This article is devoted to high level waste management. A synthesis of the high level waste (HLW) typology and key characteristics is given, showing that nuclear glass and spent nuclear fuel need to be considered for long term disposal, depending on national strategies. A rationale for selecting a relevant conditioning process is then presented, describing the parameters and constraints to take into account. A brief description of the vitrification processes, the sole industrially deployed conditioning process for HLW, is then presented. The vitrified waste interim storage strategy is described. The knowledge about the long term performance of HLW, spent nuclear fuel and nuclear glass, in geological disposal is then detailed. Finally, the development of alternative conditioning processes for HLW are briefly presented.

In the presence of “Ag2O” as a promoter, γ-MnO2 traps dihydrogen in its (2 × 1) and (1 × 1) tunnels. The course of this reaction was examined by analyzing the X-ray diffraction patterns of the HxMnO2/“Ag2O” system (0 ≤ x < 1) on the basis of pair distribution function and density functional theory (DFT) analyses. Hydrogen trapping occurs preferentially in the (2 × 1) tunnels of γ-MnO2, which is then followed by that in the (1 × 1) tunnels. Our DFT analysis shows that this process is thermodynamically favorable.

γ-MnO 2 is a material formed by random intergrowth of two phases, β-MnO 2 and R -MnO 2 . It is demonstrated here on seven γ-MnO 2 samples that pair distribution function analysis using a conventional X-ray diffraction setup (Bragg–Brentano geometry with a molybdenum anode) allows the quantification of this intergrowth simply via a simulation of the actual material by a mixture of β-MnO 2 and R -MnO 2 phases. Although this method does not take into account specifically the relaxed distances in the vicinity of the intergrowth zone, it is found to be very robust, accurate and in full agreement with the widely used quantification based on the empirical approach of Chabre & Pannetier [ Prog. Solid State Chem. (1995), 23 , 1–130].

This article presents a study on the influence of the pore size distribution on gas diffusion through CEM V cement pastes, for different water saturation degrees. The numerical results are compared to the experimental hydrogen diffusion coefficients obtained with water saturation levels ranging from 20% to 95%. The model developed in our research group accounts for the various types of transfer through the pore network: Knudsen diffusion or molecular diffusion depending on the pore size, together with hydrogen diffusion through water. The virtual pore network is created from mercury porosimetry data as a result of the combination of different sizes pore families. By testing different combinations, we could propose pore arrangements leading to diffusion coefficients corresponding to the experimental ones, and show how the combinations of the biggest pore family contribute to control the gas diffusion process.

We investigate the influence of MnO2 polymorphism form on MnO2/Ag2O hydrogen getter. The results show that the performances strongly depend on the polymorphism form of manganese oxide. The nsutite γ-MnO2 phase, which consists of a random intergrowth of MnO2–ramsdellite and MnO2–pyrolusite building blocks, shows the more promising performances to trap H2 via the formation of hydroxyl groups. This observation is especially relevant for compounds with a low pyrolusite/ramsdellite ratio and a high rate of microtwinnings.

The dismantling of uranium natural graphite gas nuclear reactor generates a large volume of fuel cladding. The fuel cladding materials are based on Mg–Zr alloy for UNGG. The dismantling strategy could be to encapsulate these wastes into an ordinary Portland cement (OPC) or Na-geopolymer (alumino-silicate material) in a form suitable for storage. Corrosion behavior of Mg–Zr in OPC interstitial solution and activating solution of Na-geopolymer has been studied in the presence and absence of sodium fluoride as corrosion inhibitor. Electrochemical methods have been used to determine the corrosion densities. Results show that the corrosion densities of Mg–Zr alloy in OPC solution are one order of magnitude more important than in activating solution of Na-geopolymer and sodium fluoride addition decreases corrosion densities in OPC interstitial solution. Hydrogen evolution of encapsulated Mg–Zr alloy has also been measured in both OPC and Na-geopolymer and results show that Na-geopolymer matrix appears to be an attractive binder in term of corrosion performance.

The dismantling of UNGG nuclear reactor generates a large volume of fuel decanning. These materials are based on Mg-Zr alloy. The dismantling strategy could be to encapsulate these wastes into an ordinary Portland cement (OPC) or geopolymer (aluminosilicate material) in a form suitable for storage. Studies have been performed on Mg or Mg-Al alloy in basic media but no data are available on Mg-Zr behaviour. The influence of representative pore solution of both OPC and geopolymer with Mg-Zr alloy has been studied on corrosion behaviour. Electrochemical methods have been used to determine the corrosion densities at room temperature. Results show that the corrosion densities of Mg-Zr alloy in OPC solution is one order of magnitude more important than in a geopolymer solution environment and the effect of an inhibiting agent has been undertaken with Mg-Zr alloy. Evaluation of corrosion hydrogen production during the encapsulation of Mg-Zr alloy in both OPC and geopolymer has also been done.

The synthesis of lanthanum phosphates in molten LiCl-KCL eutectic was chosen to address the preliminary treatment of chlorinated wastes containing fission products that are already present in a Li/Cl eutectic. The obtained monazite compound shows interesting properties to be considered as a good candidate to trap lanthanum for a long-time. The synthesis route based on LaCl(3) reaction with NH(4)H(2)PO(4) in a stoichiometric amount is a key point to obtain monazite as a pure phase. Hence, the salt composition is not modified during the synthesis reaction. The chemical reactivity of ammonium dihydrogenphosphate (NH(4)H(2)PO(4), hereafter abbreviated ADP) toward lanthanum chloride (LaCl(3)) in molten LiCl-KCl eutectic is probed by NMR spectroscopy to follow the formation of LaPO(4). Formally, a direct transformation of the two aforementioned precursors into LaPO(4), NH(4)Cl and HCl can be discarded on the basis of the low thermal stability of ADP. To shed some light on the formation of LaPO(4), in situ and ex situ NMR experiments were carried out on LiCl-KCl/LaCl(3)/ADP, as well as LiCl-KCl/ADP, KCl/ADP, and LiCl/ADP mixtures. First, the reactivity of the precursors in contact with the eutectic was studied from room temperature to 600 degrees C by means of (31)P, (35)Cl, and (139)La high temperature NMR. Second, ex situ room temperature magic angle spinning (MAS) and RadioFrequency driven recoupling (RFDR) (31)P solid-state NMR experiments were carried out on solid samples prepared in different conditions (i.e., temperature and atmosphere) and quenched at room temperature to identify frozen intermediate species in their metastable state. On the basis of this approach, we propose a model for the LaPO(4) formation based on a multistep mechanism which highlights the strong reactivity of ADP toward the alkaline salts but without final change in the composition of the solvent.

Spinel cobalt oxide nanoparticles have been nanocasted inside the pores of a SBA-15 silica using the “two solvents” technique, which implies that the silica is pre-wetted with an alkane solvent before loading the pores with an aqueous solution carrying the precursor, a nitrate salt, of the desired particle composition. TEM analysis of the samples, comparing the effect of four different solvents (n-pentane, n-hexane, n-heptane and cyclohexane), showed that the nanoparticles’ size, shape and dispersion within the silica support differ as a function of the non-polar solvent. N2 sorption, XRD and SAXS experiments have been carried out to confirm this phenomenon by more statistical data.

The precipitation of rare earth phosphates (RE = La, Ce, Pr, Nd, and Lu), from RECl3 was investigated in molten LiCl–KCl eutectic at 500 °C in air. Ammonium dihydrogenphosphate (NH4H2PO4) was used as the phosphorus precursor. X-ray diffraction analysis indicated the formation of compounds with monazite (La, Ce, Pr, and Nd) or xenotime (Lu) structures. 31P NMR spectroscopy measurements confirmed that lanthanum formed pure monazite, which indicates a LaCl3 → LaPO4 conversion factor near 100%. These results demonstrate that the stoichiometric addition of NH4H2PO4 is sufficient to obtain quantitative precipitation at 500 °C of anhydrous rare earth phosphates in molten LiCl–KCl. The use of this type of precursor, which has the advantage of not modifying the chemical composition of the medium after recovery of the rare earth phosphates, could be considered during the first step of purification of chlorinated baths containing fission products arising from spent fuel reprocessing by a pyrochemical process.

Progress on separating the long-lived fission products has notably implied basic research on specific host matrices, especially for the immobilization of cesium. Barium hollandite (BaAl2Ti6O16) ceramics have received considerable interest because of their high cesium incorporation ability and chemical stability. This study deals with the preparation of hollandite in the BaxCsy(Al,Fe)2x+yTi8–2x-yO16 (x+y<2) compositional range by an oxide route. Different parameters such as the grain size of the precursor or the temperature and duration of sintering were changed in order to optimize ceramics synthesis. To estimate the hollandite radiation resistance, external electron irradiation experiments (simulating the β particles emitted by radioactive cesium) were performed on hollandite of simple composition. The irradiation-induced defects were studied by Electron Paramagnetic Resonance (EPR) spectroscopy and their nature is discussed.