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Study on Concrete Activation Reduction in a PET Cyclotron Vault
Bakhtiari, Mahdi,Oranj, Leila Mokhtari,Jung, Nam-Suk,Lee, Arim,Lee, Hee-Seock The Korean Association for Radiation Protection 2020 방사선방어학회지 Vol.45 No.3
Background: Concrete activation in cyclotron vaults is a major concern associated with their decommissioning because a considerable amount of activated concrete is generated by secondary neutrons during the operation of cyclotrons. Reducing the amount of activated concrete is important because of the high cost associated with radioactive waste management. This study aims to investigate the capability of the neutron absorbing materials to reduce concrete activation. Materials and Methods: The Particle and Heavy Ion Transport code System (PHITS) code was used to simulate a cyclotron target and room. The dimensions of the room were 457 cm (length), 470 cm (width), and 320 cm (height). Gd<sub>2</sub>O<sub>3</sub>, B<sub>4</sub>C, polyethylene (PE), and borated (5 wt% <sup>nat</sup>B) PE with thicknesses of 5, 10, and 15 cm and their different combinations were selected as neutron absorbing materials. They were placed on the concrete walls to determine their effects on thermal neutrons. Thin B<sub>4</sub>C and Gd<sub>2</sub>O<sub>3</sub> were placed between the concrete wall and additional PE shield separately to decrease the required thickness of the additional shield, and the thermal neutron flux at certain depths inside the concrete was calculated for each condition. Subsequently, the optimum combination was determined with respect to radioactive waste reduction, price, and availability, and the total reduced radioactive concrete waste was estimated. Results and Discussion: In the specific conditions considered in this study, the front wall with respect to the proton beam contained radioactive waste with a depth of up to 64 cm without any additional shield. A single layer of additional shield was inefficient because a thick shield was required. Two-layer combinations comprising 0.1- or 0.4-cm-thick B<sub>4</sub>C or Gd<sub>2</sub>O<sub>3</sub> behind 10 cm-thick PE were studied to verify whether the appropriate thickness of the additional shield could be maintained. The number of transmitted thermal neutrons reduced to 30% in case of 0.1 cm-thick Gd<sub>2</sub>O<sub>3</sub>+10 cm-thick PE or 0.1 cm-thick B<sub>4</sub>C+10 cm-thick PE. Thus, the thickness of the radioactive waste in the front wall was reduced from 64 to 48 cm. Conclusion: Based on price and availability, the combination of the 10 cm-thick PE+0.1 cmthick B<sub>4</sub>C was reasonable and could effectively reduce the number of thermal neutrons. The amount of radioactive concrete waste was reduced by factor of two when considering whole concrete walls of the PET cyclotron vault.
Bakhtiari M.,Najar S. Shaikhzadeh,Etrati S. M.,Toosi Z. Khorram The Korean Fiber Society 2006 Fibers and polymers Vol.7 No.3
High-bulk worsted yams with different shrinkable and non-shrinkable acrylic fibers blend ratios are produced and then single jersey weft knitted fabrics with three different structures and loop lengths are constructed. The physical properties of produced yams and compression properties of produced fabrics at eight pressure values (50, 100, 200, 500, 1000, 1500 and $2000 g/cm^2$) were measured using a conventional fabric thickness tester. Then, weft-knitted fabric compression behavior was analyzed using a two parameters model. It is found that at 40 % shrinkable fibre blending ratio the maximum yam bulk, shrinkage, abrasion resistance and minimum yarn strength are obtained. It is also shown that high-bulk acrylic yarn has the highest elongation at 20 % shrinkable fibre blend ratio. The statistical regression analysis revealed that the compression behavior of acrylic weft-knitted fabrics is highly closed to two parameter model proposed for woven fabrics. It is also shown that for weft-knitted structure, there is an incompressible layer (V') which resists against high compression load. Acrylic weft-knitted fabrics with knit-tuck structure exhibit higher compression rigidity and lower softness than the plain and knit-miss structures. In addition, at 20 % shrinkable fibre blend ratio, the high-bulk acrylic weft-knitted fabrics are highly compressible.
Nonlinear supersonic flutter of truncated conical shells
Mehrdad Bakhtiari,Aouni A. Lakis,Youcef Kerboua 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.4
A numerical model was developed to investigate the flutter instability of truncated conical shells subjected to supersonic flows. The exact solution of Sanders’ best firstorder approximation was used to develop the finite elements model of the shell. Nonlinear kinematics of Donnell’s, Sanders’ and Nemeth’s theories, in conjunction with the generalized coordinates method, were used to formulate the nonlinear strain energy of the shell. A pressure field was formulated using the piston theory with the correction term for the curvature. Lagrangian equations of motion based on Hamilton’s principle were obtained. A variation of the harmonic balance method was used for developing the amplitude equations of the shell, and a numerical method was used for solving these equations. Results of linear and nonlinear flutter of truncated conical shells were validated against the existing data in the literature. It was observed that geometrical nonlinearities have a softening effect on the stability of the shell in supersonic flows.
Bioleaching kinetics of copper from copper smelters dust
Fereshteh Bakhtiari,Hossein Atashi,Mortaza Zivdar,Seyedali Seyedbagheri,Mohammad Hassan Fazaelipoor 한국공업화학회 2011 Journal of Industrial and Engineering Chemistry Vol.17 No.1
The smelting factory of Sarcheshmeh Copper Complex in Iran produces about 50 tons per day of copper dust containing 36% Cu, 22.2% Fe and 12.2% S. The dust is currently recycled to the smelters. Thismethod is not desirable in terms of operation, and energy consumption. A mixed culture of mesophilic bacteria was used to examine the bioleaching of copper from the dust. The effect of various parameters such as pulp density, nutrients, temperature, and the amount of pyrite added to the bioleaching media were examined in the dust bioleaching tests. It was shown that the bacteria contributed effectively in the leaching of copper from the dust. The collected data showed that at pH 1.8 and the pulp density less than 7%, the dissolution of copper followed shrinking core kinetic model and the process was limited by diffusion of lixiviant. With the pulp density of 7%, however, the process showed to be reaction limited.
Somayeh Bakhtiari,Meysam Shahrashoub,Ali Keyhanpour 한국화학공학회 2022 Korean Journal of Chemical Engineering Vol.39 No.9
The present study investigated the capability of magnetite nanoparticles (MNP) synthesized from the directreduction iron sludge and green tea extract for the single and competitive adsorption of copper (Cu2+) and cadmium(Cd2+). Moreover, we assessed the desorption of Cu2+ and Cd2+ in a ten-day cycle (both single and competitive systems)to evaluate their release amount from the adsorbent's surface. The adsorption process was described using threewell-known adsorption isotherms: Langmuir, Freundlich, and Dubinin-Radushkevich. The Freundlich isotherm wasemployed to describe the desorption process. The maximum adsorption capacity of Cu2+ and Cd2+ by MNP accordingto the Langmuir curve was 21.24 and 19.36mg/g, respectively. A significant difference was observed in the adsorbedvalue of heavy metals in the competitive mode and MNP selectively preferred Cu2+ against Cd2+. Results of energy-dispersiveX-ray (EDX) and elemental mapping analyses corroborated the Cu2+ and Cd2+ adsorption in both single andcompetitive systems. The findings of Fourier-transform infrared spectroscopy (FTIR) analysis revealed the role of functionalgroups in Cu2+ and Cd2+ adsorption. The results of the desorption evaluation demonstrated the higher tendencyof MNP to retain Cu2+ than Cd2+. We developed economical and environmentally friendly magnetite nanoparticles,promising in individual and competitive adsorption of Cu2+ from aqueous solutions while resisting to release it. Moreover,the adsorbent’s performance in singular removal of Cd2+ was noticeable.
Tourism and Ancient Pilgrimage Place in Yazd Chak-Chak : Zoroastrian'S Holy Shrine
Arshin Bakhtiari,Abolfazle Tajzadeh Namin 세계문화관광학회 2008 Conference Proceedings Vol.9 No.0
Pilgrims are the special tourists whose purpose is to visit the places where they become involved in the religious activities. In more recent times, however, it has been suggested that modern tourism has become the functional and symbolic equivalent of more traditional religious practices, such as festivals and pilgrimages. In Iran, Zoroastrians are not a big population but their rituals remain widely respected not only in Iran but other parts of the world. The most important holy place in Iran for Them is Chak-Chak(Pir-e Sabz) place on a hill 52 ㎞ to the desert province of Yazd (central part of Iran). This holy place is visited every year from June 14-18 by hundreds of tourists from all over the world, they cannot be considered solely as places for worship. However, little work has been undertaken to explore the position of the above named place. In this study the cultural characteristics of the Chak-Chak temple are introduced. Also the Problems related to conflicting interests of pilgrims and tourists are discussed and then some of management strategies designed to minimize these contests.