نشریه فناوری و انرژی هسته ای
پیاپی 2 (تابستان 1401)

The goal of this study was to investigate the dosimetric properties of magnesium oxide doped with lanthanide and indium impurities and also co-doped with lithium as a high sensitivity thermoluminescence material and its possible potential for high dose dosimetry. All the samples were synthesized by the solution combustion method and their crystalline nature was confirmed by using x-ray diffraction analysis. The morphology of the samples was characterized by scanning electron microscopy and it showed spherical particle distribution with average diameters of 158nm. Thermoluminescence response of magnesium oxide doped and co-doped with lanthanide, indium, and lithium exposed to gamma radiation within the dose range of 1 to 12kGy was measured and compared. Thermoluminescence glow curve of the samples showed a complex structure. In most cases, the thermoluminescence response of the materials to the exposed radiation was sublinear. Thermal fading of the samples was investigated and showed the remarkable result.

There is different approach for design of SMR reactors; these reactors may be built on land or on a floating platform. Implementation of each reactor in different industrial field must satisfy specific thermal and neurotic requirements. Ocean base SMR reactors are involved with sea waves, ocean conditions and sudden accelerations. Therefore, marine reactors are under the action of inertia force induced by the variable winds and dynamic ocean waves. These forces causing rolling and displacement of marines in different directions and rectors need tolerate the wave oscillations. The ship oscillations may treated about every axis x, y, z, independently. The ship motions include heeling, heaving, rolling, pitching, yawing, swing and surging motions. In this paper heaving and rolling motion using FLUENT code are treated and the thermos-hydraulic parameter investigated. Defining angular motion in non-inertia frame and obtaining acceleration in inertia frame, one may simulate numerically rolling and heaving motion along various amplitudes and periods. Simulation indicates that for a certain flow in an open loop and initial flow rate, amplitudes of the relative flow rate mainly depend on the relative magnitude of the pressure head against the oscillatory pressure drop. The solutions show the relative flow rate of the opened loop fluctuates periodically but not sinusoidally because that the oscillatory pressure drop is non-sinusoidal. The fluctuation amplitude increases evidently as the rolling amplitude increases, while increases slightly as the rolling period increases. For the opened loop, the oscillatory pressure drop is mainly due to the change of the gravitational pressure drop. The modelling results are in good agreement with benchmarks.

For shielding properties improvement, different percentages of boronated compound for two low and high densities were analyzed and the dose-rate in soft tissue have been calculated to decrease the risk for the operators and nearby peoples. The calculations have been performed by means of GEANT4 and MCNPX Monte Carlo codes for two different densities and two different percentages of B-10 and compared to boron-free compound. The parameters such as density, B-10 weight fractions, radiative captures and secondary gamma-ray generation have been analyzed to determine the critical items in these kinds of problems. The secondary gamma-ray from neutron radiative capture as an important side effect in neutron shielding design have been included and discussed in this study utilizing the Geant4 outputs for detail information. The GEANT4 results also were used as evaluation and confirmation of MCNP results.The dose rate of 100 μSv/h at 3 m distance from DENA come from experimental value of neutron yield of 108 neutron per pulse which is much higher than back ground value. The calculations were performed to investigate the optimized compound and thickness to reduce the equivalent dose rate in tissue to the permitted level, 0.1 μSv/h. The dose-rate calculations were obtained by two methods for confirmation as well, the deposited energies of neutron and gamma in soft tissue and transferring them to dose values and also, using the flux-to-dose conversion coefficients from ANSI/ANS standards.

Radiation safety aspects had been as a high impact parameter in design and setting up of neutron radiography (NR) facility for Tehran Research Reactor (TRR). For designing an optimized composite shield for neutron shielding in shutter, selecting the neutron absorber and composite matrix are the key elements. For this purpose, boron among the neutron absorbents, and epoxy resin as a matrix, for its specific characteristics, are more concerned. In this investigation, thermal neutron shielding ability was calculated theatrically for four boron compounds, including boron carbide, boron nitride, boron trioxide and acid boric. Indeed, by using Monte-Carlo simulation an innovated setup was introduced with high efficiency for thermal neutrons shielding. The results indicate the high efficiency of boron carbide absorbent in comparison with other boron compounds, as well as utilizing an increasing gradient neutron absorbent concentration in neutron shielding ability.

Today, membrane separation plays an important role in the industry and is widely used in various industries. One of the most important methods for separating gas components from each other is the gaseous diffusion membrane separation. Studies on the membrane, apart from the geometry and diameter and thickness of the capillaries, can be applied to the kind of membrane. Given the fact that the however the Knudsen number increase, the separation will have occurred more and effective. Therefore, selecting membranes that are capable of operating at high temperatures will increase the Knudsen number and, as a result, increase separation factor. Therefore, generally, in the gas separation industry by membrane method, the use of ceramic membranes that are capable of working at high temperatures is preferable to other membranes. In this paper, two SF6 and VF6 gases are used as two components with the same mass percentage for modeling the gas diffusion system. Due to the fact that the Knudsen number of system are relatively high and the transient flow regime dominates the system, the DSMC method, a method based on the Boltzmann and Monte Carlo equations, is used. In order to investigate the effect of the membrane temperature on the final value of the separation of this system, four temperatures of 310, 350, 450 and 800 K were used with equal conditions and inputs to evaluate the effects of temperature increase on the number of particles and, finally, the separation factor. In the results, it will be shown that with increasing temperature, changes in the enrichment of the waste and product will be higher variation than the input gas, and more efficient separation will be practically done at high temperatures. Therefore, in industries using ceramic membranes and generally membranes that are capable of working at high temperatures, it will be more cost effective than other membranes, and through the cascade and fewer steps it will reach the final richness, which will cause the setup cost Decrease.