A synergistic combination of the deterministic and Monte Carlo methods for double-heterogeneous problems

Abstract

To resolve the double-heterogeneity (DH) problem resulting from the TRISO fuel of high-temperature gas-cooled reactors (HTGRs), a synergistic combination of a deterministic method and the Monte Carlo method has been proposed. As the deterministic approach, the RPT (Reactivity-equivalent Physical Transformation) method is adopted. In the combined methodology, a reference k-infinite value is obtained by the Monte Carlo method for an initial state of a problem and it is used by the RPT method to transform the original DH problem into a conventional single-heterogeneous one, and the transformed problem is analyzed by the conventional deterministic methods. The combined methodology has been applied to the depletion analysis of typical HTGR fuels including both prismatic block and pebble. The reference solution is obtained using a Monte Carlo code MCCARD and the accuracy of the deterministic-only and the combined methods is evaluated. For the deterministic solution, the DRAGON and HELIOS codes were used. It has been shown that the combined method provides an accurate solution although the deterministic-only solution shows noticeable errors. For the pebble, the two deterministic codes cannot handle the DH problem. Nevertheless, we have shown that the solution of the DRAGON-MCCARD combined approach agrees well with the reference.