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Description
The aim of the project is to create novel types of concrete and study materials properties, using oil shale ash as an additional cementing material. Among the Baltic States, the most cement is produced in Latvia. Addition of oil shale ash (waste from the energy sector in Estonia) to the standard cement leads to lower natural resource and energy consumption, reducing pollution and raw materials expanses, as well as CO2 emissions. All above allows development of specialized concrete for a very important application - long-term storage of hazardous waste, which can be immobilized in concrete containers or directly in the concrete mass. There are several sources of hazardous waste in the Baltic and Nordic countries, from highly radioactive waste directly related to the use of nuclear energy as well as from specific medical equipment to toxic substances or metals with negligible radioactivity that can occur in various tasks such as the extraction and recycling of metals. An example of a large-scale source of radioactive waste of all levels of radioactivity is decommissioning of the Ignalina Nuclear Power Plant (NPP). Most of the Iganlina NPP radioactive waste is still in the temporary storage sites and a long-term solution is still being sought. The lack of long-term hazardous waste storage solutions and technologies may be a general problem for the entire Baltic region. During the project, it is planned to create and study a specialized oil shale ash concrete with basalt fiber reinforcement for mechanical property improvement. The filtration properties, radioactivity shielding capabilities and mechanical properties of the concrete under development will be tested. Methods and technologies to improve some of these properties will be sought. The project promoter is Riga Technical University. Partners are the Arctic University of Norway, University of Tartu, Lithuanian Energy Institute.
Summary of project results
The ICONDE (Innovation in Concrete Design for Hazardous Waste Management Applications) project investigated three important issues relevant to the Baltic States and Europe. First, it aimed to develop more "ecological" concretes with reduced cement content, as CO2 emissions from cement production contribute to the greenhouse effect and impact climate change. Second – in these new "ecological" concretes, cement will be partially replaced with oil shale ash (OSA), a waste product, accumulated in large quantities in Estonia, due to decades of oil shale combustion for electricity generation. Third, the project sought to convert these new "ecological" concretes into radioactive radiation-shielding fiber concretes - by adding short basalt-boron (BB) fibers. BB fibers effectively protect against radioactive radiation due to the boron (B) introduced into the fibers. The decommissioning of the Ignalina Nuclear Power Plant in Lithuania generates a large volume of various radioactive waste materials that must be securely stored in temporary facilities and, ultimately, in permanent storage sites. Concrete is the primary material used in waste management, making it essential for the concrete industry to develop more environmentally friendly and effective concrete formulations for handling radioactive and hazardous waste. This need is particularly urgent for Ignalina but is also relevant for all countries around the Baltic Sea and beyond.
The ICONDE project, running from May 2021 to April 2024, aimed to develop innovative concrete solutions for hazardous waste management using oil shale ash and basalt-boron fibers. The project was structured into six work packages (WPs), each focused on a distinct aspect of the research and development process.
During the first project phase, activities centered on the chemical, mineralogical, and radiological characterization of materials to be used during the experimental stage. Comprehensive material characterization was essential to understand and manage processes in the next experimental stage. The experimental stage aimed to design composite concrete mixtures tailored to the needs of hazardous waste management and disposal. The University of Tartu (UT) and Riga Technical University (RTU) completed the characterization of materials. UT and Lithuanian Energy Institute (LEI) conducted an analytical study of OSA material properties. Project partners from LEI performed radiological and chemical characterization of various types of low-, intermediate-, and high-level radioactive waste types from the nuclear industry.
In the second period, Riga Technical University in collaboration with Arctic University of Norway (UiT) performed broad experimental program, investigating mechanical properties of fiber concretes with varying concentrations of OSA and BB fibers. Based on data provided by LEI on concrete used in radioactive waste containers, four concrete recipes were accepted for future investigation: concrete with low compressive strength, medium strength, high strength, and one mix with a higher concentration of aggregates. Also, a new type of BB fiber was developed and patented.
In the third reporting period, the project’s scientific activities continued with numerical and experimental modeling of the new types of fiber concretes, which were divided into two modeling tasks: radiation shielding and modeling mechanical properties. UT and LEI conducted numerical modeling for radiation protection. While UT, LEI and RTU organized successful experimental verification of these numerical results in the Research Centre Rez (Czech Republic). RTU researchers advanced their modeling work with numerical thermo-mechanical properties of the developed fiber concretes and composites, using finite element method (FEM) approach. Stiffness, strength, load-bearing capacity (at room and at elevated temperatures) as well as crack formation and growth in fiber concrete samples were investigated. Theoretical data were validated through experiments conducted in RTU and UiT.
In the third period, LEI and UT thoroughly investigated mineralogical, elemental and microstructural properties of fiber concretes using XRD, XRF, SEM-EDS analysis. Also, differential thermal analysis; surface air and pore size distribution analysis were conducted by LEI.
Current practices and requirements for both general and specialized concrete types used in radioactive waste management during the decommissioning of the Ignalina NPP have highlighted the need to develop three categories of concrete: low-strength, medium-strength, and high-strength. All three types were successfully developed. While concrete used in hazardous waste management is highly regulated and certified, this does not always mean it is highly specialized or must meet exceptionally stringent requirements. That was our approach while planning the experimental phase. Nevertheless, concrete must withstand the test of time, effectively confine radioactive emissions, and meet the growing demands to reduce CO2 emissions.
What sets our approach apart from current practices is the reinforcement of otherwise brittle concrete with naturally sourced basalt fiber and the partial substitution of cement with oil shale ash, a waste material with cementitious properties. These modifications help make the concrete more environmentally friendly. A novel aspect of our approach also involved improvement of the basalt fiber with boron to control neutron flux through the concrete barrier. This allows thinner concrete walls to contain the neutron flux within permitted limits. This not only reduces the amount of concrete required for waste disposal but also helps lower the overall carbon footprint. The effectiveness of this approach was validated through both Monte Carlo numerical simulations and neutron shielding experiments.
A totally 1450 different fiber concrete samples were produced experimentally and tested mechanically. Their optimum shale ash concentrations have been determined, as well as their preferred fiber contents. Work has also begun on polymer composites incorporating oil shale ash.
The new type of fiber was developed, and a Latvian patent application was filed, which was not originally planned in the project.
Radioactive waste management is rather specialized and relatively low in volume, but it still needs to be addressed by every country, particularly those with nuclear power plants or industries that generate radioactive waste. But more importantly, our concrete recipes and approach to creating greener concrete can be applied to hazardous waste management more broadly.
The synergy of participating teams and the combination of approaches borne fruit - fifteen scientific publications indexed in SCOPUS have been submitted and published, project results have been presented in 16 conferences. And the work continues. An international scientific school focused on radioactive materials’ management was organized, and four Bachelor’s and Master’s theses related to the ICONDE project have been defended. Six PhD students - one in Narvik, three in Riga, two in Tartu and one in Kaunas - carried out research related to the ICONDE project’s objectives.
Key indicators of the project include the preparation of 12 joint scientific publications, one joint project proposal for further funding, one intellectual property protection claim, and altogether 27 researchers were supported.
Summary of bilateral results
The ICONDE project has significantly contributed to the achievement of the program’s objectives by fostering international cooperation between Baltic countries and establishing new connections with donor partners from Norway, specifically with the Arctic University of Norway (UiT). This collaboration has extended the possibilities for international cooperation, particularly in addressing hazardous waste management and the use of waste materials from the energy sector in Estonia and Lithuania. The partnership focused on sustainability and environmental solutions, aligning with innovative approaches to waste management.The research teams shared complementary skills, knowledge, and resources to collectively address project’s research challenges. Each partner brought specialized expertise, in areas such as radioactive waste management in nuclear power plant, concrete technology, and material testing for hazardous and radioactive waste storage. This multidisciplinary approach enabled a comprehensive understanding of the project’s challenges and facilitated effective solutions. Regular online meetings, held every two weeks, ensured continuous communication and collaboration, enabling partners to discuss scientific topics, plan experiments, and share results efficiently. And foster new contacts and future collaboration.