Waste Form Research Articles

Design and build a machine for transporting bottle trash in ditches with a gamepad control

In Indonesia, flooding is frequently brought on by the issue of garbage in ditches. Plastic bottle garbage is one of the waste forms that is frequently found. Because of this, a machine to collect gutter bottle waste and raise the bottle waste from ditches must be made. The operator can use a gamepad to control this DC motor-driven equipment. A chain transmits the rotation of the DC motor to the engine driving wheel. A chain that has been transformed into a conveyor is used as part of the system for lifting trash from the gutter to the storage tanks. The wheel base can be manually shifted to change the wheel width from 80 cm to 120 cm. The machine has a success rate of 76.6% while lifting waste, and it can move forward or backward across the ditch at a speed of 0.041-0.042 m/s while transferring up to 3 spinning waste bottles. This device can significantly help with efforts to improve the gutter environment and lower the chance of flooding brought on by rubbish clogging.

Effects of irradiation behavior on physicochemical properties of glassy radioactive contaminated soil containing various contents of actinides nuclear waste

The evaluation of radiation resistance of the treated radioactive contaminated soil is crucial. The irradiation behavior of simulated radioactive soil waste irradiated with 1.5 MeV Xe20+ ions at fluences of 1 × 1012-1 × 1015 ions/cm2 was studied. Before the irradiation experiment, all the samples were sintered by microwave. The results showed that microwave sintering may be used to treat radioactive contaminated soil. In addition, the irradiation experiment results show that when the Nd2O3 content was low (<20 wt.%), the irradiation has little effect on the sample. When the Nd2O3 content was higher, the Vickers hardness of the sample (25 wt.%) decreased by 7 % at a fluence of 1 × 1015 ions/cm2, which may be due to the high Nd2O3 content that destroyed the overall stability of the glass waste form. The low normalized leaching rate of the irradiated sample (LRNd, ∼10-6 g·m-2·d-1) also proved that it had good aqueous durability. Moreover, the radiation resistance of the sample was illustrated by studying the influence mechanism of 1.5 MeV Xe20+ irradiation on radioactive contaminated soil. This work can help to study the environmental pollution problems of radioactive contaminated soil containing various contents of actinide nuclear waste.

Co-immobilization of cesium and strontium containing waste by metakaolin-based geopolymer: Microstructure, mineralogy and mechanical properties

The present study investigated the possibility of co-immobilization of caesium and strontium containing waste by metakaolin-based (MK) geopolymer. 4% of CsNO3 and 4% of Sr(NO3)2 by weight were used as simulants for radioactive Cs and Sr. The effect of Cs and Sr on the geopolymerization kinetics was determined via isothermal calorimetry. Furthermore, the evolution of mechanical properties, microstructure, and mineralogy was analysed. The results showed that Cs exerted no noticeable effect on reaction kinetics while Sr lowered the geopolymerization degree of MK geopolymer due to part of OH− from the activating solution being consumed by Sr2+, thereby reducing the activating capacity of pore solution. In addition, the pore structure analysis showed that the incorporation of Sr coarsened the microstructure of MK geopolymer while no significant change was observed with Cs. The phase analysis showed that no new phase was formed because of Cs or Sr incorporation. The mechanical properties decreased with Cs and Sr addition and a higher strength loss was observed for Sr-bearing geopolymers than that of Cs-bearing matrices. The strength reduction in Cs-bearing matrices is associated with the accompanying nitrate ions while a more pronounced strength reduction in Sr-bearing specimens is due to the synergistic effect of nitrates and Sr2+ on the geopolymerization. Despite that, the compressive strengths for all tested MK recipes met the minimum Belgian waste form acceptance criteria indicating that MK geopolymer preserved sufficient strength even at high Cs and Sr waste loadings. Thermodynamic modelling based on speciation and saturation index revealed that Cs+ was mainly bound through ion exchange, whereas Sr2+ largely precipitated as SrCO3. More importantly, it was observed that the co-immobilization of Cs and Sr by MK geopolymer is largely influenced by Sr behaviour. Based on the findings, it can be concluded that MK geopolymer is an excellent host material for Cs and Sr-based waste.

Microstructure and radiation tolerance of molybdenum-rich glass composite nuclear waste forms

Non-active molybdenum-rich Ca/Zn glass composite materials (GCM) were prepared on the Vitrification Test Rig (VTR) in the UK. The GCM samples were subjected to Ni and Au ion irradiations to simulate the effects of alpha recoil damage and to determine how the crystallinity characteristics might affect the overall radiation tolerance of high-level wastes (HLW) generated during post-operational clean-out (POCO) operations at the Sellafield nuclear site. The typical crystal phases identified in the GCM were: powellite, ruthenium dioxide, zincochromite, zircon and cerianite. Gadolinium (a proxy for radioactive elements) accumulated mainly in powellite, zircon and cerianite crystals. Scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and grazing incidence X-ray diffraction (GIXRD) analyses showed that cerianite is a highly radiation-tolerant phase, whereas powellite and zircon became amorphous and swelled considerably after the Ni and Au ion irradiations. This research shows the first evidence of powellite amorphisation under heavy-ion irradiation and suggests that powellite is susceptible to amorphisation by alpha recoils in HLW materials, in contrast to previous findings. The evolution of cooling-related and irradiation-induced microcracks is also described. In HLW glass composite materials, the formation of microcracks is expected in the middle of the canister, where relatively large powellite and zircon crystals appear.

Computational Materials Design for Ceramic Nuclear Waste Forms Using Machine Learning, First-Principles Calculations, and Kinetics Rate Theory.

Ceramic waste forms are designed to immobilize radionuclides for permanent disposal in geological repositories. One of the principal criteria for the effective incorporation of waste elements is their compatibility with the host material. In terms of performance under environmental conditions, the resistance of the waste forms to degradation over long periods of time is a critical concern when they are exposed to natural environments. Due to their unique crystallographic features and behavior in nature environment as exemplified by their natural analogues, ceramic waste forms are capable of incorporating problematic nuclear waste elements while showing promising chemical durability in aqueous environments. Recent studies of apatite- and hollandite-structured waste forms demonstrated an approach that can predict the compositions of ceramic waste forms and their long-term dissolution rate by a combination of computational techniques including machine learning, first-principles thermodynamics calculations, and modeling using kinetic rate equations based on critical laboratory experiments. By integrating the predictions of elemental incorporation and degradation kinetics in a holistic framework, the approach could be promising for the design of advanced ceramic waste forms with optimized incorporation capacity and environmental degradation performance. Such an approach could provide a path for accelerated ceramic waste form development and performance prediction for problematic nuclear waste elements.

Free occupying mechanism of simulated tetravalent waste ions in Gd2Zr2O7 and performance evaluation of the waste forms

AbstractTo extend the practicability of ceramics in immobilizing nuclear waste with fluctuant composition, structural design should be abandoned. The simulated tetravalent actinide waste An4+ (Ce4+) was directly doped into prepared Gd2Zr2O7, and the waste forms were synthesized by high‐temperature solid‐state reaction. It has been shown that the maximum loading of CeO2 in Gd2Zr2O7 lies between 20 and 30 wt.%, and Ce elements are uniformly distributed in the matrix. Existing in Ce3+ and Ce4+, cerium ions automatically occupied both the Gd and Zr sites in Gd2Zr2O7 according to valence equilibrium. This occupation causes the change of r(A3+)/r(B4+) and eventually leads to the structure transition from pyrochlore to fluorite. In addition, the normalized leaching rate of the sample with 60 wt.% of dopant was about 2.5 × 10−7 g m−2 d−1 on the 35th day. In this study, a free occupation of simulated waste ions in ceramics was proposed.

Chemical durability of Gd2Zr2O7 transparent ceramics under different pH conditions

In this study, the chemical durability of Gd2Zr2O7 transparent ceramics was investigated under different pH environments. The influence of acidic and alkaline environments on the leaching behavior of Gd2Zr2O7 immobilization matrix were studied to simulate the disposal of nuclear waste forms in deep geological landfills. The measured results demonstrate that the normalized leaching rates in acidic environments are higher than those in alkaline and neutral environments. The macroscopic color of all samples fades after leaching, and the visible range in-line transmittance of the leached transparent ceramics decreases slightly at pH ≤ 9. The leaching behavior leads decrement of lattice volume and increment of surface roughness, but it exhibits no significant effect on the surface elemental distribution. Never the less, Gd2Zr2O7 transparent ceramic exhibits excellent chemical durability in weak alkaline environment, and the leaching process leads to the discoloration of Gd2Zr2O7 transparency.

Evaluation of physicochemical characteristics and centerline temperatures of Sr ceramic waste form

When disposing of spent fuel, nuclides such as Cs-137 and Sr-90, which generate short-term decay heat, must be removed from the spent nuclear fuel for efficient storage facility utilization. The Korea Atomic Energy Research Institute (KAERI) has been developing a nuclide management process that can enhance disposal efficiency by sorting and collecting primary nuclides and a technology for separating Sr nuclides from the spent nuclear fuels using precipitation and distillation. In this study, we prepared Sr ceramic waste form, SrTiO3, using the solid-state reaction method to immobilize the Sr nuclides, and its physicochemical properties were evaluated. Moreover, the radiological and thermal characteristics of the Sr waste form were evaluated by estimating the composition of Sr nuclides considering the spent nuclear fuel history such as burn-up and cooling period. The waste form was found to be stable with good mechanical strength and leaching properties in addition to a low coefficient of thermal expansion, which would be advantageous for intermediate storage. Based on the experimental and radiological results, the centerline temperature of the waste form caused by Sr-90 nuclide was estimated using the steady-state conduction equation. The centerline temperature increased with increasing diameter of the waste form. When generating the SrTiO3 waste form using the Sr nuclide recovered after a cooling period of 10 years, the centerline temperature was estimated to exceed the melting point of SrTiO3 at a diameter of 0.275 m, under all burn-up conditions. These results provide fundamental data for the management and intermediate storage of Sr waste.

Effect of Al2O3 on the structure–property relationship of sodium aluminophosphate glasses: A combined study of experiments, MD simulations, and QSPR analysis

AbstractAluminophosphate glasses have found wide applications in various fields, such as biomedical materials, optical components, sealing materials, and nuclear waste forms. In spite of their well‐investigated short‐range ordered structures, the relationship between the properties and the medium‐range structural features is far from being understood. In this paper, atomistic structures of sodium aluminophosphate (SAP) glasses were reproduced by molecular dynamics simulations. In addition, experimental methods, including Raman, differential scanning calorimetry, and synchrotron X‐ray total scattering, have been applied to characterize the structures of these glasses, together with the measurements of various glass properties, such as the density, glass transition temperature (Tg), coefficient of thermal expansion (CTE), and hardness. Moreover, the quantitative structure–property relationship (QSPR) analysis was performed to correlate the simulated glass structures with the experimentally measured properties. The simulation results reveal that the P–O–P linkages in the glass network are gradually replaced by the P–O–Al linkages with additional alumina to the compositions, which contributes to the property changes of the SAP glass systems. Meanwhile, the long chains in the SAP glasses tend to form ring structures, and the primitive rings are concentrated in the range between 4‐ and 20‐membered rings. Furthermore, QSPR analysis shows that the simulated structures have good correlations with the experimental properties, and the established structure–property model is promising in predicting certain properties of aluminophosphate glass systems.

Effect of Si/Al molar ratio and curing temperatures on the immobilization of radioactive borate waste in metakaolin-based geopolymer waste form

Immobilization of radioactive borate waste (RBW) using a geopolymer with a high Si/Al ratio has been challenging because boron-silicon networks lower the compressive strength and delay the setting time. In this study, metakaolin-based geopolymer waste form to immobilize simulant RBW was fabricated using different Si/Al ratios (1.0–1.4) and curing temperatures (26 and 60 ℃). The 7-day compressive strength results revealed that a certain amount of silicon and an elevated curing temperature are required to achieve high compressive strength and waste loading. Following waste acceptance criteria tests, all geopolymers exhibited compressive strengths higher than 3.445 MPa. The leachability index of boron was higher than 6.0, and the leaching mechanism was identified as diffusion. No significant structural changes in the geopolymer were observed after thermal cycling and gamma irradiation tests. The physically bound or unincorporated RBW was leached out of the geopolymer during water immersion and leaching tests; however, boron, which was chemically connected with silicon, was present as an inert phase together with a geopolymer binder. Consequently, immobilizing RBW using a geopolymer with a low Si/Al ratio (1.4) is beneficial in terms of RBW loading and structural durability.

Estimation of radionuclides leaching characteristics in different sized geopolymer waste forms with simulated spent ion-exchange resin

This study presents a method to solidify spent ion-exchange resin (IER) in a metakaolin-based geopolymer and shows results of mechanical strength, immersion, leaching, irradiation, and thermal cycling tests for waste acceptance criteria (WAC) to repository. The geopolymer waste form with 20 wt% of simulated spent IER met the WAC in South Korea (ROK), and the leaching tests of various sized-waste forms up to 15.0 × 30.0 cm and waste loadings up to 20 wt% for 1–5 d and 1–90 d achieved a leachability index, Li > 6. In a leaching test for 5 d, the cumulative fraction leached (CFL) for Cs, which leached the most, was linearly correlated with the square root of leaching time for all waste forms, and Li increased as the size of the waste form increased. The CFL was also correlated with elapsed time in the 90 d leaching test. The correlations among CFL, time, and volume-to-surface area ratio of waste forms used to estimate the Li of Cs of a 200-L sized geopolymer with 15 wt% IER showed the Li values as 14.73 (5 d) and 17.71 (90 d), respectively, indicating that the large-sized geopolymer waste form met the WAC.

Immobilization and He+ irradiation effects of Gd2Zr2O7-based ceramic waste form for radioactive waste disposal

The Gd2Zr2O7(GZO)-based ceramic waste form exhibits promising potential for radioactive waste immobilization. However, the isomorphic immobilization capacity and irradiation effects of GZO-based ceramic waste forms with varying waste loads remain inadequately understood. This study employed a facile combustion method to synthesize ceramic powders and utilized conventional sintering with a relatively short dwelling time to fabricate GZO-based ceramic waste forms. We investigated the isomorphic immobilization behavior and He ion irradiation effects of the synthesized waste forms. The outcomes demonstrate that GZO effectively immobilizes simulated waste composed of 11 types of oxides, achieving a waste load as high as 50 wt% with a single pyrochlore phase and homogeneous element distribution. Under He+ irradiation, aggravated structural degradations, including exacerbated lattice swelling, increased amorphization degree, and premature He bubble chain/microcrack formation, were observed in GZO-based waste forms with an increasing waste load.

Investigating electronic and optical properties of pyrochlore oxides Ta2A2O7 (A = Cd and Ge) for promising optoelectronic applications

Due to their stable crystal structure and controllable lattice parameters, rare earth zirconates with pyrochlore type structures have demonstrated a promise for usage in practical applications. We have investigated the electronic and optical properties of pyrochlore oxide compound named Ta2A2O7 (A = Cd and Ge) using density functional theory based on spin–orbit coupling and Hubbard (SOC + U) corrections to consider the existence electronic d orbitals of (A) and f elements (Ta). This study focuses on the characterization and investigation of pyrochlore oxides with the A2B2O7 composition, which have significant technological applications including quantum spin ices, solid oxide fuel cells, and nuclear waste forms. No evidence regarding magnetic moment is obtained from the first run with spin-polarization setup. Also, from the spectra of TDOS was showing a similar overall profile for both spin channels. The electronic properties (total and partial) densities of states as well as the optical properties such as the complex dielectric function, refractive index, absorption coefficient and reflectivity for wavelengths in the visible spectrum have been reported to explore the potential use of these compounds in technological applications. Consequently, the investigated compounds can be used in optoelectronic device fabrication.

Evaluation of the function of polymeric bentonite adsorbent to retain strontium and cobalt radionuclides in OPC matrices

The effect of polyacrylamide-bentonite (PAAmB) as an adsorbent/cement-enhancement material was examined for the retention of strontium (Sr2+) and cobalt (Co2+) ions from aqueous system. PAAmB composite was synthesized and analyzed by diverse characterization techniques. The acquired experimental data revealed that the addition of bentonite to polyacrylamide polymer (PAAmP) enhanced the adsorption of strontium and cobalt ions capacities. To examine the adsorption mechanism onto PAAmB, the experimental data were fitted using hyperbolic and Langmuir equations at different temperatures. It was found that the adsorption nature was chemisorption and the adsorbed amount of the studied ions increased with increasing the temperature. Immobilization of spent polyacrylamide-bentonite composite loaded with 85Sr and 60Co radionuclides in different extents with Ordinary Portland Cement (OPC) was investigated. The results showed that the optimal compressive strength was attained at OPC blended with 5% PAAmB composite. The leaching patterns of the studied radionuclides from the immobilized waste form were compared with the standard static long-term leaching approach of International Atomic Energy Agency (IAEA). The cumulative leaching fraction (CLF) of the studied radionuclides from PAAmB-OPC was found to be < 5% in all scrutinized conditions, which suggests the applicability of the IAEA-recommended approach for assessing the diffusion coefficient. The acquired leaching data were nonlinearly regressed with numerous mathematical kinetic models to determine the leaching parameters and to evaluate the prevailing leaching mechanism. The results from the regression scrutiny showed that 85Sr and 60Co leaching resulted from three succeeding leaching mechanisms that were the first-order reaction exchange among the waste matrix surface and the leaching solution, diffusion and dissolution. Compliant with IAEA, the calculated leachability indices values implied that the studied matrices performance was within a suitable range and the immobilized spent PAAmB matrices had an adequate mechanical efficacy.

A Design of Single-phase LaZnAl11O19 Ceramics for Disposition of Nuclear Waste Using Spark Plasma Sintering

The magnetoplumbite-structured LaZnAl11O19 ceramic possessing remarkable mechanical properties and chemical stability was deemed a promising waste form for immobilizing high-level waste. Nevertheless, the tedious procedures and relatively long dwell time constrained the development of present forming approaches. As an alternative, the single-phase LaZnAl11O19 ceramics with high density were rapidly synthesized through flux assisted spark plasma sintering (SPS) method. Systematic investigations into the factors influencing the final phase such as sintering temperature, uniaxial pressure, and dwell time were presented. The XRD and SEM results revealed that a pure phase LaZnAl11O19 could be obtained at 1450 °C with 30 MPa pressure for 20 min doping H3BO3 of 12.5 wt% as flux. Based on the structure information provided by characterizations, the SPS method was proved to be an alternative with rapid densification to the conventional solid-state reaction.

Densification and Immobilization of AgI-Containing Iodine Waste Forms Using Spark Plasma Sintering

In this study, porous Ag-xerogel (Ag-Xero), Ag-faujasite (Ag-FAU) zeolite, and Ag-mordenite (Ag-MOR) zeolite sorbents were loaded with iodine gas [I2(g)] under saturated conditions at 150 °C for 24 h, followed by densification and consolidation into monolithic waste forms using spark plasma sintering (SPS). For Ag-Xero materials, SPS pellets were made with as-loaded samples, while others were made with preheated (PH; 500 °C for 2 h) samples to help with densification. SPS processing was conducted at 50 MPa under different temperatures (T = 200–800 °C) for different times (t = 0.5–30 min), where eleven AgI-Xero samples, five AgI-FAU, and two AgI-MOR separate samples were produced. The primary goal was to look for the optimum processing parameters for each material to yield pellets with high iodine retentions, high densities, and low porosities while preventing AgI decomposition. The Ag-Xero showed the highest iodine loadings (qe = 470 mg g–1) compared to Ag-FAU (qe = 368 mg g–1) and Ag-MOR (qe = 108 mg g–1). Measured iodine concentrations were the highest in AgI-Xero pellets without PH, followed by AgI-Xero with PH, AgI-FAU, and then AgI-MOR. Silver utilization (I/Ag on a mol % basis) values were in the order of AgI-MOR ≈ AgI-Xero (no PH) > AgI-Xero (PH) > AgI-FAU. Chemical durabilities of SPS-densified AgI-Xero (PH) pellets were very favorable, with lower releases than SPS pellets made from AgI-Xero samples without PH. These results show promise for iodine waste form production.

Exploring the effects of Sr/Ce/Nd co-incorporation on the phase evolution and chemical stability of Sr0.5Zr2(PO4)3-(Ce, Nd)PO4 multiphase ceramics designed for nuclear waste forms

In this work, 0.6Sr0.5Zr2(PO4)3-0.4Ce1-xNdxPO4 (x = 0–1) multiphase ceramics were fabricated using a one-step microwave sintering technique, where Sr and Ce/Nd were utilized as the substitutes for the fission products 90Sr and actinide nuclides in high-level radionuclide wastes, respectively. The influences of Sr/Ce/Nd co-incorporation on the phase evolution, crystal structure, micromorphology, densification, and chemical stability of the as-prepared multiphase ceramic waste forms were systematically investigated. It was detected that the multiphase ceramics were composed of Sr0.5Zr2(PO4)3 (SrZP) phase and monazite phase regardless of x value, and (Ce, Nd)PO4 monazite solid solution was formed with Ce/Nd substitution. Rietveld refinement results further verified the cell parameters of (Ce, Nd)PO4 monazite solid solution regularly decreased with increasing Nd replacement, and the structural change of crystalline monazite did not affect the structure of SrZP phase. All samples presented a well-compacted and homogeneous microstructure, and their micromorphology did not change significantly with the replacement of Ce by Nd. Moreover, the relative density of the as-prepared multiphase ceramics all reached more than approximately 94.5 %, demonstrating excellent densification. Importantly, the good compatibility of SrZP and (Ce, Nd)PO4 monazite phases brought out superior chemical stability. The normalized elemental leaching rate showed no significant change for different Ce/Nd substituted samples, whose normalized leaching rates of Sr, Ce, and Nd were about 10−4 g/(m2·d), 10−7 g/(m2·d), and 10−6 g/(m2·d) order of magnitude, respectively. It is demonstrated that SrZP-(Ce, Nd)PO4 multiphase ceramics can be used as candidate materials for simultaneously immobilizing fission products and actinide nuclides of high-level nuclear wastes.

Glass, ceramic, and glass-crystalline matrices for HLW immobilisation

We briefly overview the utilisation of glasses, ceramics and glass crystalline materials (GCMs) composed of both vitreous and crystalline phases focusing on nuclear waste immobilisation and potential use of some advanced waste forms for incorporation of the rare earth elements (REE) and minor actinide (MA: Am, Cm) fraction of high-level waste (HLW).

Long-term stability of upgraded SiO2-Al2O3-P2O5 waste form in domestic groundwater for application in radioactive salt waste disposal

Long-term stability of upgraded SiO2-Al2O3-P2O5 waste form in domestic groundwater for application in radioactive salt waste disposal

The corrosion behavior of nonferrous metals in deep geological repository environments

AbstractThe advanced technologies of modern civilization produce radioactive wastes that require careful disposal if they cannot be recycled. These materials can originate from a variety of activities, such as scientific research, medicine, or nuclear power generation and, as such, can result in numerous waste forms. In this paper, the corrosion behavior of several less‐common metals is studied, specifically: aluminum, copper, lead, magnesium, zinc, and zirconium, all under simulated cementitious environments. The data reported rely on the production of hydrogen as a corrosion end‐product to calculate the uniform corrosion rate as a function of time. At 50°C, in either young cement water (pH 13.5) or saturated portlandite (pH 12.5) and after approximately 2 years of exposure, magnesium was found to corrode at ∼10 µm/year; aluminum at 1 µm/year (portlandite only); zinc at ∼100 nm/year; lead at &lt;1 nm/year and both copper and zirconium at less than 0.1 nm/year.