[en] The basic conditions of coincidence experiments are discussed and some of the properties of specific detectors covering up to 90% of 4π steradian and presenting a very large momentum bite are shown. It will appear that such detectors, compared to classical iron dipole spectrometers, present larger acceptances, but a smaller resolving power and a rather low background rejection. The choice of which of these two solutions is to be used depends on the conditions of the specific experiments

[en] A review of the state of the art is given. It shows recent proofs of success of the technology. An important R and D effort remains to be done in order to collect all the expectable benefits of RF superconductivity. (author)

[en] It is shown that improvements of the detector acceptances (in solid angle and momentum bite) is as important as increased duty cycle for coincidence experiments. To have a maximum efficiency and thus to reduce the cost of experiments, it is imperative to develop maximum solid angle systems. This implies an axial symmetry with respect to the incoming beam. At Saclay, we have investigated some of the properties of specific detectors covering up to 90% of 4π steradians for a high energy, 100% duty cycle electron accelerator. The techniques of wide angle spectrometers have already been explored on a large scale in high energy physics. However, in the case of charged particles, such detectors, compared to classical iron dipole spectrometers, present a smaller resolving power and a rather low background rejection. The choice of which of these two solutions is to be used depends on the conditions of the specific experiment

[en] Important studies are now undertaken to develop continuous wave electron accelerators with energy ranging from 1 to 4 Gev. So very important effort must be now put on the development of the experimental set-up matching the performances expected from the electron beam. Major steps in the understanding of the nuclear systems will come from more and more exclusive experiments where well defined mechanisms will be selected

[en] Major information about short range behavior of nuclear forces should be obtained through electron scattering experiments at high momentum transfer. Cross sections will be very low as is usually the case in electron scattering. In order to reach them, the solid angle of the detection system will have to be enlarged. Traditional optics cannot give correct answer to the problem. For very large apertures, it is impossible to obtain good focussing properties which provide accurate momentum/position correlation with no dependence on the entrance angles. Furthermore, the experiment will require the measurement of these angles. It means that the final system will be equipped with a complete set of position sensitive detectors able to measure positions and angles of trajectories in both planes. Then, the question arises: is it really necessary to provide good focussing, or more precisely: is it possible to get all the required information without the help of a sophisticated predetermined magnetic optics. We try to answer this question and then to sketch from a new point of view the best spectrometer we could think of

[en] Delayed-neutrons are of great importance for reactor operations. Current abundances derive from either a measurement performed in 1957 by Keepin or by a summation calculation performed by Brady and England in 1989. In this work, the CONRAD code has been written to compute a new set of delayed-neutron abundances as well as to estimate uncertainties and correlations through a Monte Carlo method and a Bayesian inference. The new set of abundances seems to better reproduce both the delayed-neutron activity and the reactivity curves than JEFF-3.1.1 with respect to the curves obtained by summation method. However, uncertainties are larger, since they take into account the large uncertainty in the microscopic decay data of each isotope. An experiment will take place in the future to verify the validity of the calculated quantities

No abstract available

[en] A tritium target, to be bombarded by an intense electron beam will energies between 200 and 700 MeV, has been realized. The problem resumes to dispose of a target with a tritium density high enough to get numerous detectable events. Liquid target, under a weak pressure, has been choosed

[en] Highlights: • To overcome GEN-3 calculation challenges, CEA has developed a new code package APOLLO2.8 based on JEFF3.1.1 library. • The Method of Characteristics allows exact-2D heterogeneous geometry calculations, and the new SHEM 281-group energy mesh enables accurate resonant absorption prediction. • We design specific experiments in CEA reactors such as PERLE experiment in EOLE that allows the reduction of the "5"6Fe uncertainty component below 1.2%. • The challenging calculation of pin-by-pin power in large GEN-3 reactors is overcome, and 3D-stochastic TRIPOLI4/JEFF3.1.1 or 2D-deterministic APOLLO2.8 calculation uncertainty is decreased from prior ±8% to current ±2.6% value. - Abstract: New French GEN-III reactors are characterized by an improved safety (core catcher for corium, stainless-steel neutron reflector to minimize vessel embrittlement, permanent in-core instrumentation thanks to SPND, …). Moreover, the assembly central guide-tube can be replaced by a fuel pin and the First core is controlled through numerous 8% Gd burnable poison fuel pins. These new features harden the neutron spectrum and increase the neutronic calculation challenge. Therefore, a new calculation package APOLLO2.8 was developed, based on an efficient Method of Characteristics (MOC) and the new SHEM 281-group energy mesh that enables accurate resonant absorption prediction. The JEFF3.1.1 recent nuclear data library, which involves the feedback from Critical Experiments and LWR Post Irradiation Experiments, was used. The experimental validation of the APOLLO2.8/JEFF3.1.1 package allowed the Uncertainty Quantification associated with PWR design parameters. In order to meet target-accuracy required in specific GEN-III parameters, targeted integral experiments where achieved. To validate heavy neutron reflector the mock-up experiment PERLE was carried out in EOLE critical facility. PERLE allowed the calculation check of SS reflector-saving δ_r_e_f_l and the improvement of Fe cross-sections. Thanks to the large French experimental database, we determined reliable covariance matrices associated to JEFF3.1.1 evaluations, in order to perform the propagation of nuclear data uncertainties. Sensitivity/uncertainty analysis has shown that the predominant component on radial power map comes from the "2"3"8U inelastic scattering cross-section. To reduce this 3% uncertainty component, we performed a "2"3"8U(n,n′) re-estimation, using relevant selected experiment benchmarks. This theoretical and experimental extensive work performed since 2003 allows a reliable prediction of the local flux and K_e_f_f (±200 pcm in 1σ) in large GEN-III reactors. The challenging pin-by-pin power prediction is today overcome, and 3D-stochastic TRIPOLI4 or 2D-deterministic APOLLO2.8 calculation uncertainty is decreased from prior ±8% to current ±2.6% value.

[en] Several calculations methods for the analysis of small-sample reactivity experiments are presented, as their main advantages and drawbacks. A numerical benchmark has been defined for this study consisting in a regular lattice of UO₂ fuel pins, in which the central one is successively poisoned with isotopes of interest (actinides, absorbers, ...). A first method, based on a forward calculation ('eigenvalues difference method'), is presented, using either a deterministic or a stochastic calculation code. A first perturbative method studied is based on the 'Exact Perturbation Theory' (EPT) implemented in the deterministic code APOLLO2.8, and gives consistent results against forward calculations. A second perturbative method, the 'correlated sampling method', implemented in the stochastic calculation code TRIPOLI4.7 is tested. It should be use carefully as it is generally validated against small atomic density changes, but can be useful for conception studies. An 'hybrid method', based on the EPT formalism, using both Monte Carlo and deterministic results is tested, and shows reliable results. (authors)