HTR spherical super lattice model for equilibrium fuel cycle analysis

Although HTR (High Temperature Reactor) fuel is rather homogeneously dispersed in the fuel graphite matrix, the heterogeneity effects in between fuel kernels and pebbles cannot be ignored. The double-heterogeneous lattice model recently developed at the Idaho National Laboratory contains tens of thousands of cubic fuel kernel cells, which makes it very difficult to deplete the fuel, kernel by kernel (KbK), for the fuel burnup analysis. In addition, it is not possible to preserve the cubic size and packing factor in a spherical fuel pebble. To avoid these difficulties, a newly developed and validated HTR pebble-bed Kernel-by-Kernel spherical (KbK-sph) model, has been developed and verified in this study.The objective of this research is to introduce the KbK-sph model and whole pebble super lattice model (PSLM), which is used for Equilibrium Fuel Cycle analysis. In this study, we show that HLM (homogeneous lattice model) and KbK-sph lattice models with any number of slices of a pebble can adequately represent whole pebble lattice neutronics burnup characteristics. The double-heterogeneous KbK-sph model with fuel pebble used in this study can handle the complex spectral transitions at the boundaries between the kernels in a straightforward fashion and treat the entire lattice at once. We show that the coupling of the Monte-Carlo code with a fuel depletion and buildup code (MCWO) and KbK-sph model can provide accurate neutronics characteristics of the particle fuel burnup performance. The MCWO-calculated results in this study indicate that there is a rather constant ΔK∞ between KbK-sph lattice model and HLM versus burnup. It shows that the PSLM can be used in the HTR equilibrium fuel cycle analysis. However, the difference of ΔXe-worth between KbK-sph lattice model and HLM is about 0.92 dollar. The KbK-sph model can simulate the double-heterogeneity of the HTR fuel unit lattice without the Dancoff correction factor preparation. The method developed in this work can be used in the HTR safety related confirmatory analysis