MEXIICO a new equipment to study the pressure impact on the irradiated fuel behavior

International audienceThe new MEXIICO experimental loop has recently been started in the LECA-STAR hot-cell facility of the CEA Cadarache. It is dedicated to the understanding of the basic mechanisms occurring in nuclear fuels during nuclear reactor power transients and accidental situations. Under such conditions the nuclear fuels are submitted to thermo-mechanical stresses. These stresses play a major role on fission product release and fuel fragmentation. Evaluating such fuel behavior represents a key issue for reactor safety analyses.In the first part of the paper, we describe the complete MEXIICO device, which main component is a hot isostatic press allowing to perform analytical experiments in the [20°C -1600°C / 10 MPa - 160 MPa] region. As shown by simulations (ALCYONE fuel performance code), the upper value of the pressure (160 MPa) is consistent with the one experienced by fuels under nuclear power transients. We also present the experimental loop starting from the argon pressurized feed-line, the furnace and its associated instrumentation and the exhaust line equipped with specific valves and flow meters controlling the pressure and flow rate. We then focus on the gamma spectrometry measurement which allows recording the fission gas release kinetics.In the second part of the paper, we detail the capability of the MEXIICO device to provide new experimental data regarding the influence of pressure on the fission gas release and fuel fragmentation, and to determine a pressure threshold above which fission gas release and fuel fragmentation may be inhibited. This device also allows investigating the impact of pressure on the microstructure evolution, coupling it with post-test microanalysis examinations this procedure will allow characterizing the effect of temperature and pressure on the bubble evolution and interconnection. Evolutions of the fuel modeling, needed to simulate correctly these new experimental data, will be also presented.In the last section of the paper, we present the commissioning tests of the MEXIICO device showing the good reproducibility of the tests performed first in conventional laboratory and then in hot-cell laboratory