Search

A systematic increase of the neutron noise levels over time has been observed in some of the pre-KONVOI PWRs operating in Europe. A possible reason for this anomaly was identified as increased mechanical vibrations of reactor internals, specifically of fuel assemblies. To verify this conjecture, the modeling of stationary vibrations of fuel assemblies and of the corresponding neutron noise is essential. In this paper, using the =d model basis, we illustrate the modeling of the neutron noise sources for fuel assembly vibrations and study the effect of homogenization of cross sections on such stationary perturbations. A comparative analysis between the classical nodal approach (both localized at the boundaries of the vibrating fuel assembly or involving the entire neighboring fuel assemblies) and a pin-wise approach shows that the ‘boundary-localized’ nodal approach seems to capture local noise information, as a pin-wise approach would do, without the need of a complex pin-by-pin model when the detectors are placed close to the perturbation. However, when considering region of the active core away from the perturbation, all three approaches lead to comparable results.

International audience; As part of a bilateral agreement on the study of large axially-heterogeneous oxide-fueled SFR cores, CEA and IPPE have recently performed neutron physics experiments in the BFS facility. The configurations of interest are pancake-shape cores with a split fissile column and a sodium plenum, designed to favor a high inner plutonium conversion ratio and a low sodium void worth. Separate effect tests, including local and global sodium void situations as well as various rodded cases, have been done. The measurements included reactivity effects, spectral indices, detailed reaction rate traverses, neutron importance, etc. The analysis of the experiments with Monte Carlo codes and recent nuclear data files shows the following trends core reactivity is predicted within 1.5 % , depending on the nuclear data file used; sodium voiding in the 91 central tubes is predicted within 0.25 %; the calculated axial reaction rate traverses match the experimental ones; the weight of the simulated control rod is predicted within 10percent.

ISBN :978-151082573-4; International audience; In complex innovative fast reactor concepts, fairly detailed core modeling is essential for reliable safety analysis during severe accident scenarios. The CFV core with its axially heterogeneous design, has a negative sodium void reactivity effect, a favorable feature wich increases the inherent system safety in case of sodium boiling. In this work, we studied the impact that the controlrod homogenization model used, and the control rod position, have on the sodium void-reactivity effect and the control rod worth, in the case of a voided CFV core. Three different control rod homogenization models were studied, the traditional 2D equivalence procedure, and two models based on a 3D equivalence procedure, taking into account the axial heterogeneity of the CFV core. It was found that the impact of control rod homogenization has a negligible effect on the sodium void reactivity effect. However, between different control rod positions, a difference of up to 1 dollar in the sodium void reactivity effect was found, hence the control rod position has to be carefully considered when calculating the sodium void reactivity effect. For the control rod worth in a voided CFV core, the traditional 2D procedure, could lead to discrepancies of up to 11% for control rod positions at the top of the core. These discrepancies could be much reduced by control rod homogenization with the 3D equivalence procedure. For the total control rod worth, all models and procedures produced results within the desired error margin of $\pm$ 5%.

In this paper, we investigate the possibility of using the CEA Cadarache MASURCA experimental reactor to deliver a well-characterized, fairly-intense beam of intermediate-to-fast energy neutrons. We report the results of numerical simulations which have been performed to establish the feasibility of such a beam. We show that it is possible to achieve a beam in- tensity of more than 108 neutrons cm-2 s-1 in the experimental room past the reactor biological shield, ~80% of the neutrons having energies above 100 keV, and 96% above 10 keV. The characteristics of this MASURCA extracted beam are compared with those of other neutron physics facilities designed to produce continuous beams of fast neutrons. The analysis shows that the MASURCA setup would have several distinctive advantages.

The joint evaluated fission and fusion nuclear data library 3.3 is described. New evaluations for neutron-induced interactions with the major actinides U , U and Pu , on Am and Na , 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., Acknowledgements The authors would like to thank all contributors to the JEFF project that shared their insights and provided their specific input for the present JEFF-3.3 evaluation and its immediate predecessors JEFF-3.2 and JEFF-3.1.2.