[en] An experimental and analytical study of thin laser-accelerated flyer plates in a confined geometry is presented. Its objective is to improve the coupling efficiency between the flyer kinetic energy and the laser energy. Performed with a 7 μm thick aluminum flyer integrated in a three-layered target using a Nd:YAG laser (1.06 μm wavelength and a pulse duration of 8 ns FWHM), this study consists in finding the best ablating material of the first layer, responsible for the plasma generation. Flyer velocities between 2 and 5.5 km/s have been achieved for the 1-7 GW/cm2 laser power density range. Best results yield coupling efficiencies of almost 50%

[en] The purpose of this study is to establish the subcriticality of a shipping cask with the loading of 7 containers of FBR fuel pins. Calculations have been carried out with the IRSN/CEA new calculation scheme called CRISTAL, based on the APOLLO2 sophisticated spectral code and on the MORET4 3D Monte Carlo code, and adopted by the French industry. The study has been performed for a heterogeneous medium (lattice of fissile pins surrounded by water) and for a homogeneous one (homogenization of fissile matter with water). The 1.015 maximum Keff obtained in case of a heterogeneous modelling of the fissile medium implies a revision of the cask capacity in order to meet the criticality safety criteria. (author)

[en] In order to avoid criticality risks, a large number of facilities using spent fuels have been designed considering the fuel as fresh. This choice has obviously led to considerable safety margins. In the early 80's, a method was accepted by the French Safety Authorities allowing to consider the changes in the fuel composition during the depletion with some very pessimistic hypothesis: only actinides were considered and the amount of burnup used in the studies was equal to the mean burnup in the 50-least-irradiated centimeters. As many facilities still want to optimize their processes (e.g. transportation, storage, fuel reprocessing), the main companies involved in the French nuclear industry, researchers and IRSN set up a Working Group in order to study the way burnup could be taken into account in the criticality calculations, considering some fission products and a more realistic axial profile of burnup. The first of this article introduces the current French method used to take burnup into account in the criticality studies. The second part is devoted to the studies achieved by the Working Group to improve this method, especially concerning the consideration of the neutron absorption of some fission products and of an axial profile of burnup: for that purpose, some results are presented related to the steps of the process like the depletion calculations, the definition of an axial profile and the criticality calculation. In the third part, some results (keff) obtained with fission products and an axial profile are compared to those obtained with the current one. The conclusions presented are related to the present state of knowledge and may differ from the final conclusions of the Working Group. (author)