• Nuclear Engineering and Technology
• /
• v.54 no.11
• /
• pp.4359-4372
• /
• 2022

Turbulent mixing in buoyant flows is an essential mechanism involved in many scenarios related to nuclear safety in nuclear power plants. Comprehensive understanding and accurate predictions of turbulent buoyant flows in the reactor are of crucial importance, due to the function of mitigating the potential detrimental consequences during postulated accidents. The present study uses URANS methodology to investigate the buoyancy-influenced flows in the reactor pressure vessel under the main steam line break accident scenarios. With a particular focus on the influence of turbulent heat flux closure models, various combinations of two turbulence models and three turbulent heat flux models are utilized for the numerical simulations of three ROCOM tests which have different characteristic features in terms of the flow rate and fluid density difference between loops. The simulation results are compared with experimental measurements of the so-called mixing scalar in the downcomer and at the core inlet. The study shows that the anisotropic turbulent heat flux models are able to improve the accuracy of the predictions under conditions of strong buoyancy whilst in the weak buoyancy case, a major role is played by the selected turbulence models with essentially a negligible influence of the turbulent heat flux closure models.

• Nuclear Engineering and Technology
• /
• v.56 no.1
• /
• pp.265-274
• /
• 2024

The current research focuses on the development of a numerical approach to forecast strongly subcooled flow boiling of FC-72 as the refrigerant in various vertical minichannel shapes for high-heat-flux cooling applications. The simulations are carried out using the Volume of Fluid method with the Lee phase change model, which revealed some inherent flaws in multiphase flows that are primarily due to an insufficient interpretation of shearlift force on bubbles and conjugate heat transfer against the walls. A user-defined function (UDF) is used to provide specific information about this noticeable effect. The influence of shape and the inlet mass fluxes on the flow patterns, heat transfer, and pressure drop characteristics are discussed. The computational results are validated with experimental measurements, where excellent agreements are found that prove the efficiency of the present numerical model. The findings demonstrate that the heat transfer coefficient decreases as the mass flux increases and that the constriction design improves the thermal performance by 24.68% and 10.45% compared to the straight and expansion shapes, respectively. The periodic constriction sections ensure good mixing between the core and near-wall layers. In addition, a slight pressure drop penalty versus the thermal transfer benefits for the two configurations proposed is reported.

• Nuclear Engineering and Technology
• /
• v.56 no.8
• /
• pp.3315-3329
• /
• 2024

Small Modular Reactors (SMRs) adopt the Helically Coiled Once-Through Steam Generators (OTSG) extensively for its compactness and higher heat transfer efficiency. As a heat exchanger between the primary side (reactor coolant system) and the secondary side (feedwater and steam system) of nuclear steam supply system, the inlet/outlet conditions both of shell side and tube side of OTSGs have significant impacts on overall system response. Considering the flexible operation of SMRs and heat application by extracting steam, a simulation tool for accurate prediction of the OTSG dynamic behaviors would be required for optimizing design and control. In this study, the OTSG dynamic simulation model has been developed. Mathematical governing equation has been derived by using moving boundary approach and a simulation module has been developed by using Modelica Language. The developed module has been compared with publicly available experimental results and benchmarked with MARS-KS calculation results. Also, it has been incorporated into the integrated SMR model (i.e., reactor core, primary side, secondary side) and dynamic behaviors with reactivity feedback and heat balancing have been investigated. In both of steady-state and transient conditions, it shows the promising accuracy.

• Plant Journal
• /
• v.10 no.1
• /
• pp.47-53
• /
• 2014

The national capacity of electricity of Korea was 81,737 MW and the peak demand was renewed by the record of 71,230 MW in 2012 which has been increasing since the first lighting ceremony had taken place in the Royal Palace(Kyung-Bok Goong) in 1887. Aa the counteract on the rapid increasing of the demand, Korean government is constructing and operating the high capacity nuclear and thermal power plants, however, the operating reserve on weekdays is small while those of weekends are more than 40% of capacity, so they are providing the pumped-storage power plants with the surplus electricity during weekends and operating the power plants which cost higher production price and located in the capital area with WSS (Weekly Start and Stop) mode including the Seoul Thermal Power Plant. Since the Seoul Thermal Power Plant is spending huge amount of expenses for more than 30 times of the WSS annually due to the high production cost even though it is in Seoul, the core of the demand, I chose the power plant unit #5 which was on the grid in 1969 for the case to confirm reducing 23% of the warm start-up time by applying the "Start-up time management program", and that reducing 35% of the water temperature increasing time by accelerate the increasing rate of the inlet temperature of the water circulating pump.

• Journal of Advanced Marine Engineering and Technology
• /
• v.32 no.8
• /
• pp.1185-1191
• /
• 2008

The core design technology for the multi-effect desalination plant using the thermo compressor (MED-TVC) was investigated by the performance test of multi effect desalination plant in this paper. The final G.O.R (gain of output ratio) of MED-TVC type desalination plant is strongly affected by the performance of thermo-vapor compressor. The present experiments for the desalinating capacity and G.O.R were obtained for the range of the motive steam pressure, 266.0, 250.0, 230.0 and 200.0 kPa. And as a practical problem, to investigate the influence of the sea water temperature to the G.O.R, the inlet steam temperature of the suction water vapor was changed in the range of $311.2{\sim}324.2$ K in the present experiment. Through the experiments, the maximum value of G.O.R was 8.5 at the condition of the motive steam pressure, 136.0 kPa and the minimum value of G.O.R was 8.1 at the condition of the motive steam pressure, 266.0 kPa. And it was confirmed that the range of desalination capacity was $355.2{\sim}264.0$ ton/day in the normal operation condition.

• Journal of computational fluids engineering
• /
• v.17 no.4
• /
• pp.41-48
• /
• 2012

A numerical analysis of thermal stratification in the upper plenum of the MONJU fast breeder reactor was performed. Calculations were performed for a 1/6 simplified model of the MONJU reactor using the commercial code, CFX-13. To better resolve the geometrically complex upper core structure of the MONJU reactor, the porous media approach was adopted for the simulation. First, a steady state solution was obtained and the transient solutions were then obtained for the turbine trip test conducted in December 1995. The time dependent inlet conditions for the mass flow rate and temperature were provided by JAEA. Good agreement with the experimental data was observed for steady state solution. The numerical solution of the transient analysis shows the formation of thermal stratification within the upper plenum of the reactor vessel during the turbine trip test. The temporal variations of temperature were predicted accurately by the present method in the initial rapid coastdown period (~300 seconds). However, transient numerical solutions show a faster thermal mixing than that observed in the experiment after the initial coastdown period. A nearly homogenization of the temperature field in the upper plenum is predicted after about 900 seconds, which is a much shorter-term thermal stratification than the experimental data indicates. This discrepancy is due to the shortcoming of the turbulence models available in the CFX-13 code for a natural convection flow with thermal stratification.

• Nuclear Engineering and Technology
• /
• v.19 no.1
• /
• pp.10-21
• /
• 1987

Uncertainty analysis of the FLB accident is performed for KNU-1 using the response surface methodology and Monte Carlo simulation. The FLB analyses using the RELAP4/Mod6 were performed a number of times to generate the data base for the uncertainty analysis, along with the EM calculation for comparison purpose. Two kinds of input sets are utilized for response surface method to investigate and compare the effects of the uncertainty of input variables on the RCS peak pressure following a FLB. The first set is composed of six major plant operational parameters and the second set is composed of five major modelling parameters. It is found through the analysis of results that the uncertainties of modelling parameters have more influence on the RCS peak pressure than the uncertainties of plant operational parameters and that the extra margin of 9% of peak pressure is gained. And one of the assumptions of EM calculation, which is usually accepted as conservative is found to be erroneous, that is, the initial core inlet temperature is found to act negatively on the RCS pressure following a FLB.

• Journal of the Korean Society of Environmental Restoration Technology
• /
• v.14 no.3
• /
• pp.15-32
• /
• 2011

This study was carried out to investigate the soil characteristics and propose the management for the Monument Beobsoo Marsh, Korea. The soil properties of O.M, $Ca^{2+}$, $Na^+$ and CEC were higher and the soil properties of pH_{1:5}$ and $P_2O_5$ were lower the studied sites than other marsh sites in Korea. Although the Heavy metals such as Pb, Hg, Cd, Cu, Zn, Cr and As were lower compare to the safety standard of soil pollution in Korea, the overall conservation management plan based on long-term monitoring should be considered just because it varied by the point and non-point source pollution within the studied marsh. The source of water pollution varied due to non-point polluting origins such as sewage inlet, degraded terrain for agriculture, fishing sites, sites of removed water grasses, pesticides, chemical fertilizers, as well as fallen leaves. The creation of an artificial marsh is recommended due to the soil environment of the studied sites may be changed owing to the accumulated contaminants from the sources of both of point or non-point contaminants. The establishment of the zones of core, buffer and transition which is basic management structure of the UNESCO MaB could be applied to manage the studied site. Simultaneously the promotion of voluntary participation and education of the local residents are needed.

• The KSFM Journal of Fluid Machinery
• /
• v.20 no.1
• /
• pp.65-73
• /
• 2017

Intercoolers for multi-stage turbocharger of the hydrogen reciprocating engine for HALE UAV are installed for reducing the charged air inlet temperature of the engine. The intercooler is air to air, cross flow, plate-fin type and the fin configuration is offset-strip fin which is referenced from the heat exchanger of the ERAST. Most of HALE UAV's cruising altitude is 60,000 ft and the density of air for this altitude is very low compared to sea level. Therefore the required heat transfer area for the HALE UAV is about three-times bigger than the sea level. Consequently, it is essential to design to meet the required efficiency of intercooler in the range of not excessively growing the weight of the heat exchanger. The quasi-one dimensional heat transfer design/analysis for satisfying the requirement of the engine are written in this paper. The numerical analyses for estimating the coolant flow rate of the engine bay and pressure loss in the header and core are also summarized.

• Proceedings of the SAREK Conference
• /
• 2008.11a
• /
• pp.611-617
• /
• 2008

Nowadays Plate Heat Exchanger (PHE) is widely used in different industries such as chemical, food and pharmaceutical process and refrigeration due to the efficient heat transfer performance, extreme compact design and efficient use of the construction material. In present study, discussed main conception of plate heat exchanger and applied in vacuum. PHE and aimed apply in the fresh water generator which installed in ship to desalinate seawater to fresh water use heat from engines. The experiment is proceeded to investigate the heat transfer between cold and hot fluid stream at different flow rate and supply temperature of hot fluid. Generated fresh water as outcome of the system. PHE is an important part of a condensing or evaporating system. One of common assumptions in basic heat exchanger design theory is that fluid is to be distributed uniformly at the inlet of each fluid side and throughout the core. However, in practice, flow mal-distribution is more common and can significantly reduce the heat exchanger performance. The flow and heat transfer are simulated by the k-$\varepsilon$ standard turbulence model. Moreover, the simulation contacted flow maldistribution in a PHE with 6 channels.