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Experimental determination and thermodynamic modeling of the Ag-Zr-In system

Alexandre Decreton has defended his thesis on 17th March 2016 at Cadarache's castle.​

Document type > *Mémoire/HDR/Thesis

Keywords >

Research Unit > IRSN/PSN-RES/SAG/LETR

Authors > DECRETON Alexandre

Publication Date > 17/03/2016

Summary

In the occurrence of a severe accident with loss of coolant on a Pressurized Water Reactor, the silverindium- cadmium absorbing alloy which constitutes the control rods is likely to interact at a high temperature with their guide tubes or with the fuel rods’ cladding, both in zircaloy.


Therefore, the thermodynamic study of the liquid phase and its associated equilibria in the Ag-Zr and Ag-Cd-In systems is a necessary step for a reliable estimate of the fission product release and of the corium progression. The aim of the thesis is to bring forth an experimental contribution to this thermodynamic study.


The silver-zirconium system is difficult to study experimentally for various reasons. First, zirconium, especially when liquid, is highly reactive with oxygen. Second, equilibria often prove difficult to reach. Last, the stabilities of the intermediate phases AgZr and AgZr2 are low. After the establishment of specific experimental protocols, the nature and the temperature of the different invariant transformations of the system were established by coupling differential thermal analysis with microstructural characterization by metallography and scanning electron microscopy (SEM EDS). A silver-zirconium phase diagram is proposed.


Solution calorimetry measurements in an aluminum bath were performed at 723°C in order to

determine the enthalpy of formation of the AgZr and AgZr2 compounds. Experimental results have shown the difficulty of dissolving the solid zirconium in molten aluminum . A model of diffusion /convection was developed to quantify the dissolution kinetics. In parallel, the formation enthalpy of the intermetallic compound AgZr was determined by solution calorimetry in an acid bath at 25 °C.


In the silver-indium-cadmium system, the enthalpy of mixing in the liquid phase was measured at 450 °C prior to the thesis. The extension in the diagram of the liquid phase stability domain has been specified by combining an isothermal method of annealing and quenching of biphasic solid / liquid samples with differential scanning calorimetry (DSC). The overall consistency of the new results between them and compared to the literature has been tested by means of a thermodynamic optimization following the CALPHAD method. 


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