Marleau, G.

Resonance self-shielding effects on Eigenvalue sensitivity

We present a quick and accurate way to compute the eigenvalue sensitivity coefficients in multigroup lattice cell calculations. We look at both the explicit and implicit sensitivities, the latter resulting from the resonance self-shielding process. A self-shielding model is presented, and we show how to obtain cross section sensitivities to a variation on a light isotope density. As an example, we look at how a perturbation on the hydrogen density affects the multigroup cross sections for resonant reactions such as U'capture and U'fission, in two uranium spheres with different enrichments. Explicit sensitivities are also computed, and we discuss the relative importance of the implicit sensitivities. (authors)