SUMMARY

Recent work by Yasseri and Rahnema has introduced a consistent spatial homogenization (CSH) method completely in transport theory. The CSH method can very accurately reproduce the heterogeneous flux shape and eigenvalue of a reactor, but at high computational cost. Other recent works for homogenization in diffusion or quasi-diffusion theory can accurately calculate core eigenvalue and assembly-homogenized reaction rates, but fail to reproduce local effects such as pin powers.

To address these issues, a consistent hybrid diffusion-transport spatial homogenization (CHSH) method is developed based on the CSH method that uses conventional flux weighted homogenized cross sections to calculate the heterogeneous solution. The key feature of the CHSH method is the introduction of an extra source term in the form of an "auxiliary cross section". The CHSH solution procedure is to solve a core-level homogenized diffusion equation with the auxiliary source term and then to apply an on-the-fly transport-based re-homogenization at the assembly level to correct the homogenized and auxiliary cross sections. The method has been derived in general geometry with continuous energy, and it is implemented and tested in fine group, 1-D slab geometry on controlled and uncontrolled BWR and HTTR benchmark problems. The method converges to within 2% mean relative error for all four configurations tested and has computational efficiency 2 to 4 times faster than the reference calculation.