• Nuclear Engineering and Technology
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• v.32 no.6
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• pp.549-558
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• 2000

A transient model for hydrogen generation in molten metal-water interactions was developed with separate models for two stages of coarse mixing and stratification. The model selves the mechanistic equations (heat and mass transfer correlation, heat conduction equation and the concentration diffusion equation) of each stage with non-zero boundary conditions. Using this model, numerical simulations were performed for single droplet experiments in the Argonne National Laboratory tests and for FITS tests that simulated dynamic fragmentation and stratification. The calculation results of hydrogen generation showed better agreement to the experiment data than those of previous works. It was found from the analyses that the steam concentration to be reached at the reaction front might be the main constraint to the extent of the metal droplet oxidized. Also, the hydrogen generation rate in the coarse mixing stage was the higher than that in the stratification stage. The particle size was the most important factor in the coarse mixing stage to predict the amount of hydrogen generation.

• KEPCO Journal on Electric Power and Energy
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• v.5 no.4
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• pp.323-330
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• 2019

The 500 MW Korean standard coal-fired power plant is the largest standardized power plant in Korea and has played a pivotal role in domestic power generation for over 20 years. In addition to the aging degradation due to long term operation, the probability of failure of power generation facilities is increasing due to frequent startup and stop caused by the lower utilization rate due to air pollution problem caused by coal-fired power plants. Among them, steam piping plays an important role in transferring high-temperature & pressure steam produced in a boiler to turbine for power generation. In recent years, failure of steam piping of large coal-fired power plant has frequently occurred. Therefore, in this study, failure analysis of high pressure piping weld was conducted. We identify the damage caused by high stress due to abnormal supporting structure of the piping and suggest improved supporting structure to eliminate high stress through microstructure analysis and piping stress analysis to prevent the occurrence of the similar failure of other power plant in the case of repetitive damage to the main steam piping system of the 500 MW Korean standard coal-fired power plant.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.11
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• pp.869-875
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• 2009

The purpose of this paper is to investigate the optimal condition of the syngas production by reforming of propane using Gliding arc plasma reformer. The gliding arc plasma reformer in 3 phases has been newly designed and developed with a quick starting and fast response time. It can be applicable to the various types of fuels (Hydrocarbons $C_xH_y$), and it has a high conversion rate of fuels and high production of hydrogen. The parametric screening studies were carried out according to the changes of a steam feed amount i.e., steam/carbon ratio, total gas flow rate and input electric power. The optimum operating conditions were S/C ratio 2.8, total gas flow rate of 14 L/min and input electric power of 2.4 kW. The result of optimum operating conditions showed the 55 % $H_2$, 14 % CO, 15 % $CO_2$, 10 % $C_3H_8$ and 4 % $CH_4$. Also, $C_3H_8$ conversion, $H_2$ yield and $H_2$ selectivity were 90 %, 42 %, 15 %, respectively. The energy efficiency and specific energy requirements were 37 % and 334 kJ/mol respectively.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.1829-1835
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• 2000

The experimental results of sodium-water reaction noise measurement in frequency range $1{/sim}200kHz$ are presented. The experiments of noise generation under the condition of sodium test facility, water leak rate $0.01{\sim}1.2g/s$ and temperature of sodium $250{\sim}500^{\circ}C$, were carried out. From theoretical study it is noted that the noise resonant attenuation on hydrogen bubbles in liquid sodium plays the significant role for leak noise spectra formation. Interaction of leak noise and hydrogen bubbles in sodium being accompanied by thermal, emission and viscosity energy dissipation was studied. Acoustic noise spectra were investigated from point of view of water leak detection in sodium/water steam generator. The results of sodium-water reaction noise absorption on hydrogen bubbles in liquid sodium by temperature $250{\sim}500^{\circ}C$ are presented. The theoretical model of noise absorption using the coefficients of attenuation was developed. From calculation the coefficients of attenuation were estimated.

• Transactions of the Korean hydrogen and new energy society
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• v.33 no.6
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• pp.723-732
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• 2022

Cracking ammonia inside solid oxide fuel cell (SOFC) stack is a compact and simple way. To prevent sharp temperature fluctuation and increase cell efficiency, the decomposition reaction should be spread on whole cell area. This leading to a question that, how does anode thickness affect the conversion rate of ammonia and the cell voltage? Since the 0D model of SOFC is useful for system level simulation, how accurate is it to use equilibrium solver for internal ammonia cracking reaction? The 1D model of ammonia fed SOFC was used to simulate the diffusion and reaction of ammonia inside the anode electrode, then the partial pressure of hydrogen and steam at triple phase boundary was used for cell voltage calculation. The result shows that, the ammonia conversion rate increases and reaches saturated value as anode thickness increase, and the saturated thickness is bigger for lower operating temperature. The similar cell voltage between 1D and 0D models can be reached with NH₃ conversion rate above 90%. The 0D model and 1D model of SOFC showed similar conversion rate at temperature over 750℃.

• Journal of the Korean Ceramic Society
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• v.47 no.1
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• pp.1-7
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• 2010

Solid oxide fuel cells (SOFCs) have been under development for a variety of power generation applications. Power system sizes considered range from small watt-size units (e.g., 50-W portable devices) to very large multi-megawatt systems (e.g., 500-MW base load power plants). Because of the reversibility of its operation, the SOFC has also been developed to operate under reverse or electrolysis mode for hydrogen production from steam (In this case, the cell is referred to as solid oxide electrolysis cell or SOEC.). Potential applications for the SOEC include on-site and large-scale hydrogen production. One critical requirement for practical uses of these systems is long-term performance stability under specified operating conditions. Intrinsic material properties and operating environments can have significant effects on cell performance stability, thus performance degradation rate. This paper discusses potential applications of the SOFC/SOEC, technological status and current research and development (R&D) direction, and certain aspects of long-term performance degradation in the operation of SOFCs/SOECs for power generation/hydrogen production.

• Proceedings of the Korean Nuclear Society Conference
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• 1995.05a
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• pp.544-549
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• 1995

An analysis for Steam Line Break (SLB) events which result in a return-to-power conditions after reactor trip was performed for a postulated Yonggwang Nuclear Power Plant Unit 3 cycle 8. Analysis methodology for post-trip return-to-power SLB is quite different from that of a no return-to-power SLB and is more complicated. Therefore, it is necessary to develop an methodology to analyze the response of the NSSS parameter and the fuel performance for the post-trip return-to-power SLB events. In this analysis, the cases with and without offsite power were simulated by crediting 3-D reactivity feedback effect due to local heatup around stuck CEA and compared with the cases without 3-D reactivity feedback with respect to fuel performance, departure from nucleate boiling ratio (DNBR) and linear heat generation rate (LHGR).

• New & Renewable Energy
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• v.20 no.1
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• pp.126-134
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• 2024

Biogas, composed mainly of methane (CH₄) and carbon dioxide (CO₂), is a renewable gas that can serve as an alternative energy source. In this study, we developed a new microwave reformer and analyzed its reforming characteristics. We observed that higher temperatures of the microwave receptor led to increased reforming efficiency. By supplying appropriate amounts of methane and steam, we could prevent carbon generated from the thermal decomposition reaction of carbon dioxide from depositing on the catalytic active layer, thus avoiding the inhibition of catalytic activity. Hydrogen generation was enhanced when maintaining the biogas ratio and steam supply at adequate levels. Increasing the SiC ratio in the receptor improved the uniformity of temperature distribution and growth rate, resulting in higher conversion rates of the reforming process.

• Nuclear Engineering and Technology
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• v.45 no.7
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• pp.895-910
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• 2013

The reflood test data from the rod bundle heat transfer (RBHT) test facility showed that the grids in the upper portion of the rod bundle could become wet well before the arrival of the quench front and that the sizes of liquid droplets downstream of a wet grid could not be predicted by the droplet breakup models for a dry grid. To investigate the water droplet generation from a wet grid spacer, a viscous linear temporal instability model of the water sheet issuing from the trailing edge of the grid with the surrounding steam up-flow is developed in this study. The Orr-Sommerfeld equations along with appropriate boundary conditions for the flow are solved using Chebyshev series expansions and the Tau-Galerkin projection method. The effects of several physical parameters on the water sheet oscillation are studied by determining the variation of the temporal growth rate with the wavenumber. It is found that a larger relative steam velocity to water velocity has a tendency to destabilize the water sheet with increased dynamic pressure. On the other hand, a larger ratio of steam boundary layer to the half water sheet thickness has a stabilizing effect on the water sheet oscillation. Droplet diameters downstream of the spacer grid predicted by the present model are found to compare reasonably well with the data obtained at the RBHT test facility as well as with other data recently reported in the literature.

• Nuclear Engineering and Technology
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• v.52 no.12
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• pp.2699-2708
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• 2020

Helical-coil steam generator (HCSG) technology is a major design candidate for small modular reactors due to its compactness and capability to produce superheated steam with high generation efficiency. In this paper, we investigate the feasibility of the passively autonomous power maneuvering by coupling the 3-D transient multi-physics of a soluble-boron-free (SBF) core with a time-dependent HCSG model. The predictor corrector quasi-static method was used to reduce the cost of the transient 3-D neutronic solution. In the numerical system simulations, the feedwater flow rate to the secondary of the HCSGs is adjusted to extract the demanded power from the primary loop. This varies the coolant temperature at the inlet of the SBF core, which governs the passively autonomous power maneuvering due to the strongly negative coolant reactivity feedback. Here, we simulate a 100-50-100 load-follow operation with a 5%/minute power ramping speed to investigate the feasibility of the passively autonomous load-follow in a 450 MW_th SBF PWR. In addition, the passively autonomous frequency control operation is investigated. The various system models are coupled, and they are solved by an in-house Fortran-95 code. The results of this work demonstrate constant steam temperature in the secondary side and limited variation of the primary coolant temperature. Meanwhile, the variations of the core axial shape index and the core power peaking are sufficiently small.