نشریه فناوری و انرژی هسته ای
پیاپی 3 (پاییز 1401)

The reactor core in a nuclear power plant has safety and economic significance. In terms of reactor control, using optimal control for reactor core in a nuclear power plant is an important step in improving safety and increasing its reliability and availability. The failure of a nuclear power plant in the desired control of the reactor core can lead to more operational costs or reduce the safety and reliability of the plant. In general, the reactor core control contains the power (or coolant temperature) control and axial power difference (power distribution) control of the core. In this paper, for the first time, an optimized PID controller is used in power maneuvering transients for the Tehran research reactor. PID controller gains are optimized (tuned) by Teaching–learning-based optimization (TLBO) method according to the minimization of a cost function. This function is based on the sum of the integral of absolute error (IAE) and overshoot. The reactor core is simulated based on the linearized fractional neutron point kinetics (FNPK) equations. The model obtains temperature feedbacks from lumped fuel and coolant. Xenon concentration changes are also considered. Simulation results indicate that the optimized control method is easy to implement and eliminates the overshoot and fluctuations, which is common in conventional control methods such as the Ziegler–Nichols tuning method. It has a faster response to load changes in power maneuvering transients. Therefore, improves the reliability and safety of the reactor.

This research is dedicated to studying the alpha-spectroscopy of U and Th isotopes of the Saghand ore Anomaly 2 and the surface part Anomaly 1. At first, for complete dissolution of the ores, the concentrated hydrofluoric acid (23M), the concentrated hydrochloric and the concentrated nitric acids were used. Then the radioactive elements U and Th were separated by ion exchange chromatography using Dowex АВ-17-8 anion exchanger. During the next stage U and Th sources were prepared by molecular plating and the radioactive sources were analyzed using the alpha–spectroscopy. In both ores the 234U/238U activity ratios showed that the secular equilibrium is maintained in the series of 238U decay. Referring to scientific arguments and designing different hypotheses, the resistance of the uranium minerals of the ores against natural leaching was investigated and finally  during two experiments for every ore, by applying the radiation the weight percents of uranium were calculated: in the Anomaly 2, 0/1149 wt % and in the surface part Anomaly 1, 0/0930  wt %.

The gas behavior within a centrifuge machine could be divided into molecular and continuum. The Boltzmann equation solving is a precise method in the molecular region (feed entrance area). DSMC method is one of the Boltzmann equation solving methods. So far, the mass source used in the Onsager-Pancake equation in the continuum region has been an assumed source and many researches have presented a different assumed mass source. In the present paper, it has been calculated feed reaching form to continuum region and its effect on the border between the two areas in the mass source form using direct Monte-Carlo method. It has been compared the mass source obtained from the DSMC method with the assumed mass source. Besides calculating the exact mass function using DSMC method in the present work, it has been obtained the flow function through substituting in the heterogeneous Onsager-Pancake equations and solving the equations by finite differential method. Afterwards, it has been calculated the separation parameters through substituting this flow function in the concentration equations. The difference between the amount of separation work by the combined method and the reference value is 7.97%.

One of the most important issues in reactor design is the neutron energy or neutron energy spectrum at the reactor core. nuclear reactors have different fuel enrichment depending on the application. Propulsion reactors are among the reactors that must have lower xenon after shutdown to be able to turn on the reactor for a long time shortly after shutdown. Therefore, determining the correct enrichment of fuel is required to study the effect of increasing enrichment on the energy of neutrons and absorption cross sections.In this paper, while validating WIMS code libraries for use in fuels with a enrichment of more than 10%, the effect of using fuels with a enrichment of more than 10% on the neutron energy spectrum and absorption cross sections, especially the thermal absorption cross section of xenon Has been investigated. The results showed that the increase in enrichment leads to a decrease in the cross-section of ​​Xenon absorption and as a result, a decrease in Xenon peak after shutdown.

Optimal use of nuclear fuel inside the core of the reactor, due to lack of natural uranium resources, production costs and processing of uranium used, is always one of the most important issues in fuel management. In order to maximize the use of reactor fuel, fuel consumption must be increased. In addition, the density power obtained from a reactor depends on the amount of heat transfer that is achieved without damaging the structural materials of the reactor or the fuel rods. Fuel design companies are always looking for a solution that can increase power density.One way to achieve this is to change the chemical state of the fuel, or to increase the thermal conductivity of the fuel rods. To achieve this goal, instead of using the usual uo2 fuel, uranium dioxide dispersed ceramic fuels with other elements such as zirconium and iron can be used(cermet). In the present study, using Fluent software, simulation of different dispersed fuel modes such as uo2-zr, uo2-Fe, has been done. This shows that the use of cermet fuel has a significant effect on increasing the thermal conductivity of reactor fuel. The thermal power density of the current generation reactors increases significantly, in addition, with less leakage of fission fragments, the burn up of reactor also increases.

Vacuum maintaining in the space between the rotor and casing during the gas-feeding and enrichment process is of great importance. Therefore, a piece named molecular pump is attached on the top side of the casing. In this paper, molecular pump simulation was performed using Sawada, Sickafus, Sickafus upgraded analytical methods, and DSMC molecular method and the results of each were compared with the experimental test results. DSMC simulations were also performed for the groove with two trapezoidal and rectangular geometries. Comparing the results with experimental tests, it was shown that the compression ratio obtained by the DSMC method is about 10% different from the experimental test results, and then the upgraded Sickafus method is the most accurate method. It was also shown that the groove with a trapezoidal cross-section increases the compression ratio of the pump by more than 10% compared to the rectangular groove.