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This present study aims to evaluate the nuclear data uncertainty on the neutron multiplication factor (k eff) in order to adjust the 235 U capture multigroup cross sections and the covariance matrix of the ENDF/B-VII.1 evaluation. For this purpose, the generalized linear-least squares method is applied. The 44 multigroup cross sections and the covariance matrix are processed with NJOY99 nuclear software, while MCNP6.1 nuclear code is used for the k eff and sensitivity profile calculations. The obtained results show that the 235 U capture cross sections require an adjustment of approximately −1% in 0-6 eV, −0.5% in 6 eV to 3 keV, 2% in 3 keV to 0.4 MeV, and −10% in 0.4-20 MeV.

In criticality and stability studies of the nuclear reactor, it is important to evaluate the impact of the uncertainties of the basic nuclear data (cross sections) on the different neutron parameters. So this work is interested in the analysis of the sensitivity and uncertainties due to the nuclear data of 1 H, 16 O, 239 Pu and 240 Pu Isotopes in the ENDF/B-VII.1 cross sections processed by the latest version of NJOY code on the effective multiplication factor. Different rapid and thermal cases of the different IHECSBE benchmarks have been studied to calculate the sensitivity vectors for 1 H, 16 O, 239 Pu and 240 Pu Isotopes. These sensitivity vectors are calculated by using the adjoint-weighted perturbation method based on the Ksen card of the Monte Carlo code MCNP6.1. Thus, the uncertainties induced by nuclear data have been calculated by combining the sensitivity vectors with the covariance matrices that are generated by the ERRORJ module of NJOY2016. We found several cross sections and covariance matrices lack the adjustment: The capture and fission cross sections of the 239 Pu and their covariance matrices lack the adjustment in the thermal energies. And all of the four cross sections (elastic, inelastic, capture and fission) and their covariance matrices for the same isotope lack the adjustment in the rapid energies. For 16 O; the elastic cross section and its covariance matrix lack the adjustment in the thermal energies. The elastic and capture cross sections of the 1 H and their covariance matrices lack the adjustment especially in the thermal energies.