Effect of burn-up on the characteristics of sintered pellets of simulated spent fuel

Effect of burn-up on the characteristics of sintered pellets of simulated spent fuel with burnup variation of 40 MWd/kgU and 60 MWd/kgU has been studied. The aim of this research is to obtain simulated spent fuel whose properties and characteristics are in close agreement with sintered pellets of spent fuel. The characteristics of simulated fission products powder for variation of burn-up such as bulk density, tap density, O/U ratio, and surface area were measured. The measurement result for simulated fission products powder of 40 MWd/kgU burn-up are bulk density : 1.0250 g/cm³, tap density : 1.9330 g/cm³, O/U ratio: 2.0319 and surface area : 0.8751 m²/g, while the measurement result of simulated fission products powder of 60 MWd/kgU burn-up are bulk density : 1.3410 g/cm³, tap density: 2.0443 g/cm³, O/U ratio: 2.0381 and surface area : 2.6688 m²/g. The simulated fission products powder of 40 MWd/kgU burn-up were pressed at a pressure of 3 Mp, 4 Mp, 5 Mp, 6 Mp, 8 Mp and 9 Mp, and the simulated fission products powder of 60 MWd/kgU burn-up were pressed at a pressure of 4 Mp, 6 Mp, 7 Mp, 8 Mp and 9 Mp to produce green pellets. The green pellets were sintered to produce simulated sintered pellets of spent fuel. The characteristics of simulated sintered pellets of spent fuel such as density and microstructure were measured. The highest density of the simulated spent fuel for 40 MWd/kgU burn-up and 60 MWd/kgU burn-up was obtained at a pressure of 9 Mp, i.e. 9.9959 g/cm³ and 9.5490 g/cm³ respectively. The microstructure analysis shows that the grain size of the sintered pellets decreases with increasing burn-up. (author)