[en] The need of sources of energy different from fossil fuels is nowadays a crucial point. As the EU-SET Plan points out, it is necessary to investigate new concepts for nuclear systems to improve the sustainability of nuclear energy. These concepts cover from energy production, through both advanced light water reactors and fast reactors foreseen in generation IV, to minimization and discharge of nuclear waste through subcritical fast systems (ADS). Despite many previous measurements and recent efforts, the present knowledge of basic nuclear data is still inadequate to fulfill the precision and accuracy required for the design and development of these new technologies. In this context the Nuclear Energy Agency addresses the most relevant isotopes, decay data, nuclear reaction channels and energy ranges that have to be investigated in more detail in the NEA High Priority Request List. The measurement of ²³⁸U(n,g) reaction cross section falls within this list because of its importance for the security of operating light water reactors and the design of generation IV reactors. Even if the number of measurements present in the EXFOR database is large, inconsistencies are still present for the ²³⁸U capture cross section both in the low energy and in the unresolved resonance region. This uncertainty influences both fast and thermal reactor systems, and contributes to the uncertainty on Pu isotope density at the end of fuel cycles. As such, there is a proposal of three independent measurement of the ²³⁸U(n,g) cross section in order to reach the required precision of 2% within an energy range from few eV to hundreds of keV. One measurement was performed at the EC-JRC-IRMM facility GELINA, while the other two at the n_TOF facility at CERN. Combined together they should lead to the desired accuracy. Here the preliminary results of the ²³⁸U(n,g) cross section measurement are presented, which was performed at n_TOF with C₆D₆ scintillation detectors on April 2012 and covers an energy range from thermal point to about 500 keV. The characteristics of the n_TOF facility, such as the very high instantaneous neutron flux, the low repetition rate and the long flight pat, i.e. the excellent energy resolution, allowed very high precision and accuracy. This, together with the detection method, would take for ²³⁸U capture cross section to a significant improvement in the unresolved resonance region and, together with the results of the other two measurements, would help to decrease the uncertainty in the resolved one down to 2%. Acknowledgement: This work is supported by the European Commission within the FP7 project ANDES (FP7-249671). (author)