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Sengupta P.,Bhabha Atomic Research Center | Mishra R.K.,Bhabha Atomic Research Center | Soudamini N.,Bhabha Atomic Research Center | Sen D.,Bhabha Atomic Research Center | And 4 more authors.
Journal of Nuclear Materials | Year: 2015

'Fused/cast Al2O3-ZrO2-SiO2 (FC-AZS)' is being considered as 'glass contact refractory' within ceramic melters, to be used for nuclear waste immobilization. Microstructural analyses reveal random distributions of baddeleyite (ZrO2) within aluminosilicate (Al2SiO5) matrix. 27Al and 29Si NMR data suggest that within aluminosilicate matrix Al occurs in both 4- and 6-fold co-ordinations whereas Si prefers a 4-fold environment. Polydispersity of pores has been studied with small-angle neutron scattering (SANS) technique. Corrosion rates of FC-AZS within 6 M HNO3, simulated wastes (500 h exposure), and borosilicate melt (975 °C, 800 h exposure) are found to be 0.38 × 103 μmy-1, 0.13 × 103 μmy-1 and 4.75 × 103 μmy-1 respectively. A comparison of chemical interaction data clearly suggests that FC-AZS exhibits better chemical durability than AZC refractory (Al2O3-ZrO2-Cr2O3, also used for similar purpose). Thermal cycling studies indicate that FC-AZS retains structural integrity (including compressive strength and density) even up to 20 cycles. © 2015 Elsevier B.V.

Nath M.,Indian Central Glass and Ceramic Research Institute | Sen S.,Indian Central Glass and Ceramic Research Institute | Banerjee K.,Nuclear Recycle Group | Ghosh A.,Indian Central Glass and Ceramic Research Institute | Tripathi H.S.,Indian Central Glass and Ceramic Research Institute
Ceramics International | Year: 2013

Highly dense alumina-chrome bodies with low porosity are usually used as corrosion and thermal resistant refractories. Alumina-chrome refractory with molar ratio 1:1 was developed using chemical grade hydrated alumina and chromium (III) oxide by conventional sintering route. Batch materials were attrition milled, isostatically pressed and sintered in the temperature range from 1000 °C to 1700 °C with 2 h soaking at peak temperature. Phase development of the sintered materials with temperature was studied by X-ray diffraction. Sintering temperature, sintering condition and addition of sintering aid (TiO 2) have immense effect on the densification of the alumina-chrome refractory. Highly dense alumina-chrome refractory with almost nil apparent porosity was developed at 1500 °C in reducing atmosphere. Flexural strength of the sintered materials at room temperature and at 1200 °C was also measured. 1 wt% TiO 2 gives the optimum result with respect to densification and flexural strength. © 2012 Elsevier Ltd and Techna Group S.r.l.

Verma A.K.,Indian School of Mines | Gautam P.,Indian School of Mines | Singh T.N.,Indian Institute of Technology Bombay | Bajpai R.K.,Nuclear Recycle Group
Arabian Journal of Geosciences | Year: 2015

The long-lived high-level spent nuclear has to be isolated from environment for the protection of ecosystem. One of the methods suggested to isolate the nuclear waste from ecosystem is its burial in deep underground repository. In this paper, discrete element method is used to disposal of spent fuel on stability of underground space and its surrounding rock strata. Effect of temperature increment on stresses-strains and temperature variation of surrounding rockmass due to heat generated by nuclear waste is studied and discussed. Simulation was performed on both strong and jointed granite rock in which tunnel is excavated. Bentonite is used as buffer because of its high sorptivity, longevity and low permeability. It has been found that both temperature and stresses at any point in the rock mass is below the design criteria which are 100 °C for temperature over a time period of 16 years. © 2015 Saudi Society for Geosciences

Kumar P.,Indian Institute of Technology Kanpur | Vincent T.,Nuclear Recycle Group | Khanna A.,Indian Institute of Technology Kanpur
Separation Science and Technology (Philadelphia) | Year: 2015

Thenoyltrifluoroacetone and Tributyl-phosphate have been used for extraction of UO2 2+ into Ionic Liquid 1-Butyl-3-methylimidazoliumbis(trifluoromethylsulfonyl)imide. Increasing acidity of uranyl solution from 0.01 to 3 mol L−1 HNO3 for TTA in IL, the distribution ratio (DU) and extraction efficiency (%E) both decreased. Further increment in acidity shows reversal of trend. Similar behavior is observed for TBP. With increasing concentration of TTA, %E increases stabilizing at 0.5 mol L−1 TTA. Adding methanol to TTA increased the DU due to active enolic formation. The developed kinetic model estimates the overall mass transfer coefficient (Ka) as 3.6 x 10−2 s−1. Synergistic effect has been observed for combination of TTA + TBP resulting in enhanced DU. Copyright © Indian Institute of Technology Kanpur.

Rani N.,University of Delhi | Shrivastava J.P.,University of Delhi | Bajpai R.K.,Nuclear Recycle Group
Journal of the Geological Society of India | Year: 2012

Obsidian glass alteration experiments under near hydrothermal conditions were performed to study mechanism and conditions of formation of altered minerals. X-ray diffraction patterns and cell dimensions of the specimens treated at 150, 200 and 300°C ( pH = 8.03) revealed appearance of three main minerals - illite (9.5-10 Å), chlorite (7.04 Å) and halloysite (10.25Å). Further increase in the pH favours matrix dissolution with the formation of secondary altered layers. SEM-EDS study show that the alteration causes smoothing of the grain surfaces. These surfaces exhibits etch pits and series of depressions, formed by the process of dissolution. SEM - Back Scattered Electron images of obsidian specimens show thin laminae of smectite, with foliated bulky rims and cellular honeycomb texture, formed by precipitation from the solution as well as by direct transformation of glass during alteration. This mechanism is resulting from the alteration of alkalis by ionic inter-diffusion with H 3O + and H + and inward diffusion of H 2O, leading to free diffusion of silica into solution and then to a local rearrangement of the glass framework. Thus, a direct transformation of glass into clay minerals is the major reaction mechanism as evidenced by the mechanism of glass dissolution and subsequent mineral precipitation.

Rani N.,University of Delhi | Shrivastava J.P.,University of Delhi | Bajpai R.K.,Nuclear Recycle Group
International Journal of Earth Sciences | Year: 2015

Deccan basaltic glass is associated with the differentiation centres of the vast basaltic magmas erupted in a short time span. Its suitability as a radioactive waste containment chiefly depends on alteration behaviour; however, detailed work is needed on this glass. Therefore, the basaltic glass was treated under hydrothermal-like conditions and then studied to understand its alteration. Moreover, comparison of these results with the naturally altered glass is also documented in this paper. Solutions as well as residue obtained after glass alteration experiments were analysed. Treated glass specimens show partial to complete release of all the ions during alteration; however, abundant release of Si and Na ions is noticed in case of almost all the specimens and the ionic release is of the order of Na > Si > K > Ca > Al = Mg > Fe > Mn > Ti. Scanning electron images of the altered residue show morphologies of smectite, montmorillonite and illite inside as well as outside of the secondary layers, and represent paragenesis of alteration minerals. It has been noticed that the octahedral cation occupancies of smectite are consistent with the dioctahedral smectite. The secondary layer composition indicates retention for Si, Al, and Mg ions, indicating their fixation in the alteration products, but remarkably high retention of Ti, Mn and Fe ions suggests release of very small amount of these elements into the solution. By evolution of the secondary layer and retention of less soluble ions, the obstructive effect of the secondary layer increases and the initial constant release rate begins slowly to diminish with the proceeding time. It has been found that devitrification of glass along the cracks, formation of spherulite-like structures and formation of yellowish brown palagonite, chlorite, calcite, zeolite and finally white coloured clays yielded after experiments that largely correspond to altered obsidian that existed in the natural environment since inception ~66 Ma ago. © 2015, Springer-Verlag Berlin Heidelberg.

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