Improved resonance self-shielding method considering resonance scattering effect

A new resonance self-shielding method has been developed to overcome drawbacks of the equivalence theory in the resonance scattering source approximation. The equivalence theory uses an inconsistent approximation for the resonance scattering source and a constant assumption for the spatial scattering source distribution within a fuel pellet. The approximation and assumption cause a significant overestimation in the effective multi-group cross sections, especially for 238U. The new resonance self-shielding method solves a pin-based pointwise energy slowing-down equation with the collision probabilities accounting for the heterogeneous geometry effect of the whole system. The multi-group cross sections determined with pointwise flux solutions and cross sections are able to take into account the resonance interference effect inherently. In addition, the number of the MOC fixed source problems for the whole system is greatly reduced in the new method. Using light water reactor problems, it was demonstrated that the new resonance self-shielding method showed very good agreement with MCNP6 solutions in eigenvalues and pin powers