جستجوی مقالات مرتبط با کلیدواژه "محیط متخلخل" در نشریات گروه "فیزیک"

The Miniature Neutron Source Reactor is a tank-in-pool research reactor that uses highly-enriched uranium as fuel, light water as coolant, and beryllium as reflector. During the operation of the reactor, the coolant temperature increases and leads to negative feedback in the reactor. Although the negative reactivity is amongst the advantages of this reactor and an inherent safety feature; it causes a decrease in both the additional available reactivity and the reactor operation time. Therefore, short operation time (about 2.5 hours) at nominal power is one of the main limitations of the MNSR reactor. The natural convection in the core, vessel and pool of the reactor was modeled through a CFD analysis and the effect of the cooling coil at the top of the reactor tank on increasing the reactor operation time was investigated. To reduce the computations the details were decreased by considering the reactor core as a porous medium and a heat source with a constant power of 30kw. The experimental values ​​and those ​​obtained from the numerical solution are in good agreement. Results show a steady upward slope in the temperature rise of the coolant in the absence of coil, and an about-2-hours rise of the temperature in its presence. After this 2-hours period, the increasing rate decreases and the temperature fluctuates in a certain range. Compared to the case without the cooling coil, the average temperature is reduced by 3 degrees and the reactor operation time is increased by 1.5 hours.

The study of the process of absorption and evaporation of fluids in porous media is of particular importance in sciences such as geology, civil engineering, environment, etc. Neutron radiography is one of the most precise methods for investigation of the mentioned processes. Due to the high cross-section of the interaction of thermal neutrons with hydrogen, precise investigation of absorption and evaporation of fluids containing hydrogen, such as water, oil, etc., is possible. In the present work, using the real-time neutron radiography technique, the vaporization of water from a porous building sample at 10 °C in the laboratory was investigated. For this purpose, a building brick was immersed into water for 24 hours, and then was placed in front of the neutron beam. During 145 minutes of reactor operation, 30 images were recorded with a 5 minutes interval from the wet sample. The obtained images showed that using the utilized technique, the distribution variations and volumetric water content inside the sample are well visible. Also, the results indicated that the volumetric water content in the sample was evaporated with a rate of 3.94×10-4 percent per seconds in the laboratory environment.