Elevated temperature nanoindentation of Zry-4 in the presence of hydrogen in solid solution

D. L. I. B. J. W. J. M. Fagnoni F

TopFuel2021 (2021) 45512

During the operation in the reactor, corrosion of the zirconium-based fuel cladding generates hydrogen, which partially diffuses into the metal. Hydrogen, both in solid solution and in its precipitated form, i.e. as hydrides, affects the mechanical performance of the cladding. Depending on the amount of hydrogen, temperature and deformation rate, different embrittlement mechanisms can be activated. While most current research on spent fuel cladding focuses on embrittlement from hydrides, this work concentrates on hydrogen in solid solution. Hydrogen tends to diffuse towards dislocations, forming Cottrell atmospheres around them. The presence of a hydrogen atmosphere reduces both the energy barrier required to generate new dislocations and the Peierls stress needed to move a dislocation, causing an overall increased ductility of the metal. This phenomenon, known as Hydrogen-Enhanced Localized Plasticity (HELP), has been extensively studied in FCC and BCC metals, but a complete understanding and description of this phenomenon in Zr based alloys and HCP metals in general is lacking. The HELP effect is source of concern as the conditions of temperature and hydrogen concentration required to activate HELP might be locally present during handling and transportation of spent fuel between the various waste storage phases. In the presented work, the effect of hydrogen in solid solution has been evaluated by elevated temperature nano-hardness testing of recrystallized Zircaloy-4 sheet material. Results show indications of hydrogen-induced softening at temperatures above 100°C at the tested hydrogen concentration of 230 wppm. 1.

DOI: https://doi.org/