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Interaction Laser-UO2 : vers une simulation du chargement thermique d’un accident de réactivité (RIA) à l’échelle du laboratoire

Thibault Vidal 1, 2 
2 ILM - ILM
FRESNEL - Institut FRESNEL
Abstract : This project falls within the general context of investigations on current and future nuclear fuels, particularly their behaviour under thermal loads representative of RIA (Reactivity Initiated Accident) type conditions in nuclear reactors. Up to now, these studies are performed thanks to dedicated integral experiments conducted in-pile (i.e. in Materials Test Reactor) with the corresponding cost and constraints. The present work aims to develop an experimental platform, at a laboratory scale, that can submit irradiated nuclear fuels and fuel cladding assemblies to annealing tests involving very high temperatures (> 2000°C) with control of thermal gradients and temporal dynamics, coupled with analysis of gas and fission product releases, micro structure evolution kinetics and fuel fragmentation.To reach such objectives, a prospective work was carried out during this thesis within the framework of a collaboration between the Fresnel Institute, which brought its expertise in the field of high power laser/material interactions and optical instrumentation, and CEA/IRESNE with expertise in thermal treatments of irradiated fuels, which has allowed to define relevant and compatible experiments with the possibility of integration into a high activity laboratory.Following preliminary numerical investigations, a concept based on the use of a high power laser was proposed and implemented, first on a mock-up material (EDM3 graphite) then on UO2. We show in this thesis that the proposed approach allows to precisely reproduce the thermal gradients characteristic of an RIA, provided that the sample studied is sufficiently fine (sub-millimeter), and that the numerical model developed allows to reproduce accurately the experimental observations and is proving to be an extremely useful tool for preparing and interpreting tests.This work should contribute in future to bring nuclear safety studies from the reactor level down to a laboratory scale and should permit, with some further developments, a full real time analysis of the irradiated nuclear fuel behaviour in case of a major mishap, including the release of radioactive gases and particles at high temperature. This will provide crucial experimental data for physical model validation implemented in nuclear fuel performance codes.
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Submitted on : Thursday, February 18, 2021 - 3:46:12 PM
Last modification on : Wednesday, November 3, 2021 - 4:05:11 AM
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Thibault Vidal. Interaction Laser-UO2 : vers une simulation du chargement thermique d’un accident de réactivité (RIA) à l’échelle du laboratoire. Optique / photonique. Ecole Centrale Marseille, 2020. Français. ⟨NNT : 2020ECDM0005⟩. ⟨tel-03145769⟩

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