Nükleer Atıklarda Bentonitin Tampon Koruyucu Özelliği ve Üstünlüğü

Aşağıda İngilizce özeti verilen çalışmada, Nükleer Atıklarda tampon koruyucu olarak kullanılan Bentonit üzerine bir çalışma yapılmış ve değişen şartlarda performansı incelenmiştir. Çalışma sonunda,

Bentonitin, ısı, sıcak buhar, demir ve çimento gibi etkenlere bağlı olarak tampon koruyucu performansında değişkenlikler gözlemlenmesine karşın, tutunma kapasitesinin son derece yüksek olduğu bu nedenle bu amaçla kullanım için en iyi tercih olduğu belirtilmiştir.

Clay Mineralogical Investigations
Related To Nuclear Waste Disposal
Madsen F. T.
Laboratory for Clay Mineralogy, Division of Geotechnical Engineering, Swiss Federal Institute of Technology, CH-8092 Zurich, Switzerland
Clay Minerals, Volume 33, Number 1, 1 March 1998 , pp. 109-129(21)
Abstract:Mineralogical and geotechnical investigations on the possible use of compacted bentonite as a buffer material in nuclear waste repositories are reported. The swelling capacity is highly dependent on the density of the compacted bentonite. Swelling pressures >30 MPa were measured for dry densities
of ~2.0 g/cm3. Added iron or magnetite
powder up to 20 wt% had no influence
on the swelling capacity.

Compacted mixtures of 20 wt% ground set cement and bentonite showed higher swelling pressures but lower swelling strain capability than compacted bentonite alone. Steam lowered the swelling pressure of compacted bentonite to ~60% of the original value. The influence was, however, reversible by ultrasonic treatment. The thermal conductivity of saturated compacted bentonite at a density of 2.0-2.1 g/cm3 is ~1.35-1.45 W/m°K. The volumetric heat capacity ranges from 3.1 x 106 to 3.4 x 106 J/m3°K. The saturated hydraulic conductivity of the compacted bentonite is <10-12 m2/s. The apparent diffusion coefficients for various ions in compacted bentonite for water contents in the range of 20 to 25 wt% are: K+: 5 x 10-11, Cs+: 6 x 10-12, Sr2+: 3 x 10-11, UO2+2: <10-13, Th4+: <10-13, Fe2+: 4 x 10-11, Fe3+: 4 x 10-11, Cl-: 1 x 10-10, and I-: 1 x 10-10 m2/s. The 'breakthrough time' for an apparent diffusion coefficient of 10-11 m2/s in compacted bentonite 1 m thick was estimated to be ~3000 years. The mineralogical longevity was investigated on natural K-bentonites from Kinnekulle, Sweden, and Montana, USA. Although these materials have undergone considerable changes during diagenesis and contain various amounts of mixed-layer illite-smectite, they still have a substantial swelling and adsorption capacity. The investigations demonstrate that although the properties of bentonite are negatively influenced to a certain extent by heat, hot steam, iron and cement, compacted bentonite is still the best choice to act as a buffer material in a nuclear waste repository.