Ba ngladesh is constructing its first commercial nuclear power installation (2×VVER-1200) at Rooppur, Pabna, which is expected to operate fully by 2026.
the national plan also includes a second nuclear plant, contributing to at least 10% of total electricity from nuclear sources by 2040. Radioactive waste management is therefore becoming increasingly important. While there is a general agreement that spent fuel from RNPP will be shipped back to the Russian Federation under intergovernmental agreements, Bangladesh must still independently manage LILW, i.e., disused sealed radiation sources (DSRS), waste generated from the 3 MW TRIGA Mark-II research reactor, and medical, industrial, and research radioactive waste streams. Bangladesh recently approved national policies assigning BAEC responsibility for developing RW management strategies and technical capacities.
the selection of a suitable geologic medium, particularly for near-surface disposal structures, is therefore an essential research priority. Near-surface disposal involves placing low and intermediatelevel radioactive waste in shallow repositories, typically at depths of up to a few hundred meters below the surface.
these types of waste have relatively short-lived radionuclides that decay quickly, so they don’t require long-term isolation. It is often situated on land where the waste is relatively easy to access for monitoring and management.
the waste is often placed in engineered barriers like concrete vaults or steel containers to prevent contact with groundwater or surface water.
the site is then sealed with soil or other materials to minimize exposure.
the advantage of near-surface disposal is lower cost compared to deep geological disposal, easier to construct, monitor, and manage, and shorter planning and construction periods. However, near-surface disposal is limited to low- and intermediate-level waste (not for high-level waste), is more vulnerable to surface disturbances (e.g., weathering, erosion, human activities), and potential for contamination of groundwater over time if not properly sealed. Basic concept of geological disposal of RW On the other hand, deep geological disposal involves placing high-level radioactive waste (HLW) deep underground, typically several hundred to thousands of meters below the earth’s surface, in stable geological formations. Primarily for high-level waste, which includes spent nuclear fuel and other materials from reactors that remain highly radioactive for thousands to millions of years.
these sites are typically located in geologically stable regions (e.g., deep sedimentary rock, granite, or salt formations) where the conditions are unlikely to change significantly over the long term.
the sites need to have very low seismic activity, minimal groundwater movement, and minimal potential for human interference.
in this system, waste is placed in canisters, which are then sealed in tunnels or vaults deep underground. Overlying rock layers act as a natural barrier to radiation, while engineered barriers (like bentonite clay) provide additional protection.
the goal is to isolate the waste for thousands to millions of years, well beyond the life of human-made structuresGlobal Geological Disposal Practices Using Clay Clay formations are widely recognized globally as one of the most promising host rocks for RW disposal due to their intrinsic physical, chemical, and geo-mechanical properties. Various countries are actively pursuing the use of natural clay in waste disposal systems. Finland has made significant strides in utilizing natural clay as part of its deep geological disposal strategy.
the Onkalo repository, located in the bedrock of the Olkiluoto nuclear power plant, is the world’s first deep geological repository for high-level radioactive waste (HLW).
the repository is designed to safely store waste for up to 100,000 years.
the Onkalo site utilizes bentonite clay (a smectite-rich clay) as a key component of the engineered barrier system (EBS). Bentonite’s low permeability, high swelling capacity, and ability to adsorb radionuclides make it an ideal material for preventing groundwater flow and ensuring the long-term isolation of radioactive waste.
extensive testing, including laboratory experiments and field trials, has demonstrated that bentonite will remain stable under the expected conditions at Onkalo, with its swelling properties providing selfsealing capabilities in case of cracks or gaps. Finland’s Onkalo project is regarded as a model for safe geological disposal, and its successful implementation of natural clay has set a global standard for future nuclear waste management projects. Sweden is also actively pursuing the use of natural clay in radioactive waste disposal, with the Forsmark repository being a key project for the disposal of high-level radioactive waste.
the repository is designed to be located at a depth of approximately 500 meters within the Swedish bedrock, where it will store radioactive waste for the long term. Like Finland, Sweden is using bentonite clay as a primary sealing material.
the clay is intended to form part of the EBS, alongside a thick layer of granite bedrock, to isolate the waste.
the Cigéo repository in France will use bentonite clay as part of the multi-barrier system, which includes a combination of rock and engineered materials. Bentonite is expected to act as a buffer between the waste containers and the surrounding rock, helping to prevent water from migrating and spreading contamination.
the French nuclear waste management agency (ANDRA) has been researching to understand the long-term performance of bentonite clay, particularly in relation to its behavior under high radiation and temperature conditions.
this is especially important as the waste will generate heat, which could affect the clay’s properties over time.
the Yucca Mountain repository in Nevada was a proposed site for the disposal of high-level radioactive waste in the United States. While the project has been politically and legally stalled for years, its design included extensive use of natural clay as a sealing material.
the proposed design for Yucca Mountain included a bentonite clay buffer, which was meant to reduce water flow and limit the migration of radionuclides.
the Opalinus Clay in Switzerland selected for HLW, spent fuel, and ILW disposal, exhibits extremely low permeability (10-13-10-11m/s) and diffusive transport-dominated migration.
the Swiss concept uses a bentonite-sand buffer around steel canisters. Boom Clay in Belgium (poorly indurated clay) was chosen for HLW and LILW, which was selected due to favorable porosity, homogeneity, retention capacity, and mechanical properties. Japan’s disposal research focuses on Neogene marine clay formations and bentonite-based engineered barriers. Studies evaluate coupled thermal and mechanical responses of bentonite under simulated repository conditions (JAEA, 2019). Clay Mineralogy and Behavior Relevant to RW Disposal Natural clays, particularly those rich in smectite minerals (e.g., montmorillonite), are characterized by several important properties that make them suitable for radioactive waste containment: Low Permeability: Clays are known for their very low hydraulic conductivity, which is a key factor in preventing the migration of radioactive isotopes.
the tightly packed mineral structure of clay forms a barrier that limits the flow of water and contaminants, reducing the possibility of leaching. High Ion-Exchange Capacity: Clays have a high cation-exchange capacity (CEC), meaning they can adsorb and immobilize a wide variety of ions, including radionuclides.
this property is crucial for reducing the mobility of radioactive elements such as cesium, strontium, and uranium. Stability under Long-Term Conditions: Natural clays, particularly those formed in stable geological environments, are generally resistant to chemical weathering and physical disruption.
their stability under both anoxic and alkaline conditions makes them ideal for long-term waste containment, where the material must remain intact for thousands to millions of years. Swelling and Self-Healing Properties: Certain clays, especially smectites, exhibit a unique ability to swell when in contact with water.
this can enhance their sealing capacity, as the swelling clays can close up cracks and gaps in the barrier.
this selfhealing ability can improve the integrity of the containment system over time.
abundance and Cost-Effectiveness: Natural clays are widely available and relatively inexpensive compared to other engineered materials.
this makes them an attractive option for large-scale waste disposal projects. Several types of natural clays have been considered for use in radioactive waste disposal systems.
among the most commonly studied are: Smectite Clays (e.g., Montmorillonite): Montmorillonite, a member of the smectite group, is particularly well-suited for radioactive waste containment due to its high swelling capacity, ion-exchange properties, and low permeability. Smectites are widely used in both laboratory and field tests for evaluating the effectiveness of clay-based barrier systems.
illite Clays: Illite clays are also considered for waste disposal applications, although they tend to have a lower swelling capacity than smectites.
they are often found in environments with more stable physical and chemical conditions, which makes them suitable for certain geological formations. Kaolinite and Chlorite Clays: Kaolinite and chlorite clays are less commonly used but are being studied for their potential in low-level radioactive waste disposal.
they have a relatively low ion-exchange capacity compared to smectites, but may still offer suitable containment properties under specific conditions. Major clay types and their repository applications.
the suitability and challenges of natural clays for radioactive waste disposal The suitability of natural clays for radioactive waste disposal depends on a variety of factors, including the type of waste, the specific characteristics of the clay, and the geological environment. The key aspects that affect the performance of clays in waste disposal systems are geochemical interactions and radionuclide retention, mechanical and thermal stability, impact of groundwater and fluid flow, and long-term performance and aging. However, there are some challenges and limitations of natural clays. Natural clays exhibit significant variability in their composition, mineralogy, and behavior, which can affect their suitability for specific waste disposal applications. Variability in smectite content, for example, can impact swelling properties and ion-exchange capacity. While clays are generally stable, they can be susceptible to physical disruption from seismic activity or erosion over long periods.
the integrity of clay barriers must be carefully considered in areas with seismic risk or active hydrological conditions.
exposure to high temperatures, radiation, or extreme pH conditions could lead to the transformation of clay minerals, potentially reducing their ability to retain radionuclides or act as effective barriers. For instance, smectite can transform into less reactive minerals like illite or chlorite under certain conditions. Madhupur clay for the radioactive waste disposal in Bangladesh The long-term disposal of radioactive waste requires materials and rock formations that provide reliable containment over geological timescales.
among the key criteria are very low permeability, high sorption capacity for radionuclides, mechanical and chemical stability, and predictable behavior under coupled thermalhydraulic-mechanical-chemical conditions. Bangladesh lies in a tectonically active deltaic region dominated by alluvial sediments, deltaic clays, Pleistocene Madhupur Clay, coastal marine clay, tertiary mudstone/shale in Chittagong Hill Tracts, and clay-rich layers in Sylhet and Bogura basins. Madhupur Clay is widely studied and geographically extensive, making it the most viable natural clay candidate.
this type of clay is described as highly weathered, reddish-brown to brickred clayey deposit, often capping uplifted blocks or terraces above alluvial flood plains. Madhupur Clay is suitable for nearsurface LILW disposal but not for deep HLW repositories. For future HLW disposal, tertiary mudstones of the Chittagong Hill Tracts show potential and need systematic exploration. Coastal and marine clays have high water content, are compressible, and saline, which makes them unsuitable for deep disposal, and may be used for engineered barriers after purification/bentonite blending.
tertiary mudstone in hill tracts lithified and indurated claystone/mudstone, comparable to argillite Boom Clay in Belgium in terms of diagenesis, which requires systematic geotechnical, hydrogeological, and mineralogical evaluation. Conclusion: Natural clay formations provide some of the most reliable and scientifically proven geological media for radioactive waste disposal. Bangladesh’s geological setting includes significant clay deposits, notably Madhupur Clay and Tertiary mudstones, which hold potential for RW containment, particularly for near-surface LILW disposal. However, extensive geotechnical, hydrogeological, mineralogical, and structural characterization is required before selecting any site for longterm RW isolation. Building a national clay characterization program and establishing a deep geological research facility will be vital steps toward a sustainable RW management strategy.
there are some research gaps and challenges, such as geological and hydrogeological data gaps, geo-mechanical characterization, groundwater flow modeling and diffusion coefficients, fault and fracture mapping at disposal depths, etc.
in addition, there are some engineering and technological gaps, such as a lack of national bentonite characterization programs, the absence of underground research laboratories, and limited experience with large-scale engineered barrier systems.
there are also regulatory and institutional challenges, including the need for site-selection guidelines, establishing RW disposal safety case methodology and skilled manpower, and RandD infrastructure development. Under these circumstances, Bangladesh can adopt the multibarrier clay-based disposal concepts used in Europe, where indigenous clay can be blended with imported sodium bentonite to create engineered barriers. For all of this, Bangladesh needs to establish regional collaboration with the IAEA, European clay disposal programs like ANDRA, NAGRA, ONDRAF, and Asian countries building clay repositories