Study and wet chemistry synthesis of Zn4Sb3 nanoparticule for realisation of thermoelectrics compounds by printing technologies

L'utilisation de la thermoélectricité passe par une amélioration du rendement du module thermoélectrique à travers l'optimisation de ses dimensions et l'augmentation du facteur de mérite des matériaux thermoélectriques, mais aussi par une réduction des coûts de synthèse et de mise en forme. Dans le cadre de cette thèse nous nous sommes intéressés à la synthèse de β–Zn4Sb3 nanométrique par une méthode de chimie douce à faible dépense énergétique. Nous avons étudié la mise en forme de ce matériau par des technologies d'impression qui permettent d'atteindre les dimensions optimales et présentent un coût réduit. β-Zn4Sb3 est obtenu en deux étapes : une synthèse à reflux suivie d'un traitement thermique à 400°C sous vide secondaire. La composition chimique (DRX, affinement Rietveld), la morphologie (MEB, TEM) et la stabilité en température (spectroscopie Raman) de la poudre sont étudiées. β-Zn4Sb3 ainsi obtenu est densifié par SPS et ses propriétés thermoélectriques sont mesurées montrant une augmentation du facteur de mérite pour des températures inférieures à 100°C. Au dessus de cette température, la présence de porosité et de zinc augmente la résistivité électrique et la conductivité thermique et les échantillons ont un facteur de mérite de 0,6 à 400°C. Enfin, la poudre est mise en forme par sérigraphie et atomisation sur substrat en verre et en Kapton. Le β-Zn4Sb3 montre une forte résistivité électrique juste après impression mais l'application de traitement mécanique et thermique permet de la diminuer. Le facteur de mérite estimé des dépôts est de 0,06 à 400°C. Cependant le faible coût de mise en forme et la possibilité d'automatisation rendent ces techniques viables.Use of thermoelectricy involves an increase of the module efficiency. In this purpose we need to optimize the dimension of the module and to increase the figure of merit of thermoelectric materials. But we also need to reduce the synthesis and shaping cost. Within the framework of this thesis, we focused on the synthesis of β-Zn4Sb3 nanoparticles by a low energy technique: wet chemistry. We also studied the shaping of this material by printing technologies. These cost-effective technologies allow reaching optimized dimensions. β-Zn4Sb3 is synthesized in two steps: a reflux synthesis flowed by a thermal treatment at 400 °C under vacuum. Chemical composition (XRD, Rietveld refinement), morphology (SEM, TEM) and thermal stability of the powder are studied. The as product β-Zn4Sb3 is densified by SPS and we measured its properties. They show an increase of the figure of merit for temperatures below 100 °C. However above this temperature the presence of zinc and porosity increase electric resistivity and thermal conductivity, leading to a figure of merit of 0.6 at 400 °C. Finally the powder is shaped by two printing technologies: screenprinting and atomization on glass and Kapton substrate. Just after printing the samples show a high electrical resistivity but a decrease is observed after mechanical and thermal treatment. The estimate figure of merit of printing β-Zn4Sb3 is 0.06 at 400 °C. However the printing techniques are cost-effective and allow mass production, which make them still interesting

Étude et synthèse par chimie douce de nanoparticules de b-Zn4Sb3 pour la réalisation de composants thermoélectriques par des solutions d'impression

L'utilisation de la thermoélectricité passe par une amélioration du rendement du module thermoélectrique à travers l'optimisation de ses dimensions et l'augmentation du facteur de mérite des matériaux thermoélectriques, mais aussi par une réduction des coûts de synthèse et de mise en forme. Dans le cadre de cette thèse nous nous sommes intéressés à la synthèse de b Zn4Sb3 nanométrique par une méthode de chimie douce à faible dépense énergétique. Nous avons étudié la mise en forme de ce matériau par des technologies d'impression qui permettent d'atteindre les dimensions optimales et présentent un coût réduit. b-Zn4Sb3 est obtenu en deux étapes : une synthèse à reflux suivie d'un traitement thermique à 400C sous vide secondaire. La composition chimique (DRX, affinement Rietveld), la morphologie (MEB, TEM) et la stabilité en température (spectroscopie Raman) de la poudre sont étudiées. b-Zn4Sb3 ainsi obtenu est densifié par SPS et ses propriétés thermoélectriques sont mesurées montrant une augmentation du facteur de mérite pour des températures inférieures à 100C. Au dessus de cette température, la présence de porosité et de zinc augmente la résistivité électrique et la conductivité thermique et les échantillons ont un facteur de mérite de 0,6 à 400C. Enfin, la poudre est mise en forme par sérigraphie et atomisation sur substrat en verre et en Kapton. Le b-Zn4Sb3 montre une forte résistivité électrique juste après impression mais l'application de traitement mécanique et thermique permet de la diminuer. Le facteur de mérite estimé des dépôts est de 0,06 à 400C. Cependant le faible coût de mise en forme et la possibilité d'automatisation rendent ces techniques viables.Use of thermoelectricy involves an increase of the module efficiency. In this purpose we need to optimize the dimension of the module and to increase the figure of merit of thermoelectric materials. But we also need to reduce the synthesis and shaping cost. Within the framework of this thesis, we focused on the synthesis of b-Zn4Sb3 nanoparticles by a low energy technique: wet chemistry. We also studied the shaping of this material by printing technologies. These cost-effective technologies allow reaching optimized dimensions. b-Zn4Sb3 is synthesized in two steps: a reflux synthesis flowed by a thermal treatment at 400 C under vacuum. Chemical composition (XRD, Rietveld refinement), morphology (SEM, TEM) and thermal stability of the powder are studied. The as product b-Zn4Sb3 is densified by SPS and we measured its properties. They show an increase of the figure of merit for temperatures below 100 C. However above this temperature the presence of zinc and porosity increase electric resistivity and thermal conductivity, leading to a figure of merit of 0.6 at 400 C. Finally the powder is shaped by two printing technologies: screenprinting and atomization on glass and Kapton substrate. Just after printing the samples show a high electrical resistivity but a decrease is observed after mechanical and thermal treatment. The estimate figure of merit of printing b-Zn4Sb3 is 0.06 at 400 C. However the printing techniques are cost-effective and allow mass production, which make them still interesting.MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

High-temperature ex-vessel corium spreading. Part 1: Experimental investigations on ceramic and sacrificial concrete substrates.

International audienceOptimizing melt spreading in the aftermath of a core disruptive accident is crucial for achieving sufficient melt cooling to maintain reactor containment integrity. Two $\approx$ 30 kg-scale experiments performed at the VULCANO facility explore the spreading of high-temperature molten corium-concrete mixtures over ceramic and sacrificial concrete substrates. Imaging of the melt front propagation revealed a 7% increase in spreading length and a 30% increase in maximum front velocity during spreading over sacrificial concrete, despite a reduced mass partaking in spreading due to holdup within the crucible. Infrared imaging of the melt indicated surface temperatures around 45 °C lower during spreading on sacrificial concrete, which is anticipated to result in a roughly three-fold increase in melt viscosity. The reduced mass and elevated viscosity during spreading on sacrificial concrete imply an enhanced spreadability on concrete greater than the observed 7% increase in spreading length. This enhanced spreadability on sacrificial concrete could be explained by the apparent gliding motion of the melt, consistent with reduced friction at the melt-substrate interface. Reduced friction at the melt-substrate interface is best explained by a diphasic film of molten concrete and gaseous concrete decomposition products acting as a lubricant between the melt and solid substrate

Temperature ramps for severe accident instrumentation in nuclear reactor cavity concrete

International audienceDistributed Optical Fiber Sensing and Self-Powered Nuclear Detectors are potential innovative instrumentation for the management of severe accidents. The former can monitor temperature, strain, and/or presence of hot melt while the latter is more dedicated to gamma radiation measurements and can also be coupled to thermocouples for temperature measurement purpose. These sensors could be installed in the basement concrete to monitor corium progression (arriving in lower head, later on in the reactor pit, reaching a predefined level in concrete before melt through…). In order to assess the temperature evolution that these sensors may experience, thermal conduction in concrete structures was modelled coupled with TOLBIAC-ICB calculation results for several typical scenarios. This confirmed that, due to concrete low thermal conductivity, ablation progresses more rapidly than conduction, except in a small zone close to the ablation front. Therefore experimental temperature profiles from prototypic corium-concrete interaction experiments can be used to specify the temperature profiles that sensors inserted in the reactor cavity can withstand during such severe accident. A first experiment, VULCANO VB-U10, has been carried out to study the behavior of 5 distributed optical fiber sensors that were installed inside a concrete crucible experiencing ablation by prototypic corium. These instruments have been used in this test to monitor the concrete temperature and/or its ablation. During this test, 50 kg of prototypic uranium-containing corium have interacted for 98 minutes with a lime-siliceous concrete leading to an axial ablation of 25 mm and a radial ablation of 80 mm. Optical fiber length measurements with Rayleigh OFDR technique have been found to be coherent with data from thermocouples installed in the concrete as in previous VULCANO experiments. Raman DTS measurements provided satisfactory temperature evolution results. This good performance of the distributed temperature measurement has been validated in conditions representative of a severe accident

A Lagrangian approach to ex-vessel corium spreading over ceramics and concrete substrate using moving particle hydrodynamics

International audiencenderstanding the spreading of molten core materials (corium) is vital for achieving post-accident heat removal and maintaining the integrity of the reactor containment during a severe nuclear accident. The spreading of highly viscous corium over sacrificial concrete and ablation-resistant ceramic substrates, consistent with recent VE-U9 experiments at the VULCANO facility, is investigated using a Lagrangian moving particle hydrodynamics (MPH) method. The spreading dynamics are coupled with a heat transfer model to account for the increase in melt viscosity due to solidification. Three alternative boundary conditions are considered at the melt-substrate interface to mimic the influence of low viscosity concrete ablation products on the spreading dynamics. Simulation of spreading under no-slip conditions closely resembled the spreading behavior observed over the inert ceramic substrate, advancing with a crawling motion with a steep profile in the proximity of the melt front. Spreading terminated due to a combination of thermal radiation from the free surface and the heat transfer to the substrate, leading to the formation of a continuous crust. Introduction of slip boundary models, to mimic lubrication of the interface by a film of low-viscosity concrete decomposition products, enabled the prediction of the gliding flow observed over the sacrificial concrete substrate, characterized by a shallow melt topology near the spreading front. The simulation results demonstrate excellent potential for Lagrangian models such as MPH to predict complex spreading dynamics in the presence of both melt solidification and lubrication at the substrate

Achievements of recent research on severe accidents at CEA/IRESNE in support of future nuclear fission technology

International audienceIn the current context of nuclear revival under the constraint of global warming and an ever-increasing world demand for energy, it is essential to take all precautions in the event of a serious accident during the design phase and to review the severe accident mitigation features of existing plants. The current nuclear revival is accompanied by the development of prototypes based on alternative concepts to light water reactors, such as the Sodium-cooled Fast Reactor (SFR), High Temperature Reactor (HTR), Molten Salt Reactor (MSR), which are also under consideration as reactors of reduced power output, or Small Modular Reactors (SMR). This paper summarizes the main outcomes and achievements of the last five years of experimental and numerical research conducted at CEA/IRESNE into prospective severe accidents within Pressurized Water Reactors (PWR) and SFRs

Long length SPNDs and Distributed Optical Fiber Sensors for Severe Accident remote monitoring and their contribution to Nuclear Safety in the post-Fukushima context

International audienceThe Fukushima-Daiichi nuclear accident of March 2011, and the subsequent loss of internal power supplies after the NPP (Nuclear Power Plant) water flooding caused by the tsunami, leaving the operator TEPCO with almost no information from the reactor pits, demonstrates that safety must always prevail. Accordingly, the French public authorities initiated the RSNR research program, to stimulate and fund new R&D projects to improve the safety of nuclear reactors in service and those of future NPPs. The DISCOMS project (Distributed Sensing for Corium Monitoring and Safety) aimed at developing and testing innovative and passive sensors dedicated to Nuclear Safety, namely an instrumented pole equipped with long length SPNDs (Self-Powered Neutron Detectors)-Thermocouple poles, and Distributed Optical Fiber Sensors, to be installed ex-core in both the reactor pit and concrete floor. The sensors, remotely operated from a safe place, will not only provide additional information during the Severe Accident, but also in post-accidental situation, even in case of loss of all power supplies.The modelling of a 60 year normal operation followed by a Severe Accident for two generations of reactors (Gen II, Gen III) permitted to demonstrate that ex-core long length SPNDs can identify differentscenarios: reactor shut down, Normal Operation, Severe Accident without corium relocation, and Severe Accident with corium pouring on the concrete floor. Long length SPNDs were designed and manufactured, along with their electronics, to measure low currents ranging from 1 pA to 100 nA collected under radiations, and qualified in a research reactor with fluxes compliant with modelled scenarios. Optical Fibers Sensor cables are devoted to monitor the Molten Core – Concrete Interaction (MCCI): temperature and strain profiles can be provided in the concrete depth by embedded cables, as a result ofusing the Raman DTS, Brillouin and Rayleigh OFDR reflectometry techniques, based on the analysis of the backscattered light in single-mode optical fibers, for distributed measurements potentially up to1000°C with Brillouin instrumentations. Additionally, such sensor cables can be used as fuses with telecom or photon counting OTDRs to detect corium vicinity.Sensor cables and radiation resistant optical fibers have been selected and tested to comply with the radiation conditions in the reactor pits as depicted by the modelling.A final MCCI experiment with prototypical corium, performed at the VULCANO CEA facility, involving also two instrumented SPNDs-Thermocouple poles, has demonstrated the ability of both kinds of sensors and corresponding instrumentations to deliver useful information about the corium status and its progression through the concrete

Long length SPNDs and Distributed Optical Fiber Sensors for Severe Accident remote monitoring and their contribution to Nuclear Safety in the post-Fukushima context

International audienceThe Fukushima-Daiichi nuclear accident of March 2011, and the subsequent loss of internal power supplies after the NPP (Nuclear Power Plant) water flooding caused by the tsunami, leaving the operator TEPCO with almost no information from the reactor pits, demonstrates that safety must always prevail. Accordingly, the French public authorities initiated the RSNR research program, to stimulate and fund new R&D projects to improve the safety of nuclear reactors in service and those of future NPPs. The DISCOMS project (Distributed Sensing for Corium Monitoring and Safety) aimed at developing and testing innovative and passive sensors dedicated to Nuclear Safety, namely an instrumented pole equipped with long length SPNDs (Self-Powered Neutron Detectors)-Thermocouple poles, and Distributed Optical Fiber Sensors, to be installed ex-core in both the reactor pit and concrete floor. The sensors, remotely operated from a safe place, will not only provide additional information during the Severe Accident, but also in post-accidental situation, even in case of loss of all power supplies.The modelling of a 60 year normal operation followed by a Severe Accident for two generations of reactors (Gen II, Gen III) permitted to demonstrate that ex-core long length SPNDs can identify differentscenarios: reactor shut down, Normal Operation, Severe Accident without corium relocation, and Severe Accident with corium pouring on the concrete floor. Long length SPNDs were designed and manufactured, along with their electronics, to measure low currents ranging from 1 pA to 100 nA collected under radiations, and qualified in a research reactor with fluxes compliant with modelled scenarios. Optical Fibers Sensor cables are devoted to monitor the Molten Core – Concrete Interaction (MCCI): temperature and strain profiles can be provided in the concrete depth by embedded cables, as a result ofusing the Raman DTS, Brillouin and Rayleigh OFDR reflectometry techniques, based on the analysis of the backscattered light in single-mode optical fibers, for distributed measurements potentially up to1000°C with Brillouin instrumentations. Additionally, such sensor cables can be used as fuses with telecom or photon counting OTDRs to detect corium vicinity.Sensor cables and radiation resistant optical fibers have been selected and tested to comply with the radiation conditions in the reactor pits as depicted by the modelling.A final MCCI experiment with prototypical corium, performed at the VULCANO CEA facility, involving also two instrumented SPNDs-Thermocouple poles, has demonstrated the ability of both kinds of sensors and corresponding instrumentations to deliver useful information about the corium status and its progression through the concrete