[en] This workshop is the continuation of the series of workshops held in Port Jefferson, USA (2008), Vienna, Austria (2011) and Santa Fe, New Mexico, USA (2014). It was open to contributions on all aspects of nuclear data covariance evaluations, for all observables (e.g. cross sections, energy and angle spectra, fission yields, and resonance parameters) from the resonance region up to the high energy range, for light to heavy nuclei. The main topics of the workshop were related to: -) covariance evaluation methodology (15 talks), -) nuclear reaction models prior uncertainties and biases (3 talks), -) measurement breakthrough to evaluate and reduce systematic uncertainties as well as biases (7 talks), -) nuclear data libraries: status of their covariance files/ representation of covariance and formatting issues (3 talks), and -) applied covariances, from nuclear reaction model parameters to various applied parameters covariances (15 talks). The major trends and advances of this CW2017 conference were related to better treatment of experimental systematic uncertainties such as normalization, detector efficiencies, background reduction,... Various talks given by experimentalists have shown their recent solutions to minimize these kind of uncertainties. In addition, theoreticians and evaluators proposed various advances to better take into account prior nuclear reaction models uncertainties with possible solutions given by more fundamental theories (microscopic ingredients)

[en] WONDER-2012 is the third International Workshop on Nuclear Data Evaluation for Reactor Applications (the first two workshops were organised respectively in 2006 and 2009). About 50 experts in the field of nuclear data were participating at 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 microscopic and integral nuclear data measurements, evaluation of nuclear data (theories, models, and codes), uncertainties and covariance matrices, processing and benchmarking, gamma spectra and fission modelling. Several posters covering these items were also presented

[en] The design work of a Gas-Cooled Fast Reactor (GFR) is currently making significant progress with latest images showing attractive features. More detailed neutronic analysis for this type of reactor is now becoming necessary. An assessment of the suitability of calculation methods has therefore been undertaken by various means i.e. analysing relevant experiments or performing comparisons with other methods. The heterogeneity and neutron streaming effects have been identified as a key point to be looked at. Due to the specific features of the Helium coolant which is already very transparent at the nominal pressure / density, calculating the depressurization effect appears a challenging issue and requires enhanced streaming algorithms even when compared to the well established CO₂ cooled Fast Reactors. Although extensively validated in the past, it was necessary to revisit the algorithms of the ECCO cell code concerning the anisotropy of streaming effects in voided cells and low density channels. The ECCO cell code includes the following features. First, the subgroup method for self-shielding calculations with different algorithms for flux-weighted cross sections such as capture or fission, and for current-weighted cross sections like transport or Legendre order 1 type total cross sections and matrices. An exponential mode of the subgroup method has been implemented specifically for shielding applications which calculates cross sections and matrices for any Legendre order. Secondly, the flux and current P1 consistent equations for both homogeneous and heterogeneous descriptions of cells, which allows an accurate treatment of leakage with both anisotropy of scattering and streaming effects. Thirdly, the anisotropy of streaming effects in voided cells and low density channels. It was found that the algorithms of the two last items required changes which are presented in this paper. The status of the validation of these new algorithms appears satisfactory. (authors)

[en] Nuclear data are widely used in many research fields. In particular, neutron-induced reaction cross sections play a major role in safety and criticality assessment of nuclear technology for existing power reactors and future nuclear systems as in Generation IV. Because both stochastic and deterministic codes are becoming very efficient and accurate with limited bias, nuclear data remain the main uncertainty sources. A worldwide effort is done to make improvement on nuclear data knowledge thanks to new experiments and new adjustment methods in the evaluation processes. This paper gives an overview of the evaluation processes used for nuclear data at CEA. After giving Bayesian inference and associated methods used in the CONRAD code [P. Archier et al., Nucl. Data Sheets 118, 488 (2014)], especially the Bayesian Monte-Carlo (BMC) method, a focus on systematic uncertainties will be given. This last can be dealt by using marginalization methods during the analysis of differential measurements as well as integral experiments. They have to be taken into account properly in order to give well-estimated uncertainties on adjusted model parameters or multigroup cross sections. In order to give a reference method, a new stochastic approach is presented, enabling marginalization of nuisance parameters (background, normalization...). It can be seen as a validation tool, but also as a general framework that can be used with any given distribution. An analytic example concerning U²³⁸ total cross-section, based on a fictitious experiment is presented to show the good agreement between the stochastic and deterministic methods. Advantages of such stochastic method are meanwhile moderated by the time required, limiting its application for large evaluation cases. Faster calculation can be foreseen with nuclear model implemented in the CONRAD code or using bias technique. The paper ends with perspectives about new problematic and time optimization. (authors)

[en] The development of a software tool (CONRAD) was initiated at CEA/Cadarache to give answers to various problems arising in the data analysis of nuclear reactions. This tool is then characterized by the handling of uncertainties from experimental values to covariance matrices for multi-group cross sections. An object oriented design was chosen allowing an easy interface with graphical tool for input/output data and being a natural framework for innovative nuclear models (Fission). The major achieved developments are a data model for describing channels, nuclear reactions, nuclear models and processes with interface to classical data formats, theoretical calculations for the resolved resonance range (Reich-Moore) and unresolved resonance range (Hauser-Feshbach, Gilbert-Cameron,...) with nuclear model parameters adjustment on experimental data sets and a Monte Carlo method based on conditional probabilities developed to calculate properly covariance matrices. The on-going developments deal with the experimental data description (covariance matrices) and the graphical user interface. (authors)

[en] Massimo Salvatores was not the man of a country, an organization, or a team. Certainly because of his origin, his education, and his culture, Massimo has always favored a broader and more open collaboration instead of a bureaucratic and shortsighted approach to the research, keeping the achievements only to a restricted inner circle. He was convinced that disinterested sharing makes one stronger and Massimo one of the few nuclear reactor physicists who elevated international collaboration to its highest level. Massimo will be remembered for his many works on reactor physics, nuclear data and fuel cycle. This article gives a short history of the major contributions that Massimo made to his dear discipline, Neutronics

[en] Evaluation of neutron cross sections between 0eV and 20MeV is based on several aspects of nuclear physics such as nuclear reaction and structure models and microscopic and integral measurements. Most of the time, the evaluation process is separately done in the resolved resonance range and the continuum. It may give rise to non-physical mismatches of cross sections and large uncertainties at boundaries. It also leads to an absence of cross correlations between high-energy domain and resonance range. In addition, integral experiments are sometimes only used to check central values (evaluation is ''working fine'' on a dedicated set of benchmarks). Eventual reduction of uncertainties on cross sections is not straightforward: ''working fine'' could be mathematically turned into reduced uncertainties. This paper will present several ideas that could be used to avoid such effects. They are based on basic physical principles, recent advances in terms of covariance evaluation methodologies, intensive use of Monte Carlo methods and High Performance Computing (HPC) and on some newly introduced models. A clear connection is made between resonance and continuum energy ranges. (orig.)

[en] This paper presents the transmutation of Americium and Curium in a heterogeneous mode in the framework of the 1991 French Law concerning waste management. Two scenarios with moderated targets are presented: a 100% frit reactor (EFR) scenario multi-recycling Pu+Np with targets of Am+Cm placed in core and a mixed PWR (UOX fuel) and fast reactor (50% of EFR) multi-recycling Pu+Np and containing targets in core and in the blanket region. The design of the target is based on classical fast fuel S/A technology (pins, spacer wires,...) and should reach the goal of 90% fission rate. (authors)

[en] The modelling of the neutron cross sections consists in their interpretation in three different energy ranges: the first one is the Resolved Resonance Range (RRR) at low energy, the second is the Unresolved Resonance Range (URR), and the third one concerns the high energies. For this, we generally use the Reich-Moore approximation of the R-Matrix formalism, the average R-Matrix formalism and optical model calculations. One of the main challenges of such a work is to study the consistency of the average parameters obtained by these different calculations. With the ESTIMA and SPRT methods, we provide a set of parameters for partial s and p waves (strength functions, effective potential scattering radius, mean-level spacing and reduced neutron width). But, in order to analyse accurately the URR domain, we need more information than the parameters associated to the orbital moments L = 0 and L = 1. This work describes the link between the average R-Matrix formalism and the optical model, especially concerning the transmission coefficients, total and shape elastic cross sections. Based on these two models, we propose a generalization of the SPRT method for L > 1, and we obtain a new set of parameters for the URR domain in terms of S_LJ and R_JL^∞. (authors)

[en] The accuracy of the neutron properties of ¹⁷⁴Hf, ¹⁷⁶Hf, ¹⁷⁷Hf, ¹⁷⁸Hf, ¹⁷⁹Hf and ¹⁸⁰Hf have been investigated on the basis of experimental work carried out at the GELINA facility of the Institute for Reference Materials and Measurements. Six transmission data were interpreted with the REFIT code in term of resolved parameters. The propagation of the nuclear data uncertainties up to multi-group cross sections were performed with Monte Carlo techniques in association with conditional probabilities. This work demonstrates the possibility to get isotopic multigroup covariance matrices by mixing various correlated or independent sources of uncertainties.