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[en] Highlights: • Presentation of many experimental local data for different configurations. • Highlight of the influence of numerical parameters used in the CFD code. • Validation of the CFD code ANSYS CFX on the basis of experimental data. - Abstract: The objective of this study is to validate the ANSYS CFX version 12 computational code on the basis of light gas dispersion tests performed in two ventilated rooms. It follows an initial study on heavy gas dispersion carried out by Ricciardi et al. (2008). First, a study of sensitivity to various numerical parameters allows a set of reference data to be developed and the influence of the numerical scheme of advection to be revealed. Second, two helium (simulating hydrogen) dispersion test grids are simulated for the two rooms studied, and the results of the calculations are compared with experimental results. The very good agreement between these results allows the code and its dataset to be validated for this application. In future, a study with higher levels of helium (on the order of 4% vol at equilibrium) is envisaged in the context of safety analyses related to the hydrogen risk, these levels representing the lower explosive limit (LEL) of hydrogen.
[en] This study takes place within the framework of nuclear facilities containment assessment. The aims are to determine gaseous flow, two-phase flow and aerosol deposition models through a crack network by using the most realistic and representative crack network characteristics. For this, the crack network is considered as two infinite parallel plates. First of all, airflow experiments are performed on three concrete walls (128 cm in width, 75 cm in height and 10 cm in thickness), cracked by shear stresses. The results enable determining aeraulic crack network characteristics, thanks to the Poiseuille model in laminar compressible flow, and elaborating an experimental friction factor correlation for the transition flow, validated up to a Reynolds number of 250. Next, aerosol deposition experiments were performed with one of the previous concrete walls in order to determine a global aerosol deposition model in a crack network. The first experiments with an aerosol diameter of 60 nm showed that the aeraulic crack network characteristics are suitable for the aerosol physics. Therefore, geometrical crack network characteristics were determined by using several types of experiment and enable - thanks to aerosol deposition experiments - constituting and validating a global model of aerosol deposition in a crack network
[en] The general context of the article is to evaluate strategies that can be used to mitigate aerosols dispersion during the fuel debris or corium retrieval of Fukushima damaged reactors. IRSN is involved in a project led by ONET Technologies along with CEA to provide relevant information's to analyze the risk of aerosol resuspension induced by fuel debris retrieval. The knowledge of the aerosol source term emitted during fuel debris retrieval operations is one of the key issues for the assessment of aerosol dispersion that can lead to the release of radionuclides into the environment and also to define efficient strategy to mitigate this risk. Spray scrubbing tests are performed in the TOSQAN facility to evaluate the scavenging coefficients of aerosol particles whose size distribution is representative of the one released during the cutting of fuel debris. The main objective of this work is to determine the relevant characteristics of the spraying system that allow to achieve the best efficiency regarding Fukushima site implementation constraints. For safety issues, the scavenging coefficients will also allow to assess the remaining airborne aerosol fraction and provide input data for the design of filtration systems ensuring the containment of radioactive material. (author)
[en] The general context of the article is related to the development of the laser cutting technique for the fuel debris retrieval on the damaged reactors of Fukushima Dai-ichi. IRSN and CEA are involved in a project, led by ONET Technologies, to develop technologies for fuel debris retrieval and to bring relevant elements to analyze the risk occurred by the dispersion of aerosols emitted by the dismantling operations. Results regarding the characterization of the aerosols source term emitted during laser cutting of non-radioactive fuel debris simulants were acquired during experiments undertaken in the DELIA cutting laser platform from CEA. IRSN realized aerosol sampling, aerosol size distribution measurement and evaluation of aerosols collection efficiency versus water level. The performed evaluations will enable the Japanese teams responsible for retrieving fuel debris or corium from the damaged reactors of Fukushima Dai-ichi to define the best strategies to implement containment, and ultimately to limit the dissemination of radionuclides into the environment. (author)
[en] Highlights: • Development of an analytical model for assessing the well-mixing length of a tracer in a duct airflow. • Validation on data from in situ experiments. • Model simplification for proposing correlations more suitable for the industrial issue. - Abstract: The aim of this study is to propose an analytical model for assessing the well-mixing length of a tracer in a ventilation duct. The first part of the article is devoted to describe an experimental bench developed for validating the proposed model. This bench allows to follow the evolution of a tracer injected at a source point in the center of a duct by using an original optical measurement technique. In a second part, an analytical model for the spatial evolution of a tracer concentration in a circular duct is developed, taking into account an eddy viscosity model. The difficulty for applying this model to industrial cases led us to propose a simplified version that can be used for a non-dimensional distance greater than 20 diameters. The latter was then inverted in order to access to two criteria: the coefficient of variation in the duct section and the difference between the local measured concentration and the expected homogeneous concentration. Each one has its interest depending on whether a global information on the duct section or a local information (on the axis for example) at a given distance is required.
[en] The Committee on the Safety of Nuclear Installations (CSNI) formed the CCVM (Containment Code Validation Matrix) task group in 2002. The objective of this group was to define a basic set of available experiments for code validation, covering the range of containment (ex-vessel) phenomena expected in the course of light and heavy water reactor design basis accidents and beyond design basis accidents/severe accidents. It was to consider phenomena relevant to pressurised heavy water reactor (PHWR), pressurised water reactor (PWR) and boiling water reactor (BWR) designs of Western origin as well as of Eastern European VVER types. This work would complement the two existing CSNI validation matrices for thermal hydraulic code validation (NEA/CSNI/R(1993)14) and In-vessel core degradation (NEA/CSNI/R(2001)21). The report initially provides a brief overview of the main features of a PWR, BWR, CANDU and VVER reactors. It also provides an overview of the ex-vessel corium retention (core catcher). It then provides a general overview of the accident progression for light water and heavy water reactors. The main focus is to capture most of the phenomena and safety systems employed in these reactor types and to highlight the differences. This CCVM contains a description of 127 phenomena, broken down into 6 categories: - Containment Thermal-hydraulics Phenomena; - Hydrogen Behaviour (Combustion, Mitigation and Generation) Phenomena; - Aerosol and Fission Product Behaviour Phenomena; - Iodine Chemistry Phenomena; - Core Melt Distribution and Behaviour in Containment Phenomena; - Systems Phenomena. A synopsis is provided for each phenomenon, including a description, references for further information, significance for DBA and SA/BDBA and a list of experiments that may be used for code validation. The report identified 213 experiments, broken down into the same six categories (as done for the phenomena). An experiment synopsis is provided for each test. Along with a test description and references, the synopsis also identifies the availability of the report and data, phenomena covered by the test, type of test (separate effect, combined effect or integral test), covers DBA and/or SA/BDBA conditions, range of key experimental parameters and past code validation/ benchmarks. This CCVM has identified experiments for 93% of the phenomena requiring validation. However, if only experiments suitable for CFD validation are considered, then only about half of the phenomena are covered by this CCVM. It is recommended that this work be reviewed in 5 years time to include new experiments and to attempt to close the identified experiment gaps (phenomena lacking suitable experiments for validation). (authors)