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International audience; The SPARCLING JIP was launched by TOTAL, AIR LIQUIDE, SHELL, GRTgaz & INERIS. The goal of the project was to produce high-quality experimental data on the size distribution and velocities of the LNG droplets using a dual PDA (Phase Doppler Anemometer), following the pressurized release of LNG. One area of particular concern is the potential for rainout and subsequent pool dispersion. The test programme was managed and run by INERIS at their test site at Verneuil-en-Halatte on behalf of the members of the JIP. The paper describes in detail the testing bench and test protocol, as well as the lessons learned from the use of the bench. The occurrence of rainout is then discussed.

Several approaches exist nowadays to predict fire consequences in enclosures, from the simplest algebraic correlations to the more complex CFD models. A quick analysis of the interests and limits of those different approaches highlights the great interest of CFD approaches to take into account numerous important parameters such as geometry, fire ventilation or heat transfer.

Flammable and toxic gas dispersion is a key issue when designing the potential consequences of industrial accident. While resulting distances for land use planning are important, models used nowadays are quite simple. It should be reminded that several levels of approach could be used for the cloud dispersion modelling. The simplest is Gaussian models based on dispersion coefficients fitted using experimental data. Integral models enable the user to model this phenomenon quite more precisely using a simplified 1D solution of fluid flow equation in the vicinity of the release, then, for larger distances, those models used a Gaussian like approach. For those two families of model, obstacles are represented using a global ground roughness. For configurations with distributed non-regular obstacles, 3D models, as CFD or LPDM, suit better. Those models enable taking into account the different obstacles with their real characteristics and their distribution on the ground. Using those models let the user able to capture specific phenomena as for example turbulence induced by the obstacles and resulting mixture and canyon effect that can reduce dispersion. While those 3D models are more and more required regarding the importance of consequence area, two main issues remain. First, very few data are available for validating those codes in an urban like configuration. Most of large-scale experimental campaigns were achieved in free filed configuration or with regularly distributed obstacles, configuration that is relevant for Gaussian or integral validation but not for pointing out the interest and specificity of 3D models. Data available in urban like area are based on small scale wind tunnel experiments with the obvious scale effect limitation. Furthermore, since few experiments were achieved in such a configuration, some physical phenomena as the interaction between atmospheric boundary layer (ABL) and large obstacles were not studied in detail. Then, after a description of this state of the art, this paper presents an experimental campaign that aims to provide reference experimental measurement in urban like area at large scale. This campaign will also offer the opportunity in studying some specific phenomena concerning the interaction of ABL with an urban geometry.

In the deep geological repository for radioactive waste in France, the Intermediate Level Long Lived Waste (ILLW) is planned to be disposed in ILLW emplacement drifts that are several hundred meters long. Inside the drift, primary nuclear waste packages received from producer is packed in concrete disposal containers which are stacked. Each disposal container contains one or several primary nuclear waste packages. Both the disposal containers and the primary nuclear waste packages contain various components that can react chemically or radiologically as e.g., by radiolysis, corrosion. These processes may consume or form oxygen and hydrogen gas. The mixture of both of those gas phase components poses the risk for an oxyhydrogen explosion (ATEX). The behavior of oxygen and hydrogen is thus a major concern for the operational safety of the repository and reversible phases with an envisaged duration of roughly one hundred years. Free oxygen is introduced to the system through ventilation of the access galleries and open emplacement drifts while at the same time, radiolysis of organic waste produces hydrogen and corrosion of concrete reinforcement, disposal container envelopes, and metallic elements in the waste may consume oxygen or produce hydrogen. The purpose of the present study is to determine the gas migration path and concentrations in ILLW disposal containers in particular with respect to hydrogen and oxygen concentrations and the induced risk for explosion. In order to characterize the relevant two-phase hydraulic conditions, two kinds of work have been undertaken. On the one hand, a numerical model was constructed and simulations were performed. On the other hand, gas release experiments have been conducted on a full scale demonstrator of an ILLW disposal container. The joint analysis of numerical simulation and experimental results improved the understanding of the gas transport processes and will allow for the optimisation of the design to avoid ATEX. For the numerical model, a two-phase multi-component thermo-hydraulic model was developed. The model geometry is based on the CAD model of the disposal containers and consists in a 3-dimensional representation of the disposal container and the waste packages (Figure 1). Interstices at e.g., container's lid and body are modelled explicitly. The components of the liquid phase are water, dissolved oxygen, dissolved hydrogen, and dissolved nitrogen. Equivalently, the gas phase consists of water vapour, nitrogen, oxygen, and hydrogen. Simulations are non-isothermal, since the emplacement tunnel and the waste container are not initially at thermal equilibrium. The emplacement conditions are considered by appropriate boundary conditions. During the exploitation phase, ventilation is taken into account in order to represent exchanges with the environment as e.g., the drying of the concrete as accurately as possible. The hydrogen formed by radiolysis, is modelled by source terms located inside the primary waste packages. The model was implemented with a custom made version of TOUGH2- MP, allowing for a material-dependant generalised Millington-Quirk representation of diffusion and its dependence on saturation and porosity. Reference calculations as well as numerous sensitivity studies were performed. The results On the experimental side, the setup is the CS4 (Andra nomenclature) concrete disposal container, which has been equipped with a gas injection line source at the location of the primary waste packages where either helium or hydrogen can be injected. Some experimental gas injection sequences have been defined, ranging from several days to several months. Those sequences have been applied successively with two different types of contacts between the disposal container's body and lid. First, the container was closed with screws and, in a second phase, the container's lid was sealed with concrete. Specific dynamic chambers [1] have been installed at several locations of the container in order to measure hydrogen or helium outflowing gas rates and to deduce concentrations by the molar mass balance method. Moreover, the environmental conditions (temperature, humidity, atmospheric pressure) are carefully measured. The measurements performed during first experiments with a screwed lid showed that the body-lid interstice is by far the most preferential escape flow path of the injected gas. This was confirmed by further tests where this interstice was temporarily confined. Thanks to the numerous measurement points, experiments also allowed to establish a cartography of the gas outflow through the container walls, distinguishing zones in function of the local effective thickness of the concrete. Following the first experimental results, the numerical model was adapted to better correspond to the experimental setup and sequences. In particular, the representation of the interstices and the concrete with its two-phase properties had to be reconsidered. Also, an evaluation of the impact of the dynamic chambers on the system behaviour was conducted and the boundary conditions were adapted to correspond to the experimental setup. This interplay between numerical modelling and experiments has improved the interpretation of the gathered experimental data and has improved the overall systems understanding of hydrogen and oxygen flow and transport processes in ILLW containers designed for a clay repository.

In the framework of land use planning, massive releases have to be modelled considering they generate important toxic effect distances. The common way to deal with such scenarios is currently based on Gaussian models or, more recently, CFD codes based on a RANS turbulence model. While the first does not enable taking account of the environment with a high level of precision, the second are not suitable for accounting for Atmospheric Boundary Layers (ABLs) anisotropy. Using LES CFD approaches then appears nowadays as promising to overcome those difficulties. However it is necessary to perform the best input parametrization among a large variety of method (recycling method, synthetic method, forcing method) to generate appropriate inflow boundary conditions. The objective of this paper is to present results obtained with the open source LES CFD code FDS by using synthetic eddy method. Parameterizations to generate inlet conditions were tested and compared to large scale INERIS ammonia releases. Comparison with the RANS CFD model Code_Saturne and the shallow layer SLAB model are also presented and discussed.

Pollutant dispersion in stable atmospheric conditions is still a phenomenon that is highly difficult to model or to reproduce in an experimental wind tunnel. However, such conditions are of major interest in the field of risk assessment because they are generally conservative and the low level of turbulence induces the most important distance for toxic impact. Using LES approach appears relevant and promising to overcome difficulties related to stable conditions modelling. The objective of this paper is to present the preliminary results obtained in terms of wind flow modelling with the open source CFD code FDS, from NIST, which is based on Large Eddy Simulation approach. It is essential to determine the best parameterization of this type of code for atmospheric gas dispersion modelling. Starting from atmospheric flow conditions that were observed during INERIS experimental campaign of ammonia release, the process related to satisfy this requirement will be presented.