A new model has been developed to evaluate the variation of few-group cross sections with local parameters and the history of the reactor. This model allows us to generate a coherent set of nuclear cross sections for a CANDU cell. The history dependence of the nuclide concentrations is taken into account by creating a pseudo-isotope, which includes actinides whose concentrations are strongly affected by local parameter history. Simple physical considerations lead us to determine the law of variation of the cross sections as a function of these parameters. They permit the computation of the cross sections for each state of the reactor core, using a unique library for each type of cell, which contains the nuclear cross sections computed at nominal conditions and feedback coefficients. To validate the feedback model, several operational situations were tested, and the results are compared to those given by a transport calculation using the DRAGON cell code.