Investigating Damage within Zirconium Systems using X-Ray Diffraction Techniques

The understanding of irradiation damage within nuclear materials, especially cladding material, is paramount to prolonging the lifespan of these materials or even preventing the potential failure mechanism they undergo. Therefore, a reliable, accessible and cost effective method of determining damage is key to stepping in the right direction.

In this work Convolutional Multiple Whole Profile (CMWP), an XRD analytical technique,
is investigated to determine its validity and viability, by using a zirconium sample of varying
deformation (as-received, heat treated, 30% cold worked, 48% cold worked and 60% cold worked) as well as different XRD radiation sources. As expected from an increase in deformation, the dislocation density increased and the crystallite size decreased. This was the same for both the Cu and Co source diffraction, with some slight quantitative differences. The discrepancy between between the Cu and Co data was determined to be due to the difference in resolution and penetration depth. The Co lab XRD was still deemed a viable option to use in conjunction with CMWP.

Current research into predicting deformation and failure mechanisms in nuclear materials primarily come from analogue, non-actively damaged samples (i.e proton or heavy ion implanted). The damage depth profile for these samples are much shallower than neutron irradiation. The grazing incident geometry was used with a NIST standard, Si, as there is known crystallite size and strain profile, to explore CMWP’s capabilities at determining these physical parameters at these shallower damage depth profiles. The strain profile/dislocation density for both grazing incident (GI) and gonio geometry were refined to zero, matching with the NIST standard documentation. The crystallite size for GI’s CMWP and TOPAS analysis and gonio’s TOPAS analysis were fairly similar at approximately 240 nm, which was roughly two thirds of the NIST standard documentation (400 nm). The discrepancy was believed to be mainly due to the post-processing of the data to reduce noise, which inherently affected peak shape and height.

It is important to look into the thermal stability of dislocations which can be investigated through a thermal gradient - this provides a way to examine the accuracy of CMWP for a range of temperatures. A previous study, using high temperature synchrotron XRD (HT-SXRD), has investigated the effects of temperature on dislocation density as well as the effects of hydrogen and temperature on zirconium lattice parameters. The benefits of using a laboratory high temperature XRD (HT-XRD), would provide a cost effective and easily accessible method of investigating active materials in a hot cell. HT-SXRD provided an accurate representation of the increase in a lattice parameter but a less accurate determination of the relation between c lattice parameter and hydrogen dissolution. Where as HT-XRD had the inverse relation; the c lattice parameter had a continual increase and the a lattice parameter had no correlation with hydrogen dissolution. This was determined to be due to the texture of the sample relative to the geometry of the experimental setup (i.e. transmission or reflection) and the scattering vector.