2018 | AFC ACCOMPLISHMENTS 79 the core recirculation pumps stop.As the coolant flow stagnates, the coolant temperatures increase, and the coolant heat transfer coefficient is decreased. The cladding temperatures slowly decrease after the reactor has scrammed, reaching a minimum at ~41 seconds.This plot also shows the cladding temperatures from theTRACE simulation that actuated the low-pressure injection at approximately 91 seconds. In theTRACE simulation the cladding temperatures begin to decrease at ~140 seconds as the core is re-flooded. However, in this BISON analysis, the temperatures continue to increase until the cladding fails. These simulations are terminated when the burst criterion is reached. These results show progressively lower temperatures for the increasing fuel burnups and very similar burst times for both cladding types. Figure 2 shows the maximum cladding hoop stress during the accident conditions simulated with BISON. Leading up to the accident scenario, the maximum cladding hoop stress is initially in a tensile state due to mechanical interaction between the fuel and cladding.After the onset of the LBLOCA conditions, the gap is reopened, as the reactor coolant pressure is reduced to atmospheric pressure.This generates significant hoop stresses in the cladding, as the fuel rod plenum pressure begins to increase with the fuel temperatures. In these simulations, the FeCrAl cladded fuel rods fail at much larger stresses their Zircaloy counterparts. These results show that the FeCrAl cladding will generally burst at a similar time and temperature as the Zircaloy cladding under the specific reactor operating and accident conditions that were simulated, but experience significantly larger cladding hoop stresses.As expected, the main driving force for differences in burst behavior between the various fuel burnups is the pressure differential across the cladding as the transient conditions evolve.The FeCrAl cladding thickness used in this analysis is thinner than the thickness expected to be deployed in commercial reactors, which would tend to increase the difference in cladding failure time for the FeCrAl rods during the accident. To further enhance this analysis, additional improvements to the FeCrAl constitutive models and operating conditions are currently underway.