Yüksek sıcaklık ve Etibor-48 mineralinin bentonitin şişme basıncı ve zemin-su karakteristik eğrileri üzerindeki etkileri

Öz

Yüksek seviyeli nükleer atıkların güvenli bertarafı için derin jeolojik depolarda tampon ve/veya dolgu malzemesi olarak sıkıştırılmış bentonit kullanımı önerilmektedir. Bentonitin yüksek şişme potansiyeli ve düşük geçirgenlik özellikleri, bu önerinin temel dayanaklarını oluşturmaktadır. Depolarda kullanılan bentonit, yeraltı suyu ile hidrate olarak kendiliğinden sızdırmaz bir bariyer oluştururken, aynı zamanda atık kutusundan yayılan yüksek sıcaklığa maruz kalacaktır. Bu süreçte, dış bölgelerde şişme eğilimi görülürken, atık kutusuna yakın bölgelerde yüksek sıcaklık nedeniyle doygun olmayan bir ortam oluşabilmektedir. Bu koşullar, bentonitin hidrolik ve mekanik özelliklerini etkileyebilir ve uzun vadeli performansını sınırlayabilir. Bu nedenle, bentonitin yeraltı suyu hareketleri ve sızdırmazlık özelliklerinin değerlendirilmesi için farklı termal koşullarda zemin-su karakteristik eğrilerinin ve şişme basıncının belirlenmesi büyük önem taşımaktadır. Sıcaklık döngüleri, bentonitin su tutma kapasitesi ve şişme basıncı gibi kritik özelliklerini olumsuz yönde etkileyebilmektedir. Bu çalışmada, bentonitin yüksek sıcaklık koşullarındaki mühendislik özelliklerini iyileştirmek amacıyla, düşük termal genleşme özelliği ile bilinen Etibor-48 (E-48) bor minerali katkı maddesi olarak kullanılmıştır. Sıkıştırılmış bentonite %10 ve %20 oranlarında E-48 bor minerali eklenerek karışımların şişme basıncı ile zemin-su karakteristik eğrileri, oda sıcaklığı ve yüksek sıcaklık (80 °C) koşullarında incelenmiştir. Şişme basıncı deneyleri sabit hacim yöntemiyle ödeometre sisteminde, zemin-su karakteristik eğrileri ise buhar denge tekniği kullanılarak belirlenmiştir. Bulgular, yüksek sıcaklık ve E-48 katkısının bentonitin su tutma kapasitesini ve şişme basıncını azalttığını ortaya koymuştur. Ayrıca kuruma yolunun nemlenme yoluyla örtüşmediği ve katkısız bentonitin, E-48 katkılı karışımlara kıyasla daha yüksek su tutma kapasitesine sahip olduğu tespit edilmiştir. Bu sonuçlar, yüksek sıcaklık koşullarında bentonit bazlı tampon malzemelerin performansını değerlendirmek ve optimize etmek için katkı maddelerinin etkisini anlamada önemli bilgiler sunmaktadır.

Anahtar Kelimeler

• Nükleer atık
• Yüksek sıcaklık
• Bentonit
• Şişme basıncı
• Zemin-su karakteristik eğrisi
• Etibor-48

Effects of high temperature and Etibor-48 mineral on the swelling pressure and soil-water characteristic curves of bentonite

Abstract

Compacted bentonite as a buffer and/or backfill material in deep geological repositories is recommended to safely dispose of high-level nuclear waste. The high swelling potential and low permeability properties of bentonite are the main bases for this recommendation. Bentonite used in the repositories will hydrate with groundwater to form a self-sealing barrier while exposed to the high temperature emitted from the canister. In this process, the outer zones tend to swell, while the zones close to the canister may become unsaturated due to the high temperature. These conditions can affect the hydraulic and mechanical properties of bentonite and limit its long-term performance. Therefore, determining soil-water characteristic curves and swelling pressure at different thermal conditions is of great importance for evaluating groundwater movement and sealing properties of bentonite. Temperature cycles can adversely affect critical properties of bentonite, such as water retention capacity and swelling pressure. In this study, Etibor-48 (E-48) boron mineral, known for its low thermal expansion properties, was used as an additive to improve the engineering properties of bentonite under high temperature conditions. E-48 mineral was added to the compacted bentonite at 10% and 20% ratios, and the swelling pressure and soil-water characteristic curves of the mixtures were investigated at room temperature and high temperature (80 °C) conditions. The swelling pressure tests were performed using the constant volume method in an oedometer system, and the soil-water characteristic curves were determined using the vapor equilibrium technique. The results showed that high temperature and E-48 addition decreased the water retention capacity and swelling pressure of bentonite. It was also found that the drying path did not overlap with the wetting path, and the additive-free bentonite had a higher water retention capacity than the E-48-added mixtures. These results provide important insights into understanding the effect of additives to evaluate and optimize the performance of bentonite-based buffer materials under high-temperature conditions.

Keywords

• Nuclear waste
• High temperature
• Bentonite
• Swelling pressure
• Soil-water characteristic curve
• Etibor-48

References

1. [1] He Y, Ye WM, Chen YG, Chen B, Ye B, Cui YJ. “Influence of pore fluid concentration on water retention properties of compacted GMZ01 bentonite”. Applied Clay Science, 129, 131-141, 2016.
2. [2] Marcial D, Delage P, Cui YJ. “On the high stress compression of bentonites”. Canadian Geotechnical Journal, 39(4), 812-820, 2002.
3. [3] Martín PL, Barcala JM, Huertas F. “Large-scale and long-term coupled thermo-hydro-mechanic experiments with bentonite: the FEBEX mock-up test”. Journal of Iberian Geology, 32(2), 259-282, 2006.
4. [4] Dutt R, Sharma R, Singh A. “Groundwater infiltration and its implications in nuclear waste containment”. Hydrogeology Journal, 20(4), 677-688, 2012.
5. [5] Fraser H, MacDougall J, Reid C. “Swelling pressure behavior of bentonite under hydration conditions”. Geotechnical and Geological Engineering, 33(6), 1387-1398, 2015.
6. [6] Xie M, Qian L, Yang Y. “Impact of decay heat on the performance of nuclear waste repositories”. Journal of Nuclear Materials, 354(1-3), 55-61, 2006.
7. [7] Sultan N, Delage P, Cui YJ. “Temperature effects on the volume change behaviour of Boom clay”. Engineering Geology, 64(2-3), 135-145, 2002.
8. [8] Bag R, Rabbani A. “Effect of temperature on swelling pressure and compressibility characteristics of soil”. Applied Clay Science, 136, 1-7, 2017.

9. [9] Romero E, Gens A, Lloret A. “Temperature effects on the hydraulic behaviour of an unsaturated clay”. Geotechnical and Geological Engineering, 19(3-4), 311-332, 2001.
10. [10] Bachmann J, Horton R, Grant SA, van der Ploeg RR. “Temperature dependence of water retention curves for wettable and water-repellent soils”. Soil Science Society of America Journal, 66(1), 44-52, 2002.
11. [11] Pusch R, Karlnland O, Hokmark H. “General Microstructural Model for Qualitative and Quantitative Studies of Smectite Clays”. SKB Technical Report 90-43, Stockholm, Sweden, 1990.
12. [12] Pusch R. “Permeability of compacted highly bentonitic clay”, Engineering Geology, 14(1-2), 111-119, 1980.
13. [13] Villar MV, Lloret A. “Influence of temperature on the hydro-mechanical behaviour of a compacted bentonite”. Applied Clay Science, 26 (1-4), 337-350, 2004.
14. [14] Cho WJ, Lee JO, Kang CH. “Influence of temperature elevation on the sealing performance of a potential buffer material for a high-level radioactive waste repository”. Annals of Nuclear Energy, 27(14), 1271-1284, 2000.
15. [15] Özkan ŞG, Çebi H, Delice MD. “Bor minerallerinin özellikleri ve madenciliği”. 2 Endüstriyel Hammaddeler Sempozyumu, İzmir, Türkiye, 16-17 Ekim 1997.
16. [16] Alkan M, Doǧan M. “Dissolution kinetics of colemanite in oxalic acid solutions”. Chemical Engineering and Processing, 43(7), 867-872, 2004.
17. [17] Demir F, Sarıkaya M, Özbayoğlu G. “Production and application of boron compounds”. Journal of Chemical Technology and Biotechnology, 86(4), 475-482, 2011.
18. [18] ASTM International. “Standard Test Methods for Specific Gravity of Soil Solids by Water Pycnometer, ASTM D854-14”. West Conshohocken, PA, USA, 2014.
19. [19] ASTM International. “Standard Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index of Soils, ASTM D4318-05”. West Conshohocken, PA, USA, 2005.
20. [20] ASTM International. “Standard Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass, ASTM D2216-19”. West Conshohocken, PA, USA, 2019.
21. [21] ASTM International. “Standard Test Methods for pH of Soils, ASTM D4972-19”. West Conshohocken, PA, USA, 2019.
22. [22] ASTM International. “Standard Test Methods for Determining the Amount of Material Finer than 75-μm (No. 200) Sieve in Soils by Washing, ASTM D1140-00”. West Conshohocken, PA, USA, 2000.
23. [23] Tessier D. Etude Expérimentale de L’organisation des Matériaux Argileux: Hydratation, Gonflement et Structuration au Cours de la Dessiccation et de la Réhumectation. Thèse de Doctorat d’état, Université de Paris VII, Paris, Fransa, 1984.
24. [24] Romero E. Characterization and Thermo-Hydro-Mechanical Behaviour of Unsaturated Boom Clay: An Experimental Study. PhD. Thesis, Universitat Politècnica de Catalunya, Barcelona, Spain, 1999.
25. [25] Delage P, Cui YJ. L’eau Dans les Sols non Saturés. Techniques de l’Ingénieur – Traité Construction, C301, Paris, Fransa, 2000.
26. [26] Villar MV. Caracterizacion termo-hidro-mecanica de una bentonita de Cabo de Gata. Ph.D. Thesis, Universidad Complutense de Madrid, Madrid, Spain, 2000.
27. [27] ASTM D4546. "Standard Test Methods for One-Dimensional Swell or Settlement Potential of Cohesive Soils". ASTM International, West Conshohocken, PA, USA, 2021.
28. [28] Vanapalli SK, Fredlund DG. Comparison of different procedures to predict unsaturated soil shear strength. Editors: Shackelford CD, Houston SL, Chang NY. Advances in Unsaturated Geotechnics (ASCE Geotechnical Special Publication), 195–209, Reston, VA, USA, ASCE, 2000.
29. [29] Fredlund DG, Rahardjo H. Soil Mechanics for Unsaturated Soils. 1st ed. New York, USA, John Wiley & Sons, 1993.
30. [30] Durukan S, Pulat HF, Yukselen-Aksoy Y. “Suction characteristics of compacted zeolite-bentonite and sand-bentonite mixtures”. Waste Management & Research, 32(2), 149-156, 2014.
31. [31] Lambe TW. “The structure of compacted clay”. Transactions of the American Society of Civil Engineers, 125(1), 682-705, 1960.
32. [32] Gens A. Modern issues in non-saturated soils: Constitutive laws. Editors: Gens A, Jouanna P, Schrefler BA. Modern Issues in Non-Saturated Soils, 129–158, Wien, Austria, Springer Verlag, 1995.
33. [33] Delage P, Graham I. “State of the art report - understanding the behavior of unsaturated soils requires reliable conceptual models”. 1st International Conference on Unsaturated Soils, Paris, France, 6–8 September 1995.
34. [34] Tang AM, Cui YJ. “Controlling suction by the vapour equilibrium technique at different temperatures and its application in determining the water retention properties of MX80 clay”. Canadian Geotechnical Journal, 42(1), 287-296, 2005.
35. [35] Romero E, Gens A, Lloret A. “Temperature effects on the hydro-mechanical behaviour of bentonite”. Journal of Geotechnical and Geoenvironmental Engineering, 126(3), 199-212, 2000.
36. [36] Ye WM, Cui YJ, Qian LX, Chen B. “An experimental study of the water transfer through compacted GMZ bentonite”. Engineering Geology, 108(3-4), 169-176, 2009.
37. [37] Kim M, Lee S, Cheon E, Kim M, Yoon S. “Thermochemical changes on swelling pressure of compacted bentonite”. Annals of Nuclear Energy, 151(2), 107882, 2021.
38. [38] Martikainen J, Laurila T, Kumpulainen S, Leupin OX. “Bentonite Swelling Pressure Response to Temperature Change”. Applied Clay Science, 260, 107504, 2024.
39. [39] Cui S, Zhang H, Zhang M. “Swelling characteristics of compacted GMZ bentonite-sand mixtures as a buffer/backfill material in China”. Engineering Geology, 141-142, 65-73, 2012.
40. [40] Sato H, Suzuki S. “Fundamental study on the effect of an orientation of clay particles on diffusion pathway in compacted bentonite”. Applied Clay Science, 23(1/4), 51-60, 2003.
41. [41] Chen YG, Dong XX, Zhang XD, Ye WM, Cui YJ. “Combined thermal and saline effects on the swelling pressure of densely compacted GMZ bentonite”. Applied Clay Science, 166, 318-326, 2018.
42. [42] Chen YG, Dong XX, Zhang XD, Ye WM, Cui YJ. “Cyclic thermal and saline effects on the swelling pressure of densely compacted Gaomiaozi bentonite”. Engineering Geology, 255, 37-47, 2019.
43. [43] Villar MV, Gómez-Espina R, Lloret A. “Experimental investigation into temperature effect on hydro-mechanical behaviours of bentonite”. Journal of Rock Mechanics and Geotechnical Engineering, 2(1), 71-78, 2010.