2017 | AFC ACCOMPLISHMENTS 55 far, the time to first melting point and time to onset of significant hydrogen generation has been used as a figure of merit byTRACE and MELCOR, respectively.The results thus far show notable but modest gains in coping time with FeCrAl cladding under various scenarios including unmiti- gated large break loss-of-coolant accident and short term station black out for a 3-loop PWR design. Both codes capability has also been extended to include ability to model cladding coatings. At PSU, the MARMOT mesoscale fuel performance tool has been used to investigate the impact of high thermal conductivity additives BeO and SiC on UO2 thermal conductivity using 2D and 3D simulations.These results informed the development of a macroscale model of the fuel thermal conductivity with high thermal conductivity additives that will be implemented in the BISON fuel performance tool (Figures 3 and 4, respectively).The impact of these additives on fission gas release will also be investigated using MARMOT simulations. Initial simulations by MIT in collaboration with AREVA and INL on chromia doped pellets against experimental data from Halden reactor showed a gap in mechanistic predic- tion of fission gas release that will be further investigated next year. MIT in collaboration with ANATECH and INL has performed a detailed steady state and transient fuel perfor- mance modeling of a Zr4 cladding with FeCrAl, Cr, Mo/FeCrAl coatings using the BISON fuel performance framework.An in-house fuel performance tool along with finite element analysis tool,ABAQUS, were used to verify BISON calculations. It was found that plasticity models are typically required under steady state, especially during pellet-to-clad mechanical interaction due to thermal expansion and mechanical properties mismatch of each coating layer with Zr4 and each other. Under power ramp conditions, it was found that the coatings are loaded upon contact which may result in onset of cracks. During upcoming year, additional physics informed by generated data will be used to improve the coated cladding models. Figure 4. Summary of the thermal resistor model that predicts the thermal conductivity of UO2 accident tolerant fuel with high thermal conductivity additives, where an illustration of the approach used to determine the connectivity of the additive is shown on the left, and a plot of the performance of the model is shown on the right.