Advanced High Temperature gas-cooled Reactors (HTR) currently being developed (GFR, VHTR, PBMR, and GT-MHR) are able to achieve a simplification of safety through reliance on innovative features and passive systems. One of the innovative features in these HTRs is reliance on ceramic-coated fuel particles to retain the fission products even under extreme accident conditions. The objective of this research is to introduce the Kernel-by-Kernel Fuel (KbKF) model, and to show the capabilities of KbKF model in the HTR fuel cycle burn-up analysis. This study reports the validation of a HTR unit lattice - KbKF spherical model, and summarizes the KbKF-calculated results of the HTR fuel burn-up analysis. Although HTR fuel is rather homogeneously dispersed in the graphite matrix, the heterogeneity effects in between fuel kernels and pebbles cannot be ignored. The effect of the irregular pebble lattice is addressed through the use of Danc-off correction factors in the resonance treatment. The double-heterogeneous MCNP model recently developed at the Idaho National Engineering and Environmental Laboratory (INEEL) contains tens of thousands of cubic fuel kernel cells, which not only makes it very difficult to deplete the fuel, kernel by kernel, for the fuel cycle analysis, but also has a profound neutron streaming effect. To avoid these difficulties, a newly developed and validated HTR pebble-bed KbKF spherical MCNP model, is used in this study. A Monte Carlo code, MCNP, coupled with an isotope depletion code, ORIGEN-2, via MCWO can use the above-mentioned KbKF model to deplete the fuel kernels individually. Double-heterogeneity of the PBMR fuel unit cell was taken into account, i.e. self-shielding of the fuel kernels, in the KbKF model. The spherical mesh in the KbKF model contained 32 subdivided fuel pebble, equal volumes, mini-shells. These mini-shells are then divided the (θ Φ) into 21.65 (square root of 15000 kernels per pebble /32) equalinterval angles, such that in sub-divided mini-cell contains a fuel kernel. The KbKF model can handle the complex spectral transitions at the boundaries between the mini-cells in a straightforward fashion and treat the entire lattice at once. The ESKOM PBMR unit cell was chosen as a reference case in this study to build the KbKF model for the fuel cycle burnup analysis. The MCWO and KbKF-calculated results, such as, K-inf, U and Pu isotopic concentrations, and Pu / ~(238)U ratio versus EFPDs, and detailed radial fuel kernel fission power profile versus pebble's fraction of radius (r/r0) at different burnups are discussed.
展开▼
