Experimental investigation of the radiative properties of the project reactor astrid vessels

International audienc

ATTILHA A novel experimental setup for thermodynamic and thermophysical properties measurements on nuclear materials

International audienceIn order to obtain experimental data on the complex corium pool involved during a severe accident in a nuclear reactor as a first approximation U-Zr-Fe-O experiments at very high temperatures have to be performed (T>2300 K). However, when samples are in direct contact with the instrumentation (e.g., thermocouples) or with a crucible, inevitable chemical interactions affect the experimental measurements. Furthermore, handling radioactive materials impose radioprotection restrictions.In this framework, a novel experimental setup called ATTILHA has been conceived and developed CEA Saclay. The setup has the final objective to study the high temperature thermodynamics and thermophysical properties of liquid nuclear materials. This apparatus is based on a laser heating technique coupled with contactless temperature monitoring and an aerodynamic levitation system. Spherical samples levitate within a controlled gas flux out of an Al levitation nozzle. Experimental gaseous conditions reducing or oxidizing are suited choosing the carrier levitation gas. The setup may be placed inside an and#945;-shield glove-box to comply with radioprotection limitations.In a first step, the setup has been used to investigate the liquid miscibility gap in the Fe-Zr-O ternary system a tie-line has been obtained between a metallic liquid enriched in Fe and an oxide liquid of composition close to ZrO2. The solubility of Fe in ZrO2 liquid has been therefore quantified. UO2 will be used to validate the setup with radioactive materials.To validate the setup for thermal-physical properties acquisition, experiments have been conducted first on non-radioactive materials, namely liquid Al2O3 and ZrO2. Forced oscillations were transmitted through the levitation gas by an acoustic system. Surface tension and density were obtained using an ultra-high speed camera coupled with a Python code, which allows to detect the resonant oscillations of the levitating liquid sample on the camera images

Development of ATTILHA - Experimental setup for high temperature investigations of U-containing systems (…soon)

International audienc

High temperature experimental contribution to the thermodynamic modeling of corium pools

International audienceDuring a severe accident in a Pressurized or Boiling Water nuclear reactor, extreme temperatures may be reached (T>2500 K). Under these conditions, the oxide fuel (UO2) may react with the Zircaloy cladding and with the steel vessel, forming a mixture of solid-liquid phases called in-vessel corium. In the worst scenario, this very high temperature mixture may pierce the vessel and spread on the concrete underneath the reactor to form an ex-vessel corium. New high temperature thermodynamic data are needed to better predict the high temperature behaviour of the corium+concrete system.To approach these very high temperature interactions between the fuel, the structural materials and the concrete, the LM2T at CEA Saclay Centre uses an approach combining the thermodynamic modeling of a chemical system representative of a simplified prototypic corium using the Calphad method (Al-Ca-Fe-Si-U-Zr-O) and the development of a specific high temperature setup dedicated to the measurement of phase equilibria at high temperature (up to 2400 K) on interesting corium sub-systems.To reach such high temperatures, this setup uses an aerodynamic levitation device and a CO2 laserheating technique that makes it possible to melt metallic or oxide samples at temperatures above3000 K. This technique avoids the interactions between the sample and the crucible and permits toobserve the formation of miscibility gaps that often forms in such high temperature liquids.In this framework, new phase equilibria data on the Fe-Zr-O system and on the Al-Ca-Si-Zr-Osystem were carried out. The thermal arrest measurements together with the composition andmicrostructure analyses will be presented for some metallic and oxide samples representative for invessel and ex-vessel samples. These experimental results will be compared to the thermodynamic calculations from the thermodynamic database under development

Experimental investigation and thermodynamic modelling of the in-vessel corium for severe accident studies in PWR reactors

International audienceDuring a severe accident in a PWR reactor, the oxide nuclear fuel (UO2 or MOX) reacts at high temperature with the zirconium alloy clad and the steel vessel to form a partially or fully molten mixture so-called in-vessel corium . In such a case, the corium forms a pool in the bottom of the vessel, constituted of two liquid phases, metallic and oxide. The formation of such a configuration of the corium pool is due to the existence of a miscibility gap in the liquid state. The fractions and compositions of these liquid phases have to be well known in order to model the thermal hydraulic properties of the pool. The aim of the present work is to investigate experimentally the thermodynamic properties of the U-Zr-O-Fe system representative for the in-vessel corium to improve the thermodynamic modelling using the Calphad method. Laser heating techniques as well as heat treatments are used to measure solid/liquid transition temperatures and to highlight the miscibility gap in the liquid state. Experimental data are used to assess the thermodynamic properties of this key system. Both experimental and theoretical results will be presented