مجله علوم و فنون هسته ای
سال چهل و ششم شماره 2 (پیاپی 112، تابستان 1404)

FAs (Fuel Assembly) lateral deformation under mechanical, hydraulic, thermal, and radiation loads in the reactor core is called FA bowing. This phenomenon has different consequences for reactor safety and its operation. Bowing causes the local change in distance between the FAs, which leads to a neutron perturbation that affects the power distribution and its asymmetry. This research determines the bowing pattern of FAs in the VVER-1000 reactor core by using an artificial neural network and C-shape bowing assumption. That will be done based on power distribution caused by the presence of FA bowing. This issue will help the operator design the arrangement of FAs in the next cycle by knowing the bowing pattern in the reactor core. It will prevent the expansion of the bowing and its consequences in the next fuel cycles.

Identification of the changes of aluminum structure due to neutron radiation is very important in the reactor fuel clad. In some cases, ion (usually proton beam) irradiation method is implemented for this investigation. The changes in the holes of Al are in the range of picometers by the radiation of energetic protons. In this research, positron annihilation lifetime spectroscopy, was used to investigate the changes of holes in Al-6061 and Al-303 due to the radiation of 2.2 MeV protons at different amounts of radiation. This method has the ability to evaluate the dimensions of the holes in the range of picometers and nanometers. For both investigated aluminum samples, the results show that the value of τave first decreased and then increased. It indicates the holes became smaller and decrease the vacancy defects in the initial stages of irradiation. Then, the holes became larger in the continuation of irradiation, which indicates increasingin the interstitial defects. These results were also confirmed by XRD test. It can be seen that the crystal size of the irradiated aluminum increased at the in the initial stages of irradiation and then decreased in the continuation of irradiation.

The design calculations of the spent fuel pool require the consideration of various parameters such as neutronic, thermal-hydraulic, safety, shielding, economic and operation. Considering the high cost of designing and building of a new spent fuel pool as well as the existence of empty spaces in the pool of some research reactors, neutronic and shielding calculations for the feasibility of using second pool of a typical research reactor as a spent fuel pool is done using ORIGEN2.1 and MCNP6 codes. The first step is the determination of the distance between fuels (grid pitch) in such a way that the effective multiplication factor for the worst possible case is less than 0.95, that 13 cm grid pitch fulfills this condition. Source term calculation for a fuel with the highest burnup (60%) is done as the most pessimistic condition. Continuous operation and 24 hours cooling are considered as the shortest possible time to transfer spent fuels to the storage rack in order to have the most pessimistic conditions in the design of spent fuel rack. For a rack with 100 spent fuels that is 87 cm away from the pool wall on each side, a 300 cm layer of water on top of the fuels and 85 cm thick concrete wall are enough for the possibility of using second pool as a spent fuel pool. It has been found that it meets the dose rate criteria of less than 1 and 10 μSv/h behind the wall and above the pool water level.

In this paper, in the framework of the interacting boson model (IBM), the method of mixed U(5) and SO(6) symmetry limits has been used to calculate the electric quadrupole transition rates between different levels in the isotopic chain of Cadmium (110-104Cd) and in the E < 3 MeV region. In this method, wave functions of different intruder levels are considered as a combination of wave functions in the two N and N+2 bosons spaces and the effect of electric quadrupole transition's operator is determined by them. The effective charges of the transition operator are extracted in comparison with the experimental values of the quadrupole transition rates and then, theoretical predictions of two methods, using only U(5) dynamical limit and mixed of symmetries are compared with each other. The results show that the accuracy of the predictions are increased via mixed of symmetries method in all of considered transitions. On the other hand, the U(5) dynamical limit is only successful in examining the quadrupole transitions between the levels of the ground band and levels with a longer half-life and confirms the existence of a closed neutron sub-shell in the 106Cd nucleus. Also, for such inter-bands transition and also transitions are originated from intruder states, the exactness of the mixed symmetries prediction are obvious.

Technetium-99 in nuclear waste as one of the toxic and hazardous radioactive pollutants should be quantitatively and qualitatively identified before final disposal. In the present research work, Technetium -99 in the aqueous phase of the concentrated waste of Bushehr nuclear power plant was qualified and quantified. To achieve this goal, Cesium-134 and 137 were firstly separated using potassium cobalt hexacyanoferrate(II) adsorbent. Then, tritium was removed using thermal treatment at 60˚C, and finally technetium-99 in this media was purified by removing beta emitter radioisotopes such as cobalt- 60, iron-55, and nickel-63 using precipitation process with iron(III) hydroxide. The samples were qualitatively and quantitatively evaluated using gamma spectrometry and liquid scintillation counter instruments. The results showed that purified Technetium-99 has a high radiochemical purity and other radioisotopes were removed from the media with an efficiency of about 100%. Also, the beta spectrum of the sample was in complete accordance with the beta spectrum of the standard samples. The total yield of the proposed processes using the increase of Technetium-99m tracer to the original sample was equivalent to 80.69%. Taking into account the 93% efficiency of the liquid scintillation counter and the processes yield (80.69%), the specific activity of Technetium-99 was calculated as 10554.13 Bq.L-1.

In this research, uranium extraction from a phosphoric acid solution produced from a new phosphate ore from a Syrian mine was carried out for the first time using D2EHPA-TRPO solvents in kerosene. The goal of the research was to produce yellowcake from the phosphoric acid solution. The process involved primary solvent extraction, primary stripping, secondary solvent extraction, scrubbing, and finally secondary stripping with precipitation. Based on the results obtained, the optimal values for primary solvent extraction factors were: O/A ratio of 1/3, temperature of 40°C, mixing time of 7 minutes, and TRPO concentration of 6% (v/v). The optimal values for primary stripping factors were: O/A ratio of 34/1 (two steps with O/A ratio of 17/1), temperature of 40°C, and mixing time of 40 minutes. The efficiency of these two processes was 86.40% and 95.60%, respectively. The optimal conditions for the secondary solvent extraction process included an O/A ratio of 1/4, temperature of 40°C, and mixing time of 7 minutes. For scrubbing the charged solvent with sulfuric acid (w/v), 2.5% of the optimal values of O/A ratio of 10/1, temperature of 40°C, and mixing time of 7 minutes were used. Finally, for secondary stripping and precipitation of yellowcake, a 2M solution of ammonium carbonate was used at a temperature of 40°C, and the stirring time was 15 minutes.

Studying the structure of the nucleus through the consideration of pairing correlation between nucleons plays a crucial role in determining the thermodynamic properties of the nucleus. In this study, we examined the thermodynamic characteristics of the nucleus using the BCS model, which incorporates pairing correlation. The gap parameter serves as the symbol of pairing correlation in this model. By calculating the gap parameter at various temperatures using the BCS model, we were able to determine the excitation energy, temperature-dependent level density parameter, and nuclear level density. Additionally, we calculated the nuclear level density using the BSFG model and the temperature-dependent level density parameter. Finally, we compared the results of the nuclear level density obtained through these methods with each other and experimental data.

This article investigates the structural, electronic, optical, and thermoelectric properties of a titanium atom doped into a C3N monolayer using the Wien2K computational code and first principles calculations within the density functional theory framework. The study of electronic properties reveals metallic behavior in this two-dimensional structure. Optical properties demonstrate optical anisotropy in both the x and z directions. Analysis of the thermoelectric properties of the C3N@Ti single layer using the semi-classical Boltzmann theory indicates that this layer not only possesses a low Seebeck coefficient but also exhibits very small thermoelectric efficiency, limiting its thermoelectric application.

In this study, an online homogenous sedimentation method was utilized for the in situ production of micro particles to be used as an adsorbent for solid-phase extraction of molybdenum. The process involved the dissolution of yellow cake and the conversion of molybdenum (VI) into a hydrophobic complex, followed by the addition of n-dodecyltrimethylammonium bromide as a precursor to the sample solution. A precipitant reagent, sodium hexafluoride, was then introduced into the solution through a T connection in a flow system. Micro particles were produced as a result of the interaction between the precursor and the precipitant reagent, which then adsorbed the molybdenum complex. After filtration, a desorption reagent was passed over the filter to release the adsorbed molybdenum, which was subsequently measured using ICP-OES. The method yielded a linear range of 0.2-200 µg/L, with a limit of detection of 0.05 µg/g. The repeatability of the method (RSD) was found to be 8.1% and 4.3% for concentrations of 10 and 100 µg/g, respectively. Overall, this method demonstrates potential for the precise and accurate determination of molybdenum in yellow cake samples.

A Ni-Cu (70.4-29.6 wt%) ferromagnetic alloy coated with an absorber layer of iodine-125 was used as the core in the Thermo-Brachytherapy (TB) system. The absorber layer, which was 100 μm thick and had a microcrystalline graphite structure, consisted of silver-doped activated carbon and polystyrene in a 70:30 weight ratio. Activated carbon is a preferred adsorbent for iodine capture due to its porous nature. Silver doping in the carbon enhances the trapping of iodine-125 through chemical adsorption. Polystyrene, acting as a binder in the absorptive layer's structure, facilitates the physical absorption of iodine on the surface of the silver-doped activated carbon-coated core. Results showed that the extraction efficiency of iodine-125 (as sodium iodide solution) with an average activity of 5 mCi on the nickel-copper core/polystyrene/silver-doped activated carbon was 20.31% after 2 hours. Coating the nickel-copper ferromagnetic core with gold or silver before depositing the silver-doped activated carbon increased the extraction efficiency to 32.77% and 60.23% after 2 hours, respectively. These findings highlight the significant impact of silver or gold coating on enhancing extraction efficiency. Moreover, a multi-step extraction process was employed in this research, where extraction steps were repeated to increase the recovery of iodine-125.

Radiotherapy treatment planning requires accurate delineation of organs at risk (OAR), which is typically a manual and time-consuming process. This research aims to explore the feasibility of using deep learning algorithms as an automatic tool for segmenting CT scan images. Accordingly, the performance of several convolutional neural networks (CNNs), including U-Net, Residual U-Net, and SegResNet, was compared as tools for automatic segmentation of OARs in pelvic CT scans (bladder, prostate, rectum, left femoral head, and right femoral head) against manual segmentation by specialists. This study involved 238 patients for prostate segmentation and 218 patients for the other four organs. The models' performance was assessed using metrics such as the Dice similarity coefficient, Jaccard index, and Hausdorff distance. The SegResNet model, providing the best performance, achieved Dice coefficients of 0.956, 0.832, 0.864, 0.980, and 0.985 for the bladder, prostate, rectum, left femoral head, and right femoral head, respectively. In summary, the results indicate that convolutional neural networks can accurately segment organs at risk in radiotherapy planning, with accuracies above 95% for bones and bladder, and over 83% for the rectum and prostate, while also speeding up the segmentation process.

The X-ray backscatter imaging systems have unique inspection capabilities and practical features due to their high sensitivity to organic materials, low radiation dose, and ability to scan from one side of the object. The scan is performed by an X-ray pencil beam. The shape, size, and intensity of the beam play a significant role in the image quality and the radiation dose received by the person. To create a pencil-shaped beam, the cone-shaped beam of the X-ray tube passes through a fan beam collimator and a chopper wheel. Different designs were simulated to optimize the fan beam collimator and chopper wheel, considering factors such as length and gap of the collimator, as well as the slit width of the disc using the MCNPX2.6 code. To minimize leakage dose, a 4-mm tungsten/copper alloy disc was determined to be the most suitable in terms of thickness and material. Based on the simulation results from image quality tests, it was found that a collimator with a length of 20 cm, a 1 mm gap, and a 1 mm slit width of the disc produced the most optimal X-ray beam for backscatter whole-body imaging systems. The best image quality was achieved at a disc rotational speed of 1500 rpm and a relative speed of vertical movement at 40 cm/s.

Khoshoumi Anomaly 6 is a significant uranium deposit located in the Bafq-Saghand metallogenic belt within the Central Iran zone. The gneiss serves as the primary host for uranium mineralization in block 1 of Khoshoumi Anomaly 6. Field emission electron microscopy studies have identified two stages of uranium mineralization within the area: primary mineralization (hypogene) and uranyl silicate (supergene). Primary uranium minerals found in the hypogene zone include uraninite, with minor amounts of thorouraninite, brannerite, and uranothorite. Uranyl silicate mineralization is observed along fractures in the form of boltwoodite and soddyite. Over time, boltwoodite undergoes alteration into sodium-boltwoodite and uranophane. Field evidence and mineralogical studies suggest that meteoric fluids, with a neutral to alkaline pH and low temperature, played a role in leaching uranium, silicon, potassium, sodium, and calcium from the gneiss. These elements were then deposited along fractures as uranyl silicate minerals, accompanied by calcite, clay, and chlorite. The presence of calcite alongside uranyl silicates indicates the transport of uranium in the form of uranyl carbonate complexes within the fluid.

In recent years, the advancement of electron synchrotron light sources has been crucial for synchrotron radiation users. Improving electron beam qualities, such as stability and intensity, has been key to generating high-brightness photon beams. To achieve a brighter photon beam, electron synchrotron accelerators have been undergoing significant design changes. A critical aspect of their design is precise control of particle trajectories and correction of errors to achieve a stable electron beam and, consequently, a high-intensity photon beam. One interesting approach in this field is the use of neural networks to correct the electron beam position in the storage ring, a process known as beam control. In this study, a convolutional neural network model has been developed for the first time to control the ELETTRA 2.0 storage ring, a synchrotron light source in Italy. The performance of this model, based on machine learning techniques, is approximately 6% better than the ISVD method, while also demonstrating high robustness to real-world data.

It is important to maintain the vacuum in the space between the rotor and the body of a gas centrifuge machine during the gasification and enrichment process. For this reason, a molecular pump is connected to the upper part of the body. The pump has grooved that particles collide with as they move. Depending on the direction of the grooves, the particles are deflected and return to the rotor. One method of analyzing the gas flow inside the molecular pump is by solving the flow equations using the Sickafus method and his colleagues. This method is useful because it reduces calculation time. In this article, four meta-heuristic algorithms were used to determine the optimal geometric and operational parameters of the molecular pump. The results indicate that among the meta-heuristic algorithms, optimization with the humpback whale algorithm (WOA) produces the highest compression ratio for the molecular pump. The average absolute deviation value of the logarithm of the pressure density ratio, when compared to values predicted by the upgraded Sickafus method with optimal parameters, shows a very good agreement between the experimental method and the upgraded Sickafus method using the meta-heuristic WOA algorithm.

Among promising radioisotopes, 132/135La stands out as a theranostic pair, offering specific advantages for the preparation of a wide range of radiopharmaceuticals. In this study, the theranostic pair 132/135La was produced through the interaction of natBa(p,x)13xLa, using theoretical calculations with the nuclear codes ALICE-91, TALYS-1.8, and SRIM-2013. The natural barium target was then irradiated in a 30 MeV cyclotron with 22.5 MeV protons and a current of 100 μAh. After the lanthanum was separated from the irradiated target, the solution's chemical purity, radiochemical purity, and radionuclide purity were examined using ICP-OES, RTLC, and gamma spectrometry, respectively. The study also investigated the effect of increasing the concentration of the chelator DOTA (1-100 nanomolar) on its labeling with lanthanum. The results showed that the average total amount of metal ions in the final solution was less than 0.1 ppm, with radiochemical and radionuclide purities above 99% and 99.5%, respectively. The labeling of the chelator DOTA with lanthanum demonstrated that even with the addition of 1 nmol of this chelator, a radiochemical purity higher than 93% was achieved. This study indicates that it is possible to produce lanthanum radionuclides with the required quality for the development of theranostic radiopharmaceuticals.

In this research, the recovery of rare earth elements from Chahgaz ore has been investigated through an acid leaching process. The effect of different parameters on the dissolution of rare earth elements was also explored. The results indicated that factors such as acid concentration, leaching temperature, ore particle size, liquid to solid ratio, and leaching time are crucial in recovering rare earth elements from the ore. Specifically, the recovery percentage of rare earth elements in sulfuric acid was found to be higher compared to other acids. Increasing the temperature to 85 degrees Celsius was observed to accelerate the leaching reaction and enhance the recovery of rare earth elements. Moreover, increasing the liquid to solid ratio up to 2 led to improved contact between the solid and liquid phases, as excess acid in the reaction medium facilitated a higher leaching rate of rare earth elements. Optimal conditions for the leaching process were determined to be a temperature of 85 degrees Celsius, a leaching time of 6 hours, a sulfuric acid concentration of 1.5 M, a liquid to solid ratio of 2, and a particle size of 150 microns. Under these conditions, a recovery percentage of 95% for rare earth elements from Chahgaz ore was achieved.

Neutron filter crystals are widely used in the nuclear industry, particularly in research reactors. One of the most important crystals used is sapphire crystal, which is grown in several countries to ensure good quality. This research aims to compare the neutron performance of sapphire crystals made in Iran with those of externally supplied crystals. An Am-Be source was used in this study to assess the ability of these sapphire crystals to remove fast neutrons. Additionally, a monochromatic neutron beam was used to study the impact of these crystals on reducing the intensity of the neutron flux. To verify the accuracy of computational codes in simulating the neutron behavior of these filter crystals, the McStas code was utilized. The results of this simulation were then compared with available experimental data. Comparing the experimental results with those published worldwide revealed that the domestically grown crystals performed comparably to the foreign samples. The experimental findings showed that a 2.5 cm sapphire crystal filtered the monochromatic neutron beam with an energy of 0.06 eV by only about 5.5%, and fast neutrons with an energy of more than 200 keV by about 33%. Increasing the crystal thickness to approximately 6 cm increased the filtration of fast neutrons to about 60% and monochromatic neutrons to about 16.5%. Overall, the results of this study indicated that the discrepancies between the simulation and experimental values may be attributed to the lack of detailed information necessary for crystal modeling in the computational code.

Tokamaks are recognized as one of the most promising devices for achieving nuclear fusion, operating within complex environments with high radiation levels. Upgrading these devices to enhance plasma efficiency and duration inevitably leads to increased radiation levels, making precise radiation dose estimation and the design of effective shielding systems essential. The Damavand tokamak, with its pure hydrogen plasma, generates both soft and hard X-rays. With sufficient data on these indirect ionizing radiations, the potential adverse effects can be minimized. Planned upgrades to the Damavand tokamak will extend plasma pulse duration from 22 ms to approximately 200 ms, resulting in a significant increase in radiation levels, estimated to be up to ten times higher in work areas, posing safety risks for personnel. In this study, we estimate the radiation dose in different areas of the upgraded Damavand tokamak laboratory based on experimental data, and we calculate specifications for new radiation shields using the MCNPX code to ensure laboratory safety. The required shielding dimensions were calculated for lead and concrete materials, allowing for a cost and feasibility assessment to guide the selection of the optimal implementation material.

The impact of pre-ionization using a 330 MΩ shunt resistor on the performance characteristics of a Mather Type plasma focus device with 2.4 kJ of energy, charged by a 12 μF capacitor bank to a maximum voltage of 20 kV, will be discussed in relation to hydrogen gas. In this study, the signal characteristics of the current and the current derivative of the device were measured and compared with and without pre-ionization at an optimal operational pressure of 0.85 Torr. Additionally, the emitted hard X-rays and ion beam in each shot were measured using a Ne102 X-ray plastic scintillation detector and Faraday cup, respectively. These measurements were conducted and compared with and without pre-ionization at the optimal pressure. The results from the current and current derivative signals of the device indicate that with initial pre-ionization, the signals exhibit a deeper and sharper fracture at the pinch time compared to when the pre-ionization circuit is inactive. This suggests that a stronger and more defined pinch occurs with pre-ionization. Furthermore, analysis of the Faraday cup signal amplitudes reveals that the intensity of emitted hard X-rays is significantly higher when pre-ionization is utilized compared to when it is not. Therefore, pre-ionization markedly enhances the efficiency of the plasma focus device, increases the intensity of emitted hard X-rays, and generates an ion beam with a higher current.