Preparation and Study of Corrosion Behavior of Some Simulated Radioactive Waste Glasses

To safe environment from radioactive waste it is important to fix them as radioactive waste glasses. The corrosion behavior of radioactive waste glasses in water is significantly important. Radionuclides return to the biosphere by means of leaching from waste form into ground water. Finally the ground water containing the radionuclide are transported to the surface. In this study, the preparation, characterization and leaching behavior of some borosilicate (BS) and lead iron phosphate (LIP) of different chemical composition doped with simulated nuclear waste oxide were investigated. We measured the pH found to be in the range from 6.78 up to 7.79 of the leachate solution at normal temperature and at varying time intervals. Leaching study of these glasses were conducted with the help of Soxhlet distillation apparatus with distilled water upto 24 hours and for BS9 - BS12 upto 100 hours duration. Weight losses were are measured with respect to time of leaching. Leach rate of some borosilicate glass samples loaded with uranium are calculated from surface area measurements. The results are reported in the range 1.34x10-4 g.m-2.hr-1 and 6.26 x 10-4 g.m-2.hr-1 respectively at 90°C.

Beneficiation of rejects slime of iron ore by means of sequential leaching

The present research work has been conducted to remove gangue contents from rejects slime of iron ore, having particle size < 20 µm by circulating leaching with aqueous hydrofluoric acid (HF) followed by nitric acid (HNO3) washing. Effects of acid concentration, slurry ratio, reaction time, stirring speed and temperature on gangue removal have been examined. The gangue contents (alumina and silica) are reduced from 13 weight percentage (wt.%) to around 1 wt.%. The iron value has also been increased from 58.74 wt.% to 68.47 wt.% with more than 95% iron recovery. The gangue matter remaining after leaching consists mainly of aluminium and silicon, which is most likely encapsulated in the goethite phase. The leaching kinetics has also been studied to establish an overall leach-rate equation. The shrinking core model is very suitable to describe the kinetics of gangue removal.

The effect of phosphate melt cooling rate on phase composition and leach resistance of final waste form

ABSTRACTSlow cooling of phosphate melt at liquid nuclear waste solidification yields glass-crystalline material. Partial crystallization during melt solidification results in elemental partitioning among crystalline phase and glass: Al, Cr, Fe are concentrated in the crystalline phosphate phase while Ca, Ni, La, U enter predominantly in the residual glass. Glass dissolution rate and leach rate of La and U as rare earth and actinide surrogates depends strongly on the glass composition, for example reduction of Al2O3 content in the glass to ∼10-12 wt.% increases leachability by three orders of magnitude as compared to the glass with specified composition (∼18-22 wt.% Al2O3).

Consolidation of High-Level Radioactive Wastes into Strontium Titanate by CS Method

Strontium Titanate synroc samples were synthesized by combustion cynthesis (CS). Sr directly took part in the synthesis process. As a result, loading content issue is basically resolved. The products were characterized by density, microhardness X-ray diffraction, and scanning electron microscopy (SEM/EDS). The leaching rate was measured by the method of PCT. The results indicate that the Sr2+-SrTiO3 compound with high density, low leach rate and high property stability and the synthesis process is feasible in technology and economy. It can be concluded that the Strontium Titanate synroc is a perfect material to immobilize HLW Keywords: Strontium Titanate, high-level radioactive waste (HLW), immobilization, self –propagating high –temperatures synthesis (SHS).

Leaching Properties of Immobilization of HLW into SrTiO3 Ceramics

In this work, Strontium Titanate samples were synthsized by self-propagating high-temperature synthesis (SHS). Sr2+ directly took part in the synthesis process. As a result, immobilization limitation issue is basically resolved. The Strontium titanate was characterized by crystal structure, dense properties, leach rate, microstructure and scanning electron microscopy. And the synthesis process is feasible in technology and economy. It can be concluded that the strontium titanate synroc is a perfect material to immobilize HLW.

Study of the Radioactive Silt Sediment Cementation Techniques

Radioactive silt deposits (RSD) of the spent fuel rod cooling pools were used as an object of these studies. In this paper the following techniques were considered for the silt processing: the cementation of silt without a prior treatment, cementation of the dried silt product, cementation of the calcined silt product, and the impregnation of the calcined silt with high penetrating cement grouts. This paper reports the results of the following studies: the chemical and isotope silt composition, physicochemical silt properties, properties of the cement grouts and solidified compounds, obtained as a result of various silt processing techniques. For every processing technique the following cement compound quality index stated in the Russian standard GOST R 51883-2002 was determined: the mechanical strength, freeze-thaw resistance and leach rate of 137Cs. Effects of variations in the thermal silt treatment mode, in the water/cement ratio, and in the binder material type have been determined. Based upon the results of the studies a comparative assessment of the silt cementation techniques has been performed.

Magnesium Phosphates Binding Systems for Immobilizing Solvent Radioactive Wastes

The immobilization process of radioactive solvent wastes produced during nuclear power plants operation tends to be safe and technically feasible perhaps its most important advantage from the safety point of view is the low chamber temperature and lower explosion risk. Radioactive solvent wastes resulted from Cernavoda NPP decontamination operations consist of miscellaneous acetone, toluene, methanol, chloroform, trichloroethan, white spirit, ethylene glycol and water. Magnesium phosphate binding systems are new cement-materials which could be used for the immobilization of radioactive wastes for the set-retarding effect of solvent radioactive waste in other matrices (Portland cement, composite cement). The paper presents the influence of mineral additive on the properties of solvent waste form, mainly the setting time and the leach rate of tritium. Results of the experiments have shown that using magnesium phosphate binding systems-mineral additive, could do the solidification of solvent radioactive wastes by better results. It can thus be anticipated that the level of expectation towards magnesium phosphate binding systems will remain high and probably increase for the other organic radioactive wastes (oils, scintillation liquids).