b'Figure 4. Effect of helium fill pressure on the peak fuel temperature.demonstrate the impact of diamondEffect of helium fill pressuredoping on the fission gas release inon the fuel temperature andin UO 2fuel irradiated to 7.2 GWd/ fission gas releasetHM.Evidently, the use of diamondAs mentioned above, ATF-1 rodlets doping resulted in marked reductionwere filled with helium gas at the of the fission gas release.Therefore, itatmospheric pressure of 0.084 MPa.is concluded that diamond doped UO 2 To assess the effect of helium fill shows promise as an ATF based on thepressure on the fuel temperature and results of this initial screening test. fission gas release, a fuel performance Thermal conductivitycalculation assuming prototypic LWR Comparison of the beginning ofhelium fill pressure of 2.62 MPa was life thermal conductivity for theexecuted and compared with that of standard UO 2fuel and for the UO 2 -5the reduced fill pressure rodlets. As vol % diamond composite is shownevident from Figures 4 and 5, rodlets in Figure 3. Comparison of thewith reduced fill pressure exhibit thermal conductivity for the standardhigher fuel temperature and fission UO 2fuel and for the UO 2 -5 vol %gas release.When the fission gas diamond composite. release begins, rodlets with reduced fill pressure experience greater degradation of the gap conductance because the same amount of released 158 2019|AFC ACCOMPLISHMENTS'