XPZ: Development of a lattice code for HTR

• The XPZ code is development for the HTR lattice physics computation.
• The Dancoff factor obtained from the double-heterogeneous model is used for resonance treatment.
• Self-shielding factors are used to account for the spatially self-shielding effect.
• The fuel compact is homogenized with preserving the first-collision probabilities.
• The double heterogeneity effect is analyzed for the HTR fuel pebble.

The XPZ code is developed for the lattice physics computation in the high temperature reactors (HTRs). This paper introduces the methodologies adopted in the XPZ code, including the resonance treatment, equivalent homogenization, transport calculation, and burnup calculation. Emphasis is put on the treatment of the double heterogeneity effect, which involves the following two strategies. Firstly, the Dancoff factor obtained from the double-heterogeneous model is used in the resonance treatment. Secondly, with considering the spatially self-shielding effect in dispersed particles, the fuel compact is equivalently homogenized into a homogeneous media so that the conventional transport calculation can be applied. The effectiveness and accuracy of the methodologies are examined against Monte Carlo solutions. Numerical results demonstrate that the XPZ code is promising for lattice physics computations in HTRs.