JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY
Year:2008 | Volume:- | Issue:2 (44)|Papers Count:10

In this research work, the recovery and separation of La (III), Ce(III), Sm(III), Dy(III) and Nd(III) from Saghand uranium ore have been studied by precipitation and ion-exchange chromatography methods using Dowex 50W-X8 cation exchanger. At first, some preliminary and preconcentration experiments such as combination, sieve analysis, gravity table and electrostatic in preconcentration of lanthanides were performed. Then, acidic digesting and leaching procedure were used. The results of experiments showed that rare earth elements, along with interfering ions such as Al (III), Fe (III), Mg (II) and Mn(II) present in the leach liquor solution. The investigation of separation process by precipitation method revealed that precipitation and then fast separation using centrifugal technique had the best results in the elimination of interference elements. In order to separate the lanthanides and to obtain their elution curves, the chromatographic column containing Dowex 50W-X8 resin was employed. For efficient separation of lanthanides from interference elements the hydrochloric acid with concentration of two and six molar was used respectively. Recovery of lanthanides from the leach liquor solution was achieved more than 85%.

A fuel element in nuclear reactors generally consists of fuel pellets, gaseous gap and cladding. Normally the pellets and cladding are coaxial. In this case; heat conduction equation in the fuel element is two dimensional, independent on angle ( q). Certainly elimination of gaseous gap in one direction (eccentricity of fuel pellets), will increase cladding and coolant temperature at the same direction. In this work, three dimensional analytical and numerical steady state heat transfer behavior in eccentric fuel element were studied to determine maximum temperature of fuel pellets, cladding, and coolant. Good agreement between analytical and numerical results was obtained. It is concluded that because of eccentricity of fuel element, melting of cladding and boiling in coolant will not occur.

Hydrated cerium (IV) dioxide has been synthesized by adding excess cerium sulphate to 4M ammonia solution at 25°C and pH=12.5 with constant stirring. The properties of the compound were investigated by means of infrared and thermogravimetric techniques. The effect of temperature and pH on the adsorption of Ba and Sr ions and also the distribution coefficients of Cs and Eu at various pH values on cerium (IV) dioxide were considered. The distribution coefficient results showed that with the increase of pH of the media, the amount of adsorption of Ba and Sr cations on the surface of cerium (IV) dioxide increases, and this is due to their amphoteric nature of this oxide.

Determination of natural and man-made radionuclide inventories in water resources is of great importance. Gross a and b measurements are usually carried out as part of such studies. These paper reports measurements performed on water samples from springs in the southwest of caspian region by liquid scintillation method using Wallac-Quantulus 1220 system, 20ml polyethylene vials and Optiphase Hisafe 3 cocktail. With a counting time of 500min, the MDL for gross a and b measurements are 5.36 and 22.26 mBq l-1, respectively. Measurements by EPA 900 technique have also been applied for some samples and the results are compared.

In the study of stability of VVER-1000 reactor core the state variables method and Routh criterion were used. By calculating temperature reactivity coefficients for fuel and moderator we have shown that the reactor core remains stable against 1$ reactivity or less than 1$. The coefficients were calculated for different concentration of boric acid as a function of temperature. The concentration above 1800ppm prevails itself as a positive effect. It should be noted that 1800ppmboric acid concentration had minimal effect on fuel temperature reactivity coefficient. The simulation calculation for 1$ reactivity insertion showed that the prompt neutron life time between 2 to 50 ms causes sharp rise in flux for shorter lifetime, while decays remain more or less the same for 2 to 50ms prompt neutron lifetime.

The adsorption behavior of natural vermiculite for cesium (137Cs), in radioactive aqueous waste, has been investigated. Our experiments, aimed at the study of the effect of some parameters such as residential time (for batch equilibrium), pH, temperature, and flow rate (for column tests) on the efficiency of adsorption operation. The adsorption experiments were performed using both static batch equilibration and flow-through tests. The maximum adsorption was observed in alkaline condition (0.01 mol L-1 NaOH solution), using 1 gr of adsorbent for 100mi of radioactive liquid waste at 60°C, in 24h of residential time for a batch experiment. Finally, with the result of the column experiments, the breakthrough isotherm has been drawn. The present work deals with a series of experiments to assess the potential of vermiculite for the removal of radio cesium from radioactive aqueous waste. The results of these investigations are expected to be valuable, in order to reach at a higher degree of radioactive waste decontamination.

Solid-liquid separation is one of the most important sections in mineral processing. High percentage of clay material and fine particles (-200 mesh) cause different problems in separation of uranium leach liquor from the residual solid particles in filtration unit of Bandar Abbas Uranium Plant (BUP). The laboratory tests showed that thickener is a suitable device for solid-liquid separation, after leaching unit. For this reason, thickeners were selected for separating of leach liquor from the residual solid particles. For determination of the size and number of thickeners, sedimentation experiments were performed with different flocculants, "Magna floc LT-25" was selected as a suitable flocculent in 75 g/ton. The diameter of thickener was determined to be 13-14 m. In the counter current decantation (CCD), the loss percentage of uranium, using 5 thickeners, was selected to be 2.09%.

A new design of hardware and software required for networking a computer controlled radiation monitoring system is presented. This radiation monitoring system comprises a network of area radiation monitors connected to a central computer via an interface module. The monitors are employed for area dose-rate measurement and controlled via the network. For increasing the distance between monitors and central control and reducing the transmission error, a kind of bus networking which is controlled by the interface module is used. The interface module is specially designed for network control and acts as an bus master. With this interface, there is no need to Ethernet cards in each dose monitor. Communication between the monitors and bus master is carried out by two transmission lines to send and receive, using RS485 standard to benefit by a low cost and simple hardware. In this communication platform, a special protocol is used to reduce the transmission error. This kind of networking is an optimum solution for distributed monitoring systems.