فهرست مطالب s. j. ahmadi

Hydrogen isotope separation can be achieved by confinement to small mesoporous structures or by strong adsorption sites. MOFs are attractive candidates for isotope separation, considering their tunable pore structures and the potential to introduce adsorption sites. In this research, we investigate the formation of elongated dihydrogen complexes near MOF’s open metal sites as a promising reaction for isotope separation. The electronic structure of all MOFs (M is the first-row transition metal) is studied based on density functional theory. The quantum chemical approach suggests Fe-MOF as a promising candidate for isotope separation by modeling the non-covalent interactions with the active site/H2 cluster.

In the present study, high-density polyethylene (HDPE)/hexagonal boron nitride (hBN) and HDPE/Boron nitride nanosheets (BNNSs) nanocomposites with different contents were fabricated using the melt mixing method. The morphology, properties, and mechanical and thermal performance of composites and nanocomposites containing boron nitride were investigated. Also, the neutron shielding performance of the designed composites was investigated using the thermal column of the Tehran Research Reactor and foil activation method. The results were compared with those of using pure HDPE. HDPE/BNNSs nanocomposites have shown higher modulus and tensile strength, higher thermal stability, and better neutron shielding performance than HDPE/hBN. The results showed that by reaching hBN content to 0.5 wt. %, the neutron shielding of the composite was improved by 25% compared with the pure HDPE. However, there is a 43% increase in neutron absorption by nanocomposites compared with HDPE. The result of this work is expected to cause a natural synergy between applied nanocomposite and neutron shields and lead to the commercial production of Leigh-weight, inexpensive, and effective neutron-shield nanocomposites.

Due to the limited uranium reserves and advantages of thorium fuels over uranium fuels, the development of the thorium fuel cycle in various countries including Iran, has been considered significantly. One type of thorium fuels used in nuclear reactors is a mixture of uranium dioxide and thorium. The type of powder synthesis method is a key point in improving the efficiency of this fuel in the reactor. The main objective of the present study was to achieve mixed nanoparticles of 30-70% (Th-U)O2. The effect of four parameters including concentration, time, initial percentage of uranium-thorium nitrate in solution, and temperature was studied using Taguchi's experimental design. The synthesized nanoparticles were characterized by XRD, BET, EDS, and SEM analyses. The results showed that at the best conditions, the nanoparticles were synthesized with a weight percentage of 32.28 and 67.72%, a particle size of 13.25 nm, high purity, and high surface area. Also, the results showed that the supercritical hydrothermal method has performed well for mixed nanoparticles of 30-70% (Th-U)O2 production.

Epoxy resin as a thermoset polymer has a suitable thermal resistance with high mechanical properties. In addition, the resin exhibits good continuum presentation for both neutron and gamma beams. Consequantly, it is the primary concern in the nuclear industry. In a neutron shielding, energetic secondary gamma products are unavoidable. For attenuating these gamma rays, the elements with high atomic number in the polymeric matrix are inevitably used. Because of various problems of lead shield, studies are inclined to the lead free shielding. In this investigation and, by using Monte Carlo method, the ability of secondary gamma attenuating was studied on a polymeric shielding based on reinforced epoxy with different weight percentages of 5, 10 and 20 of tungsten oxide and lead oxide without any neutron poisons. The results show that by the same weight percentage, the reinforced composite shield with tungsten oxide could afford better shielding performance. The more increase in the weight percentage of the reinforced material, in addition to an increase in the weight of the shield, reduce the ability of shielding performance.