Volume 2, Issue 9 (October 2005)
The Effect of Liner Component Iron Content on Cladding Corrosion, Hydriding, and PCI Resistance
This paper focuses on the effect of liner component Fe content on cladding corrosion, hydriding and Pellet-Cladding Interaction (PCI) resistance. A multitude of experimental techniques is used to evaluate the various properties. The PCI resistance is evaluated through mandrel testing of un-irradiated claddings as well as by ramp tests of pre-irradiated fuel segments in the Studsvik R2 reactor. The results from the mandrel testing indicate that an increase of the iron concentration from 0.05 to 0.21 wt% has a rather small impact on the PCI properties. The ramp data, on the other hand, show a clear decrease in the PCI resistance as the Fe content approaches and exceeds 0.19 wt%. The phenomena involved in secondary degradation are complex, and separate tests are used to evaluate the corrosion resistance in steam as well as the hydriding resistance in pure hydrogen. The corrosion test includes cladding tubes with ZrSn-liner components with iron concentrations from 0.025 to 0.21 wt%. The results show that the corrosion resistance is dramatically increased as the Fe content is increased from 0.025 to 0.05–0.06 wt%, but that a further increase of the Fe concentration only has a minor impact on the corrosion resistance. However, increasing the Fe content from 0.05 to 0.21 wt% increases the hydrogen pick-up rate. The 0.21 wt% Fe liner has a significantly higher density of Secondary Phase Particles (SPPs) as well as slightly larger SPPs than the 0.05 wt% Fe liner. Consequently, it is believed that the SPPs offer sites where hydrogen can easily be absorbed into the Zr-based material, and the frequency of these sites is important for the hydrogen pick-up rate. It is finally concluded that even though the optimization of the Fe concentration in the liner is complex, an iron level regime exists that provides a good balance of resistance against PCI, corrosion, and hydriding.