Monte Carlo burnup in HTR system with various TRISO packing

• We performed burnup calculation for the fuel block with various TRISO arrangement.
• We observed the depletion discrepancies between models with constant fuel mass.
• The criticality trends are consistent with static simulations in other papers.
• The stochastic lattice without truncation by rod seems to be the most reliable.
• Considered models have different computational cost.

Monte Carlo codes allow for the calculation of precise representation of complex HTR geometry including the double heterogeneity of a fuel. Various approaches to coated fuel particles (TRISO) placement can be applied and the impact on criticality calculations have been already assessed by several authors. Because static neutron transport simulations are affected by different fuel lattice modeling, it can be expected that the systematic discrepancies should appear during burnup calculation as well.In this paper we compare the impact of different TRISO placement and packing factor in the model on the results of the depletion simulation. For numerical tests we chose simplified model of the fuel block from High Temperature Reactor of prismatic type and the continuous energy Monte Carlo burnup code MCB5. Burnup dependent discrepancies of kinf and nuclide concentrations have been successfully observed. Five arrangement models of fuel kernels have been compared in our work: cuboidal lattice truncated by fuel rod, cubic and hexagonal lattices without rod truncation, cubic lattice with stochastic geometry option and rod filled with one layer of randomly located particles. We put emphasis on the constant mass of fuel kernels in the system and correlate obtained results with physical and statistical aspects of TRISO packing so as to explain observed discrepancies.

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