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

Kaynakça

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