[en] The aim of the present invention is a remote control pyrotechnic device to cut plates and tubes, more particularly for mechanical piece dismantling in contaminated atmosphere. The present device is compact, easy to use inexpensive and can be disposed of with metallic wastes after its utilization. The device is described in detail, its operation way is also presented

[en] Minor actinides (Np, Am, Cm) are mainly responsible for the long-term radiotoxicity of high level radioactive wastes. New matrices, particularly suited for their immobilisation, are currently searched. Within this framework, zirconolite (CaZrTi₂O₇) is a good candidate because of its good actinide containment capacity and its excellent chemical durability. Investigations of zirconolite ceramics have confirmed the capacity of this phase to incorporate high lanthanide amounts (minor actinides surrogates such as neodymium) as solid solution into the calcium site of its crystal lattice. In this case, charge compensation can be ensured by aluminium ions in one of the three titanium sites of zirconolite. Spectroscopic measurements (ESR, optical absorption and fluorescence) indicate a distribution of local environments around the calcium site. Zirconolite-based glass-ceramics have been prepared by controlled devitrification of (TiO₂, ZrO₂)-rich calcium aluminosilicate glasses. Heat treatment conditions (nucleation, crystal growth) were optimised to only obtain zirconolite crystals in the bulk of glass-ceramics. The structure and the microstructure of zirconolite crystals were studied for various crystal growth temperatures T_c and durations. Notably, a progressive ordering of zirconolite structure occurs with increasing T_c. Moreover, the crystallisation of silicate phases (titanite CaTiSiO₅ and anorthite CaAl₂Si₂O₈) from glass surface is observed. The degree of crystallinity V and the - proportion R of surrogate ions preferentially incorporated into the zirconolite phase were estimated. It appears that R increases with decreasing T_c, the total amount of surrogate and the ionic radius or the charge of the surrogate ion. Parent glass composition changes were also performed in order to improve V and R. (author)

[en] Laser plasma interaction (LPI) is a critical issue in ignition target design. Based on both scaling laws and two-dimensional calculations, this article describes how we can constrain a laser megajoule (LMJ) [J. Ebrardt and J. M. Chaput, J. Phys.: Conf. Ser. 112, 032005 (2008)] target design by mitigating LPI. An ignition indirect drive target has been designed for the 2/3 LMJ step. It requires 0.9 MJ and 260 TW of laser energy and power, to achieve a temperature of 300 eV in a rugby-shaped Hohlraum and give a yield of about 20 MJ. The study focuses on the analysis of linear gain for stimulated Raman and Brillouin scatterings. Enlarging the focal spot is an obvious way to reduce linear gains. We show that this reduction is nonlinear with the focal spot size. For relatively small focal spot area, linear gains are significantly reduced by enlarging the focal spot. However, there is no benefit in too large focal spots because of necessary larger laser entrance holes, which require more laser energy. Furthermore, this leads to the existence, for a given design, of a minimum value for linear gains for which we cannot go below.

[en] Nucleation and growth of crystal in an oxide glass was studied in a Si B Al Zr Nd Ca Na O system. The nucleation and growth process were monitored by thermal analysis and isothermal experiments. The effect of the network modifier was studied. Therefore for a Ca rich sample the crystallization is homogeneous in the bulk showing a slow increase of crystallinity as temperature increases. On the other hand, a Na rich sample undergoes several crystallization processes in the bulk or from the surface, leading to bigger crystals. The activation energy of the viscous flow and the glass transition are of same magnitude when that of crystallization is a lot smaller. Early diffusion of element is done with a mechanism different than the configurational rearrangements of the liquid sate. The global density and small size of the crystals within the Ca rich matrix confirmed that it would be a profitable waste form for minor actinides. (authors)

[en] We present millimeter-scale numerical studies we have performed about laser-plasma interaction. We have developed for that purpose a specific software, which we call Hρα (Hera) and that we use for studying filamentation, Brillouin and Raman instabilities. We assume the paraxial wave propagation and bi-temperature quasi-neutral fluid approximations. A brief description of the main models within Hρα, as well as some computation results, are presented. First simulations present realistic backscattering rates and intensity profiles which might be compared to experimental results. (authors)

[en] For the first time indirect drive ignition targets have been designed with the constraint of limiting laser-plasma instabilities. The amplification of these instabilities is directly proportional to the luminous flux density, it means to the sizes of the focal spots too. This study shows that increasing the sizes of the focal spots does not reduce linear amplification gains in a proportional way because the global optimization of the target implies changes in hydrodynamical conditions that in turn have an impact on the value of the amplification gain. The design of the target is a 2-step approach: the first step aims at assuring a uniform irradiation and compression of the target. The first step requires information concerning the laser focusing spots, the dimensions of the hohlraum, the inert gas contained in it, the materials of the wall. The second step is an optimization approach whose aim is to reduce the risk of laser-plasmas instabilities. This optimization is made through simulations of the amplification gains of stimulated Raman and Brillouin backscattering. This method has allowed us to design an optimized target for a rugby-shaped hohlraum. (A.C.)

[en] Zirconolite-based (nominally CaZrTi₂O₇) glass-ceramics belonging to the SiO₂Al₂O₃-CaO- ZrO₃-TiO₂ system are good waste forms for the specific immobilisation of actinides. The understanding of their crystallisation processes implies to investigate the structure of the glass. Thus, the environment around Ti, Zr (nucleating agents) and Nd (trivalent actinides surrogate) was characterised in parent glasses. Electron spin resonance (ESR) study of the small amount of Ti³⁺ occurring in the glass enabled to identify two types of sites for titanium: the main one is of C_4v or D_4h symmetry. EXAFS showed that Zr occupied a quite well defined 6-7-fold coordinated site with second neighbours which could correspond to Ca/Ti and Zr. Nd environment was probed by optical spectroscopies (absorption, fluorescence), ESR and EXAFS. All these techniques demonstrated that the environment around Nd was very constrained by the glassy network. Notably, Nd occupies a highly distorted 8-9-fold coordinated site in the parent glass. (authors)

[en] New nuclear glass compositions, able to immobilize highly active liquid wastes arising from high burn-up UO₂ fuel reprocessing, are being studied. Investigations are being performed on rare earth rich glasses, known as durable matrices. After a preliminary study, a basic glass composition was selected (Glass A, wt. %): 51.0 SiO₂ - 8.5 B₂O₃ - 12.2 Na₂O - 4.3 Al₂O₃ - 4.8 CaO - 3.2 ZrO₂ - 16.0 Nd₂O₃. The aim of this study is to determine the local environment of the rare earth in this glass and its evolution according to neodymium. To achieve this objective, glasses were prepared from the baseline Glass A with variable neodymium oxide amounts (from 0 to 30 wt. % Nd₂O₃). By coupling characterization methods such as EXAFS (Extended X-Ray Absorption Fine Structure) spectroscopy at the neodymium LIII-edge, optical absorption spectroscopy, ¹¹B, ²⁷Al MAS-NMR and Raman spectroscopy, pieces of information the rare earth surroundings in the glass were obtained. (authors)

[en] The stationary ray tracing method, commonly used in hydrodynamic codes to describe the laser propagation and energy deposition, is reformulated to include energy exchanges between laser beams, referred to as cross-beam energy transfer (CBET), as well as laser beam backscatterings from acoustic (Brillouin) and electron (Raman) plasma waves. These energy exchanges and scatterings are described by a Monte Carlo method simulating the creation/annihilation of rays. The algorithm has been validated against other numerical solvers and, in the case of CBET, by means of kinetic simulations. The method is efficient and can be easily implemented in already existing ray tracing packages used in many hydrodynamic codes. It can be further extended to describe other kinds of wave mixing processes such as side-scatterings and collective scatterings. (authors)

[en] Published in summary form only