• Energy Research

The (n,γ ) cross section of 96Zr has been investigated at the CERN n TOF spallation neutron source. Highresolution time-of-flight measurements using an enriched ZrO2 sample allowed us to analyze 15 resonances below 40 keV with improved accuracy. On average, the capture widths were found to be 25% smaller than reported in earlier experiments. If complemented with the contribution by direct radiative capture, the derived Maxwellian averaged cross sections are consistent with activation data at kT = 25 keV. The present results confirm the astrophysical implications for the s-process branching at 95Zr.

The importance of improving the accuracy on the capture cross-section of 238U has been addressed by the Nuclear Energy Agency, since its uncertainty significantly affects the uncertainties of key design parameters for both fast and thermal nuclear reactors. Within the 7th framework programme ANDES of the European Commission three different measurements have been carried out with the aim of providing the 238U(n,γ) cross-section with an accuracy which varies from 1 to 5%, depending on the energy range. Hereby the final results of the measurement performed at the n_TOF CERN facility in a wide energy range from 1 eV to 700 keV will be presented.

The 241Am(n,¿ ) cross section has been measured at the n_TOF facility at CERN with the n_TOF BaF2 Total Absorption Calorimeter in the energy range between 0.2 eV and 10 keV. Our results are analyzed as resolved resonances up to 700 eV, allowing a more detailed description of the cross section than in the current evaluations, which contain resolved resonances only up to 150–160 eV. The cross section in the unresolved resonance region is perfectly consistent with the predictions based on the average resonance parameters deduced from the resolved resonances, thus obtaining a consistent description of the cross section in the full neutron energy range under study. Below 20 eV, our results are in reasonable agreement with JEFF-3.2 as well as with the most recent direct measurements of the resonance integral, and differ up to 20–30% with other experimental data. Between 20 eV and 1 keV, the disagreement with other experimental data and evaluations gradually decreases, in general, with the neutron energy. Above 1 keV, we find compatible results with previously existing values.

The neutron-induced fission cross-section of 233U has been measured at the CERN n TOF facility relative to the standard fission cross-section of 235U between 0.5 and 20MeV. The experiment was performed with a fast ionization chamber for the detection of the fission fragments and to discriminate against α-particles from the natural radioactivity of the samples. The high instantaneous flux and the low background of the n TOF facility result in data with uncertainties of ≈ 3%, which were found in good agreement with previous experiments. The high quality of the present results allows to improve the evaluation of the 233U(n,f) cross-section and, consequently, the design of energy systems based on the Th/U cycle.

Abstract Uncertainties estimation is essential for a sound assessment and a clear definition of safety margins, which in turn are crucial for licensing approval of new nuclear reactors by safety authorities. Moreover, uncertainties are also matter for target accuracy requirements (TARs), whose achievement could disclose new or enhanced opportunities. The concept of target accuracy requirements has been over the years one of the returning focuses of Massimo Salvatores, who just recently relaunched an update exercise within the OECD/NEA Working Party on International Nuclear Data Evaluation Co-operation (WPEC) aiming at providing new estimates having as reference the advanced systems meant for tomorrow. This work presents an evaluation of the current accuracies on the main core integral parameters of the Advanced Lead-cooled Fast Reactor European Demonstrator (ALFRED), as a starting point to discuss which would be the target values that might introduce beneficial improvements in the design. Despite the use of one of the most recent nuclear data libraries (ENDF/B-VIII.0), and the broad margins set in the design of ALFRED according to its mission as demonstrator, room for improvement is found on the multiplication factor. Then, moving from the target accuracies on the integral parameters, an inverse uncertainty problem is solved to derive the corresponding target accuracies on nuclear data, meeting which would guarantee the achievement for the former ones. The inverse problem is solved introducing three different sets of cost parameters, reflecting possible challenges related to the execution of the differential experiments requested to achieve the aimed reductions of the accuracies. By this, the resulting target accuracies on nuclear data here presented are deemed useful to obtain information for the high-priority lists driving the selection of isotopes and reactions for future refinement experiments.