Further development of methodology to model TRISO fuel and BISO absorber particles and related uncertainty quantification using SCALE 6

In the 350 MW Modular High Temperature Gas-Cooled Reactor (MHTGR-350), not only is the fuel double heterogeneous but so are the lumped burnable poisons (LBPs). The LBPs are composed of Bi-Structural Isotropic (BISO) particles and the fuel is composed of Tri-Structural Isotropic (TRISO) particles. This work investigates different methods to model coated particles using KENO-VI and NEWT of SCALE 6. The most efficient way of modelling TRISO particles in terms of packing and randomization is established in continuous energy (CE) mode and its impact on kinf is investigated. In the multi-group (MG) treatment, coated particles are modelled with the DOUBLEHET function which is only designed for particles that contain fuel. The LBP BISO particles could therefore not be modelled. Hence a method called the LBP Trace method is developed to model the LBP BISO particles using the DOUBLEHET function. It was found that kinf changed by 1500 pcm compared to the conventional (homogenized) case, when using the LBP Trace method. However, no significant change was observed in the macroscopic absorption cross section that would be passed to a nodal core calculation. Furt hermore, the LBP Trace method showed small changes in the nuclear data uncertainty when compared to conventional cas