Abstract
In the context of in-vessel retention (IVR) strategy in order to better assess the risk of reactor vessel failure, the knowledge related to the kinetics of immiscible liquid phases stratification phenomenon needs to be further improved. So far, only one medium-scale experiment (MASCA-RCW, in the frame of the OECD MASCA program) gives direct information regarding the transient relocation of metal below the oxide phase through post-mortem measurements. No experimental characterization of the stratification inversion kinetics when heavy metal becomes lighter and relocates at the top exists. Further investigation of these hydrodynamic and thermochemical processes could be made possible thanks to on line instrumentation enabling to follow displacement of oxidic and metallic phases into the corium pool. At CEA Cadarache, studies are under progress to set up innovative technologies for corium stratification monitoring which would be integrated to a cold crucible induction melting furnace. Based on space and time resolution specifications, three on-line measurements techniques were selected and studied. The first one is an ultrasonic technique using a refractory material waveguide and based on a time-of-flight measurement. We present the feasibility approach with the preliminary results obtained during experiments at high temperature on VITI facility. The second method consists in electromagnetic characterization of the corium pool thanks to an excitation by a magnetic field induced by surroundings coils and measurement of magnetic response by sensors placed around the crucible. A modelling study has enabled to define an appropriate experimental configuration. An experimental set up has also been tested to verify the calculation results. The third technique is 2D X-rays imaging. A feasibility study for a real-time X-ray imagingwith a framerate of 1 image/s has been performed using home-made simulation software MODHERATO, accounting forscattering, based on corium behavior previsions. Results on thedetection of interfaces between different type of corium phases(oxide, light metal, heavy metal) are shown.
Highlights
I N case of a nuclear severe accident, when core meltdown occurs, the main objective is to limit the consequences on environment and populations, in terms of contamination and radiation
Is the in vessel retention (IVR) strategy which aims at minimizing the risk of vessel failure by reflooding the reactor pit and whose likelihood of success is determined by the assessment of the heat flux from the corium pool to the vessel
This is why there is an interest in the knowledge related to the kinetics of immiscible liquid phases stratification phenomenon
Summary
I N case of a nuclear severe accident, when core meltdown occurs, the main objective is to limit the consequences on environment and populations, in terms of contamination and radiation. Is the in vessel retention (IVR) strategy which aims at minimizing the risk of vessel failure by reflooding the reactor pit and whose likelihood of success is determined by the assessment of the heat flux from the corium pool to the vessel. This is why there is an interest in the knowledge related to the kinetics of immiscible liquid phases stratification phenomenon. The set-up is based on the induction melting technique in a cold crucible in order to perform medium-scale experiments with a ~50 kg corium pool as in MASCA-RCW. We used a Framatome® TUCSS high temperature transducer (able to operate at 200 °C)
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