Laboratoire d'Énergétique Moléculaire et Macroscopique, Combustion

The concept of a safe geological repository for managing radioactive waste relies on a multi-barrier system comprising both the host rock and various engineered barriers, these latter being referred to as the engineered barrier system (EBS). The robustness of the EBS depends directly on the materials used, which play a crucial role in ensuring its performance. These materials must demonstrate exceptional durability, stability, and compatibility with the host rock and the types of waste expected in the future repository. Moreover, they must remain intact over timescales ranging from hundreds to thousands of years, depending on the repository’s design.Regardless of the repository concept, a disposal container is required to encase the primary HLW package. Currently, reference materials are primarily metals such as steel or copper. In the case of steel, particularly carbon steel, one significant drawback is the production of H₂(g) during corrosion under anoxic conditions. Minimising or eliminating this phenomenon would facilitate easier and even safer waste management within the disposal facility. This issue is a key motivation for exploring alternative solutions, such as ceramic materials, which do not generate gas when altered.Research on ceramics as alternatives to metals began in the late 1970s and has periodically regained interest. However, the topic has largely been addressed conceptually, with few concrete research programmes dedicated to tackling this challenge. Since the mid-2000s, Andra has initiated a long-term R&D programme to assess the technical feasibility of a ceramic HLW container that meets the safety requirements of the Cigéo repository concept.This presentation aims to provide an overview of global research activities related to ceramic options for HLW containers, with a particular focus on the Cigéo concept. Both bulk ceramics and ceramic coatings will be considered. The advantages and limitations of these solutions will be discussed, along with potential approaches to address identified challenges. It is important to note that this contribution does not seek to provide exhaustive details on all related topics but rather offers a scientific and technical overview of ongoing work in this field, which may be of interest to stakeholders in the field of radioactive waste geological disposal.

Abstract Aircraft engine manufacturers develop new combustion technologies to comply with stricter regulations on pollutant emissions such as nitrous oxides (NOx) or soots. Staged systems coupled with lean premixed combustion show promising prospects to reduce these emissions through correct mixing of the fuel ahead of the combustion chamber but are more prone to thermo-acoustic instabilities. Hence guaranteeing the stability over the entire operating range is more challenging. The thermo-acoustic behaviour of lean staged systems is investigated experimentally on the laboratory-scale BIMER combustor, an atmospheric pressure test rig composed of a two-stage swirled injector reminiscent of industrial systems and fuelled with liquid dodecane. It uses a simplex atomizer in the pilot stage, multipoint injection in the main stage and can be externally forced using a siren device located upstream of the injector. This study focuses on the thermo-acoustic behaviour of the pilot stage of the BIMER combustor. Flame response to acoustic perturbations at different pre-heating temperatures (ranging from 383 to 473K) is assessed. To this end, Flame Describing Functions (FDF) are measured using acoustic forcing, a photomultiplier with an OH* filter for heat release rate fluctuation measurements and the multi-microphone method to determine acoustic velocity fluctuations. An acoustic network model of the combustor using the L-ζ model for the injector is used to compute acoustic velocity fluctuations at the base of the flame. This model is parameterised using only the burner geometrical configuration, with no tuning to fit reference experimental data. The accuracy of the model prediction is discussed. Measurements also display flame shape bifurcations from V to Tulipshape flames generated by acoustic forcing at certain frequencies and amplitudes. High-speed imaging of flame chemiluminescence in the visible range is used to describe these bifurcations. The role of acoustic forcing is highlighted through phase-averaging.

This work presents the development of a protocol for the measurement of collisional deexcitation rate constants of N$_2$(C$^3\Pi_u$ , $\nu$ = 0-4) States by O$_2$, N$_2$, H$_2$, CO$_2$ and CH$_4$. Excited nitrogen is produced using nanosecond repetitively pulsed discharges. The applied voltage and the repetition frequencies are adjusted to minimize rotational and gas heating while keeping high electronic and vibrational excitation levels. The populations of the vibrational levels are measured using optical emission spectroscopy of the N$_2$(C $\to$ B,$\Delta_\nu=0$) vibrational bands. Rate coefficients for each vibrational level are then determined from the measured lifetimes. The results are compared to the available literature and new values are provided for the missing vibrational levels.

Rationale: Idiopathic pulmonary fibrosis (IPF) is a debilitating lung disease characterized by excessive deposition of extracellular matrix (ECM), resulting in lung function impairment. Heparan sulfate mimetics (HSm) have been suggested to have potential antifibrotic effects by regulating ECM. This study aims to investigate the impact of a specific HSm named OTR4120 on fibrotic processes in ex vivo, in vitro and in vivo models. Methods: Human Precision Cut Lung Slices (hPCLS) treated with a fibrotic cocktail alone or with OTR4120 were evaluated using second-harmonic imaging microscopy (SHIM) to assess collagen deposition. Human embryonic fibroblast WI-38 cell line and primary fibroblasts obtained from human donors were differentiated into myofibroblasts (MYF) using TGF-beta1 and treated with OTR4120 or a control vehicle. Gene expression analysis for MYF markers was performed using quantitative PCR (qPCR). Protein expression of MYF markers was evaluated using immunofluorescence techniques. Bulk-RNA sequencing analysis on WI-38 cells cultured under different experimental conditions was conducted. Finally, the therapeutic effects of OTR4120 on a bleomycin-induced fibrosis mouse model were investigated. Results: SHIM analysis on OTR4120-treated hPCLS showed a decrease in collagen deposition. OTR4120 treatment of primary fibroblasts and WI-38 cells exposed to TGF-beta1 significantly reduced the expression of MYF markers. Bulk-RNA sequencing analysis on OTR4120-treated WI-38 cells showed significant impacts on fibrosis-related processes. Therapeutic application of OTR4120 in vivo to bleomycin-induced fibrosis mice resulted in enhanced fibrosis resolution. Conclusion: OTR4120 has potential therapeutic benefits as an antifibrotic agent in the context of lung fibrosis. Further investigations are necessary to understand the precise mechanism through which OTR4120 exerts its antifibrotic effects.

Nitric oxide (NO) was generated inside capillary microwave discharges of 1-mm diameter, operating at 2.4 ÷ 2.5 GHz in mixtures of argon and air at atmospheric pressure. Time-resolved Mid-IR Quantum Cascade Laser Absorption Spectroscopy (QCLAS) was employed to measure the absolute density of NO molecules in ex situ conditions. The capillary post-discharge was coupled into a 50-cm White multi-pass cell where the laser was scanned over the ro-vibrational transition R (6.5), v(0→1), in the NO electronic ground state X1/2 at 1900.076 cm−1. It was found that NO density can be tuned over three orders of magnitude by varying the gas mixture and the discharge power. Enhancing the heat flux through the capillary has significantly extended the operating range of the discharge, increased the NO density and flowrate by almost one order of magnitude, and consequently reduced the energy cost. Molar fractions of NO up to 3,000 ppm (7.1 × 1016 cm−3) with flowrates up to 7.2 sccm for discharge powers below 100 W have been obtained. Using a thermally controlled configuration, the energy cost of NO was found to be comparable to other efficient plasma sources at atmospheric pressure.