[en] About 60 experts in the field of nuclear data were participating in this workshop. The main objective was to review the current modelling and evaluation methods of nuclear data for reactor applications (GEN. II, III, IV) and to discuss possible areas of improvements. Presentations were organised in sessions on: integral and microscopic measurements, evaluation of nuclear data (theory, models, codes), decay data and delayed neutrons, thermal diffusion laws, data processing and benchmarking, nuclear fission (prompt particles emission, fission yields...), uncertainties and covariance matrices (methodology and impact on reactor calculations)

[en] Delayed neutron parameters of fast zero-power VENUS-F reactor core configurations are determined with Monte Carlo calculations using various nuclear data libraries. Differences in the calculated effective delayed neutron fraction and the impact of the delayed neutron data (6- or 8-group precursors) that are applied in the experimental data analysis on the measured reactivity effects are studied. Considerable differences (up to 15%) are found due to the application of ²³⁵U and ²³⁸U delayed neutron data from JEFF, JENDL and ENDF evaluations. (authors)

[en] This paper describes the current status of GALILEE-1 that is the new verification and processing system for evaluated data, developed at CEA. It consists of various components respectively dedicated to read/write the evaluated data whatever the format is, to diagnose inconsistencies in the evaluated data and to provide continuous-energy and multigroup data as well as probability tables for transport and depletion codes. All these components are written in C++ language and share the same objects. Cross-comparisons with other processing systems (NJOY, CALENDF or PREPRO) are systematically carried out at each step in order to fully master possible discrepancies. Some results of such comparisons are provided. (authors)

[en] Delayed neutron data is essential in inherent reactor safety and in reactor control. The different sources and results of delayed neutron data in international databases will be discussed. In addition to direct measurement, these data can be obtained by calculations based on fission yields (FY) and radioactive decay data (RDD). Unfortunately, FY are only given at three energies in the European library JEFF. GEF-FY is a Monte Carlo code able to provide FY at almost any neutron energy This works proposes to use GEF-FY energy dependence. to extrapolate JEFF-FY at other energies. The preliminary results highlight that GEF energy dependence is not always suitable to reproduce experimental values and that more measurements are needed at high energies

[en] In a recent measurement of prompt γ rays from the spontaneous fission of ²⁵²Cf an experimental setup was chosen that allowed the study of angular correlations between γ rays and the nuclei from which they were emitted. The observed angular distribution of prompt fission γ rays was then analyzed to estimate the relative contributions from radiations of different multipolarity. Preliminary results are presented and compared with previous angular correlation measurements from different fission processes and with recent results from calculations with the Monte Carlo Hauser-Feshbach code FIFRELIN. (authors)

[en] The results of the Point-by-Point (PbP) model and sequential emission modellings describe very well the recent experimental data of ²³⁵U(n,f). The application of the sequential emission treatment to 49 fission cases has emphasized systematic behaviours of different quantities characterizing the fragments and the prompt emission. These allowed the determination of a general form of the residual temperature distribution for each emission sequence and the inclusion of sequential emission into the Los Alamos model (LA model) of prompt emission. The comparison of the LA model calculation for prompt neutron centre-of-mass spectrum agrees well with experimental data

[en] A method to account for model deficiencies in nuclear data evaluations in the resonance regime is proposed. The method follows the ideas of Schnabel and coworkers and relies on Gaussian processes with a novel problem-adapted version for the covariance matrix of model uncertainties extending the formalism to the energy region of resonances. The method was used to evaluate a set of schematic but realistic neutron reaction data generated by an R-matrix code and a well defined model defect. Using the extended version for model defects the Bayesian evaluation successfully recovered the built-in model defect in size and structure thus demonstrating the applicability of the method. (authors)

[en] Correlations between neutron inelastic scatterings angular distributions are not included in the Joint Evaluated Fission and Fusion (JEFF) nuclear data library, while they are key quantities for uncertainty propagation of nuclear data. By reproducing the angle-integrated cross sections and uncertainties of JEFF-3.1.1, the present work obtains covariance matrix of ⁵⁶Fe between high energy model parameters using the least square method implemented in the CONRAD code. With this matrix, it is possible to generate correlations between angle-integrated cross sections and angular distributions, which are usually presented by Legendre coefficients. As expected, strong correlations are found, for example, between the Legendre coefficients of elastic and first-level-inelastic scatterings and the angle-integrated total, elastic, total inelastic cross sections. (authors)

[en] Integral experiments can be used to adjust nuclear data libraries. Here a Bayesian Monte Carlo method based on assigning weights to the different random files is used. If the experiments are inconsistent within themselves or with the nuclear data it is shown that the adjustment procedure can lead to undesirable results. Therefore, a technique to treat inconsistent data is presented. The technique is based on the optimization of the marginal likelihood which is approximated by a sample of model calculations. The sources to the inconsistencies are discussed and the importance of considering correlations between the different experiments is emphasized. It is found that the technique can address inconsistencies in a desirable way. (authors)

[en] In this work the ²³⁵U(n,f) low-background and high-resolution experimental data obtained at the CERN-nTOF facility is combined with previous high-resolution experimental data, in order to produce a very fine grid dataset with normalisation to the IAEA Reference file. The extremely high energy calibration required to reproduce the resonance sharp profiles is based on the nTOF DAQ system with a resolution below 0.1% with reference to the 8.78 eV resonance and to the sharp Al(n,g) capture dip at 5.904 keV. The comparison of the so-evaluated profile with the experimental data and with the evaluated ones will be discussed. (authors)