Internal Interface Perturbations: Calculational Method Using the Eigenvalue Innplicit Expansion of the Conditioned Problem

A new method for solving internal interface perturbations is offered. The technique used is based on a pattern recognition method that allows conditioning the referential problem and then enforcing the spatial term of the eigenvalue expansion equal to zero. This method is implemented in the VAREC and VARYX codes and is used to calculate variations of the moderation ratio in pressurized water reactor cells caused by an increase in the cladding thickness.