The National Nuclear Security Administration (NNSA)/DP French Alternative Energies and Atomic Energy Commission (CEA)/DAM agreement on cooperation on fundamental science is a U.S.-French collaborative effort to combine intellectual and experimental resources and further the relevant nuclear science. Recently, both the NNSA and CEA experimental teams performed high-statistics measurements of the 239Pu(n, f) prompt fission neutron spectrum (PFNS) at the Los Alamos Neutron Science Center, both of which were recently published in the journal Physical Review C. These separate measurements used the same experimental area and a common neutron detector array, but differ in many aspects, including background assessments, data acquisition systems and philosophies, fission detectors, and PFNS extraction techniques. Hence, some aspects of the experimental methods and associated uncertainties are highly correlated while others are independent. The results from both measurements broke new ground for PFNS measurements given their higher accuracy and more detailed study of corrections necessary for the measured quantity compared to existing literature measurements, and both will significantly impact PFNS nuclear data evaluations for the foreseeable future. The focus of this work is to document a comparison of the results from these distinct measurements in terms of the acquired data, the PFNS results, and the measured average PFNS energies. While systematic differences between the PFNS results are present on the 1–3% level, the acquired data relative to each respective measurement at low incident neutron energies are in remarkable agreement, as are the conclusions regarding the magnitude and position of features in the PFNS relating to second-chance fission, third-chance fission, and pre-equilibrium neutron emission.

Cross sections and fission yields can be correlated, depending on the selection of integral experimental data. To support this statement, this work presents the use of experimental isotopic compositions (both for actinides and fission products) from a sample irradiated in a reactor, to construct correlations between various cross sections and fission yields. This study is therefore complementing previous analysis demonstrating that different types of nuclear data can be correlated, based on experimental integral data.

We recall Jacques Raynal’s career, his main bibliographical data and achievements, summarizing his topics of interest and works. We also give some biographical and personal data. We have collected a few words about him from friends and colleagues, in addition to those given by the authors of the articles published in this EPJA issue in memory of the Emperor of the ECIS code.

There is a long-standing controversy on nuclear data uncertainty assessment for general purpose nuclear data libraries. On the one hand, nuclear data users would like the libraries to predict uncertainties for selected integral quantities consistent with the integral experimental uncertainties, while on the other hand, doing so could make evaluations dependent on selected integral datasets breaking the general applicability of the library to any existing or future applications. This article studies the hypothesis that certain correlations between nuclear data, which come from the immutable nature of the reactor physics in the integral experiment used as benchmarks, and can be estimated almost independently of the choice of selected integral experiments, nuclear data library, or evaluation methodology. This article reports the findings of an international computational inter-comparison study carried out under the auspices of the Working Party on International Nuclear Data Evaluation Co-operation. The participants represented 5 different organizations, on three different continents and used different initial nuclear data libraries and different calculation methodologies. This study focused on estimating the correlation coefficients between fission, capture and nu-bar for Pu-239 which would arise in the final evaluated nuclear data library if a plutonium metal fast-neutron-spectrum critical experiment with typical integral-measurement uncertainty of 100 pcm was used in the validation and feedback to compile the nuclear data library. The additional knowledge of the correlation coefficients can effectively reduce the propagated uncertainty on criticality experiments from the extended library. This exercise helped to improve understanding the different approaches used, to identify weaknesses and provide indications where further work is required to develop a scientifically rigorous method. This article does not aim at recommending these methods as standards. It aims at honoring the effort of Massimo Salvatores, who was instrumental in pushing studies that should lead to development of uncertainty estimation and by participating in them.

The joint evaluated fission and fusion nuclear data library 3.3 is described. New evaluations for neutron-induced interactions with the major actinides $$^{235}\hbox {U}$$ , $$^{238}\hbox {U}$$ and $$^{239}\hbox {Pu}$$ , on $$^{241}\hbox {Am}$$ and $$^{23}\hbox {Na}$$ , $$^{59}\hbox {Ni}$$ , Cr, Cu, Zr, Cd, Hf, W, Au, Pb and Bi are presented. It includes new fission yields, prompt fission neutron spectra and average number of neutrons per fission. In addition, new data for radioactive decay, thermal neutron scattering, gamma-ray emission, neutron activation, delayed neutrons and displacement damage are presented. JEFF-3.3 was complemented by files from the TENDL project. The libraries for photon, proton, deuteron, triton, helion and alpha-particle induced reactions are from TENDL-2017. The demands for uncertainty quantification in modeling led to many new covariance data for the evaluations. A comparison between results from model calculations using the JEFF-3.3 library and those from benchmark experiments for criticality, delayed neutron yields, shielding and decay heat, reveals that JEFF-3.3 performes very well for a wide range of nuclear technology applications, in particular nuclear energy.

The joint evaluated fission and fusion nuclear data library 3.3 is described. New evaluations for neutron-induced interactions with the major actinides $$^{235}\hbox {U}$$ 235U , $$^{238}\hbox {U}$$ 238U and $$^{239}\hbox {Pu}$$ 239Pu , on $$^{241}\hbox {Am}$$ 241Am and $$^{23}\hbox {Na}$$ 23Na , $$^{59}\hbox {Ni}$$ 59Ni , Cr, Cu, Zr, Cd, Hf, W, Au, Pb and Bi are presented. It includes new fission yields, prompt fission neutron spectra and average number of neutrons per fission. In addition, new data for radioactive decay, thermal neutron scattering, gamma-ray emission, neutron activation, delayed neutrons and displacement damage are presented. JEFF-3.3 was complemented by files from the TENDL project. The libraries for photon, proton, deuteron, triton, helion and alpha-particle induced reactions are from TENDL-2017. The demands for uncertainty quantification in modeling led to many new covariance data for the evaluations. A comparison between results from model calculations using the JEFF-3.3 library and those from benchmark experiments for criticality, delayed neutron yields, shielding and decay heat, reveals that JEFF-3.3 performes very well for a wide range of nuclear technology applications, in particular nuclear energy.

Premiere partie d’un ensemble de deux articles exposant le processus d’evaluation des donnees nucleaires, cet ensemble presente l’etat actuel de la connaissance theorique des phenomenes de physique nucleaire mis en jeu. Lors de l’evaluation, la connaissance theorique et experimentale est condensee et synthetisee dans des fichiers informatiques utilises par les codes de simulation. Apres un survol du contenu des fichiers evalues, nous decrivons les differentes methodes utilisees pour l’evaluation des donnees nucleaires. Nous exposons particulierement leur modelisation. Des exemples tires de la pratique quotidienne de l’evaluation sont presentes.

We present a microscopic description of neutron and proton elastic and inelastic scattering off Pb-206,Pb-207,Pb-208 and Bi-209 together with new medium-energy (7.5-15.5 MeV) neutron elastic and inelastic scattering measurements for various low-energy levels. The Jeukenne, Lejeune, Mahaux (JLM) semimicroscopic folding model provides the relevant optical and transition potentials used to calculate the elastic and inelastic cross sections. Rearrangement corrections that account for proton and neutron density variations during the transition are considered. The nuclear diagonal and transition densities are calculated from a (quasiparticle) random phase approximation [(Q)RPA] structure model implemented with the Gogny D1S interaction. Calculated differential elastic and inelastic cross sections are mostly in very good agreement with available data. Predicted nuclear structure properties as well as scattering calculations and measurements for the yrast quadrupole excitation in Pb-206 are carefully discussed. The rearrangement corrections to inelastic scattering form factors are shown to reduce medium energy nucleon inelastic cross section by up to 55%. The magnitude of these corrections changes depending on the probe, incident energy, multipolarity, and nature of the transitions considered. The combined analysis of nuclear structure properties and those for nucleon scattering cross sections measured previously over a range of incident energies provides stringent tests of present microscopic models and helps distinguish those scattering data which most likely call for revision.

This paper presents an application of the Backward-Forward Monte Carlo (BFMC) method using measured critical boron concentrations for a specific PWR cycle. The considered prior nuclear data are the fission cross sections, $\overline{\nu}_{p}$ for 235U and 239Pu and the capture cross section of 238U. The posterior nuclear data exhibit cross-isotope correlations, moderate changes for the average quantities and reduced uncertainties. This work is the first one considering the BFMC method and an integral system mostly sensitive to thermal neutrons. It contributes to show the impact of integral experimental data for the evaluation of nuclear data and their covariance matrices, leading to cross-isotope correlations and a nuclear data uncertainty reduction.

. This paper presents an application of the Backward-Forward Monte Carlo (BFMC) method using measured critical boron concentrations for a specific PWR cycle. The considered prior nuclear data are the fission cross sections, ν_p for 235 U and 239 Pu and the capture cross section of 238 U. The posterior nuclear data exhibit cross-isotope correlations, moderate changes for the average quantities and reduced uncertainties. This work is the first one considering the BFMC method and an integral system mostly sensitive to thermal neutrons. It contributes to show the impact of integral experimental data for the evaluation of nuclear data and their covariance matrices, leading to cross-isotope correlations and a nuclear data uncertainty reduction.

In this paper, we present three Monte Carlo methods to include integral benchmark information into the nuclear data evaluation procedure: BMC, BFMC and Mocaba. They allow to provide posterior nuclear data and their covariance information in a Bayesian sense. Different examples will be presented, based on 14 integral quantities with fast neutron spectra (keff and spectral indices). Updated nuclear data for 235U, 238U and 239Pu are considered and the posterior nuclear data are tested with MCNP simulations. One of the noticeable outcomes is the reduction of uncertainties for integral quantities, obtained from the reduction of the nuclear data uncertainties and from the rise of correlations between cross sections of different isotopes. Finally, the posterior nuclear data are tested on an independent set of benchmarks, showing the limit of the adjustment methods and the necessity for selecting well representative systems.

This paper presents a Bayesian approach based on integral experiments to create correlations between different isotopes which do not appear with differential data. A simple Bayesian set of equations is presented with random nuclear data, similarly to the usual methods applied with differential data. As a consequence, updated nuclear data (cross sections, [see formula in PDF], fission neutron spectra and covariance matrices) are obtained, leading to better integral results. An example for 235U and 238U is proposed taking into account the Bigten criticality benchmark.

The CIELO collaboration has studied neutron cross sections on nuclides that significantly impact criticality in nuclear technologies – 16O, 56Fe, 235,8U and 239Pu – with the aim of improving the accuracy of the data and resolving previous discrepancies in our understanding. This multi-laboratory pilot project, coordinated via the OECD/NEA Working Party on Evaluation Cooperation (WPEC) Subgroup 40 with support also from the IAEA, has motivated experimental and theoretical work and led to suites of new evaluated libraries that accurately reflect measured data and also perform well in integral simulations of criticality.

Nowadays, reliance on nuclear models to interpolate or extrapolate between experimental data points is very common, for nuclear data evaluation. It is also well known that the knowledge of nuclear reaction mechanisms is at best approximate, and that their modeling relies on many parameters which do not have a precise physical meaning outside of their specific implementations in nuclear model codes: they carry both specific physical information, and effective information that is related to the deficiencies of the model itself. Therefore, to improve the uncertainties associated with evaluated nuclear data, the models themselves must be refined so that their parameters can be rigorously derived from theory. Examples of such a process will be given for a wide sample of models like: detailed theory of compound nucleus decay through multiple nucleon or gamma emission, or refinements to the width fluctuation factor of the Hauser-Feshbach model. All these examples will illustrate the reduction in the effective components of nuclear model parameters, through the reduced dynamics of parameter adjustment needed to account for experimental data. The significant progress, recently achieved for the non-fission channels, also highlights the difficult path ahead to improve our quantitative understanding of fission in a similar way: by relying on microscopic theory.

Most recent evaluated nuclear data files exhibit excellent integral performance, as shown by the very good agreement between experimental and calculated keff values over a wide range of benchmark integral experiments. However, the propagation of the uncertainties associated with those nuclear data to integral observables, generally produces calculated distribution which are much (3–5 times) wider than the experimental uncertainties. Reducing the variances of the evaluated data to achieve consistency at the integral level would lead to unreasonably narrow variances in the light of differential experimental data. One way of solving that paradox could be to allow, for different observables like fission cross-sections (σf), the prompt fission neutron spectra (χ), and the average multiplicity of fission neutrons ([see formula in PDF]) to be correlated in a Bayesian-like, Total Monte-Carlo approach, under constraints from integral experiments from the ICSBEP (International International Criticality Safety Benchmark Evaluation Project) benchmark compilation. Future developments will be highlighted and restrictions imposed by the current formatting of nuclear data will be discussed.

Direct inelastic scattering to discrete excitations and pre-equilibrium emission are described within a microscopic model. Nuclear structure information are obtained in the (Quasi) Random Phase Approximation ((Q)RPA) framework implemented with the Gogny force. The relevant optical and transition potentials are build considering the JLM folding model. Various successful applications are shown for (n,n), (n,n'), (n,xn) and (n,xnγ) reactions for spherical and axially deformed even-even or odd targets. The rearrangement corrections to transition potentials and the contribution of unnatural parity excitations to pre-equilibrium emission are discussed. Our model predictions for (n,n'γ) reactions, for intra- and inter-band transitions in 238U, and for the 239Pu(n,2n) cross section are analyzed.

Numerous domains, in fundamental research as well as in applications, require the study of reactions induced by neutrons with energies from few MeV up to few tens of MeV. Reliable measurements also are necessary to improve the evaluated databases used by nuclear transport codes. This energy range covers a large number of topics like transmutation of nuclear waste, design of future fission and fusion reactors, nuclear medicine or test and development of new detectors. A new facility called Neutrons For Science (NFS) is being built for this purpose on the GANIL site at Caen (France). NFS is composed of a pulsed neutron beam for time-of-flight facility as well as irradiation stations for cross-section measurements. Neutrons will be produced by the interaction of deuteron and proton beams, delivered by the SPIRAL-2 linear accelerator, with thick or thin converters made of beryllium or lithium. Continuous and quasi-mono-energetic spectra will be available at NFS up to 40 MeV. In this fast energy region, the neutron flux is expected to be up to 2 orders of magnitude higher than at other existing time-of-flight facilities. In addition, irradiation stations for neutron-, proton-and deuteron-induced reactions will allow performing cross-section measurements by the activation technique. After a description of the facility and its characteristics, the experiments to be performed in the short and medium term will be presented.

This paper presents a Bayesian approach based on integral experiments to create correlations which do not appear with differential data. Some quantities such as the fission cross section (sigma), neutron multiplicity ((nu) over bar (p)), neutron spectra (chi), etc. are usually neither modeled together nor measured in coincidence, thus there is no correlation matrices in evaluated nuclear data libraries. One can nevertheless use the information from integral experiments such as fast criticality-safety benchmarks to correlate such quantities for possible inclusion in nuclear data libraries. A simple Bayesian set of equations is presented with random nuclear data, similarly to the usual methods applied with differential data. An example for Pu-239 is proposed.