Influence of the cement composition on the radiolytic behavior under irradiation
Résumé
Cement based materials are used for the conditioning of Low and Intermediate Level Wastes (LILW)
due to their low cost, their ease of making and their ability to immobilize radioelements. Nevertheless,
hydrogen gas is produced radiolytically under irradiation. For the safety of nuclear waste disposals, it
is important to limit as much as possible the hydrogen gas release.
A comparison of the behavior of Portland and Ciment Fondu® cements under irradiation taking into
account both real cement pastes and synthetic hydrates was performed to find out the role of the cement
composition on the radiolytic behavior under irradiation. First, γ-irradiations were performed using
a 60Co source (dose rate: 0.17 - 0.25 Gy.s-1, dose: up to 500×103 Gy). Thermogravimetric analysis
measurements were performed in order to determine the amount and the type of water involved. H2
gas production was measured by gas chromatography. Regardless of the water to cement ratio (W/C)
chosen (0.2, 0.4 and 0.6), it is shown that Ciment Fondu® pastes produce less H2 under irradiation. In
agreement with a recent study by Kadissy et al. [1], it is shown that the amount of gas produced by
portlandite and gibbsite, which are respectively the constitutive hydrates of Portland and Ciment Fondu
® cements, strongly depends on the nature of the hydrate. Secondly, portlandite and gibbsite were
irradiated by electrons up to 270 MGy and 3.5 GGy using the LSI SIRIUS accelerator platform. X-Ray
Diffraction analyses were performed before and after irradiation in order to investigate the structural
damage. Despite some observed disorder, results show a good structural stability for both hydrates
under irradiation.
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