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