Hybrid diffusion–transport spatial homogenization method

•A new hybrid diffusion–transport homogenization method.•An extension of the consistent spatial homogenization (CSH) transport method.•Auxiliary cross section makes homogenized diffusion consistent with heterogeneous diffusion.•An on-the-fly re-homogenization in transport.•The method is faster than fine-mesh transport by 6–8 times. A new hybrid diffusion–transport homogenization method has been developed by extending the consistent spatial homogenization (CSH) transport method to include diffusion theory. As in the CSH method, an “auxiliary cross section” term is introduced into the source term, making the resulting homogenized diffusion equation consistent with its heterogeneous counterpart. The method then utilizes an on-the-fly re-homogenization in transport theory at the assembly level in order to correct for core environment effects on the homogenized cross sections and the auxiliary cross section. The method has been derived in general geometry and tested in a 1-D boiling water reactor (BWR) core benchmark problem for both controlled and uncontrolled configurations. The method has been shown to converge to the reference solution with less than 1.7% average flux error in less than one third the computational time as the CSH method – 6 to 8 times faster than fine-mesh transport.