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Inhibition de la production d'hydrogène radiolytique dans les déchets nucléaires de type « enrobés bitumineux » :
étude de l'interaction entre l'hydrogène et l'hydroxosulfure de cobalt

Abstract : In the nuclear field in France, the bitumen is mainly used for the conditioning of the radioactive muds generated by the fuel reprocessing. However, the self-irradiation of the bitumen induces a production of hydrogen which generates safety problems. The comparison of various storage sites showed that the presence of cobalt hydroxosulphide limited such a production. Consequently, this compound was regarded as an « inhibitor of radiolytic hydrogen production » However, the origin of this phenomenon was not clearly identified.
In order to propose an explanation to this inhibition phenomenon, model organic molecules were used to represent the components of the bitumen. Irradiations were carried out by protons to simulate the alpha radiolysis. The organic molecules irradiations by a proton beam showed that cobalt hydroxosulphide CoSOH, does not act as a hydrogenation catalyst of unsaturated hydrocarbons, nor as a radicals scavenger, but consists of a trap of hydrogen.
Experiments of hydrogen trapping at ambient temperature were carried out according to two
techniques: gravimetry and manometry. The solid was characterized before and after interaction with hydrogen (infrared and Raman spectroscopies, X-ray diffraction). The initial solid was composed of amorphous cobalt hydroxosulphide and a minor phase of cobalt hydroxide. The gravimetry and manometry experiments showed that the maximum of hydrogen trapping capacity is equal to 0.59 ± 0.18 mole of hydrogen per mole of cobalt. After interaction with hydrogen, the Co(OH)2
phase disappeared and a new solid phase appeared corresponding to Co9S8. These observations, as well as the analysis of the gas phase, made it possible to conclude with the following reaction (1):
9 CoSOH + 11/2 H2 = Co9S8 + 9 H2O + H2S (1).
Gravimetry experiments at temperatures between 50 and 210°C revealed the desorption of water but not of hydrogen sulphide. The absence of hydrogen sulphide in gaseous phase and the Co(OH)2 phase disappearance, could be explained according to the reaction (2):
9 Co(OH)2 + 8 H2S + H2 = Co9S8 + 18 H2O (2).
By taking account of (1) and (2), the theoretical ratio of the quantity of hydrogen fixed per mole of cobalt is 0.56, which is in agreement with the experimental value (0.59). The analysis of the kinetic curves deduced from the gravimetry experiments were qualitatively analysed in terms of nucleation and growth processes in order to explain the phenomenon of « trapping » at various temperatures.
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Contributor : Caroline Pichon <>
Submitted on : Tuesday, May 22, 2007 - 11:41:41 AM
Last modification on : Wednesday, June 24, 2020 - 4:18:31 PM
Long-term archiving on: : Thursday, April 8, 2010 - 5:23:31 PM

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  • HAL Id : tel-00148343, version 1

Citation

Caroline Pichon. Inhibition de la production d'hydrogène radiolytique dans les déchets nucléaires de type « enrobés bitumineux » :
étude de l'interaction entre l'hydrogène et l'hydroxosulfure de cobalt. Génie des procédés. Ecole Nationale Supérieure des Mines de Saint-Etienne, 2006. Français. ⟨tel-00148343⟩

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