• Proceedings of the Korean Nuclear Society Conference
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• 2001.05a
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• pp.205-205
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• 2001

• Proceedings of the KWS Conference
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• 2008.05a
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• pp.45-45
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• 2008

• Proceedings of the Korean Nuclear Society Conference
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• 1998.10a
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• pp.182-182
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• 1998

• Advances in aircraft and spacecraft science
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• v.8 no.1
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• pp.31-51
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• 2021

Selective laser melting (SLM), one of the most widely used powder bed fusion (PBF) additive manufacturing (AM) technology, enables the fabrication of customized metallic parts with complex geometry by layer-by-layer fashion. However, SLM inherently poses several problems such as the discontinuities in the molten track and the steep temperature gradient resulting in a high degree of residual stress. To avoid such defects, thisstudy proposes a temperature thread multiscale model of SLM for the evaluation of the process at different scales. In microscale melt pool analysis, the laser beam parameters were evaluated based on the predicted melt pool morphology to check for lack-of-fusion or keyhole defects. The analysis results at microscale were then used to build an equivalent body heat flux model to obtain the residual stress distribution and the part distortions at the macroscale (part level). To identify the source of uneven heat dissipation, a liquid lifetime contour at macroscale was investigated. The predicted distortion was also experimentally validated showing a good agreement with the experimental measurement.

• Nuclear Engineering and Technology
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• v.32 no.4
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• pp.379-394
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• 2000

As an in-vessel retention (IVR) design concept in coping with a severe accident in the nuclear power plant during which time a considerable amount of core material may melt, external cooling of the reactor vessel has been suggested to protect the lower head from overheating due to relocated material from the core. The efficiency of the ex-vessel management may be estimated by the thermal margin defined as the ratio of the critical heat flux (CHF）to the actual heat flux from the reactor vessel. Principal factors affecting the thermal margin calculation are the amount of heat to be transferred downward from the molten pool, variation of heat flux with the angular position, and the amount of removable heat by external cooling In this paper a thorough literature survey is made and relevant models and correlations are critically reviewed and applied in terms of their capabilities and uncertainties in estimating the thermal margin to potential failure of the vessel on account of the CHF Results of the thermal margin calculation are statistically treated and the associated uncertainties are quantitatively evaluated to shed light on the issues requiring further attention and study in the near term. Our results indicated a higher thermal margin at the bottom than at the top of the vessel accounting for the natural convection within the hemispherical molten debris pool in the lower plenum. The information obtained from this study will serve as the backbone in identifying the maximum heat removal capability and limitations of the IVR technology called the Cerium Attack Syndrome Immunization Structures (COASISO) being developed for next generation reactors.

• Journal of Welding and Joining
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• v.22 no.1
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• pp.71-76
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• 2004

In the standpoint of the arc pressure, the effects of the filler wire feed rate on the penetration was investigated in this study. The pure Ar gas was used as a shield gas and the parameters investigated were the welding current and the filler wire feed rate. By making the experiment on the arc pressure, we could know that the arc pressure was fluctuated as the depth-into-arc of the tungsten rod. Instead of the filler wire, the tungsten rod was supplied into the molten pool to make this experiment. Because the filler wire melted in arc and then we couldn't measure the arc pressure. So, the tungsten rod - the highest melting point - was used. According to the depth-into-arc of the tungsten rod, the arc pressure could be measured by using the manometer. It was proved that the arc pressure got higher as the wire feed rate was slow. It is reported the arc pressure is proportion to welding voltage and the square of welding current. But, in the filler wire TIG welding, we could blow that arc pressure was fluctuated as the depth-into-arc of filler wire was changed. We could measure the arc pressure by the variation of the filler wire feed rate and could verify that it affected bead shape and penetration.

• Journal of Welding and Joining
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• v.28 no.5
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• pp.93-98
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• 2010

The properties of GTA weld for ferritic stainless steel have been studied with different $O_2$ contents in Ar shielding gas at the constant welding speed. A small amount of $O_2$ (0.01~1.0%) was mixed in Ar shielding gas in order to improve the weld penetration. The fully penetrated GTA weld was acquired at 160A weld current shielded by pure Ar gas. Addition of oxygen larger than 0.1% made a full penetration at lower weld current than 160A. The small addition of $O_2$ in Ar shielding gas improved the penetration properties of GTA weld because the $O_2$ in the molten pool accelerated the flow of molten pool and changed the flow pattern from outward to inward direction. The impact energy and DBTT (Ductile- Brittle- Transition-Temperature) of the GTA weld shielded by Ar+$O_2$ (less 0.3%) was similar and the corrosion properties of GTA weld was slightly inferior to those of GTA weld shielded by pure Ar gas.

• Nuclear Engineering and Technology
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• v.47 no.7
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• pp.907-914
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• 2015

The energetic steam explosion caused by contact between the high temperature molten core and water is one of the phenomena that may threaten the integrity of the containment vessel during severe accidents of light water reactors (LWRs). We examined the dependence of steam explosion loads in a typical reactor cavity geometry on selected model parameters and initial/boundary conditions by using a steam explosion simulation code, JASMINE, developed at Japan Atomic Energy Agency (JAEA). Among the parameters, we put an emphasis on the water pool depth that has significance in terms of accident mitigation strategies including cavity flooding. The results showed a strong correlation between the load and the premixed mass, defined as the mass of the molten material in low void zones (void fraction < 0.75). The jet diameter and velocity that comprise the flow rate were the primary factors to determine the premixed mass and the load. The water pool depth also showed a significant impact. The energy conversion ratio based on the enthalpy in the premixed mass was in a narrow range ~4%. Based on this observation, we proposed a simplified method for evaluation of the steam explosion load. The results showed fair agreement with JASMINE.

• Journal of Powder Materials
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• v.28 no.4
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• pp.301-309
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• 2021

In this study, an AISI 316 L alloy was manufactured using a selective laser melting (SLM) process. The tensile and impact toughness properties of the SLM AISI 316 L alloy were examined. In addition, stress relieving heat treatment (650℃ / 2 h) was performed on the as-built SLM alloy to investigate the effects of heat treatment on the mechanical properties. In the as-built SLM AISI 316 L alloy, cellular dendrite and molten pool structures were observed. Although the molten pool did not disappear following heat treatment, EBSD KAM analytical results confirmed that the fractions of the low- and high-angle boundaries decreased and increased, respectively. As the heat treatment was performed, the yield strength decreased, but the tensile strength and elongation increased only slightly. Impact toughness results revealed that the impact energy increased by 33.5% when heat treatment was applied. The deformation behavior of the SLM AISI 316 L alloy was also examined in relation to the microstructure through analyses of the tensile and impact fracture surfaces.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.12
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• pp.1887-1897
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• 2001

Korea Atomic Energy Research Institute (KAERI) launched an intermediate scale steam explosion experiment named "Test for Real Corium Interaction with water (TROI)" using reactor material to investigate whether the molten reactor material would lead to energetic steam explosion when interacted wish cold water at low pressure. The melt-water interaction experiment is performed in a pressure vessel with the multi-dimensional fuel and water pool geometry. The novel concept of cold crucible technology, where powder of the reactor material in a water-cooled cafe is heated by high frequency induction, is firstly implemented for the generation of molten fuel. In this paper, the lest facility and cold crucible technology are introduced and the results or the first series of tests were discussed. The 5 kg of molten ZrO$_2$jet was poured into the 67cm deep water pool at 30 ∼ 95 $\^{C}$. Either spontaneous steam explosions or quenching was observed. The morphology of debris and pressure wave profiles clearly indicate the differences between the two cases.