b'Figure 2. Moderator TemperatureReactivity Coefficient vs. burnup.fuel and moderator temperature reac- candidate materials proposed by LANLThe cycle length and discharge burnup tivity coefficients, and soluble boronwere evaluated to provide and initialbased on the Linear-Reactivity-Model and control worth were determined asestimate of their impacts on reactor(LRM), and 3-batch fuel management functions of burnup. performance and safety characteristics:for the non-Ta coatings were approxi-Accomplishments: TaN, TaNi, TaC, NbC, SiC, ZrC, Mo, Zr . mately 700 days/60 GWd/t, while Uranium-nitride (UN) has severalThe major observations can be for the Ta-based coatings they were characteristics the make it an attractivesummarized as: approximately 550 days/46 GWd/t.fuel for utilization in existing commer- The corresponding values for UO 2are cial LWRs; these include higher density There is no difference between these~530 days/61 GWd/t.and thermal conductivity than tradi- coatings for the fuel temperature andTransient/accident analyses will need to tional UO 2fuel.These characteristicssoluble boron reactivity coefficients vs.be performed to quantify the impacts can reduce the enrichment requiredburnup, but both are less negative thanof the observed differences in reactivity to achieve desired cycle length andfor UO 2reflecting the harder spectrumand control coefficients.discharge burnup, and improved reactorfrom UNperformance in normal and accident For K-infinity and MTC, most coatings conditions. However as noted above, UNexhibit a similar and stronger nega-reacts adversely with light-water andtive than for UO 2 ; this is especially therefore must be protected in the eventpronounced for TaN and TaC.Results of a cladding breach. Coatings of severalfor both k-infinity and MTC are shown in Figure 1 and 2 respectively.2020|AFC ACCOMPLISHMENTS 121'