Nuclear waste management
Cation exchange resins
Cation exchange resins are commonly used in nuclear power plants in water purification systems used as coolant, as well as in irradiated fuel storage pools. The resin is based on a styrene / divinylbenzene copolymer. These resins, both anionic and cationic, are arranged in mixed bed units within purification / demineralization systems and undergo several regeneration cycles until chemical concentrations exceed the levels stated in the operating specifications. At that time, they are replaced and the spent resins are treated as a waste, generally of low activity. These wastes are conditioned and immobilized in cement-based mortars inside metal containers, for their subsequent transfer and storage in El Cabril (Córdoba, Spain).
Progress in nuclear engineering, with its associated generation and accumulation of nuclear waste, and the increasing requirements for environmental safety, have created an urgent need to improve materials and seek new approaches for safer immobilization of waste.
Various technologies have been used in recent decades to treat hazardous waste, such as pyrometallurgical and hydrometallurgical treatment, biological treatment, incineration method and solidification / stabilization (S / S), etc. Currently, Portland cement is the most widely used material for solidifying low and intermediate level radioactive waste, but it does not always guarantee the necessary efficiency of immobilization and accommodation of large amounts of waste of diverse composition
Compared with other materials, such as glass, ceramic, plastic, etc., cement has a variety of advantages, including ease of processing, low cost of raw materials, and low temperature for processing. However, most cement-based materials are porous, which makes radionuclides leach easily, combined with low thermal stability, a susceptibility to chemicals in the waste, which will affect hydration. and the hardening of the cement and a poor resistance to acid corrosion makes the retention of radionuclides in the cement matrix sometimes not the ideal.
To address the health and environmental risks associated with long-term storage of radioactive waste, better performing alternatives to Portland cement matrices have been sought in recent years; These alternatives include calcium aluminate, calcium sulfoaluminate, magnesium phosphate and alkaline activated cements, which can have higher efficiencies than Portland cement. Alternative cements produce a wide range of reaction products which, when compared to Portland cement, are characterized by lower solubility and higher ion exchange properties, different pH, faster setting and lower permeability of hardened pastes, etc. The differences in the composition and in the reaction products formed between the alternative cements and Portland cement suggest that there will be differences in the immobilization mechanism of the residues.