8.05-5: Experimental & Numerical Studies-V
Numerical Modelling of the Thermal Behavior of Severely Damaged Core of Indian PHWR under Large Break Loss of Coolant Accident
Indian Institute of Technology Roorkee
The thermal behavior of a reactor channel after critical break LOCA (Loss of coolant accident) is a prime concern for the structural integrity of the containment and release of volatile fission product radionuclides. During an impaired cooling environment, the integrity of the fuel bundle may be breached, which leads to slumping of fuel pins at the bottom surface of the pressure tube (PT). The present study is aimed to analyze the thermal characteristics of a large capacity Indian PHWR channel housing disassembled fuel pins using numerical approach. ANSYS fluent 19.0. SIMPLE scheme is used to perform a steady-state analysis. The momentum, energy and radiation equations are discretized using the second-order upwind scheme. The radiation in the channel is modelled using Discrete Ordinates (DO) Model. The 37-element bundle is assumed to collapse and rearrange at the bottom surface of the PT into a form of a closed stack of pins. The heat interactions in the different components of the channel under postulated LBLOCA (large break loss of coolant accident) situation is thoroughly investigated. The steady-state circumferential temperature distribution in the fuel pins, PT and (Calandria tube) CT are obtained at various axial positions. The results show that significant circumferential temperature gradient is developed in the PT due to slumping of fuel pins. The maximum temperature is obtained at the bottom sector of the PT, which is in contact with the fuel pin.
Critical Heat Flux Enhancement Using Hybrid Nano-grass/flower Structure
City University of Hong Kong
Enhanced critical heat flux extends the limitation of the safety in heat transfer engineering applications especially in nuclear power plant. Advanced approaches, such as changing the property of the working fluid, advanced materials, and surface modification, have been employed to enhance CHF for decades, but the underlying mechanism of nano/micro-structure on surface led CHF enhancement requires more research to reveal the complex principle. Due to the surface properties can be presented by many parameters, such as wettability, roughness, rewetting ability, and capillary ability, etc. Some studies concluded that the effect of those parameters on CHF enhancement should be separated, and other experimental results stated that only a certain factor is responsible for the CHF enhancement. In this article, we fabricate hybrid nano-grass/flower textured surface with different coverage and different wettability with the aim to decouple the effect of the surface wettability and the textured structure on CHF enhancement. In the first group, the different coverage of nano-grass on surface is fabricated with the intention of studying the effect of different texture structure on CHF enhancement at the same wettability (hydrophilic surface with small contact angle and hydrophobic surface with large contact angle). In addition, at a fixed wettability, hybrid structure with nanograss-flower on surface is also tested for the CHF. Moreover, for each textured surface, the wettability of the surface is also changed from the hydrophilic to the hydrophobic. The experimental results is compared and discussed in this article.
Experimental investigation on the Critical Heat Flux of Nanofluid Flow Boiling Under different Thermal Conditions
1Nuclear Power Insitute of China; 2Xi’an Jiaotong University
The In-Vessel Retention (IVR) strategy is a key technology to alleviate the consequence of core melt. It is a boundary of severe accident that whether the pressure reactor vessel is broken or not. It is very important to enhance the capacity of IVR. Nanofluid is a new kind of working fluid which is investigated widely because of its excellent thermal physical properties. It is an effective method to improve the capacity of IVR treating nanofluid as the working fluid. In present work, the critical heat flux of nanofluid flow boiling in a vertical tube is experimentally studied with the consideration of different kinds of nanofluid for nanoparticle types and concentration. In addition, a new mechanism of nanofluid CHF enhancement is proposed from the point view of sublayer adsorption. This work lays a foundation for nanofluid application in nuclear power system.
CFD Analysis to develop Porous Ceramic Structure for Ion-Exchanger
1Khalifa University; 2Korea Advanced Institute of Science and Technology
During the normal operation of nuclear reactor, several corrosion elements can be produces owing the degradation of the reactor structural materials. Thus, these impurities must be removed from the reactor coolant cycle to preserve the performance of reactor coolant. At present, a group of researchers at KAIST are developing a new adsorption porous ceramic filters can replace the currently used bed type polystyrene ion exchange resins. In this study, a CFD numerical analysis using porous media model is conducted to investigate the effect of flow velocity and pressure drop distribution on the pore structure through the ion exchange resins. The study focuses on the pressure force distribution which is very important for the ion exchange immobilization and degradation. The flow velocity and retention time through the porous media play an important role regarding the adsorption rate. Wide range of beds diameter [0.001-1.0 mm] have been utilized. Large beds will decrease the pressure drop; however, the adsorption rate will reduce. New configuration of ion exchange resin will be developed to enhance the functionality of these filters, whereas better flow velocity distribution and less pressure drop can be achieved