• Journal of the Korean Society of Safety
• /
• v.31 no.6
• /
• pp.129-134
• /
• 2016

Standard design of APR+(advanced power reactor plus) was certified at 2014 by Korea regulatory body. Based on the experience gained from OPR1000 and APR1400, the APR1400 was being developed as a 1,500MWe class reactor using Korean technologies for design code, reactor coolant pump, and man-machine interface system. APR+ has been basically designed to have the seismic design basis of safe shutdown earthquake (SSE) 0.3g, a 4-train safety concept based on N+2 design philosophy, and a passive auxiliary feedwater system (PAFS). Also, safety issues on the Fukushima-type accidents have been extensively reviewed and applied to enhance APR+ safety. APR+ provides higher reliability and safety against tsunami and earthquake. The purpose of this paper is to implement probabilistic safety assessment considering these design features and to analyze sensitivity of core damage frequency for large loss of coolant accident of APR+.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
• /
• 2004.04a
• /
• pp.71-76
• /
• 2004

To deal with ship collision or grounding, double hull structure has been applied to ships carrying dangerous cargoes. Studies about ability of double hull structure to absorb collision energy and determining fracture state are still under researching. In this study, commercial analysis code, LS-DYNA3D, is used to analyze collision strength of ships in various scenarios. 46K Chemical／Product Carrier is used as analysis subject ship. Study about Energy-Indentation and Force-Indentation is conducted under conditions that weight and collision velocity are changed. Results of this study are very helpful to make mechanism of collision accident clear and to supply useful information about collision strength criteria.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.19 no.5
• /
• pp.570-576
• /
• 2018

In reinforced concrete structures, the joints of ordinary rebars are usually lap joints, which are bound by binding wires with rebars, and mechanical joints by couplers. In domestic design standards (concrete design code), welded lap joints are restricted for ordinary rebars, but overseas standards allow welded lap joints of ordinary rebars through pre-heating. This study investigated the domestic and international standards/criteria and evaluated the fracture strength by performing the tensile test on the lap welded joint of SD400 grade rebars, which is used the most in the construction sites. The weld length of the specimen for weld lap joints is based on the minimum weld length (8d) given in the KS standard (KS B ISO 17660-1). According to AWS D1.4, the preheating temperature was set to $150^{\circ}C$ for D19 and below, and $260^{\circ}C$ for D22 and above. In the test results, the tensile strength of rebars with welded lap joints exceeded the required strength (125% of the yield strength) according to the concrete design code. To analyze the effect of preheating, the tensile strength of the welded rebars after preheating was not significantly different from that of the welded rebars without preheating. The carbon equivalent content (Ceq) of the rebars used in the test was 0.45% or less. Under AWS D1.4, no preheating is required if the carbon equivalent is less than 0.45%. All specimens with a welded lap length of 8d failed by a bar fracture. The effect of preheating was confirmed to be insignificant due to the low carbon equivalent of the rebar.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.24 no.2
• /
• pp.157-162
• /
• 2018

The increase of risk in port due to the increase in ship size and sea level rises, the standard crown height will increase. In this study, cruise and container ships will need to raise their crown height due to the projected wind pressure areas becoming larger due to the ships' size increase. The mooring assessment was evaluated with the rise of the crown height. The cruise ship of GT 100,000 tons exceeded the permissible breaking force of the mooring line under the crown height conditions of wind speed of 30 kts when the wind direction was $45^{\circ}$ to the direction of the bow. Also, the elevation angle of the pier and mooring line was analyzed and exceeded the crown height, and it was determined that it is necessary to adjust the crown height. Container ships of DWT 100,000 tons were analyzed to exceed the limit of sway motion at the crown height and it was determined that they need to be adjusted to the minimum crown height standard.

• Nuclear Engineering and Technology
• /
• v.23 no.1
• /
• pp.66-80
• /
• 1991

The LOFT intermediate break experiment L5-1, which simulates 12 inch diameter ECC line break in a typical PWR, has been analyzed using the reactor thermal/hydraulic analysis code RELAP5/MOD2, Cycle 36.04. The base calculation, which modeled the core with single flow channel and two heat structures without using the options of reflood and gap conductance model, has been successfully completed and compared with experimental data. Sensitivity studies were carried out to investigate the effects of nodalization at reactor vessel and core modeling on major thermal hydraulic parameters, especially on peak cladding temperature(PCT). These sensitivity items are : single flow channel and single heat structure (Case A), two flow channel and two heat structures (Case B), reflood option added (Case C) and both reflood and gap conductance options added (Case D). The code, RELAP5/MOD2 Cycle 36.04 with the base modeling, predicted the key parameters of LOFT IBLOCA Test L5-1 better than Cases A,B,C and D. Thus, it is concluded that the single flow channel modeling for core is better than the two flow channel modeling and two heat structure is also better than single heat structure modeling to predict PCT at the central fuel rods. It is, therefore, recommended to use the reflood option and not to use gap conductance option for this L5-1 type IBLOCA.

• Journal of Korean Society of Steel Construction
• /
• v.25 no.5
• /
• pp.463-474
• /
• 2013

Many experimental and numerical researches for thin-walled carbon steel and austenitic stainless steel single shear bolted connections have been conducted and the modified design equations of ultimate strength were proposed. In this study, the tests of double shear bolted connections with bolt arrangements ($2{\times}1$, $2{\times}2$) and end distance parallel to the loading direction as main variables were performed. Specimens were planed with a constant dimension of edge distance perpendicular to the loading direction, bolt diameter, pitch and gauge like single shear bolted connections. The test results such as ultimate strength and fracture mode were compared with those of current design standards. Furthermore, modified block shear equations for double shear bolted connections were suggested.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.20 no.9
• /
• pp.2894-2900
• /
• 1996

The stream generator tubes represent an integral part of a major barrier against the fission product release to the environment. So, the rupture of these tubes could permit flow of reactor coolant into the secondary system and injure the safety of reactor coolant system. Therefore, if the crack was detected during In-Service Inspection of tubes the cracked tube should be evaluated by the pulgging criteria and plugged or not. In this study, the fracture mechanics evaluation is carried out on the thru-wall axial crack due to Primary Water Stress Corrosion Cracking in the roll transition aone of steam generator tube to help the assurence the integrity of tubes and estabilish the plugging criteria. Due to the Inconel which is used as tube material is more ductile than others, the plastic instability repture theory was used to calculate the critical and allowable crack length. Based on Leak Before Break concept the leak rate for the critical crack length and the allowable leak rate are compared and the safety of tubes was given.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2005.05a
• /
• pp.163-166
• /
• 2005

A hole expansion process is an important process in producing a hub-hole in a wheel disc of a vehicle. In this process, the main parameter is the formability of a material that is expressed as the hole expansion ratio. The hub-hole expansion process is different from conventional forming processes or hole flanging processes from the view-point of its deformation mode and forming of a thick plate. In the process, a crack is occurred in the upper edge of a hole as the hole is expanded. Since prediction of the forming limit by hole expansion experiment needs tremendous time and effort, an appropriate fracture criterion has to be developed fur finite element analysis to define forming limit of the material. In this paper, the hole expansion process of a hub-hole is studied by finite element analysis with ABAQUS/standard considering several ductile fracture criteria. The fracture mode and hole expansion ratio is compared with respect to the various fracture criteria. These criteria do not predict its fracture mode or hole expansion ratio adequately and show deviation from experimental results of hole expansion. A modified ductile fracture criterion is newly proposed to consider the deformation characteristics of a material accurately in a hole expansion process. A fracture propagation analysis at the hub-hole edge is also performed for high accuracy of prediction using the new fracture criterion proposed.

• Journal of Korean Society of Steel Construction
• /
• v.12 no.5 s.48
• /
• pp.463-473
• /
• 2000

This paper presents the results of the experimental and analytical investigation for the fatigue strength of welded details frequently used in steel bridges, especially for the details with relatively lower fatigue strength. The welded details included four kinds of welded details corresponding to the categories C, D, E and E' which represent the flange attachment details, web attachment details, transverse stiffeners and cover-plate details. Tensile fatigue tests were performed. The test results were compared with other available test results and the fatigue criteria of AASHTO, JSSC and Eurocode specifications. Generally, our test results were well agreed with other test results and satisfied with above-mentioned fatigue design provisions. However, it was found that transversely loaded weld-details showed lower fatigue strength than longitudinally loaded weld-details in transverse stiffener detail, and the test results of those details were not satisfied with AASHTO fatigue provisions. Examining the effect of length of gusset plate attachment details, welded details with longer attachment showed relatively lower fatigue strength, especially for the out-of-plane gusset plate details. It is recommended to perform additional fatigue tests with various loading and detail parameters and to establish the more detailed fatigue categories such as Eurocode or JSSC

• Journal of the Korea Concrete Institute
• /
• v.28 no.3
• /
• pp.365-373
• /
• 2016

Ultra-High-Performance Steel Fiber-Reinforced Concrete (SUPER Concrete) exhibits improved compressive and tensile strengths far superior to those of conventional concrete. These characteristics can significantly reduce the cross sectional area of the member and the anchorage strength of a headed bar is expected to be improved. In this study, the anchorage strengths of headed bars with $4d_b$ or $6d_b$ embedment length were evaluated by simulated exterior beam-column joint tests where the headed bars were used as beam bars and the joints were cast of 120 or 180 MPa SUPER Concrete. In all specimens, the actual yield strengths of the headed bars over 600 MPa were developed. Some headed bars were fractured due to the high anchorage capacity in SUPER Concrete. Therefore, the headed bar with only $4d_b$ embedment length in 120 MPa SUPER Concrete can develop a yield strength of 600 MPa which is the highest design yield strength permitted by the KCI design code. The previous model derived from tests with normal concrete and the current design code underestimate the anchorage capacity of the headed bar anchored in SUPER Concrete. Because the previous model and the current design code do not consider the effects of the high tensile strength of SUPER Concrete. From a regression analysis assuming that the anchorage strength is proportional to $(f_{ck})^{\alpha}$, the model for predicting anchorage strength of headed bars in SUPER Concrete is developed. The average and coefficient of variation of the test-to-prediction values are 1.01 and 5%, respectively.