مجله علوم و فنون هسته ای
سال سی و ششم شماره 4 (پیاپی 74، زمستان 1394)

The main objective of this study is to predict the neutronic behavior of nanofluids as a coolant in the fuel assembly of the HPLWR. The high-performance light water reactor (HPLWR) is the European version of the supercritical-pressure water cooled reactor (SCWR). Light water reactor at supercritical pressure which is currently under the design, is considered as a new generation of nuclear reactors. The variations of neutron cross sections and effective multiplication factor have been investigated in different concentrations of nanoparticles in the coolant and moderator channel. In the present analysis, water-based nanofluids containing various volume fractions of Al2O3, TiO2, CuO and Cu nanoparticles are studied. The neutronic properties of nanofluids with the optimum concentration of nanoparticles are calculated using WIMS-D5 and CITATION-LDI2 codes. The results show that at low concentrations of less than 1 volume percentage, alumina is the optimum nanoparticle for the normal operation of a reactor.

In pool-type research reactors, utilizing thermal column irradiation facilities through the fission process in the core, gamma rays are produced and absorbed by lead slab as a gamma rays shield of thermal column. Consequently, heat is generated in the lead slab surface which induces flow by the thermal buoyancy force. In the present work, 3D, CFD simulation of flow and heat transfer in a channel, formed by the thermal column and core edge, is considered. The aim is to obtain the temperature distribution on the lead surface and also a solution to prevent boiling, which may occur on the lead surface. It is observed that the hot spot on the lead surface exceeds the boiling point in natural convection mechanism. Therefore, the grid plate is extended underneath the channel so that water can flow through the channel and exit to the plenum causing forced convection to be established as an effective way to eliminate the boiling occurrence.

In this paper, a numerical model is presented to analyze a series of reactivity insertion and loss of flow transients in TRR. The model predictions are compared with the experimental data and PARET code results. The model uses the piecewise constant method and the lumped parameter methods for the coupled point kinetics and thermal-hydraulics modules, respectively. The advantages of the piecewise constant method are simplicity, efficiency and accuracy. A main criterion for the applicability range of this model is that the exit coolant temperature remains below the saturation temperature, i.e. no bulk boiling occurs in the core. The calculated values of power and coolant temperature, in both positive reactivity insertion and loss of flow scenario’s, are in good agreement with the experiment values. However, the model is a useful tool for the transient analyses of most researches encountered in reactors in practice. The main objective of this work is using simple calculation methods and benchmarking them with the experimental data. This model can also be used for training purposes.

<p>Bone metastasis is a major clinical concern that can cause severe pain, bone fractures, spinal cord compression, hypercalcemia and other problems for patients. Variuos β emitter radionuclides have been used for bone pain palliation, but recently α emitter radionucliedes also have shown acceptable results of treatment of bone metastasis. Radium-223 (t1/2=11.43 d) is one of the suitable α emitters that emits high energy α particles (Ēav=5.64 MeV) with high linear energy transfer (LET) that delivers a killing dose to the tumor cells. In this research, the feasibility of production of radium-223 from radium-226 was studied in Tehran Research Reactor (TRR) in thermal neutron flux of 4×1013 cm-2 s-1 using MATLAB software. Then, the data were compared with the experimental results. On average, over 80 percent agreement was observed between the calculated and experimental data, and under appropriate conditions the acceptable activity of 227Ac as a precursor of 223Ra was obtained. The results showed that with one month neutron bombardment of 2.5 mg 226Ra in TRR and cooling for 4 months, it is theoretically possible to achieve about 8.51 MBq (0.23 mCi) activity of 223Ra, that with respect to injection of about 3.7 MBq (0.1 mCi) per patient (with normally 70 kg weight), it is possible to administer the produced 223Ra to more than 2 patients in every equilibrium period.</p><p> </p>

In this research work, the biosorption of thorium from aqueous solutions by orange peel (OP) and orange peel cellulose (OPC) was studied and compared with each other. The kinetic studies showed that the Elovich and pseudo-second order kinetic models are well matched with the experimental results for the OP. For the case of OPC, the pseudo-second order kinetic models are well matched with the experment. The Langmuir, Freundlich, Dubinin–Radushkevich, Temkin and Redlich-Peterson isotherm models were also investigated. In order to find the best isotherm, three error analysis methods, i.e., correlation coefficient (R2), root mean square error (RMSE) and Chi square (χ2) were used. The error analysis showed that Redlich-Peterson, Temkin, Dubinin–Radushkevich and Freundlich models had miner errors, while the OPC Freundlich model had the smallest. Experimental results showed that the time required to reach the equilibrium is 4 h in the case of using OP as a biosorbent. In the case of using OPC as a biosorbent, the needed time to reach the equilibrium was about 1 h. Using OPC increases the adsorption rate and reduces the needed equilibrium time.

Batch extraction investigation was carried out to elucidate the stochiometry of the extracted Th(IV) species. The effects of nitric acid concentration, extractant concentration and temperature were studied. The results showed that the extraction of thorium follows solvation mechanism in the low  (0.001 mol L-1) and high (8 mol L-1) nitric acid concentration, while the cation exchange mechanism dominates the middle acidic area (1 mol L-1). The extracted species was found to be Th(OH)2(NO3)A.HA on the basis of the slope analysis method. The results of the thermodynamic investigations indicated that the extraction process is spontaneous (DG<0), exothermic (DH<0), and less random in nature (DS<0). The value of activation energy of the extraction reaction was calculated to be 17.46 kJ mol-1 which indicates that the extraction reaction is controlled  by the diffusion process.

In this paper, first, with bombardment of solid targets via spectra of electrons produced from the laser–plasma interaction, the created Bremsstrahlung X-ray is simulated using MCNPX code. Then, by the interaction of the produced photons with a secondary solid target, a simulation for the neutron generation is studied. The purpose of this work is to evaluate appropriate parameters of electron source and target to create photons and neutrons, more efficiently. Therefore, we are able to estimate the best conditions for the source and target, for instance, the optimum selection of the target material and its thickness, proper electron spectrum, and the optimum angle of photon emission so as to increase the efficiency of X-ray generation. This results in improved production of photo-neutron flux to be used in  various applications such as medical uses. The results show that by increasing the electron peak energy, the optimum thickness and output efficiency are enhanced. Furthermore, for materials with higher density and atomic number, the increment of Bremsstrahlung photon emission, which occurs at smaller thicknesses, results in greater generation of neutron flux.

Because of its wide applications in plasma based equipment, plasma parameters of a trigatron switch are investigated with the intention of the switch optimization. The theoretical method is based on the simulation of a closed switch discharge circuit, included the main capacitor, total circuit inductance, and plasma resistance, in an under damped oscillator. The charging voltage is between 6 to 15 kilovolts, the switch pressure is between 1 to 1.5 atmospheres and the gap is 1.4 or 2.8 mm. The density of the discharge plasma of the switch in self-breakdown mode is determined using the recorded time varying voltage and the switch current. The obtained electron density of plasma is (0.5-3.5)×1024 per cubic meter, which is in good agreement with the results published in standard references for arc and spark plasma in atmospheric pressure, based on the streamers mechanism.

At present, about 20 to 25 percent of agricultural products are removed as waste from the consumption cycle. Using gamma radiation is one of the methods to reduce waste in agricultural products, especially in potato (Solanumtuberosum L.). Under current conditions, gamma radiation is used in the farm products in which fertilization is based on farmer's conventional fertilizer use (urea and phosphate). The idea is to observe the effect of gamma radiation on decreasing the agricultural storage waste when fertilization is done according to the soil analysis results. To study the role of the balanced fertilization in increasing the effect of gamma radiation, a factorial experiment was conducted in the form of randomized complete block design with three replications in Pikasocultivar. In this experiment, the three factors used were: a) fertilizer application, i. e., farmer's conventional fertilization and balanced fertilization methods;  b) irradiation with gamma radiation, i. e., control and irradiate; and c) measuring the storage time factor, i. e., before and after 6 months of storage. The samples were irradiated with the dose of 0.15 kGy, then all samples were stored for 6 months at 15 to 20°C at the relative humidity of 40 to 60%. Percentages of dry matter and the concentrations of nitrate and cadmium were measured before and after the storage. The results revealed that, while the percentage of the dry matter in the samples of farmer's conventional fertilization method, that were not irradiated, increased from 16.86%to 21.44%, the irradiated samples increased from 17.68% to 19.41% during the storage period. These changes in the balanced fertilization samples in those which were not irradiated, increased from 20.09% to 23.18% and in the irradiated samples increased from 19.75% to 20.65%. By considering the obtained results, as the rate of weight loss in the tubers under the balanced fertilization was minimum, the effectiveness of gamma radiation in the condition of the balanced fertilization on the shelf life of potato tubers was proved. While the superiority of the balanced fertilization [fertilization on the basis of pre-plant soil analysis results over farmer's conventional fertilization method (N and P-fertilizers)] has been proven, gamma radiation in the condition of the balanced fertilization for increasing the potato tubers shelf life shows to act effectively, mainly due to high tubers dry matter percentage. Therefore, performing further experiments and analyses for other agricultural products under the crop balanced fertilization is highly recommended.

The high-level radioactive waste will be encapsulated in copper canisters and stored in a deep repository. High power electron beam welding was the only viable method available at that time for welding thick section copper. In recent years, friction stir welding has been replaced with electron beam welding because of the promotion in mechanical properties and corrosion resistance of copper canisters. FSW is used in solid state, therefore residual stresses produced in the weld is less than that of other welding processes which are performed in the molten state. To obtain optimum rotational speed, FSW was carried out in copper plates with a thickness of 4 mm at a constant speed of 25 mm/minute. The temperature distribution indicated a severe increasing of temperature upon increasing the rotational speed from 900 to 1200 rpm. Also, analysis of the metallographic images showed that the grain size in the nugget zone increases by increasing the rotational speed. Vickers hardness test was conducted on the welded samples and the maximum hardness was obtained at a rotational speed of 900 rpm. Results of tensile tests and their comparison with those of the base metal showed that the maximum strength and minimum elongation are achieved at the same rotational speed.

In this paper, a process for solid-liquid separation was investigated by thickening method on the slurry obtained from leaching process under optimum conditions (Saghand Anomaly 1 soil). In mineral processing industries, the correct selection of the type and amount of flocculant can reduce the diameter of thickener, leading to an increase in the efficiency of the separation process and reducing the costs. Thus, in the present work, the experimental thickening was carried out by varying the amount of flocculant K-300 for solid-liquid separation process. By comparing the sedimentation rate of each experiment, the optimal value of flocculant for solid-liquid separation process (Saghand Anomaly 1 soil) was 80 g/tonore.

A common and routine method for producing nitrogen-13 is 16O (p, α) 13N reaction, where nitrogen-13 is produced with the bombardment of O-16 through the induced proton, and is accompanied by emission of α-particles. Target material for N-13 production is pure water. The first experiment is carried out with a gold target. Because of the gold reaction with nitrogen-13, labeled ammonia (Au++n 13NH3=Au(13NH3)+n), a new liquid target made of niobium, was designed to overcom this drawback. One of the advantages of niobium element is its high chemical resistivity. The 13N radioisotope was produced at the Agricultural, Medical and Industrial Research School (AMIRS), where the target was irradiated with proton particles of 17.5 MeV energy and the current of 12 μA for 20 min. The yield of the radioisotope was about 84.5 mCi/μA h.