# Interface Characterization within a Nuclear Fuel Plate
## 5 Conclusions  
One of the goals of the USHPRR project is to develop a fuel plate manufacturing process that delivers fuel plates having robust and reliable fuel-cladding interfacial strength. The goal of the LST testing technique is to develop a reliable and easy-to-perform method to quantify the fuel-cladding interface strength, allowing relative comparisons to be made between fabrication variants, as well as pre- and post-irradiation. One critical step in the manufacturing process is the application of the Zr coating. As discussed in this report, bond strength testing has been performed on fuel plates manufactured at LANL using the baseline co-rolling Zr application process foils, on fuel plates with Zr-electroplated foils processed at PNNL and Zr plasma sprayed foils processed at LANL. Another significant concern relates to the cleanliness of the plate surfaces during the manufacturing of fuel plates, which was also evaluated in this study. In addition to a nominally cleaned reference co-rolled Zr fuel plate specimen, several plates were tested having various surrogate contaminants (hydrocarbon and oxide) and different levels of contamination. The results from LST testing are somewhat surprising, suggesting that contamination introduced during manufacturing did not negatively impact the fuel-cladding bond strength. These results are corroborated by interfacial fracture energy measurements made on specimens from the same fuel plates by bulge testing at LANL. The experimental uncertainty in the data is too large to quantify differences between the different samples but it is clear that the type of surface preparation or lack thereof had little effect on the resulting interface strength. The present results also suggest that Zr co-rolled foils have significantly stronger fuel-cladding interfaces compared to either Zr electroplated and Zr plasma sprayed foils by 200% to 300%. Another surprising result is that the fuel plate containing a Zr electroplated foil that had obvious Zr blisters in  
Figure 15: Laser UT inspection of the 102-D1 fuel plate is shown. The A-scan image shows ringing between the two yellow lines indicative of sound bouncing between a debonded ligament on the back interface (see Figure 6). the as-received (prior to HIP) condition exhibited a debond area at least twice the size of the incident shock laser spot size used to generate the debond, whereas typically the debond area is less than the incident shock laser spot size. The Zr plasma spray specimen has a slightly higher bond strength value than the blistered Zr-electroplated specimen and yet has a debond area less than the incident shock laser spot size, as is typical in LST testing. This is an indication that there is an additional failure mechanism in the plate made with the blistered Zr foil. Microscopy was performed on one LST location in the 102-D-1 electroplated plate. The interface separated at the Zr layer from the DU fuel foil. This is an indication that the Zr and DU interface is the weakest. The results from laser shock testing clearly suggests that the application process of the Zr layer onto the fuel foil can make a significant difference in bond strength. The co-rolled process is seen to have higher bond strength than the electroplated and plasma sprayed process. When the LST is installed in the hot cell, similar determinations can be made on irradiated fuel to determine bond strength performance and the fabrication processes that enable high performance. The characterization of the effects due to contamination will be important to reduce fabrication costs. By understanding which types of contamination have significant effects on bond strength, the fabricators can focus their remediation efforts and practices on specific contaminates and determine the appropriate tolerance levels. It is interesting to note that test contamination did not significantly reduce bond strength as expected. Author contributions: Author contributions were as follows: Conceptualization, J.S. and B.R. ; Methodology, J.S., C.S. and B.B.