[en] The resonance parameters of Uranium 238 and Plutonium 240 are known with an uncertainty which induces an inaccuracy in the calculation of the effective multiplication factor of light water lattices. This effect was computed by using the different available files which take into account the successive improvements of the resonance parameter measurements. For Uranium 238, although the reactivity shift between UKNDL 68 and the new evaluations is about 270x10^-5, the recent values seem to be satisfactory for the reactor physicist. It is not the same thing for Plutonium 240. For this nuclide the resonance parameters are not known with a good enough accuracy and their values must be improved, specially for the 1.056 eV resonance