• Bonnaillie, P.
• Dupin, N.
• Lugrin, E. Lizon A.
• Guéneau, C.
• Poissonnet, S.
• Alpettaz, T.
• Gossé, S.
• Quaini, A.

Abstract

During 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.

Topics

• melt
• steel
• forming
• liquid phase
• CALPHAD