Solidification/Stabilization Technology for Radioactive Wastes Using Cement: An Appraisal.

Across the world, any activity associated with the nuclear fuel cycle such as nuclear facility operation and decommissioning that produces radioactive materials generates ultramodern civilian radioactive waste, which is quite hazardous to human health and the ecosystem. Therefore, the development of effectual and commanding management is the need of the hour to make certain the sustainability of the nuclear industries. During the management process of waste, its immobilization is one of the key activities conducted with a view to producing a durable waste form which can perform with sustainability for longer time frames. The cementation of radioactive waste is a widespread move towards its encapsulation, solidification, and finally disposal. Conventionally, Portland cement (PC) is expansively employed as an encapsulant material for storage, transportation and, more significantly, as a radiation safeguard to vigorous several radioactive waste streams. Cement solidification/stabilization (S/S) is the most widely employed treatment technique for radioactive wastes due to its superb structural strength and shielding effects. On the other hand, the eye-catching pros of cement such as the higher mechanical strength of the resulting solidified waste form, trouble-free operation and cost-effectiveness have attracted researchers to employ it most commonly for the immobilization of radionuclides. In the interest to boost the solidified waste performances, such as their mechanical properties, durability, and reduction in the leaching of radionuclides, vast attempts have been made in the past to enhance the cementation technology. Additionally, special types of cement were developed based on Portland cement to solidify these perilous radioactive wastes. The present paper reviews not only the solidification/stabilization technology of radioactive wastes using cement but also addresses the challenges that stand in the path of the design of durable cementitious waste forms for these problematical functioning wastes. In addition, the manuscript presents a review of modern cement technologies for the S/S of radioactive waste, taking into consideration the engineering attributes and chemistry of pure cement, cement incorporated with SCM, calcium sulpho-aluminate-based cement, magnesium-based cement, along with their applications in the S/S of hazardous radioactive wastes.

Review of the destruction of organic radioactive wastes by supercritical water oxidation.

Organic materials, such as ion exchange resins, plastic, oils, and solvents, are widely used in the operation and decommission of nuclear facilities. The generated radioactive organic wastes are both radioactive and organic; therefore, the degradation of such wastes becomes more difficult. Due to delays in the disposal of radioactive organic wastes, potential safety risks are increasing. With the advantages of degrading refractory organics rapidly and thoroughly, supercritical water oxidation (SCWO) has become a potential alternative way to degrade radioactive organic wastes. This review focused on the degradation characteristics of different radioactive wastes from the perspective of potential practical applications. Some improved methods for facilitating the degradation of radioactive wastes by SCWO are considered and analyzed. Moreover, the kinetics and intermediate pathways of radioactive organic wastes are further analyzed. The distribution, migration and transformation of radionuclides during the SCWO reaction, as well as the further processing of radionuclides in gas-, liquid- and solid-phase products, were summarized and discussed. Furthermore, some fruitful areas for further work were reviewed for the highly efficient degradation of radioactive organic wastes. This review can provide useful information and guidance for the industrial applications of SCWO treatment for radioactive wastes.

Radioactive waste treatments by using zeolites. A short review.

Radionuclides in the environment is an important issue, many techniques have been developed for the removal of radionuclides from the environment. One of those techniques is the adsorption and natural and synthesized materials have been used to remove different radionuclides from water. The adsorbents used for removal of radionuclides should have high retention capacity and they should be resistant to radiation. One of the natural materials used is the zeolites due to its high ion exchange capacities, adsorption efficiency, resistance to radiation and abundance. The present review describes the advances made on radioactive waste treatments using zeolites as adsorbents, the elements: cesium, strontium, cobalt, molybdenum, uranium, plutonium, americium, samarium, and europium were selected according to their nuclear importance and their presence in the environment. Firstly, a brief description of the zeolites is given and then a review on the separation of these radionuclides from water by using zeolites is presented.

Study of the Hydrolytic Stability of Fine-Grained Ceramics Based on Y2.5Nd0.5Al5O12 Oxide with a Garnet Structure under Hydrothermal Conditions.

The hydrolytic stability of ceramics based on Y2.5Nd0.5Al5O12 oxide with a garnet structure obtained by the spark plasma sintering (SPS) method has been studied. The tests were carried out in distilled water under hydrothermal conditions in an autoclave and, for comparison, in a static mode at room temperature. The mechanism of leaching of Y and Nd from the ceramics was investigated. It has been shown that at "low" temperatures (25 and 100 °C), the destruction of pores occured, and the intensity of the leaching process was limited by the diffusion of ions from the inner part of the sample to the surface. At "high" test temperatures (200 and 300 °C), intense destruction of the ceramic grain boundaries was observed. It was assumed that the accelerated leaching of neodymium is due to the formation of grain-boundary segregations of Nd3+ in sintered ceramics.

Liquid Low-Level Radioactive Waste Treatment Using an Electrodialysis Process.

In this work, the possibility of using electrodialysis for the treatment of liquid low-level radioactive waste was investigated. The first aim of the research was to evaluate the influence of the process parameters on the treatment of model solutions with different compositions. Subsequent experimental tests were conducted using solutions containing selected radionuclides (60Co and 137Cs), which are potential contaminants of effluents from nuclear power plants, as well as components often found in waste generated from industrial and medical radioisotope applications. The results of the experiments performed on real radioactive waste confirmed that electrodialysis was a suitable method for the treatment of such effluents because it ensured high levels of desalination and rates of decontamination. The most important parameters impacting the process were the applied voltage and electrical current. Moreover, this research shows that the application of the ED process enables the separation of non-ionic organic contaminants of LLW, which are unfavorable in further stages of waste predisposal.

Removal of Radioactive Iodine Using Silver/Iron Oxide Composite Nanoadsorbents.

Efficient and cost-effective removal of radioactive iodine (radioiodine) from radioactive contaminated water has become a crucial task, following nuclear power plant disasters. Several materials for removing radioiodine have been reported in the literature. However, most of these materials exhibit some limitations, such as high production cost, slow adsorption kinetics, and poor adsorption capacity. Herein, we present silver/iron oxide nanocomposites (Ag/Fe3O4) for the efficient and specific removal of iodine anions from contaminated water. The Ag/Fe3O4 were synthesized using a modified method and characterized via scanning electron microscopy, transmission electron microscopy, and X-ray diffraction analyses. This adsorbent showed a high adsorption capacity for iodine anions (847 mg/g of the adsorbent) in pure water. Next, Ag/Fe3O4 was applied to the removal of radioiodine, and high removal efficiencies were observed in water. In addition, its desalination capacity was retained in the presence of competitive ions and varied pH. After the adsorption process, Ag/Fe3O4 was easily removed from the water by applying an external magnetic field. Moreover, the same operation can be repeated several times without a significant decrease in the performance of Ag/Fe3O4. Therefore, it is expected that the findings presented in this study will offer a new method for desalinating radioiodine in various aqueous media.

Insights into the effect of NaOH on the hydration products of solidified cement-NaNO3 matrices and leaching behavior of Sr2.

The low-level and intermediate-level radioactive waste is generally an alkaline solution with high concentration of sodium salts. Moreover, extra NaOH will be added into the matrices when the high content of mineral admixtures is used in the preparation of solidified cement matrices. This study mainly researches the influence of NaOH on the structure of C-S-H gels and the leaching rate of Sr2+ in the solidified cement matrices by isothermal conduction calorimetry, X-ray diffractometry, thermogravimetry, 29Si nuclear magnetic resonance, mercury intrusion porosimetry and inductively coupled plasma. The results show that the addition of NaOH accelerated the hydration of cement in the early age but decreased the normalized hydration heat until 28 days. Also, the fraction of total Ca(OH)2 decreased with the increasing content of NaOH. Moreover, NaOH promoted the formation of C-S-H gels along the main chain by increasing the mean chain length but decreased the Q3 sites. However, the addition of NaOH has optimized the pore structure through reducing the porosity and median pore diameter. At last, the cumulative leaching fraction of Sr2+ at the NaOH content of 10% decreased by 17.5% compared to the NaOH content of 0.82%. Based on the results, it can be concluded that NaOH enhanced the adsorption capacity of C-S-H gels to Sr2+ and improved the immobilization performance of solidified cement matrices.

A nuclear real-world experiment: Exploring the experimental mindsets of radioactive waste management organisations in France, Belgium and Canada.

Following the theoretical approach of Herbold (1995), Gross and Krohn (2005), and Van de Poel et al. (2017), this article argues that nuclear waste management is a real-world experiment. Based on this first assumption, we examine how radioactive waste management (RWM) organizations conceive or organize their experiments. Through three illustrative case studies in France, Belgium and Canada, we highlight how the RWM organizations obliged to participate in complex networks and unable to completely control the experimental process, adopt two different attitudes: an "open" or "closed" experimental mindset. We argue that these mindsets provide different answers to the questions: which main variables to focus on, how and who should design them, how to deal with conflicts and unexpected events, what are the justifications for participation and expert analysis, and what are the expected outputs and outcomes. The findings underline that although some RWM organizations have -at least since the participatory turn- had some 'open' mindset moments in some cases, they quickly revert to a closed mindset. We conclude by emphasizing the need for practitioners and scholars to further examine and evaluate the virtues of the open mindset when the experimenter assumes the program has a real-world experimental status. This status recognizes the limits of control over experimental conditions, allows for more substantial moral considerations when making technical choices before wider audiences and allows for collective sharing of responsibility, knowledge production and trade-offs over such a long-term and controversial program.

A review on solid phase extraction of actinides and lanthanides with amide based extractants.

Solid phase extraction is gaining attention from separation scientists due to its high chromatographic utility. Though both grafted and impregnated forms of solid phase extraction resins are popular, the later is easy to make by impregnating a given organic extractant on to an inert solid support. Solid phase extraction on an impregnated support, also known as extraction chromatography, combines the advantages of liquid-liquid extraction and the ion exchange chromatography methods. On the flip side, the impregnated extraction chromatographic resins are less stable against leaching out of the organic extractant from the pores of the support material. Grafted resins, on the other hand, have a higher stability, which allows their prolong use. The goal of this article is a brief literature review on reported actinide and lanthanide separation methods based on solid phase extractants of both the types, i.e., (i) ligand impregnation on the solid support or (ii) ligand functionalized polymers (chemically bonded resins). Though the literature survey reveals an enormous volume of studies on the extraction chromatographic separation of actinides and lanthanides using several extractants, the focus of the present article is limited to the work carried out with amide based ligands, viz. monoamides, diamides and diglycolamides. The emphasis will be on reported applied experimental results rather than on data pertaining fundamental metal complexation.

Diseño conceptual de un sistema nuclear avanzado para la transmutación de desechos y aplicaciones energéticas sostenibles / Conceptual desing of advanced nuclear system for waste transmutation and sustainable energy applications

En el trabajo se evaluaron los avances en el diseño conceptual de un sistema transmutador de lecho de bolas refrigerado por gas. El dispositivo permite aplicaciones energéticas de alta eficiencia en modo de cogeneración, tanto para la producción de electricidad como calor de alta temperatura para la producción de hidrógeno. Una característica particular del sistema es su operación en modo subcrítico, manejado por una fuente de neutrones activada por un acelerador. Lo anterior produce una significativa ventaja desde el punto de vista de la seguridad y flexibilidad en la operación con tipos de combustible nuclear no tradicionales, lo que posibilita reducir las cantidades de residuos nucleares y además aprovecharlos para la producción de energía con una alta eficiencia. En el trabajo se evaluaron las posibilidades del sistema para trasmutar los desechos del combustible gastado de los reactores nucleares de agua ligera.

In this paper the progress in the conceptual design of a gas cooled pebble bed transmuter system was evaluated. This device allows highly efficient energy applications in cogeneration mode, both, for electricity power production and high temperature heat for hydrogen production. A particular feature of the system is subcritical operation mode, driven by a neutron source activated by an accelerator. This produces a significant advantage from the point of view of safety and operational flexibility in the operation of nuclear non-standard fuel types, allowing the possibility of reducing the amount of nuclear waste and also using them for high efficiency energy production. The possibilities of the system to transmute nuclear reactors spent fuel wastes into light water were evaluated.

An overview of radioactive waste disposal procedures of a nuclear medicine department.

Radioactive wastes from hospitals form one of the various types of urban wastes, which are managed in developed countries in a safe and organized way. In countries where growth of nuclear medicine services are envisaged, implementations of existing regulatory policies and guidelines in hospitals in terms of handling of radioactive materials used in the treatment of patients need a good model. To address this issue, a brief description of the methods is presented. A designed prototype waste storage trolley is found to be of great help in decaying the I-131 solid wastes from wards before releasing to waste treatment plant of the city. Two delay tanks with collection time of about 2 months and delay time of 2 months alternately result in 6 releases of urine toilet effluents to the sewage treatment plant (STP) of the hospital annually. Samples of effluents collected at releasing time documented radioactive releases of I-131 much below recommended levels of bi-monthly release. External counting of samples showed good statistical correlation with calculated values. An overview of safe procedures for radioactive waste disposal is presented.

Iodoterapia: avaliação crítica de procedimentos de precaução e manuseio dos rejeitos radioativos / Iodotherapy: critical assessment of the precautionary and handling procedures of radioactive wastes

Investigações sobre os procedimentos de precaução e manipulação dos rejeitos radioativos, gerados na iodoterapia, são muito pouco discutidas na literatura. A aplicação destes procedimentos de precaução, atendendo às normas da legislação vigente, depende diretamente do grau de conhecimento da equipe de enfermagem na manipulação do 131 I, radioisótopo empregado na iodoterapia. Este trabalho apresenta uma avaliação crítica dos procedimentos de precaução e manipulação adotados pela equipe de enfermagem na terapêutica da iodoterapia utilizando um instrumento de análise, validado por um pré-teste e aplicado à equipe de enfermagem da unidade de internação da iodoterapia, em três hospitais (A, B - filantrópicos; C - privado), analisando: conhecimento específico da equipe de enfermagem e atendimento às normatizações. A análise comparativa mostrou significativa diferença dos procedimentos realizados na iodoterapia pela equipe de enfermagem nos hospitais estudados. Os procedimentos de precaução e a adequação da infra-estrutura na realização da terapêutica da iodoterapia dependem fundamentalmente da fiscalização dos órgãos competentes, doconhecimento específico e responsabilidade do profissional responsável pelo serviço de Medicina Nuclear, e do incentivo da direção do estabelecimento prestador de saúde.