• Bulletin of the Korean Chemical Society
• /
• v.26 no.11
• /
• pp.1783-1789
• /
• 2005

Modeling of a steam generator crevice in a nuclear power system needs to take into account both thermalhydraulic and chemical phenomena. As a first step towards developing a reliable model, a chemical equilibrium model was developed to predict chemical speciation in a magnetite-packed crevice by adopting the “tableau” method. The model was benchmarked with the available experimental data and the maximum deviation did not exceed two orders of magnitude. The developed model was applied to predict the chemical speciation in a magnetite-packed crevice. It was predicted that caustic environment was developed by the concentration of NaOH and the dissolution of magnetite. The model indicated that the dominant aqueous species of iron in the caustic crevice was $FeO_2\;^-$. The increase of electrochemical corrosion potential observed in the experiment was rationalized by the decrease of dissolved hydrogen concentration due to a boiling process. It was predicted that under the deaerated condition magnetite was oxidized to hematite.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.24 no.1
• /
• pp.29-38
• /
• 2000

It is observed that the cooling capacity of impinging water jet is affected by the seasonal conditions in steel manufacturing process with large scale. To confirm this phenomena, the cooling experiments of a hot steel plate by a laminar jet were conducted for two different initial ambient air temperature($10^{\circ}C$ and $40^{\circ}C$) in a closed chamber, and an inverse heat conduction method is applied for the quantitative comparison. It is found that the cooling capacity under $10^{\circ}C$ air temperature is lower than that under $40^{\circ}C$, as is the saturated water vapor is more easily observed, and the amount of total extracted heat in the case of $10^{\circ}C$ is smaller by nearly 15% than that of $40^{\circ}C$ case. From these results, it is thought that the quantity of water vapor, which could be absorbed until saturation, effects on the mechanism of boiling heat transfer.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.16 no.6
• /
• pp.1150-1155
• /
• 1992

The cooling characteristics of a hot steel plate by a laminar impinging water bar were investigated experimentally. The dynamic parameters investigated were nozzle height L between nozzle and the hot plate, flow rate Q, and initial cooling temperature. Because the boiling phenomena on a hot steel plate are unsteady and change discontinuously, it is difficult to analyze the cooling characteristics directly. In this study the cooling efficiency was estimated by using the temperature decay rates and expansion speed of the water cooling zone. Temperature in the water cooling zone decreased rapidly and the radius of the water cooling zone expanded nearly in proportion to square root of the cooling time. With increasing initial temperature of a hot steel plate, the cooling efficiency became descendent. The cooling curve in the case of L/D = 30 showed the largest temperature decay rate and excellent cooling performance.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.24 no.3 s.174
• /
• pp.710-717
• /
• 2000

Tensile and fracture toughness tests of the cold-rolled STS 304 steel plate for membrane material of LNG storage tank were performed at wide range of temperatures, 11 IK(boiling point of LNG), 153K , 193K and 293K(room temperature). Tensile strength significantly increases with a decrease in temperature, but the yield strength is relatively insensitive to temperature. Elongation at 193K abruptly decreases by 50% of that at 293K, and then decreases slightly in the temperature range of 193K to 111K. Strain hardening exponents at low temperatures are about four times as high as that at 293K. Elastic-plastic fracture toughness($J_c$) and tearing modulus($T_{mat}$) tend to decrease with a decrease in temperature. The $J_c$ values are inversely related to effective yield strength in the temperature range of 111K to 293K. These phenomena result from a significant increase in the amount of transformed martensite in low temperature regions.

• Nuclear Engineering and Technology
• /
• v.49 no.2
• /
• pp.426-433
• /
• 2017

This paper describes the development process, the innovative techniques used and insights gained from the latest integrated, full scope, multistate Level 2 PSA analysis conducted at the Leibstadt Nuclear Power Plant (KKL), Switzerland. KKL is a modern single-unit General Electric Boiling Water Reactor (BWR/6) with Mark III Containment, and a power output of $3600MW_{th}/1200MW_e$, the highest among the five operating reactors in Switzerland. A Level 2 Probabilistic Safety Assessment (PSA) analyses accident phenomena in nuclear power plants, identifies ways in which radioactive releases from plants can occur and estimates release pathways, magnitude and frequency. This paper attempts to give an overview of the advanced modeling techniques that have been developed and implemented for the recent KKL Level 2 PSA update, with the aim of systematizing the analysis and modeling processes, as well as complying with the relatively prescriptive Swiss requirements for PSA. The analysis provides significant insights into the absolute and relative importances of risk contributors and accident prevention and mitigation measures. Thanks to several newly developed techniques and an integrated approach, the KKL Level 2 PSA report exhibits a high degree of reviewability and maintainability, and transparently highlights the most important risk contributors to Large Early Release Frequency (LERF) with respect to initiating events, components, operator actions or seismic component failure probabilities (fragilities).

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.19 no.10
• /
• pp.2586-2594
• /
• 1995

Two phase flow phenomena are observed in many industrial facilities and make much importance of optimum design for nuclear power plant and various heat exchangers. This experimental study has been investigated the classification of the flow pattern, the local void distribution and convective heat transfer in swirl and non-swirl two phase flow under the isothermal and nonisothermal conditions. The convective heat transfer coefficients in the single phase water flow were measured and compared with the calculated results from the Sieder-Tate correlation. These coefficients were used for comparisons with the two-phase heat transfer coefficients in the flow orientations. The experimental results indicate, that the void probe signal and probability density function of void distribution can used into classify the flow patterns, no significant difference in voidage distribution was observed between isothermal and non-isothermal condition in non-swirl flow, the values of two phase heat transfer coefficients increase when superficial air velocities increase, and the enhancement of the values is observed to be most pronounced at the highest superficial water velocity in non-swirl flow. Also two phase heat transfer coefficients in swirl flow are increased when the twist ratios are decreased.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.20 no.4
• /
• pp.1472-1480
• /
• 1996

The phenomena of drag reduction using small quantities of a linear macromolecules has attracted the attention of experimental investigations. It is well known that drag reduction in single phase liquid flow is affected by polymer materials, molecular weight, polymer concentration, pipe diameter and flow velocity. But the research on drag reduction in two phase flow has not intensively investigated. Drag reduction can be applied to phase change system such as chemical reactor, pool and boiling flow, and to flow with cavitation which occurs pump impellers. The purpose of the present work is to evaluate the drag reduction by measuring pressure drop, mean liquid velocity, and turbulent intensity and determine the effects of polymer additives on drag reduction in horizontal two phase flow. Experimental results show higher drag reduction using co-polymer comparing with using polyacrylamide. Mean liquid velocities increase as adding more polymer, and turbulent intensities decrease as the distance for the wall in inversed.

• Nuclear Engineering and Technology
• /
• v.50 no.1
• /
• pp.1-17
• /
• 2018

This article reviews the multiscale nature of stress corrosion cracking (SCC) observed by high-resolution characterizations in austenite stainless steels and Ni-base superalloys in light water reactors (including boiling water reactors, pressurized water reactors, and supercritical water reactors) with related opinions. A new statistical summary and comparison of observed degradation phenomena at different length scales is included. The intrinsic causes of this multiscale nature of SCC are discussed based on existing evidence and related opinions, ranging from materials theory to practical processing technologies. Questions of interest are then discussed to improve bottom-up understanding of the intrinsic causes. Last, a multiscale modeling and simulation methodology is proposed as a promising interdisciplinary solution to understand the intrinsic causes of the multiscale nature of SCC in light water reactors, based on a review of related supporting application evidence.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.13 no.3
• /
• pp.508-516
• /
• 1989

The objective of this study is to investigate on the pulsating combustion of a granular coal in a Rijke type pulse combustor. The combustor is made of a 120cm long pipe with a honeycomb as a fire grate in the lower half. A fixed amount of coal is laid on the honeycomb and burned downward after ignition by using propane gas. Then the combustion driven acoustic oscillation occurs and makes the combustion pulsate with a very high amplitude. The effect of the pulsation and the air flow rate on the combustion characteristics is examined in comparison with the normal combustion. The non-pulsating combustion is made possible by placing absorbing material under the honeycomb. The combustion phenomena are observed visually, the burning time is measured in order to evaluate the combustion rate, and the variation of the gas temperatures is recorded. It is found that the fuel particle is greatly agitated like boiling by the flow pulsation and the burning-down velocity is so fast that the fuel is burned almost simultaneously. The combustion rate can be increased as twice as that of non-pulsating combustion with increase of the air flow rate. And the combustion becomes clean with less soot deposit and emission.

• Nuclear Engineering and Technology
• /
• v.54 no.4
• /
• pp.1343-1354
• /
• 2022

Experiments were performed to measure the critical heat flux (CHF) on a vertical surface abutting a coarse packed bed of spherical particles. This geometry is representative of a CANDU reactor calandria tubesheet facing the end shield cavity during the in-vessel retention (IVR) phase of a severe accident. Deionized light water was used as the working fluid. Low carbon steel shielding balls with diameters ranging from 6.4 to 12.7 mm were used, allowing for the development of an empirical correlation of CHF as a function of shielding ball diameter. Previously published data is used to develop a more comprehensive empirical correlation accounting for the impacts of both shielding ball diameter and heating surface height. Tests using borosilicate shielding balls demonstrated that the dependence of CHF on shielding ball thermal conductivity is insignificant. The deposition of iron oxide particles transported from shielding balls to the heating surface is verified to increase CHF non-trivially. The results presented in this paper improve the state of the knowledge base permitting quantitative prediction of CHF in the CANDU end shield, refining our ability to assess the feasibility of IVR. The findings clarify the mechanisms governing CHF in this scenario, permitting identification of potential future research directions.