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Détection des ruptures de gaines sur RNR-Na par spectrométrie gamma hauts taux de comptage

Emmanuel Rohée 1
1 LCAE - Laboratoire Capteurs et Architectures Electroniques
DM2I - Département Métrologie Instrumentation & Information : DRT/LIST/DM2I
Abstract : The question of clad failures detection, through the monitoring of potentially released fission products in the primary sodium, is of utmost importance for SFR type generation IV reactors, and in particular for the future ASTRID industrial demonstrator. This thesis aims to propose ways to significantly improve the nuclear instrumentation dedicated to clad failures detection. A first study regarding the signal-to- noise ratio of the existing instrumentation, which is based on Delayed Neutron Detection (DND), is proposed. The experience feedback, as well as the Monte Carlo simulations, shows a disturbance of the useful neutron signal by photoneutrons produced in the polyethylene. A material replacement solution based on the use of graphite is proposed, and its performances are evaluated by Monte Carlo simulations and experiments. The second lead followed, technologically more ambitious, consists in enriching the existing instrumentation by introducing an innovative method, based on high count rate gamma spectroscopy on the primary sodium. In addition to bringing redundancy to the current instrumentation, such a spectroscopy would permit to enrich the clad failure diagnosis with an earlier and more complete measure (broader range of accessible fission products). First, a feasibility study is carried out using Monte Carlo simulations, by modeling a measurement station and simulating the HPGe detector response. Minimal detectable activities are calculated for the fission products of interest, and compared with results from simulations of release following a clad failure scenario. In a second stage, high count rate gamma spectroscopy using the ADONIS spectrometry system developed by CEA LIST was tested and validated in a real environment, by installing a measuring station on the ISABELLE 1 fuel pin irradiation loop at the OSIRIS reactor. Several irradiations have been monitored in this thesis, two of which allowed to follow a clad failure process using this approach.
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Emmanuel Rohée. Détection des ruptures de gaines sur RNR-Na par spectrométrie gamma hauts taux de comptage. Instrumentations et Détecteurs [physics.ins-det]. Normandie Université, Université Caen Normandie, 2016. Français. ⟨NNT : 2016CAEN2049⟩. ⟨tel-01781260⟩

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