Remarkable hydrogen storage properties of MgH2 doped with VNbO5

The present work concerns the catalytic effect of VNbO5, a ternary oxide prepared via a solid-state route, on the sorption performance of MgH2. Three doped systems, namely 5, 10 and 15 wt% VNbO5– MgH2 have been prepared by ball milling and thoroughly characterized. Hydrogen sorption, evaluated by temperature programmed desorption experiments, revealed a significant reduction of the desorption temperature from 330 1C for the un-doped sample (prepared and tested for comparison) to 235 1C for the VNbO5-doped sample. Furthermore, more than 5 wt% of hydrogen can be absorbed in 5 minutes at 160 1C under 20 bar of hydrogen, which is remarkable compared to the 0.7 wt% achieved for the un-doped system. The sample doped with 15 wt% of additive, showed good reversibility: over 5 wt% of hydrogen with negligible degradation even after 70 consecutive cycles at 275 1C and 50 cycles at 300 1C. The kinetics analysis carried out by Kissinger’s method exhibited a considerable reduction of the activation energy for the desorption process. Finally, pressure-composition-isotherm experiments conducted at three different temperatures allowed estimating the thermodynamic stability of the system and shed light on the additive role of VNbO5

Stochastic approach to hydraulic barrier design: an example in northeastern Italy

Volatile organic compounds, groundwater contamination, multi-layered aquifer syste

Phenomenology of liquid metal thermal-hydraulics

The cooling system of the Energy Amplifier (EA) is based on a Lead flow driven by natural circulation [1]. In the Energy Amplifier Demonstration Facility (EADF) a Lead-Bismuth eutectic is used and natural circulation, although enhanced through a gas injection system, is the pumping force for the cooling of both the target (only in the case of the window-type target) and the primary circuit[2]. Numerical simulation is extensively used for the design and analysis of these flows, using both commercial and in-house codes. However, liquid metals properties are very different from that of common fluids, so the physical models to be used in the simulations should be carefully assessed. In general the numerical simulation of any kind of flow requires: (i) the thermodynamic modelling of the fluid; (ii) the fluid dynamics governing equations; (iii) the turbulence modelling. In this work the thermodynamic model for heavy liquid metals is presented, starting with the derivation of the equations of state for a general fluid from the basic laws of thermodynamics. This thermodynamic model is then used for the analysis of a one-dimensional natural convection loop, in order to put in evidence the main physical mechanisms governing this particular kind of flow and the simplifications that can be applied to the one dimensional governing equations. An extensive analysis of the tree-dimensional fluid dynamic governing equations and of the turbulence models for liquid metal flows can be found in [7] and [8] respectively

Numerical methodologies for the simulation of liquid metal flows

The fluid-dynamic modelling for the simulation of the Lead-Bismuth flow in the EADF was reviewed. The general form of the non-dimensional governing equation was derived, and the analysis of the orders of magnitude of the different terms in the case of a the liquid metal flows in the EADF was performed, through a flow-Mach number asymptotic analysis. It was found that the resulting form of the equations is the one commonly used in commercial CFD codes for the simulation of liquid flows, which can then be used for our applications. The most common numerical methods for flow-Mach number applications were also presented. These methods are general and can be applied to liquid metal flows without any modification. The peculiarity of the numerical simulation of liquid metal flows lies in the modelling of the turbulent heat transfer, due to the flow Prandtl number of this type of fluids. This subject is discussed in [21]

Integration of numerical tools for the combined thermal-hydraulics and structural analysis of energy amplifier components

The CRS4 R&D activity on the Energy Amplifier Demonstration Facility (EADF) [1] concerns the thermal fluid-dynamic and structural computational analysis in support to the design of some of the crucial components of the machine. We are currently studying the operating conditions of the spallation target [2-3] and the sub-critical core [4-5], including steady state, transient [31-32] and accidental conditions. The simulation activity also includes the analysis of multi-phase (liquid-gas systems with high void fractions) [6-7] and free surface Liquid Metal (LM) flows [8-9]. A parallel activity of benchmarking of numerical codes on LM experiments is in progress [10-12, 33-34], joined with a critical theoretical review of numerical models applied to LM flows [13-15]

Thermo-mechanical stresses on the beam window

The Centre for Advanced Studies, Research and Development in Sardinia (CRS4) is participating to an Italian R&D program, together with Ansaldo, ENEA and INFN, devoted to the design of a 80 MW prototype of the Energy Amplifier proposed by C. Rubbia. The use of advanced numerical tools has been of practical support in the design of critical elements of the machine such as the fuel element and the beam target. The aim of this work is to study the sensitivity of beam window stresses to the beam distribution, size and interruption. In order to compute thermal stresses, the heat deposition in the window and in the coolant generated by the interaction with the proton beam is calculated and used as input data for the fluid dynamic simulation of the natural convection flow of the target coolant

Numerical studies related to the design of the beam target of the energy amplifier prototype

The Centre for Advanced Studies, Research and Development in Sardinia (CRS4) is participating in an Italian R&D program, together with Ansaldo, ENEA and INFN, devoted to the design of a 80 MW prototype of the Energy Amplifier proposed by C. Rubbia et al.. The use of advanced numerical tools has been of practical support in the design of critical elements of the machine such as the fuel element and the beam target. The aim of this work is to show the design and optimization of the Liquid Metal Spallation Target, which consists in an axial-symmetric vertical cylinder, where a Pb-Bi eutectic, in a natural convection driven flow regime, works at the same time as spallation material and coolant for the target and the beam window. The most critical part of the target is the window itself, where the highest temperatures and thermal stresses are reached. The minimization of such temperatures and stresses is the goal of the optimization. The main geometrical dimensions of the target (i.e. beam pipe, beam window and external container) are somehow fixed since they are related to the proton beam distribution and to the EA core design. The optimization therefore acts on the suitable design of the flow guide which separates the hot rising flow from the cold one. In the region where the flow is heated by the proton beam the flow guide has a funnel shape which accelerates the liquid metal. The numerical simulations are performed by using three different tools. The FLUKA Montecarlo code is used to calculate the heat source distribution in the window and in the coolant generated by the interaction with the proton beam. The results of these calculations are used as input data for the thermal fluid dynamic simulations performed with the STAR-CD commercial software. The resulting temperature and pressure fields are finally introduced in the NASTRAN code used for the structural analysis of the solid components

CO2 Hydrogenation Induced by Mechanochemical Activation of Olivine With Water Under CO2 Atmosphere

A study on the mechanochemical activation of the olivine in presence of H2O and under CO2 atmosphere have been approached, focusing both on the structural nature of the transformation and the conversion of CO2 to methane and light hydrocarbons. The mechanochemical process was carried out by high energy laboratory mills, with milling vials properly modified in order to be used as batch reactors. Chemical reactivity and reaction rates were investigated under different experimental conditions, evidencing increased performance with respect to the thermally activated process reported in literature. Mechanical treatment induced H2O and olivine activation, with consequent release of molecular H2 which, in turn, allowed hydrogenation of activated CO2. This last reaction also led, through a competitive process, to the precipitation of carbonate phases, whose composition and structural features were dependent of the CO2/H2O ratio.Fil: Farina, Valeria. Università Degli Studi Di Sassari; ItaliaFil: Gamba, Nadia Soledad. Comisión Nacional de Energía Atómica. Gerencia de Área de Aplicaciones de la Tecnología Nuclear. Gerencia de Investigación Aplicada; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche | Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche; ArgentinaFil: Gennari, Fabiana Cristina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia de Área de Aplicaciones de la Tecnología Nuclear. Gerencia de Investigación Aplicada; ArgentinaFil: Garroni, Sebastiano. Università Degli Studi Di Sassari; ItaliaFil: Torre, Francesco. Università Degli Studi Di Cagliari; ItaliaFil: Taras, Alessandro. Università Degli Studi Di Sassari; ItaliaFil: Enzo, Stefano. Università Degli Studi Di Sassari; ItaliaFil: Mulas, Gabriele. Università Degli Studi Di Sassari; Itali

Determination of gaseous elemental mercury (GEM) emissions by a non-stationary static accumulation chamber. The case study of Portoscuso (South-West Sardinia)

This work describes the methodology based on a non­statonary statc accumulaton chamber used for measuring the GEM emissions at the soil­atmosphere interface in some residental and agricultural areas of the Portoscuso Municipality (South­West Sardinia). Afer a preliminary risk assessment of soil contaminaton, the investgated areas highlighted potental significant human health risks for volatlizaton pathways related to total Hg content in the soil. The aim of this study is to use the GEM emission rate to estmate indoor and outdoor human exposure according to the specific use of the areas. Acceptable GEM emissions (AGEM), i.e. maximum emissions associated with an acceptable human exposure and health risk, were defined accordingly and compared with measured ones. The measured GEM emissions probably consttute the sum of two contributons: • a real flux of GEM “through the soil­atmosphere interface”. This flux is originated by the presence of sources (both natural and/or related to potental contaminaton) in the first meters of depth and is regulated by mainly advectve mechanisms; • a component produced “at the soil­atmosphere interface”, as a response to the acton of UV radiaton on divalent Hg (II) in soil partcles. In this study the contributon of each of these two components has not been evaluated; however the main results showed, at the scale of the single sample representatve area (Thiessen polygon), few values (8 out of 163, about 5%) exceeding the AGEM values for the indoor scenario. These results are poorly indicatve of a real unacceptable risk, given their extremely punctual extent not representatve of a long­term human exposure. Conversely, GEM emissions for each macroarea showed a general compliance with acceptable thresholds emission (AGEM) computed for both outdoor and indoor scenarios. Further investgatons will be aimed at discriminatng the two components that originate the measured GEM flux values