b'and additional simulations will behoop stress in the coating based on the performed of integrated experiments tothermal expansion coefficient is shown benchmark these developed capabilitiesin Figure 1b. Here, there is a significant and elucidate supplemental data. change in the predicted hoop stress with Accomplishments:variation of the thermal expansion in For this analysis, simulations werethe coating. Leading up to gap closure, performed using a 15m zirconiumthe hoop stress decreases slightly, dioxide coating to demonstratebecoming more compressive. After the coating capabilities of BISON. gap closure occurs, the hoop stresses While these results are not intendedbecome rapidly become very large. to provide quantifiable results forAlthough no creep or plasticity models a particular case, they do displayare used in this analysis of the impact of general trends of a material withthe coating, large tensile stresses typi-these properties, i.e., increased fuelcally indicate mechanical failure. rod temperatures due to poor coatingFigure 2 shows the radial distribution thermal conductivity and increasedof hoop stress across the coating and coating stresses due to the absencecladding at 60 MWd/kgU. There is of a creep or plasticity model. Asan extremely large jump in stressesFigure 2. The hoop stress plotted as a well, an initial parametric evaluationmoving radially into the coating due tofunction of cladding radius. A drastic increase in hoop stress is shown has been performed to demonstratethe thermal expansion mismatch andbetween the cladding to the coating the effect of varying the thermalthe lack of a plasticity model to relievedue to thermal expansion mismatch expansion coefficient (by 2 andstresses. The cladding, however, showsbetween the materials.) on the coating and claddingonly a slight difference based on the stress state. Successful use of BISONcoating properties. to model the effects of zirconiumThis highlights the need to identify dioxide on cladding properties andcoating properties that are compatible fuel performance also represents anto those of zircaloy for favorable important first step in modeling ofperformance, and these results other coating materials.demonstrate that a framework is in This analysis is performed using proto- place to model the coating and fuel rod typical Boiling Water Reactor (BWR)performance as more representative operating conditions and fuel geometry. material properties are established. In an Figure 1a shows the maximum claddingeffort to provide high-fidelity simulation hoop stress resulting from the presenceresults and leverage the versatility of of a 15m coating, with a constantBISON as a finite element tool, current thermal expansion coefficient duringefforts will also include modeling the modeled operation, up to 60 MWd/ ongoing thermal-mechanical property kgU. As the thermal expansion coef- testing.This consists of developing test ficient is increased, the cladding stressgeometry and implementing relevant state is more tensile and the claddingconditions to simulate the property test creep down behavior is slowed, resultingand assess the accuracy of the current in delayed gap closure. The maximummaterial models.2019|AFC ACCOMPLISHMENTS 161'