During Fukushima Daiichi nuclear reactor accident, several hundred tons of fuel debris (the mixture generated by the reactor core melting and its interaction with structural materials) have been formed. Japanese government plans to dismantle within 30 to 40 years Fukushima Daiichi nuclear power station, which implies recovering the fuel debris that were formed during these accidents.
CEA is participating within an ONET Technologies/ASNR/CEA consortium to several projects aiming at developing fuel debris cutting. Mastering the risks due to radioactive aerosols generated during these operations is one important aspect of this R&D. In this framework, CEA has fabricated fuel debris prototypes corresponding to chemical compositions that have been estimated for these severe accidents. The French consortium has collected and analysed aerosols produced during mechanical cutting as well as during high temperature heating simulating thermal cutting.
The aim of this postdoctoral research is to exploit this large experimental database to study aerosol generation and transformation mechanisms for both thermal and mechanical cutting. For thermal cutting, an important source of aerosol seems to be partial evaporation/condensation, close to fractional distillation, of many chemical species that are present in the fuel debris. A thermodynamic modelling shall be proposed, using the NUCLEA or TAF-ID databases, coupled with some kinetic effects.
For mechanical cutting, relations between the phases observed on the bulk samples and the observed aerosols will be considered in view of determining a phenomenological understand and in a second stage modelling it. Then, the observed of the cutting atmosphere (humidity, air vs. nitrogen) should be explained and its mechanisms could be quantified.
This postdoctoral work will start with a bibliographical study. In addition to the state of the art on aerosols produced by mechanical and thermal cutting, there shall be a comparison with the literature dedicated to radioactive aerosol release during severe accidents.
Then, a critical synthesis of the experimental results achieved by this French consortium will be carried out. The experimental database encompasses several fuel debris simulant block compositions (in- and ex-vessel fuel debris, with or without depleted uranium). It includes characterization of samples before the cutting processes as well as size and chemical characterization of released aerosols. This experimental database can be completed if needed by the chemical or crystallographic analyses of samples already in the laboratory but not yet analysed.
A last phase of this work would consist in developing a model of fuel debris aerosols generation and transformation phenomena, in particular, evaporation/condensation during thermal processes and/or agglomeration of aerosol particles.

PhD requested in  material engineering, aerosol science, applied chemical thermodynamics or nuclear engineering.