[en] This paper presents an application of the Backward-Forward Monte Carlo (BFMC) method using measured critical boron concentrations for a specific PWR cycle. The considered prior nuclear data are the fission cross sections, ${\stackrel{¯<!--\; ??\; -->}{\mathrm{\nu <!--\; ??\; -->}}}_p$ for ²³⁵U and ²³⁹Pu and the capture cross section of ²³⁸U. The posterior nuclear data exhibit cross-isotope correlations, moderate changes for the average quantities and reduced uncertainties. This work is the first one considering the BFMC method and an integral system mostly sensitive to thermal neutrons. It contributes to show the impact of integral experimental data for the evaluation of nuclear data and their covariance matrices, leading to cross-isotope correlations and a nuclear data uncertainty reduction.