Geopolymers are a class of material that could potentially be used for sealing and repair of damaged concrete structures. This application is important for both decommissioning activities and ...standard industrial applications. The purpose of this article is to investigate the interface between ordinary Portland cement and geopolymer. The surface microstructure of the cement is investigated by SEM, EDX, and micro-Raman after embedding in geopolymer or immersion in the activation solution of a geopolymer for various durations. It is found that immersion in the solution induces a dendritic carbonation profile into the cement structure following the CSH gel. On the contrary, embedding in the geopolymer creates a dense, impermeable interface with a thickness of a few micrometers. This interface is found to be dense and brittle and it decreases the permeability of the surface, preventing the penetration of silicates into the cement structure. However, this brittle interface is sensitive to dehydration and can rupture under intense drying. This phenomenon can be utilized to separate the geopolymer and cement but is concerning if the integrity of the material must be guaranteed under extreme conditions.
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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.
When the gas diffusion constant of a wasteform is low compared to the hydrogen production rate, the gas can accumulate in the material and be trapped or available to participate in recombination reactions. To estimate the hydrogen explosion risk of a geopolymer based wasteform, the hydrogen production was measured experimentally and compared to a model to estimate the extent of recombination.
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BFBNIB, DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UILJ, UKNU, UL, UM, UPUK
For the safe storage of zeolite wastes generated by the treatment of radioactive saline water at the Fukushima Daiichi Nuclear Power Station, this study investigated the fundamental properties of ...herschelite adsorbent and evaluated its adsorption vessel for hydrogen production and corrosion. The hydrogen produced by the herschelite sample is oxidized by radicals as it diffuses to the water surface and thus depends on the sample's water level and dissolved species. The hydrogen production rate of herschelite submerged in seawater or pure water may be evaluated by accounting for the water depth. From the obtained fundamental properties, the hydrogen concentration of a reference vessel (decay heat = 504 W) with or without residual pure water was evaluated by thermal-hydraulic analysis. The maximum hydrogen concentration was below the lower explosive limit (4%). The steady-state corrosion potential of a stainless steel 316L increased with the absorbed dose rate, but the increase was repressed in the presence of herschelite. The temperature and absorbed dose at the bottom of the 504 W vessel were determined as 60 °C and 750 Gy/h, respectively. Under these conditions, localized corrosion of a herschelite-contacted 316L vessel would not immediately occur at Cl
−
concentrations of 20,000 ppm.
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► We develop novel microcapsules enclosing selective Cs-adsorbents. ► The microcapsules have excellent Cs-selectivity and chemical stability. ► Relatively large uptake above 97% is accomplished from ...simulated and real high-level liquid wastes. ► The microcapsules are effective for the selective separation and recovery of Cs
+.
A fine crystalline ammonium tungstophosphate (AWP) exchanger with high selectivity towards Cs
+ was encapsulated in biopolymer matrices (calcium alginate, CaALG). The characterization of the AWP-CaALG microcapsule was examined using SEM/WDS, IR and DTA/TG analyses, and the selective separation and recovery of
137Cs were examined by the batch and column methods using simulated (SHLLW) and real high-level liquid waste (HLLW). The free energy (
ΔG°) of the ion exchange (NH
4
+
↔
Cs
+) for fine AWP crystals was determined at −13.2
kJ/mol, indicating the high selectivity of AWP towards Cs
+. Spherical and elastic AWP-CaALG microcapsules (∼700
μm in diameter) were obtained and fine AWP crystals were uniformly immobilized in alginate matrices. Relatively large
K
d values of Cs
+ above 10
5 cm
3/g were obtained in the presence of 10
−3–1
M Ca(NO
3)
2, resulting in a separation factor of Cs/Rb exceeding 10
2. The irradiated samples (
60Co, 17.6
kGy) also exhibited large
K
d values exceeding 10
5
cm
3/g in the presence of 2.5
M HNO
3. The
K
d values in the presence of 0.1–9
M HNO
3 for 67 elements were determined and the order of
K
d value was Cs
+
≫
Rb
+
>
Ag
+. The breakthrough curve of Cs
+ had an S-shaped profile, and the breakpoint increased with decreasing flow rate; the breakpoint and breakthrough capacity at a flow rate of 0.35
cm
3/min for the column (0.7
g AWP-CaALG) were estimated at 25.2
cm
3 and 0.068
mmol/g, respectively. Good breakthrough and elution properties were retained even after thrice-repeated runs. The uptake (%) of Cs
+ in SHLLW (28 metal components-1.92
M HNO
3, SW-11, JAEA) was estimated at 97%, and the distribution of Cs
+ and Zr/Ru into the AWP and alginate phases, respectively, were observed by WDS analysis. Further, the selective uptake of
137Cs exceeding 99% was confirmed by using real HLLW (FBR “JOYO”, JAEA). AWP-CaALG microcapsules are thus effective for the selective separation and recovery of Cs
+ from HLLWs.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Palladium complexation in concentrated nitric acid solutions was studied by UV/Vis absorption spectrophotometry. The ionic strength of the solutions was fixed to
I
= 1, 3, or 5 mol dm
−3
(M) by ...mixing of HNO
3
and HClO
4
. The major palladium species were found to be Pd
2+
, PdNO
3
+
, and Pd(NO
3
)
2
. The formation constant of PdNO
3
+
was determined to be
β
1
= 1.32 (
I
= 1 M), 1.49 (
I
= 3 M), or 1.47 (
I
= 5 M), while that of Pd(NO
3
)
2
to be
β
2
= 0.45 (
I
= 3 M) or 0.14 (
I
= 5 M).
When nuclear waste is immobilized in cement or geopolymer, gases may be generated by corrosion and radiolysis. This production must be accurately predicted, and waste loading and countermeasures ...selected accordingly to avoid overpressure and limit the risk of explosion in the case of dihydrogen (H2). We measured and simulated H2 generation and release from water-saturated geopolymer confined in a glass bottle under 60Co gamma irradiation. It was observed that confinement of H2 in the pores of a high pH geopolymer could lead to recombination of more than 99.9 % of the hydrogen generated by radiolysis. Shrinkage can allow hydrogen to diffuse between the geopolymer and the vessel, reducing the fraction of recombined H2 to 90 % at our experimental scale. We then used a model to scale up the results of our experiments. The hydrogen release of a saturated geopolymer in a standard 200 L drum is expected to be equivalent to that of a hydraulic binder containing approximately 2 % moisture. Harnessing the effects of recombination would make it possible to preserve the capacity of countermeasures such as H2 absorbers, increase the loading capacity of waste packages, and reduce the cost of nuclear waste immobilization.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The gas production of wasteforms is a major safety concern for encapsulating active nuclear wastes. For geopolymers and cements, the H
2
produced by radiolytic processes is a key factor because of ...the large amount of water present in their porous structure. Herein, the gas composition evolution around geopolymers was monitored online under
60
Co gamma irradiation. The transient evolution of the hydrogen release yield was measured for samples with different formulations. Its evolution and the final values are consistent with the presence of a pseudo-first-order chemical reaction consuming hydrogen in the samples. The results show that this phenomenon can significantly reduce the hydrogen source term of geopolymer wasteform provided their diffusion coefficient remains low. Lower hydrogen production rates and faster kinetics were observed with geopolymer formulations in which pore water pH was higher. Besides hydrogen release, a steady oxygen consumption was observed for all geopolymer samples. The oxygen consumption rates are proportional to the diffusion coefficients estimated in the modelization of hydrogen recombination by a pseudo-first-order reaction.
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After the severe accident at the Fukushima-1 nuclear power plant, large amounts of contaminated stagnant water have accumulated in turbine buildings and their surroundings. This rapid communication ...reports calculation of the radionuclide inventory in the core, collection of measured inventory in the stagnant water, and estimation of radionuclide release ratios from the core to the stagnant water. This evaluation is based on data obtained before 3 June 2011. The release ratios of tritium, iodine, and cesium were several tens of percent, whereas those of strontium and barium were smaller by one or two orders of magnitude. The release ratios in the Fukushima accident were equivalent to those in the accident of the Three Mile Island, Unit 2 (TMI-2).
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