On the hydrogen production of geopolymer wasteforms under irradiation

Abstract

The hydrogen gas (H2) production of wasteforms is a major safety concern for encapsulating nuclear wastes. For geopolymers, the H2 produced by radiolytic processes is a key factor because of the large amount of water present in their porous structure. Herein, the hydrogen production was measured under 60Co gamma irradiation. The effect of water saturation and sample size were studied for pure geopolymers, or using zeolites as an example waste. To interpret results, a simple model was used, considering only hydrogen production, a potential recombination and its diffusion in the geopolymer matrix. When geopolymer monolithic samples were large and saturated by water, the hydrogen released was measured up to two orders of magnitude lower with a 40‐cm long cylinder samples (1.9 × 10−10 mol/J) than a sample in powder form (2.2 × 10−8 mol/J). Knowing the diffusion constant of the matrix, the model was able to reproduce the evolution of the hydrogen release as a function of the water saturation level and predict accurately the evolution when sample size is increased up to 40 cm.

Microparticles with diverse sizes and morphologies from mechanical and laser cutting of fuel debris simulants and geopolymer as a covering material

“…The metakaolin was added to the activator solution to bring the composition of the product to the molar ratios of 3. [22]. The resulting mortar was cast in a cylindrical mold (bottom diameter 20 mm, height 15 mm) with or without the fuel debris simulant inside and cured under room temperature and 100% RH condition for 7 days.…”

Effect of exposure of metakaolin‐based geopolymer cements to gamma radiation

“…Gamma irradiation has been shown to remove additional water from geopolymer [20][21][22] or Portland cement 10,11,23 wasteforms when compared with specimens subjected to heating to the same temperature reached upon radiation exposure. The liberation of water is seen between 50 • C and 150 • C. 20 Gamma irradiation also induces carbonation within certain cement samples, which can be analyzed using thermogravimetric analysis coupled with mass spectroscopy (TG-MS). 11 This is believed to be due to the dehydration of the sample through radiolysis, removing the mobility of the free water, and increasing the effect of atmospheric carbonation on the sample with an increase in cracking.…”

“…Gamma irradiation has been shown to remove additional water from geopolymer 20–22 or Portland cement 10,11,23 wasteforms when compared with specimens subjected to heating to the same temperature reached upon radiation exposure. The liberation of water is seen between 50°C and 150°C 20 .…”

Evolution of the microstructure of unconsolidated geopolymers by thermoporometry

“…Indeed, the carbon footprints of geopolymers concretes are sometimes considered lower than that of Ordinary Portland cement (OPC)—although this is still a matter of debate 1 . Anyhow, it remains that geopolymers could advantageously replace conventional cement‐based materials in specific applications such as follows: castable refractory, encapsulation of nuclear waste, thermal and acoustic isolation, stabilization/solidification of municipal solid waste incineration residue, and cementing of oil wells 2‐6 …”