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Cementitious material is the most commonly used encapsulation medium for low and intermediate level radioactive waste. This paper focuses on the aqueous durability of a Materials Testing Reactor (MTR) cementitious wasteform – a possible candidate for the proposed intermediate level waste management facility in Australia. A series of medium term (up to 92 months) durability tests, without leachate replacement, were conducted on samples of this wasteform.
The wasteform was made from cement, ground granulated blast furnace slag and a simulated waste liquor. The compressive strength (39 MPa) was typical of MTR cement wasteforms and well above that required for handling or storage. The wasteform was an inhomogeneous mixture containing calcite, a calcium silicate hydrate phase, hydrotalcite and unreacted slag particles. After leaching for 92 months the crystallinity of the calcium silicate hydrate phase increased.
The majority of the releases of Ca, Si, Al, Sr, S, Na and K was reached within 4 days of leaching, with the maxima ie. the highest concentrations in the leachates, occurring at 3 months for Ca, Al, Sr, S, Na and K, and at 1 month for Si. For the longer leach periods (6 months and 3 months respectively) there was a slight reduction in concentration in the leachates, and these levels were similar to those for the longest period of 92 months, suggesting steady-state conditions prevailing after 3 to 6 months of leaching. The highest releases of matrix elements were for Na (37%), K (40%) and S (16%). Releases for elements such as Ca, Na, Al and Sr were similar in magnitude to those reported by the UKAEA in earlier MTR studies.
After leaching for 92 months there was an alteration layer about 80 ∞m deep where calcium has been depleted. Na, K and Sr showed signs of diffusion towards the outer part of the cement samples.
Calcined high-level radioactive waste (HLW) stored at the Idaho National Laboratory (INL) will eventually be immobilised in a suitable wasteform before disposal. A tailored glass-ceramic wasteform, produced by hot isostatic pressing in stainless steel (SS) cans, has been developed at ANSTO as a cost-saving alternative to glass which would improve waste loading and density, and reduce waste volume. We have studied the SS/wasteform interactions under HIPing conditions to understand whether such interactions would have any detrimental effect on long-term wasteform stability. This has been demonstrated by carrying out aqueous durability tests, under near-neutral and alkaline conditions, on the wasteform at the interaction layer, and on the wasteform distal to this reaction edge. Reaction during HIPing resulted in Cr diffusion from the can wall into the wasteform, however without any detectable detrimental impact on the HIP can or the aqueous durability of the wasteform.
Chemical extraction techniques and scanning electron microscopy were used to study the distribution and behavior of actinides and rare earth elements (REE) in hydrothermal veins at Adamello, (Italy). The six samples discussed in this paper were from the phlogopite zone, which is one of the major vein zones. The samples were similar in their bulk chemical composition, mineralogy, and leaching behavior of major elements (determined by extraction with 9M HCl). However, there were major differences in the extractability of REE and actinides. The most significant influence on the leaching characteristics appears to be the amounts of U, Th and REE incorporated in resistant host phases. Uranium and Th are very highly enriched in zirconolite grains. Actinides were more readily leached from samples with a higher content of U and Th, relative to the amount of zirconolite. The results show that REE and actinides present in chemically resistant minerals can be retained under aggressive leaching conditions.
Diffusion and sorption are potentially the most important factors governing the transport of radionuclides in clays and under stationary subsurface environmental conditions. Preliminary studies have been performed to measure the transport of 137Cs and 60Co with no advection, using reconstituted samples of three regolith materials collected from a region in South Australia. The samples were saturated with CaSO4 solution to imitate the pore water chemistry of the in situ environment. A double diffusion cell testing apparatus made of polycarbonate resin was used to measure the transport of the selected radionuclides through the samples. A curve fitting procedure employing one-dimensional contaminant equations with a “stop-start” technique was used to estimate the diffusion (D) and sorption coefficients (Kd) from the measured concentration-time profiles. Results from these experiments are compared with those obtained from batch sorption tests.
Clofoctol [2-(2,4-dichlorobenzyl)-4-(tetramethyl-l,l,3,3-butyl) phenol] is a synthetic antibacterial compound with activity against both Gram-positive1 and Gram-negative2 microorganisms. Although the specific mechanism of Clofoctol action has not been fully elucidated, it is reported to alter the permeability of the cytoplasmic membrane in Bacillus subtilis, and is used clinically to treat upper respiratory tract infections in humans. Staphylococcus aureus is a major human Grampositive pathogen that causes a variety of human diseases ranging from localized skin suppuration and food poisoning to life threatening presentations such as septicemia and endocarditis. Several clinical isolates of S. aureus have recently been identified that are resistant to all currently available antibacterial therapies. Consequently, the identification of new antimicrobial targets in this organism is of paramount importance. The purpose of this study was to investigate the in vitro effects of Clofoctol on S. aureus.
Ultrastructural examination of S. aureus revealed a population of actively dividing cells.
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