General Context
The safe management of radioactive waste is a critical challenge for environmental protection and public health, as nuclear energy emerges as a key driver in the global transition to green energy. Our research line focuses on the design, synthesis, and characterization of advanced adsorbent materials, such as 2D silicates and their derived composites, aimed to minimize the environmental risks associated with nuclear energy. Our studies encompass the entire spectrum of high-level radioactive waste management processes.
Dry Storage of nuclear waste fuel
Dry storage is an essential solution for the long-term safe management of spent nuclear fuel, using specialized containers that preserve the fuel without the need for active water cooling. Traditionally, these containers feature a neutron barrier made of a polymeric matrix: high in hydrogen to moderate fast neutrons, and dispersed with boron-based materials to absorb slow neutrons. However, these matrices often suffer from low mechanical and thermal stability, low melting points, and poor expansion coefficients, which can compromise their integrity under the extreme heat of spent fuel. Our research focuses on incorporating natural nanoclays to create highly resilient nanocomposites to improve these properties. Furthermore, thanks to their exceptional actinide adsorption and retention capacity, these clays act as chemical immobilizers for radionuclides, significantly enhancing the barrier’s overall preventive capabilities.
Vitrification and Immobilization
The treatment of high-level waste demands extremely durable immobilization techniques to prevent long-term environmental leaching. Complementary to traditional vitrification processes—where waste is confined in a glass matrix—our research explores theoretical and experimental approaches to alternative ceramic and crystalline matrices. A prime example is our work with zirconium and hafnium silicate ($Zr_{1-x}Hf_xSiO_4$), which serves as a highly stable matrix for radioactive waste immobilization. Additionally, we are pioneering the development of innovative luminescent sensors for the continuous, real-time monitoring of confined waste.
Deep Geological Repository
Deep geological repositories represent the ultimate, globally accepted containment solution for high-level radioactive waste. In this critical area, our scientific work evaluates the long-term viability and stability of both geological and engineered barriers.
Specifically, we investigate the acid stability of clay minerals and its direct implications for geological disposal processes. By analyzing the thermodynamic and structural behavior of natural and synthetic clays exposed to nuclear waste corrosion products in the near-field, our research aims to guarantee a secure, durable, and permanent seal for future generations.
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A Technological Approach Based on Engineered Nanoclay Composites for Cesium and Iodine Retention.
Chemosphere, 2023
The development of effective and environmentally friendly methods for separating hazardous radionuclides from waste poses a significant technological challenge. 137Cs and 131I are among the most important radionuclides discharged into the environment by nuclear power plants. One of the best ways to eliminate them involves adsorption on clay minerals. In this regard, studies have demonstrated that organofunctionalized clay minerals are effective adsorbents. Thus, this study investigates the capability of organofunctionalized synthetic design clay minerals to jointly eliminate cesium and iodine. The adsorbents studied are a range of organofunctionalized clay minerals with alkylammonium cations of different alkyl chain lengths (2, 3 and 18) and some physical mixtures of raw clay minerals and octadecylammonium compounds. Organofunctionalized synthetic swelling highly charged micas are effective adsorbents for the simultaneous adsorption of cesium and iodine. In addition, the optimal system is a mixture of Na-M4 with octadecylammonium (50% w/w).
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Insight into the Role of Temperature, Time and pH in the Effective Zirconium Retention Using Clay Minerals
Journal of Environmental Management, 2022
The use of zirconium in chemical industries generates a potential risk of Zr contamination in the environment, with particular concern for the decommissioning of uranium-graphite reactors. Among the natural adsorbents employed for the treatment of nuclear waste, clay minerals showed a very high affinity adsorption for radionuclides, but the influence of the chemical composition, pressure, temperature and time reaction have not yet been analysed on deep. Thus, the objective of this research is to explore several experimental conditions for an actual prediction of the behaviour of zirconium immobilization by clay minerals. The results have shown that factors such as zirconium cation nature (Zr4+ or ZrO2+), temperature, time and pH influence the extent of zirconium immobilization by clay minerals and the zirconium phases generated. At moderate conditions, zirconium tectosilicates are formed and evolve to zircon at high temperature and a longer time reaction.
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Exploring the Local Environment of the Engineered Nanoclay Mica-4 under Hydrothermal Conditions Using Eu3+ as a Luminescent Probe
R. Martín-Rodríguez, F. Aguado,
M. D. Alba, R. Valiente,
E. Pavón, and A.C. Perdigon-Aller
Journal of Alloys and Compounds, 2022
High charge mica Na4Al4Si4Mg6O20F4, Mica-4, is a promising candidate as a filling material to immobilize high-level radioactive waste in deep geological repositories due to its extraordinary adsorption capacity. In contrast to traditional clay materials, the structural composition of this mica, with a high content of aluminum in the tetrahedral sheet, enhances its chemical reactivity, favoring the formation of new crystalline phases under mild hydrothermal conditions, and thus providing a definitive isolation of the radionuclides in the engineered barrier. Moreover, this synthetic clay has some features that allow its use as an optical sensor by doping with luminescent rare earth cations such as Eu3+. In this paper we discuss the local structure of the nanoclay Mica-4 using Eu3+ as a local probe to track the physical and chemical modifications under hydrothermal conditions. For that purpose, a set of hydrothermal experiments has been carried out heating Mica-4 and an aqueous Eu(NO3)3 solution in a stainless steel reactor at different temperatures and times. Optical properties of the as-treated samples were characterized by spectroscopic measurements. The fine peak structure of emission and the relative intensity of different Eu3+ transitions as well as the luminescence lifetime have been correlated with the structure and composition of this nanoclay, and the interaction mechanisms between the lanthanide ions and the clay mineral at different temperatures and times. Special attention has been paid to understanding the role of the aluminum content, which may act as either an aggregating or dispersing agent, in the optical features and reactivity of the system. © 2022 The Authors
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Influence of Temperature and Time on the Eu3+ Reaction with Synthetic Na-Mica-n (N=2 and 4)
Chemical Engineering Journal, 2016
Bentonite is accepted as the best clay material for the engineered barrier of Deep Geological Repositories (DGRs). The performance of clay as the main component of the engineered barrier in the DGR has been intensively studied and the structure of the selected clay mineral play a crucial role. In this sense, a new family of synthetic swelling silicates, Na-Mica-n, with tuned layer charge (n) values between 2.0 and 4.0 per unit cell has recently been synthesized and a general synthetic method has been reported. These swelling high-charge micas could be highly valuable for the decontamination of harmful cations. The ability of these micas to immobilize Eu3+ under subcritical conditions has been probed. The adsorption was in both non-specific sites (cation exchange mechanism) and specific sites (chemical reaction or surface defects adsorption). Moreover, its adsorption capacity, under the same conditions is higher than in saponite and far superior to the bentonites. © 2015 Elsevier B.V.