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IRSN, Institut de radioprotection et de sûreté nucléaire

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Enhancing Nuclear Safety


Research

Thesis proposal

Tritium retention inside the ITER facility: from monitoring of tritium inventory to the source term evaluation during accidents


Thesis location: IRSN, Cadarache (PACA district, France), a training period of several months at the CIRIMAT institute (Toulouse, France) is planned at the beginning of the thesis.

 

Start of the project: October 2018

 

 

Knowledge requirements

 

  • MSC in chemistry, physics or material science.
  • Computational skills are required.
  • Basic knowledge of ab-initio method like DFT as well as molecular dynamic would be better.

 

 

 

Thesis topic

 

 

The ITER facility aims at demonstrating the feasibility of obtaining a net amount of energy from a magnetically confined plasma of deuterium and tritium. The choice for the protective materials for the vacuum vessel is limited due to the fact that several criteria must be fulfilled, e.g. resistant to extreme temperature and neutron fluxes during normal operations, having a low impact on the plasma, as well as a limited capacity to retain tritium for safety objectives. Considering these different constraints, beryllium has been selected for the first walls of the vacuum vessel.

 

The aim of this present work is the study of the tritium interaction with the extended defects of beryllium which will be created in a large amount in the material due to irradiation. These defects can be dislocations, voids, gas bubbles or precipitates like beryllium oxide. Some of them could trap a large amount of tritium. This work should support the improvement of the model which will be employed to assess the efficiency of the protective equipment of the ITER facility. The thesis work is then divided into two different topics as following explained. 

 

 

Investigations of inter-granular extended defects


The type of extended defects created by neutron irradiation in the beryllium material can be deduced from experimental data. Therefore, during the first step work, the student will perform a state of the art regarding to the morphology of these defects. Tritium trapping and detrapping energies in the defect vicinities will be calculated within the DFT approach, where the void be modelled by a slab approach. The second step will correspond to the analysis of nucleation mechanism of gas bubble as well as their impact on the tritium release kinetic. The study will be carried out with the molecular dynamic method. Then, a work related to the development of the inter-atomic potentials Be-Be and Be-T will be necessary. 

 

 

Investigations of tritium behaviour inside beryllium oxide


The second topic will be focused on the beryllium oxide. During the normal operation of the ITER facility, the formation of oxidised film onto the first walls as well as at grain boundaries is expected. Therefore, the understanding of the tritium behaviour in the beryllium oxide is of importance. The diffusion process will be studied either by atomic scale method like DFT or by a mesoscale approach as molecular dynamic. The obtained data will support the simulations, performed with a coupled reaction diffusion code, devoted to the calculations of the tritium release. Furthermore, the critical review related to diffusion process of tritium in metallic beryllium could be improved by taking into account the effect of thin oxidized film which always exists onto the beryllium samples. Finally, tritium reactivity with the beryllium oxide should allow exploring the formation mechanism of beryllium hydroxides.



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