Hydrogen can cause embrittlement which affects safety and performance of Zirconium cladding materials used in nuclear applications. Hydrogen uptake and precipitation in zirconium alloys used in reactors have been potential causes of deterioration of cladding mechanical properties. Liner fuel claddings were developed to protect against Pellet-Cladding interaction (PCI) used as inner liner in BWRs or to improve corrosion resistance in PWRs as an outer liner.
Non-irradiated cladding sections with, without liner, hydrogenated, and with different cooling rates and under stress gradients were analysed. A strong relation between cooling, hydrogen concentration and its diffusion in cladding with the presence of a liner is observed. This paper focuses on the effect of the presence of the liner (inner and outer) and the comparison and quantification of hydrides present and their impact on the mechanical properties of the cladding materials. The result indicates that using very slow cooling rates hydrogen can diffuse to and precipitate in the liner. As in most post-irradiation examinations where the fuel rod typically also undergoes slow cooling, one observes a high number of hydrides in the liner, the hydrides density in the nearby cladding area are depleted. Whether the higher concentration in the outer liner can lead to a higher susceptibility for delayed hydride cracking is unclear.
The investigation of the effect of different liner material on the hydrides under different cooling rates, and with different hydrogen content is important to better assess the mechanical behaviour of the cladding. Understand the hydrogen diffusion, precipitation and re-orientation under certain cooling rates and stress was study by employing the newest method of neutron radiography at PSI. Experimental techniques like OM, SEM and hot gas extraction were also used to compare experimental results as well as validation methods.
Quantitative hydrogen concentration results measured by high-resolution neutron imaging, allowing analysis on stress-induced hydrogen concentration fields in a sub-10 um scale for different stress field and cooling rates will be presented with particular focus on the liner-bulk interface.