2017 | AFC ACCOMPLISHMENTS 82 4.9%-enriched UO2 Fuel Fuel-Clad UO2-Zr 90UO2-10UN/Zr* 60UO2 -40UN-Zr* Discharge burnup (GWd/t) 61.6 59.2/61.0 54.3/60.7 Cycle length in effective full-power days (EFPDs). 533 512/527.7 470/526 Accomplishments: Activities in FY17 continued the assessment of ATF concepts and assembly-level calculations focused on composite UO2-UN fuels with Zircaloy cladding. Results for the UO2-UN/Zircaloy configurations based on a detailed, explicit model of a 17x17 pressurized water reactor (PWR) assembly with 4.9 w/o enrichment are shown inTable 1. for discharge burnup (Gigawatt-days per metric-ton) and cycle length (Effec- tive-Full-Power-Days).Two “bounding compositions for the nitride fuel were considered, i.e., 10% and 40%. For each composition, two cases were evaluated assuming 100% N-14 and 100% N-15, respectively to quantify the poisoning impact of N-14. Based on the results inTable 1, a 10% volume fraction of UN would have a relatively minor impact, while a 40% fraction would result in a significant penalty unless the nitrogen was fully enriched in N-15. Based on detailedTRITON assembly calculations for UO2/Zr and UO2/ FeCrAl, PARCS Beginning-of-Life (first core) models were used to calculate kinetics parameters and power distributions (including pin powers) for Hot-Zero-Power (HZP) and Hot Full Power (HFP) for an AP1000-like core.A $1.05 reactivity insertion accident (RIA) was analyzed using conventional point kinetics with PARCS andTRACE, for both HZP and HFP conditions. Figure 1. shows the normalized reactor power for the RIA.The FeCrAl-cladded fuel with its shorter neutron lifetime reached a higher peak power at a slightly earlier time than the Zr-cladded fuel. In both cases the negative fuel temperature reactivity coefficient was responsible to limit the increase in reactor power. The reactor scram on power occurred after the peak power was reached. Figure 2. shows a comparison of the RIA at the HFP condition as predicted by theTRACE and PARCS code respectively.The treatment of Table 1. Three-Batch Cycle Length for Composite UO2- UN Fuel Plus Zr Cladding. *UN with 100% N-14//UN with 100% N-15