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Etude des effets d'irradiation sur le Phosphate Diphosphate de thorium (beta-PDT) ; conséquences sur la durabilité chimique.

Abstract : Since Thorium Phosphate Diphosphate (β-TPD) can be considered as a potential host
matrix for long-term storage in underground repository, it is necessary to study the irradiation
effects on the structure of this ceramics and the consequences on its chemical durability.
Sintered samples of β-TPD and of associated solid solutions of β-TUPD were irradiated
under ion beams and then altered in aqueous solutions. Depending on the electronic LET
value, β-TPD can be completely or partly amorphized. Furthermore, the ability of
recristallization of the amorphous material by thermal annealing was also demonstrated. Some
leaching tests, realized on these irradiated samples, have shown a significant effect of the
amorphous fraction on the normalized dissolution rate which was increased by a factor of 10
from the crystallised to the fully amorphized material. Correlatively, the amorphous fraction
also modified the delay to reach the saturation conditions associated to the thermodynamic
equilibria involved. On the other hand, it exhibited no influence neither on other kinetic
parameters, such as activation energy of the dissolution process or partial order related to the
proton concentration, nor on the nature of the neoformed phase formed at the saturation of the
leachate and identified as Thorium Phosphate HydrogenoPhosphate Hydrate (TPHPH).
β-TUPD samples were also irradiated by γ and α rays during leaching tests to study the
effects of radiolysis in the leaching medium on the normalized leaching rate. It appeared that
the radiolytical species occurring in the dissolution mechanism were unstable, disappearing
quickly when stopping the irradiation. Their oxidizing properties toward tetravalent uranium
enable to explain the difference of behavior between both metallic cations (U and Th).
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https://tel.archives-ouvertes.fr/tel-00011749
Contributor : Marie-Christine Blanchet <>
Submitted on : Friday, March 3, 2006 - 3:15:34 PM
Last modification on : Wednesday, October 14, 2020 - 3:42:22 AM
Long-term archiving on: : Saturday, April 3, 2010 - 8:29:18 PM

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  • HAL Id : tel-00011749, version 1

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Citation

Claire Tamain. Etude des effets d'irradiation sur le Phosphate Diphosphate de thorium (beta-PDT) ; conséquences sur la durabilité chimique.. Physique Nucléaire Théorique [nucl-th]. Université Paris Sud - Paris XI, 2005. Français. ⟨tel-00011749⟩

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