• Nuclear Engineering and Technology
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• v.37 no.5
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• pp.401-422
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• 2005

We review here research and development progress achieved in US Plasma Chamber technology roughly over the last decade. In particular, we focus on two major programs carried out in the US: the APEX project (1998-2003) and the US ITER TBM activities (2003-present). The APEX project grew out of the US fusion program emphasis in the late 1990s on more fundamental science and innovation. APEX was commissioned to investigate novel technology concepts for achieving high power density and high temperature reactor coolants. In particular, the idea of liquid walls and the related research is described here, with some detailed examples of liquid metal and molten salt magnetohydrodynamic and free surface effects on flow control and heat transfer. The ongoing US ITER Test Blanket Module (TBM) program is also described, where the current first wall/blanket concepts being considered are the dual coolant lead lithium concept and the solid breeder helium cooled concepts, both using ferritic steel structures. The research described for these concepts includes both thermofluid MHD issues for the liquid metal coolant in the DCLL, and thermomechanical issues for ceramic breeder packed pebble beds in the solid breeder concept. Finally, future directions for ongoing research in these areas are described.

• Journal of Korea Foundry Society
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• v.42 no.6
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• pp.331-336
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• 2022

In this study, we investigated the casting designs for fuel tank valves for LPG automobiles. The valves we studied have two cavities inside the part. There is inevitable air entrapment inside the cavities. In order to reduce this kind of casting defect, we carried out computer simulations of molten metal flow during the diecasting process of the target products. The main process parameters were the ingate position, product direction, and injection velocity. We also examined the possible use of vacuum diecasting. The position of the air entrapment was almost identical for all the ingate positions and product directions. We found that the change of the injection velocity affects the position of the air entrapment. In case of vacuum diecasting, the position of the air entrapment was similar to the previous cases, but it is expected that the air entrapment will be highly reduced in a real situation due to the vacuumed space.

• Journal of Korea Foundry Society
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• v.25 no.4
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• pp.168-172
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• 2005

In this study, the effects of chill layers occurred in shot sleeve on the molten metal filling were analyzed through computer simulation and the behavior of chill layers with temperature variation of shot sleeve set from 200 to $280^{\circ}C$ was also investigated. The simulation results showed the chill layers set in the in-gates during the injection process change the main filling direction and cause turbulent flow pattern, resulting in porosities inside the castings. The amount of chill layers with the increasing temperature of shot sleeve was considerably reduced. And particularly, at the setting temperature of $280^{\circ}C$ by heat control unit, the big reduction in chill layers, excellent trimmed surface and the highest densification were achieved, suggesting that as the optimal sleeve condition in diecasting, especially for the highly complex parts like valve body.

• Korean Journal of Materials Research
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• v.14 no.10
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• pp.719-724
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• 2004

Production of fine tantalum powder by calciothermic reduction of tantalum oxides ($Ta_{2}O_5$) pellet through an electronically mediated reaction (EMR) has been investigated. $Ta_{2}O_5$ pellet feed and reductant calcium-nickel (Ca-Ni) alloy were charged into electronically isolated locations in a molten $CaCl_2$ bath. The current flow through an external path between the feed (cathode) and reductant (anode) locations was monitored. The current approximately 4.7A was measured during the reaction in the external circuit connecting cathode and anode location. Tantalum powder with approximately 99 $mass\%$ purity was readily obtained after each experiment. Tantalum powder by EMR using $Ta_{2}O_5$ pellet feed was fine compared with that of metal powder by metallothermic reduction and EMR using $Ta_{2}O_5$ powder feed.

• Korean Journal of Materials Research
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• v.16 no.11
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• pp.698-704
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• 2006

In this study, the effect of chill layers occurred in shot sleeve on the molten metal filling was analyzed through computer simulation. The behavior of chill layers with temperature variation of shot sleeve set from 200 to $280^{\circ}C$ was also investigated. The simulation results showed the chill layers set in the in-gates during the injection process change the main filling direction and cause turbulent flow pattern, resulting in porosities inside the castings. The amount of chill layers with the increasing temperature of shot sleeve was considerably reduced. Particularly, at the setting temperature of $280^{\circ}C$ by heat control unit, the biggest reduction in chill layers, excellent trimmed surface and the highest density were achieved, suggesting that as the optimal sleeve condition in aluminum high pressure diecasting, especially for highly complex parts like valve body.

• Journal of the Korean Society for Precision Engineering
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• v.14 no.12
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• pp.73-85
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• 1997

The rolling force and roll deformation behavior in the twin roll type strip continuous casting process has been computed to estimate the thermal charcteristics of a caster roll. To calculation of rolling force, the relationship between flow stress and strain for a roll material and casting alloy are assumed as a function of strain-rate and temperature because mechanical properties of a casting materials depends on tempera- ture. The three dimensional thermal dlastic-plastic analysis of a cooling roll has also been carried out to obtain a roll stress and plastic strain distributions with the commercial finite element analysis package of ANSYS. Temperature fields data of caster roll which are provided by authors were used to estimated of roll deformation. Roll life considering thermal cycle is calculated by using thermal elastic-plastic analysis results. Roll life is proposed as a terms of a roll revolution in the caster roll with and without fine failure model on the roll surface. To obtain of plastic strain distributions of caster roll, thermomechan- ical properties of roll sleeve with a copper alloy is obtained by uniaxial tensile test for variation of temperature.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.12 no.3
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• pp.179-189
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• 2014

Pyroprocessing has been developed for the purpose of resolving the current spent nuclear fuel management issue and enhancing the recycle of valuable resources. An electrolytic reduction of the pyroprocessing is a process to reduce oxides into metals using LiCl as an electrolyte and requires a post-treatment process due to the inclusion of residual salt in porous metal products. A vacuum distillation has been adopted for various molten salt systems and could be applied to the post-treatment process of the electrolytic reduction. The residual salt in the metal products includes LiCl, alkali chlorides, and alkaline earth chlorides. In this paper, vapor pressures of chlorides have been estimated and the composition changes on the residual liquid during the vacuum distillation process have been calculated. A model combining a material balance and vapor-liquid equilibrium relations has been proposed under a constant vapor discharging flow rate and liquid composition changes have been calculated using the vapor pressures with respect to a dimensionless time. The behaviors have been compared with temperature and molten salt composition changes to simulate the process condition variation. The distillation of the residual salt has been dominated by LiCl which is the main component of the salt and CsCl of which vapor pressure is higher than that of LiCl would be readily removed. RbCl exhibits similar vapor pressure with LiCl and maintains its composition. However, $SrCl_2$ and $BaCl_2$ of which vapor pressures are much lower than that of LiCl are concentrated with time and expected to be possibly precipitated during the distillation when the initial compositions are increased.

• Korean Journal of Metals and Materials
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• v.49 no.1
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• pp.64-72
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• 2011

The spot weldability of dissimilar metal joints between austenitic stainless steels (STS316)/IF steels and ferritic stainless steels (STS430)/IF steels was investigated. This study was aimed to determine the spot welding parameters for a dissimilar metal joint and to evaluate the dissimilar metal joint's weldability, including its welding nugget shape, tensile-shear strength, hardness, and microstructure. The comparison of these results was described in terms of fracture behavior. Compared with the weld lobe of similar metal joints, dissimilar metal joints (STS430/IF) had reduced weld current range. However, the weld lobe of STS316/IF steel joint showed increased weld current range. This is because the dilution of chemical composition in the molten weld pool suppressed the heat input being caused by Joule heat with current flow through the samples. The microstructure of the fusion zone was fully martensite and mixture of ferrite and martensite for austenitic stainless steel/IF steel and ferritic stainless steel/IF steel combination, respectively. The experimental results showed that the shape of nugget was asymmetric, in which the fusion zone of the austenitic and ferritic stainless steel sheet was larger due to the higher bulk-resistance. The predicted microstructure by using the Schaeffler diagram was well matched with experimental results. After peel test, the fracture was initiated from heat affected zone of ferritic stainless steel sheet side, however the final fracture was propagated into the IF steel sheet side due to its lower strength.

• Nuclear Engineering and Technology
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• v.52 no.2
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• pp.248-257
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• 2020

This study presents an initial design for a novel system consisting in a coupled nuclear reactor and a phase change material-based thermal energy storage (TES) component, which acts as a buffer and regulator of heat transfer between the primary and secondary loops. The goal of this concept is to enhance the capacity factor of nuclear power plants (NPPs) in the case of high integration of renewable energy sources into the electric grid. Hence, this system could support in elevating the economics of NPPs in current competitive markets, especially with subsidized solar and wind energy sources, and relatively low oil and gas prices. Furthermore, utilizing a prismatic-core advanced high temperature reactor (PAHTR) cooled by a molten salt with a high melting point, have the potential in increasing the system efficiency due to its high operating temperature, and providing the baseline requirements for coupling other process heat applications. The present research studies the neutronics and thermal hydraulics (TH) of the PAHTR as well as TH calculations for the TES which consists of 300 blocks with a total heat storage capacity of 150 MWd. SERPENT Monte Carlo and MCNP5 codes carried out the neutronics analysis of the PAHTR which is sized to have a 5-year refueling cycle and rated power of 300 MW_th. The PAHTR has 10 metric tons of heavy metal with 19.75 wt% enriched UO₂ TRISO fuel, a hot clean excess reactivity and shutdown margin of $33.70 and -$115.68; respectively, negative temperature feedback coefficients, and an axial flux peaking factor of 1.68. Star-CCM + code predicted the correct convective heat transfer coefficient variations for both the reactor and the storage. TH analysis results show that the flow in the primary loop (in the reactor and TES) remains in the developing mixed convection regime while it reaches a fully developed flow in the secondary loop.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.6
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• pp.482-489
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• 2020

This study conducted a prototype development and evaluation by performing die-casting mold design, mold manufacturing, and injection condition optimization based on flow and solidification analysis to meet the needs of the coupling parts produced by die casting. Through flow analysis, the injection conditions suitable for 100% filling in the cavity were found to be a molten metal temperature of 670 ℃, injection speed of 1.164 m/s, and filling pressure of 6.324~18.77 MPa. In addition, solidification close to 100 % occurred in all four cavities when the solidification rate was 69.47 %. A defect inspection on the surface and inside the product revealed defects, such as poor molding and pores. In addition, the dimensions of the injected product were within the target tolerance and showed good results. Through the feedback of the results of flow and solidification analysis, it was possible to optimize the mold design, and the injection optimization conditions were confirmed to be a total cycle time of approximately 6.5 seconds. Good quality carrier parts with an average surface hardness of approximately 45 mm from the gate measured at 97.48(Hv) could be produced.