Influence of Spatial Discretization on Burnup Calculationof Dispersed Particulate Fuel

Pin cell burnup calculation is the basis of the whole core burnup calculation. The spatial discretization of burnup region has significant influence on the accuracy of burnup calculation. The spatial discretization of dispersed particulate fuel is more complicated due to the double heterogeneity. Based on the lattice physics code ALPHA, the effect of macroscopic discretization at pin level and microscopic discretization at particle level was analyzed. Cases included UC particle pin cell, Gd₂O₃-layered QUADRISO particle pin cell and a double-particle pin cell filled with Gd₂O₃ particles and UC particles. The numerical results show that case without poison should set at least 3 macroscopic burnup regions while cases with Gd₂O₃ need at least 5 macroscopic burnup regions. No microscopic discretization is required for case without poison. QUADRISO particle containing Gd₂O₃ layer should set 2 microscopic burnup regions in the fuel region, and the Gd₂O₃ particle of double-particle cell need 12-15 microscopic burnup regions.