S.K. Mukerjee

Oxidation and hydrolysis kinetic studies on UN

Abstract The reaction of oxygen and water vapour with UN microspheres containing 0.78 and 10.9 mol% UO2 as impurity was studied under non-isothermal heating conditions in a thermobalance under different partial pressures of oxygen, a fixed pressure of water vapour in argon, and in air. Uranium mononitride was ultimately converted to U3O8, with the formation of UO2 and U2N3 as intermediates. The end product of pyrohydrolysis was UO2. The kinetic parameters were evaluated and the mechanism of the reaction was suggested. Different kinetic models were used to explain the oxidation behaviour of UN.

Kinetic study of the carbothermic synthesis of uranium monocarbide microspheres

Abstract Uranium monocarbide microspheres were synthesized by carbothermic reduction of porous uranium oxide microspheres with uniformly dispersed carbon black. Kinetics of the reduction was studied under vacuum and flowing inert gas from 1250 to 1550° C. The carbon monoxide gas concentration in the effluent stream during reduction was used to determine the rate of carbide formation. Under vacuum, reduction was found to be controlled by reaction at the reactant-product interface whereas under flowing gas conditions, the diffusion of carbon monoxide gas through the carbide layer was the rate controlling process. The activation energy was 335.1 ± 8.6 and 363.7 ± 7.6 kJ/mol for reduction under vacuum and flowing gas, respectively.

Kinetics of the carbothermic synthesis of uranium mononitride microspheres

Abstract The mononitride of uranium is an important nuclear fuel material. Kinetics of UN microspheres preparation by the reaction of carbon containing porous uranium oxide microspheres with nitrogen was studied in the temperature range of 1573 to 1823 K. Carbon monoxide concentration in the nitrogen stream during the reaction was used to determine the rate of formation of the nitride. The results show that the carbothermic synthesis of the mononitride microspheres follows a first order rate equation and the value of the energy of activation for the reaction was found to be 365.7±14.9 kJ/mol. The diffusion of carbon monoxide through the product layer appears to be the rate controlling step.

The oxidation of uranium monocarbide microspheres

Abstract The reaction of oxygen with UC microspheres was studied as a function of heating rate, partial pressures of oxygen and sample size under nonisothermal heating conditions. The ultimate product of the oxidation was U3O8 with the formation of UO2 as an intermediate. The kinetic parameters were evaluated and conditions suggested for ignition free bulk oxidation of UC.

Kinetics and mechanism of UO2 + C reaction for UCUC2 preparation

Abstract The kinetics of the carbothermic conversion of (UO2 + C) microspheres to UC UC 2 in the temperature range of 1473 to 1973 K has been studied under nonisothermal heating conditions in vacuum and flowing argon. Reduction of UO2 microspheres, dispersed in a carbon matrix was also studied under vacuum. The carbon monoxide gas concentration in the effluent stream during reduction was used to determine the rate of carbide formation. A model representing stepwise conversion of the reactant to the product has been proposed and the probable rate controlling steps, under different reaction conditions, have been identified. The reaction of oxide with carbon under vacuum appears to be controlled by diffusion of carbon. However, under flowing gas conditions, the diffusion of carbon monoxide gas through the carbide layer was the rate-controlling process. The activation energies for the reaction carried out under different conditions varied between 332 to 373 kJ/mol.

Carbothermic reduction of (UO3 + C) microspheres to (UO2 + C) microspheres

Abstract Carbothermic reduction of UO3 gel microspheres containing uniformly dispersed carbon was carried out in order to obtain (UO2 + C) gel microspheres suitable for the preparation of UC or UN. The reaction was observed to proceed in two stages (i) the conversion of UO3 to U3O8 and (ii) the reduction of U3O8 to UO2 by reaction with carbon. Reaction conditions were optimised to suppress the side reaction of UO3 with ammonia present in the microspheres and also its thermal decomposition to facilitate its quantitative conversion to UO2 through reaction with carbon so that a predetermined C/UO2 mole ratio is obtained in the product (UO2 + C) microspheres. Kinetic parameters were evaluated for both the stages of conversion, under nonisothermal heating conditions in flowing argon as well as vacuum, by using thermogravimetric technique. Studies were also carried out to obtain kinetic parameters for the conversion of pure UO3 microspheres to U3O8.

Fabrication Technologies for ThO2-based Fuel

Fuel fabrication technology, particularly once through utilization of uranium, has been mastered over the years. However, with the increasing demand of electricity at an affordable cost and depleting resources of uranium, introduction of thorium in the fuel cycle has become essential. The large-scale utilization of thorium requires adoption of closed fuel cycle scheme. Many of the fuel cycle technologies developed for uranium can be readily adopted for thorium, however, the man-rem problem associated with this fuel is a major concern. Therefore, fuel fabricators have, in recent past, initiated new R&D programs to solve this problem either through elimination of powder handling or making the unit operations of the production process amenable to remote handling and automation.

Synthesis of mesoporous γ-alumina by sol–gel process and its characterization and application for sorption of Pu(IV)

Mesoporous γ-alumina samples were prepared by the sol–gel process from the boehmite sol having different template solutions. Copper doped material was also prepared from sol containing template solution along with copper nitrate. Studies were performed to understand the influence of templates on the morphology of the synthesized samples particularly with respect to specific surface area and porosity. Synthesized samples were used to study sorption of Pu(IV) from nitric acid–oxalic acid solutions. Distribution ratios (D) for Pu(IV) were determined using the γ-alumina samples with an objective to employ these for the recovery of Pu.

Studies on sorption of plutonium from carbonate medium on polyacrylhydroxamic acid resin

Polyacrylhydroxamic acid resin synthesized by functionalization of polyacrylamide with hydroxylamine has been investigated for the sorption of plutonium(IV) from carbonate medium, aiming at its application for the removal of plutonium from alkali wash effluent generated during purification of TBP in PUREX process. Batch experiments have been carried out to determine distribution coefficient of plutonium(IV) between this exchanger and various compositions of carbonate medium. Effect of the concentration of sodium carbonate, sodium bicarbonate and pH of the solution on the distribution coefficient have been studied to optimize the conditions for the uptake of Pu(IV) by this exchanger. Column experiments were carried out to determine the practical capacity of the exchanger for plutonium. Elution studies were also carried out to recover the loaded plutonium from the ion exchange column The exchanger displayed good exchange capacity for Pu(IV) from feed solution simulating the conditions of carbonate wash effluent generated in PUREX process. The exchanger also exhibited fast elution of Pu, suggesting the feasibility of using it for the recovery of Pu from carbonate based wash effluent.

Preparation of porous titania–silica microspheres for treatment of radioactive waste

Titania–silica microspheres have been prepared by sol–gel process. Internal gelation route, which use hexamethylenetetramine as the source of ammonia was used for the preparation spherical gel particles. A cationic surfactant, cetrimide was added in the feed broth for introducing meso-porosity in the gel network. Further paraffin oil emulsion was incorporated in the feed broth before gelation for the formation of larger pores in the gel network. The spherical gel particles thus obtained were washed and heat treated under controlled conditions to remove the entrapped surfactant, paraffin oil and other organic compounds resulting in highly porous intact titania–silica microspheres. The material was characterized by surface area, porosity and by SEM photomicrographs. The ion exchange property of this material was studied using the sorption of plutonium on this material from carbonate medium by distribution coefficient studies and ion exchange column loading and elution experiments.