# Interface Characterization within a Nuclear Fuel Plate
## Materials and Methods
### Alternative Zr Coating Process Specimens  
The USHPRR Fuel Fabrication (FF) Pillar supplied INL with several developmental fuel plate test specimens that were used for scoping studies. All the specimens consisted of Depleted Uranium (DU) fuel foils; however, the Zr diffusion barrier was applied using alternative fabrication processes under development by FF. Most specimens contained fuel foils that were Zr coated by an electroplating process at Pacific Northwest National Laboratory (PNNL), whereas one specimen contained two partial fuel foils that were Zr coated by plasma spray at LANL. All of these fuel plates were clad in 6061 Al by a HIP process conducted at the INL [9] with nominally identical conditions. The PNNL electroplated foils were clad in HIP run 102 while the LANL plasma spray foils were clad in HIP run 104.  
The following fuel plate test specimens underwent LST testing:  
1. 102-C-2B (electroplated Zr, as-plated)
2. 102-D-2B (electroplated Zr, post-plating heat treatment)
3. 102-E-2B1 (electroplated Zr, as-plated, obvious Zr blisters on as-received foils)102-D-1 (electroplated Zr, as-plated)
5. 104-6 (plasma sprayed Zr, contained two partial foil pieces with unknown pedigree  
Photographs of the four Zr electroplated fuel foils supplied by PNNL, as received at INL prior to HIP, are shown in Figure 2. PNNL foils 21C-2B and 21D-1 appeared relatively uniform and had consistent surface finish, while foil 21D-2B appears to have some surface discoloration on the right end. Foil 21E-2B1 had obvious Zr blisters on the left end and some discoloration on the right end. There are no known documentation or photos prior to HIP of the plasma sprayed Zr foil pieces that were supplied by LANL.  
After the plates were processed by HIP at INL, they were given a light sanding treatment but were otherwise not surface machined to a specified final thickness. Interestingly, once the foils were processed by HIP into fuel plates, the plates made from the different types of Zr coated foils appear unremarkable and show similar characteristics when imaged by conventional ultrasonic testing (UT). Figure 3 shows the through-transmission (i.e., debond) images of the fuel plates after HIP. The debond images show no signs of debonds in the as-HIP fuel plates. The debond images show the location of the fuel in the Al cladding. The fuel and cladding appear to be generally uniform and perhaps indicate some surface roughness such as on the right side of plate 104-6, which may be attributed to the sanded surface finish. It is interesting to note that, according to the UT debond image, the HIP process appears to have healed the obvious Zr blisters that were apparent on the as-received foil 21E-2B1.  
Figure 3: Ultrasonic C-scan images depicting bonded interfaces that let sound travel through the fuel plate. The hot isostatic pressing (HIP) process appears to have healed the coating blisters on foil 21E-2B1. Also note the presence of possible surface indentations and/or un-bonded areas indicated by the lack of transmission (dark spots).  
Figure 2: The plate fuel specimen and geometries for laser shock testing is shown.