are investigated. It is ascertained that the crack propagation in the Zr members of fuel assemblies under action of hydrogen is possible due to mechanism of delayed hydride cracking. An influence of irradiation on the crack propagation intensity is studied for E110, E110K and E635 alloys with coatings.