محسن اسدی اسد آباد

At present, Maximum Temperature Crystal Sensors (MTCS) are of great interest in the design and optimization of engines and turbines with high efficiency. These sensors are made in very small dimensions and can measure the maximum temperature in the desired location, for example inside the turbine. It is worth mentioning that a high fluence of fast neutrons is required to produce these sensors. The MTCS method is based on the high temperature phenomenon to restore changes made in the crystal lattice caused by neutron irradiation. Calculations of the maximum fast neutron flux for the diamond sample were performed using MCNP6 with the simulation of the core of the Tehran Research Reactor (TRR). Activity calculations were done using ORIGEN2, dose rate calculations through MCNP6, and temperature calculations with ANSYS software at different points of the sample. The highest fast neutron flux was calculated, and the activity of the sample decreased significantly after 40 days, with the dose rate at a distance of one meter reaching 1.4 µSv/h. Temperature calculations showed that the maximum temperature at the lowest speed of the channel was 402 K, which would not cause any thermal problems. Additionally, using the X-Ray diffraction (XRD) method, the lattice number and unit cell volume were calculated for the sample. The results obtained suggest that the diamond sample, from the perspective of neutronics, dosimetry, thermohydraulics, and changes in crystal lattice structure, can be recommended as a crystal sensor in the Tehran Research Reactor.

The present study investigated the structural, mechanical, and nuclear properties of two types of polymeric and metallic composites containing boron carbide particles. The neutron transmission test obtained lower neutron transmission in BPAER reinforced with B4C nanoparticles compared to the microparticle-reinforced composite. The stress-strain diagrams obtained from the tensile test show the improvement of the mechanical properties of the epoxy resin composite reinforced with B4C nanoparticles compared to the microparticles. The neutron transmission test also indicates an improvement in the nuclear properties of the Al-B4C nanocomposite compared to the Al-B4C micro composite. On the other hand, the density of this nanocomposite shows an increase compared to the micro composite. Also, regardless of the size and amount of carbide particles added, the density of all composite samples was lower than that of aluminum. Also, the hardness of the composite increased with increasing the amount of reinforcing phase, which was more in the nanocomposite samples than in the micro composite samples.

Zr-1%Nb alloy is the most common alloy used as nuclear fuel cladding in Russian reactors. In producing a nuclear fuel cladding, the cold rolling (pilger) and the final straightening lead to the creation of residual stresses and a change in the distribution of these stresses within the fuel cladding. The residual stresses are known to be effective in increasing the hydride fraction in nuclear fuel pods formed under working conditions by hydrogen adsorption of water and have destructive effects. In this study, the residual stresses created in different stages of fuel cladding fabrication, including samples before annealing, post-annealing, and straightening, were measured using X-ray diffraction and splitting. In addition, the amount of hydride fraction in different samples was evaluated. The effect of annealing on the orientation of hydrides was performed in annealing at 500, 540, and 580 °C for 4 hours.

The use of metal matrix composites can provide a combination of desirable properties of metals as well as the special physical properties of neutron absorber reinforcing particles such as boron carbide, which alone may be brittle. Therefore, in the present study on neutron attenuation power of composite shielding, several Al-B4C composite samples with weight fractions of 5, 10 and 20% B4C have been used. In order to investigate the neutron absorption properties of the studied samples, the MCNP Monte Carlo code and the neutron source of the dry channel of the MNSR reactor with a flux of 2.13E+5 n.cm-2.s-1 have been used  ,which provided in nominal reactor power of 30 kW. The results show that the neutron flux in the presence of 5, 10 and 20% boron carbide samples is predicted to be 1.32E+05 n.cm-2.s-1,1.12E+05 n.cm-2.s-1 and 1.07E+05 n.cm-2.s-1, respectively. With this increase in the percentage of reinforcement phase, neutron flux is reduced down to 50%.

Change in the position of atoms in the material’s crystalline lattice is caused by the radiation. Changes in the macroscopic properties of the material will be created by the change in structure. Knowing the amount of variation of material properties is necessary for materials in high-radiation environments. In this paper, the effect of 2.5 MeV proton irradiation on TSX grade graphite structure is investigated. This graphite is used as a reflector in the Tehran research reactor. The radiation has been carried out with the proton for 276 minutes. Microhardness test, Raman test, and SEM images were used in this study. The results show an increase in the microhardness of the material due to the radiation. Increased vacancy and interstitial clusters have also been observed in the Raman spectrum. The creation of cavities on the surface of irradiated graphite is observed in SEM images. The results can be verified by using the point defect model.

The displacement of the atoms from their lattice sites is one of the results of neutron irradiation on materials. The primary knocked-on atoms spectrum and their angular distribution should be calculated for consideration of neutron radiation damage calculation. The AMTRACK program has been developed to calculate this information. This program extracts and analyzes information about the primary knocked-on atoms by using Ptrac output of the MCNPX code. In this study, Stainless Steel 316, one of the most important alloys in the reactor pressure vessel, is investigated. The material is irradiated by single energy neutrons of 1keV to 10MeV, the fraction of produced PKAs, their average energy, their maximum energy, and radiation damage value are calculated. The calculations are performed by using the neutron spectrum of the Bushehr reactor. Using this method, the amount of damage in the Bushehr reactor pressure vessel (for Stainless Steel 316) is equal to 7.2×10-22 (dpa/ fluence).

Safety is one of the most critical issues in any test. The flexural test is a significant one to obtain material specifications. In this paper, a standard sample dose rate was calculated for the graphite flexural test in Tehran research reactor. Using different standards, the dose was computed at different distances and two periods of radiation, 15-40 days. Our calculations were performed with the ORIGEN and MCNPX codes. The impurity amounts of the material were measured by two methods of X-ray Fluorescence (XRF) and Inductively Coupled Plasma, Atomic Emission Spectroscopy (ICP-AES). The obtained results show that the Claiborne & Trubey standard is more stringent than other standards, and it has less than 2 μSv/h dose with the observance of 100cm distance and 20 days after irradiation. Moreover, calculations of the transfer chamber indicate that there is no limitation for the transport of the samples. Finally, it can be concluded that the considered method of this research can be used also for other materials at the reactor core.

One of the most important results of neutron irradiation on targets is that atoms are displaced from their lattice sites after that a nuclear reaction. The neutron irradiation damage is often simulated by using light/heavy ion irradiations, which prepare flexible irradiation conditions. The knowledge of primary knock-on atoms (PKA) and point defect energy distribution is the first step to simulate radiation damage induced by neutrons and also calculation of the amount of damage in “displacements per atom” (DPA) and damage profile in target is another purpose. In this study the MCNP code and SRIM code have been used to simulate the interaction of neutrons and energetic ions with materials then a new program was written by MATLAB software, AMTRACK, which analyzed PKA and point defect specifications. Finally the comparison of fraction of recoils spectra as well as weighted recoil spectra induced by ions/neutrons leads to determine best ions and its energy to simulate damage in reactors and our final goal is to be able to predict the amount and profile of radiation damage by best ion and neutron spectrum

At the present study, the mechanical alloying method was used to produce the nanocrystalline Cu-5Ta alloy. In order to achieve a specimen with desirable properties, effects of size of milling ball, atmosphere and temperature of sintering were investigated on crystalline structure, electrical conduction and microhardness of specimen. The microstructural studies indicated that a finer crystallite size was attained when the complex size of milling balls being composed of 10 and 5 millimeters was applied rather than simple one of 10 millimeters. After milling, cold press and subsequent sintering were done under different atmospheres such as nitrogen, argon and vacuum at temperature of 550C. The sintered specimen under vacuum showed the better properties compared to the others. The further evaluations on specimen properties was conducted by sintering at temperatures of 700 and 850C under vacuum. The results indicated that with increasing the sintering temperature, electrical conduction and microhardness increase. Overall, the specimen milled by the complex ball size and sintered at temperature of 850C under vacuum experienced a electrical condition of 15.7% IACS and microhardness of 196.2 HV which was the best conditions to produce Cu5Ta.

The morphology of zirconium sponge formed during the Kroll process could be more important due to its effect on composition, amount of impurities and efficiency of the sponge durability in the subsequent intermediate processes. In this research, various samples were prepared from different stages of the process and different zones of the products. In order to evaluate the products, scanning electron microscopy (SEM) and X-Ray diffraction (XRD) techniques were used. XRD analysis of the zirconium sponge showed that the amounts of magnesium chloride and retained magnesium in sponge texture were at a high level after the reduction process and were distributed non-uniformly in various parts of the sponge in which the amounts of impurities in the center was higher than the other parts. Also, examination by the scanning electron microscopy showed that the prime morphology of the zirconium sponge particles is irregular. Chemical analysis indicated that the excretion of magnesium impurities from the sponge will be more desirable in the distillation process, when the sponge morphology is in needle–like shape. If there is not enough time for the distillation process, the amount of magnesium and chloride impurities in the center of zirconium sponge will be higher in comparison to the other areas. So, for maximum elimination of such impurities in the distillation process, sufficient time duration has to be considered. Despite the fact that the distillation process is time-consuming and expensive, the impurity elimination compared to the proceses of chemical purifying is more favourable.

In this study, zirconium carbide (ZrC) coatings are electrodeposited on zirconium substrate by electrolysis from molten salt at 772 oC. Electrodeposition is carry out at 120 and 380 mA/cm2 as electrolysis current densities. The coatings have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and Fourier transform infrared spectroscopy (FTIR) methods. Corrosion resistance of coatings are investigated using potentiodynamic polarization test in a solution containing boric acid (H3BO3) and lithium hydroxide (LiOH) at pH= 6.85. The production of zirconium carbide coatings has been confirmed by XRD, FTIR and EDX analysis methods. The results show that zirconium carbide coatings improve the corrosion resistance of zirconium. Moreover, the passivation zone has been expanded by ZrC coatings. The electrodeposition current density shows incredible effect on electrocrystallization, nanostructure and consequently corrosion resistance of ZrC coatings. As the coating electrodeposited at 120 mA/cm2 shows lower corrosion rate. Nanostructure, coherency of ZrC particles, and absence of cracks in the coating are affected this behavior of zirconium carbide coatings.

In this study, the effects of process parameters including weld current and electrode force on the microstructure of resistance spot welding on Zr-1%Nb alloy sheets of 0.3mm thickness were investigated. In the microhardness investigation of the weld nugget cross section, the Vickers hardness measurement was performed in the direction of the weld nugget diameter on a base metal, HAZ, and weld nugget for the welded specimens with different parameters. Applying more electrode force in the same welding time yielded the grain growth which was found to be an important observation in this study. In the metallographic images, it was observed that the grains were deformed to be longer in the heat flow direction when more electrode force was applied. The hardness measurement of the weld zones and base metal showed that, the weld nugget had a maximum amount of hardness where it decreased in HAZ and subsequently in the base metal. This difference is due to transformation of the α+β and β phases. Transformation from β to α phase, which was carried out by a massive diffusion process and formation of the Widmanstatten α structure was achieved by slow cooling. The mentioned structure was found to be harder and stronger than the equiaxed α microstructure of the weld metal.

In this work, the effect of metallurgical factors on corrosion behavior of Zr-1%Nb in %3.5 NaCl media at 60oC was investigated. After different processes, the microstructure of the treated alloy was analyzed by optical and scanning electron microscopes. Corrosion behavior of the specimens was evaluated by electrochemical impedance spectroscopy (EIS) and potensiodynamic polarization. The results showed that addition of Nb as alloying element, result in increasing both the hardness and polarization resistance of the alloy. While strengthening by deformation process led to refining the grains of the alloy but it had reverse effects on corrosion behavior of the alloy as it decreased the polarization resistance, up to 7 times less than untreated sample. This shows that it is necessary to optimize the conditions of deformation process to access high strength alloy together good corrosion resistance.

In this study، the four Cr-Mn- (Ni-free) austenitic steels were fabricated by vacuum induction furnace. Then plates with 10 mm thickness were fabricated by hot-rolling. Corrosion behaviour of the four Cr-Mn steels in 0. 1 M H2SO4 solution was investigated using by open-circuit potential، potentiodynamic polarization، and electrochemical impedance spectroscopy (EIS). The results indicated that the open-circuit potentials of the four Cr-Mn austenitic steels were found to shift towards positive direction. Also، the potentiodynamic polarization curves suggested that the four Cr-Mn austenitic steels showed comparable passive behaviour in sulfuric solutions.