مجله علوم و فنون هسته ای
سال سی و هشتم شماره 4 (پیاپی 82، زمستان 1396)

In the present paper, development of the Galerkin Finite Element Method-Kinetic-3 Dimentional (GFEM-KIN-3D) computational code for the calculation of the kinetic parameters is reported. To this end, the static neutron diffusion and corresponding adjoint equations are solved using Galerkin Finite element method in the 3 dimensional geometry. Then, the calculated neutron and adjoint flux distributions are used in the perturbation theory to calculate the effective delayed neutron fraction and mean generation time of the neutrons. There is no benchmark problem that includes the information such as the delayed neutron fraction, prompt and delayed neutron spectrum. Therefore, some problems were designed by the author and the kinetic parameters were calculated for the considered problem. Since the neutron diffusion solver was previously validated against the well-known benchmark problems and the equations of perturbation theory is available, we conclude that if the required information is known, the kinetic parameters will be calculated with high accuracy. The developed GFEM-KIN-3D is applicable to the core calculation of the both hexagonal and rectangular reactor cores.

In this paper, a two phase flow in a vertical channel is simulated implicitly using the drift flux model. Unconditional stability and also second order accuracy in time are advantages of the fully implicit approach. So far, Newtonʼs method has been used for solution of the nonlinear system of equations arising from the fully implicit discretization of the physical field equations. Lack of convergence robustness arising from the weak initial guess and the Jacobian matrix construction, have created some difficulties for researchers. In this article, using the SIMPLE algorithm, a fully implicit model for simulation of the two phase flow is provided. The model does not have the two mentioned drawbacks of the Newtonʼs method. For a wide range of conditions, the key thermo-hydraulics parameters obtained by the present model are in good agreement with both the experimental data and the RELAP code results. Based on the performance assessment, the model has a second order accuracy in time and the time step need not be limited to maintain stability.

Side coupled standing wave accelerating cavities are widely used in a low energy linear accelerator because of relatively high accelerating gradient and low sensitivity to construction tolerances. The effective interaction of particles and electromagnetic fields is important to accelerate electrons to the intended energy with the greatest efficiency and beam quality output. Beam dynamics study is essential for determining the coordinates of the output beam from the cavity. In this paper, we present the beam dynamics of a 6 MeV accelerating cavity using a space charge tracking algorithm (ASTRA). The designed accelerating cavity that feeds by magnetron with a maximum power of 3.2 MW is operating in π/2 mode at a frequency of 2856 MHz. The results show that after the construction of the designed cavity, the vertical and horizontal emittances of the output beam, the transverse profile and the beam energy spread respectively 3.55 pi-mm-mrad, 1 mm and 0.88 MeV as expected.

Thermoluminescence dosimeters are widely used for dosimetry in different radiation fields. In this study, the feasibility of the application of the cold-pressed sintered LiF:Mg,Ti dosimeter pellets, produced by the melting method in our TL laboratory, was investigated for gamma high dose dosimetry. The relation of sensitivity reduction with increasing of the dose is used to determine the high gamma doses. To obtain the dose response-reduction curve for these dosimeters to high doses, 60Co gamma doses between 1 to 500kGy were used. The resulting dose response-reduction curve shows a logarithmic response reduction to the absorbed dose. The correlation between the Ti dopant concentration and the range of dose response reduction curve was studied. Considering the reproducibility, this method could be used for a wide range of high doses.

In this research, zirconium tetrachloride production is studied as one of the stages of zirconium production. Basically, there are two main methods for producing zirconium tetrachloride from zirconium dioxide: The first and older method used in Iran is the fixed bed process. Despite the advantage of the process and equipment simplicity, this method has a lot of problems, including low efficiency and operator safety problems. In this study, the efficiencies of this method and a newer technique that is fluidized bed reactor were compared. Although the capacity of the reactors are very different, according to that comparison which is based on the unit weight of zirconium production, the result has enough validity. Based on this study, the efficiency of the fluidized bed reactor is 14% higher than that of the fixed bed.

Heavy metal sequestration from industrial wastewater is a serious environmental problem especially in developing countries. Among various treatment technologies, it seems that biosoprtion is a promising alternative method. Microbial–based biosorbents are effective and applicable for heavy metals removal from aqueous solutions. The present study investigated the ability of Pseudomonas putida immobilized on chitosan to adsorb uranium (VI) from the aqueous solution. The biosorption process factors were screened using Plackett–Burman design. The results showed that the biosorbent dosage, initial concentration, biosorbent particle size, bacteria wt.% in the biosorbent and pH were the most significant parameters, respectively while temperature was the only insignificant parameter in the biosorption process. Maximum practical biosorption capacity was 536.08 mg g–1 obtained from 15 wt.% of the bacterial cells immobilized on chitosan. Biosorption equilibrium isotherms were analyzed by Langmuir, Freundlich and Dubinin–Radushkevhch models. For Pseudomonas putida immobilized on chitosan, the Langmuir isotherm model (R2=0.983) was proved to fit the equilibrium data best with the maximum capacities of 588.23 and 454.54 mg g–1 for the biosorbent and pure chitosan, respectively. In conclusion, the present study indicated that the prepared composite biosorbent could be a suitable candidate for uranium (VI) biosorption.

The Nb-Ge doped titanosilicate nanoparticles were synthesized using a hydrothermal method and their adsorptive behavior for 90Sr and 137Cs radionuclides was investigated in liquid radioactive waste of Tehran research reactor in a batch method. Crystalline phases and morphology of the synthesized samples were studied by X-ray diffraction (XRD) method and scanning electron microscopy (SEM) technique, respectively. Elemental analyses of the samples were performed using X-ray fluorescence (XRF) technique. Surface areas of the samples were measured by the BET method. The effects of  temperature, contact time, and pH of liquid radioactive waste were studied. The obtained results showed that the synthesized samples have a good potential for removal of Sr-90 and Cs-137 radioisotopes from liquid radioactive waste of Tehran research reactor and in general, for the liquid wastes treatment. The samples doped up to 25 wt% with equal amounts (50 wt%) of niobium and germanium, removed almost 98.5% of  137Cs and 86.3% of  90Sr  from liquid radioactive waste of Tehran research reactor.

In this article, the activities to fabricate the polystyrene micro-shells by the microencapsulation method for laser fusion targets are presented. To reduce the Rayleigh-Taylor hydrodynamic instabilities in the process of target compression, the target requires a spherical symmetry, excluding any impurity with pre-defined elemental distribution. The polystyrene shells have wall thickness 27±2 µm and diameter 750±50µm, respectively. The transmission holographic Mach-Zehnder interferometer method has been utilized to characterize the micro-shell quality by measurement of the wall thickness and nonuniformity of the micro-shells.

The grains of cultivars Rapeseed Sarigol and RGS003 were irradiated with gamma rays at doses 0, 800, 1000 and 1200 Gary (GY). For M2 generation, the grain of each plant was cultivated in a separate row and all plants were individually investigated during cultivation. According to the observed changes in agronomic traits such as pod length, the number of pods and flowering during M2 generation, 18 and 12 candidate mutant lines were obtained from Sarigol and RGSOO3, respectively. The differences among gamma rays doses were not statistically significant for seed sterility, while they were significant for pollen sterility at the level of 1%. Maximum pollen sterility was observed in 800 GY. Induced mutations in RGS003 and Sariglo cultivars were mostly obtained in 1200 and 800 GY, respectively. The M3 mutant lines in both Rapeseed cultivars contained a variation on traits such as the number of pod per the main stem, the number of pod per plant, pod length, the number of grain per pod, grain weight and flowering duration.

Nowadays, many researches have been done to improve the efficiency of the nuclear power plants, one of which is the use of the dual cooled annular fuel which is an internally and externally cooled annular fuel with many advantages in heat transfer characteristics. Also, some studies have suggested that the usage of the nanoparticles in a fluid as nano-fluid can provide dramatic improvements in the thermal properties of fluid. Howere, the  usage of neutronics and the thermal hydraulic codes in order to investigate the nano-fluid effects in the nuclear reactors is complex, uneconomical and time consuming. Therefore, in this paper, to investigate the nano-fluid effects on the important parameters of the VVER-1000 nuclear reactor with dual-cooled annular fuel, effects of Al2O3/ water nano-fluid concentration and size on neutronics and the thermal-hydraulic parameters in the VVER-1000 nuclear reactor are investigated using a proper Artificial Neural Network. Results show that the trained Neural Network has good convergence and accuracy in determination of the neutronics and the thermal-hydraulic parameters. Using the presented Neural Network, important reactor parameters can be determined without neutronics and the thermal hydraulic codes, thus saving time.