• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.11 no.4
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• pp.311-324
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• 2013

To ensure the reliability of computer programs used for the post-closure safety assessment in the Wolsong LILW Center, the results from MASCOT, SAFE-ROCK and GOLDSIM programs are compared with a problem for degradation. Advantages and disadvantages of each computer programs are individually analyzed. Effects on the individual dose are assessed with each computer programs. MASCOT and SAFE-ROCK showed similar results for $^{129}I$ and $^3H$. However, GOLDSIM represented different results for $^{129}I$ and $^3H$. It is analyzed further and compared with the fluxes in each barrier of the disposal system. Througout the benchmarking testing of the computer program, the limitation of computer program can be continuously found out for the mature post-closure safety of Korean radwaste disposal system.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.15 no.4
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• pp.403-409
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• 2017

For dry storage of the spent nuclear fuel (SNF) stored in the storage pool of a nuclear power plant, essentially all moisture must be removed to prevent corrosion of the assembly and canister internals and/or degradation of fuel cladding integrity after SNF canister loading operation. R&D work is now in progress on a forced gas drying system that can be used to remove residual water in canisters. In this work, preliminary design is performed to manufacture the forced gas drying system. This process includes a case study of dry methods for canister moisture removal, relative codes and standards, confirmation of adequate dryness, needs analysis at plant sites, and characteristics of SNF stored in pools. Through this preliminary design work, we obtained a conceptual flow diagram and preliminary P&ID of the forced gas drying system. The results of this study can be used to determine details of the design to manufacture the forced gas drying system.

• Journal of the Korean Applied Science and Technology
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• v.30 no.4
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• pp.701-714
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• 2013

Recently, due to the activation policy of biodiesel, the blending biodiesel to petroleum product is increasing. Low-temperature fluidity and oxidation stability are the most significant issues to the marketers and end users of biodiesel. Thus, the way to control the quality of biodiesel blended fuels was investigated by duplicating the real storage situation of biodiesel blended fuels and evaluating the effect of oxidation trend and quality degradation. From the results of oxidation degradation test of biodiesel blended fuels, no special quality degradation has been observed through the evaporation for 18 weeks in a summer season under a storage circumstance without exposure to the sun light. However, the severe quality degradation was observed in PE vessel in only 2 weeks of storage. This oxidation degradation was also verified with FT-IR spectrum change. However, the special symptom cannot be distinguished by the quality test because the quality specifications were satisfied despite of the drastic oxidation degradation. Namely, the problem in a vehicle could be occurred by oxidation materials(polymer, organic acid. etc.) under oxidation even though it satisfied the quality specification.

• Journal of the Korean Academy of Esthetic Dentistry
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• v.22 no.1
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• pp.30-46
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• 2013

Porcelain fused to metal crown has been used mostly over the last 50 years for restorations in dentistry. However, the patients' awareness of aesthetic aspect, biocompatibility and the problems such as an allergy to metals led to the growing interest in the 'metal free restoration'. In particular, the price of the precious metals that have been mainly used to date has risen drastically, which made them impossible to play their role as oral restorative materials anymore, and in addition, the PFM restoration has intrinsic problems of chipping and fracture. Therefore, the CAD/CAM has been drawing more attention than ever due to the popular needs for the material that is more aesthetic and stronger for restoration of the molar implant. Considerations in carrying out the full zirconia restoration are as follows: 1) strength, 2) combination work, 3) light penetrability, 4) treatment of cracks, 5) the color reproducibility of the block, 6) the abrasivity of antagonistic tooth, 7) low temperature degradation. In this presentation, the color reproducibility of the block will be discussed. One of the biggest reasons for avoiding the full zirconia restoration is that it is difficult to reproduce the natural color compared to the conventional PFM restoration. Thus, many clinicians show reluctance due to the exposure of the ugly block when the coloring on the surface is removed after occlusal adjustment. From the experience of using blocks by Zirkonzahn for more than 4 years, it is considered that these problems can be addressed to some degrees. Accordingly, how to make restorations that are well in harmony with surrounding prosthesis or natural teeth will be discussed.

• Journal of Technologic Dentistry
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• v.34 no.2
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• pp.83-93
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• 2012

Purpose: The objective of this study is to find out physical properties and the flexural strength changed by the low temperature degradation of the block which is needed to make bio-prosthetic dentistry which is better than feldspar affiliated ceramic made by building up ceramic powder and also to apply this to the clinical use of zirconia monolithic all-ceramic crown. Methods: Flexural strength of each sample was evaluated before and after the Low Temperature Degradation, and physical properties of the Tetra Zirconia Block containing 3mol % was evaluated as well. The average and standard deviation of each experimental group were came out of the evaluation. Statistical package for social science 18.0 was used for statistics. Results: The average density of the monolithic all-ceramic crown was $6.0280{\pm}0.0147g/cm$, the relative density was 99.01 %. When the sample was sintered at $1480^{\circ}C$ the diameter of average particle was $396.62{\pm}33.71nm$. All the samples had no monolithic peak after XRD evaluation but only had tetragonal peak. There were statistically significant differences in the result of flexural strength of the samples evaluated after and before the low temperature degradation, the flexural strength before the low temperature degradation was $1747.40{\ss}{\acute{A}}$, at the temperature of $130^{\circ}C$ the flexural strength after the low temperature degradation was 1063.99MPa (p<0.001). There was statistically significant difference in the result of strength of 1020.07MPa after the low temperature degradation at the temperature of $200^{\circ}C$ (p<0.001). Conclusion: The block which was made for this evaluation possesses such an excellent strength among dental restorative materials that it is thought to have no problems to use for tetragonal zirconia polycrystal.

• KOREAN JOURNAL OF PACKAGING SCIENCE & TECHNOLOGY
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• v.23 no.2
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• pp.75-81
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• 2017

Modified atmosphere packaging (MAP) of vacuum, 60% $N_2/40%$ $CO_2$, 100% $N_2$ and 100% $CO_2$ were examined to preserve fried fish cakes and extend their shelf life. When product packages in air were stored at 5, 10, and $15^{\circ}C$ with measurement in quality attributes, aerobic bacterial growth was found to be primary quality factor to determine the shelf life of the product. Huang's model was adopted to obtain the parameters for use in shelf life determination for a variety of packaging and storage conditions. Temperature dependence expressed in Arrhenius equation showed activation energies of 139.4 and 41.8 kJ/mol for inverse of lag time and growth rate of the microbial spoilage, respectively. MAP of 100% $CO_2$ could double the product shelf life at $10^{\circ}C$ compared to air package. High $CO_2$ concentration MAP at low temperature was found to be effective to prolong the shelf life.

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.2
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• pp.191-198
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• 2008

Flow accelerated corrosion (FAC) phenomenon of low alloy carbon steels in nuclear power plant has been known as one of major degradation mechanisms. It has a potential to cause nuclear pipe rupture accident which may directly impact on the plant reliability and safety. Recently, the equipotential switching direct current potential drop (ES-DCPD) method has been developed, by the present authors, as a method to monitor wall loss in a piping. This method can rapidly monitor the thinning of piping, utilizing either the wide range monitoring (WiRM) or the narrow range monitoring (NaRM) technique. WiRM is a method to monitor wide range of straight piping, whereas NaRM focuses significantly on a narrow range such as an elbow. WiRM and NaRM can improve the reliability of the current FAC screening method that is based on computer modeling on fluid flow conditions. In this paper, the measurements by ES-DCPD are performed with signal sensitivity analyses in the laboratory environment for extended period and showed the viability of ES-DCPD for real plant applications.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.5
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• pp.458-463
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• 2010

Since the acoustic nonlinearity is sensitive to the minute variation of material properties, the nonlinear ultrasonic technique(NUT) has been considered as a promising method to evaluate the material degradation or fatigue. However, there are certain limitations to apply the conventional NUT using the bulk wave to thin plates. In case of plates, the use of Lamb wave can be considered, however, the propagation characteristics of Lamb wave are completely different with the bulk wave, and thus the separate study for the nonlinearity of Lamb wave is required. For this work, this paper analyzed first the conditions of mode pair suitable for the practical application as well as for the cumulative propagation of quadratic harmonic frequency and summarized the result in for conditions; (1) phase matching, (2) non-zero power flux, (3) group velocity matching, and (4) non-zero out-of-plane displacement. Experimental results in aluminum plates showed that the amplitude of the secondary Lamb wave and nonlinear parameter growed up with increasing propagation distance at the mode pair satisfying the above all conditions and that the ration of nonlinear parameters measured in Al6061-T6 and Al1100-H15 was closed to the ratio of the absolute nonlinear parameters.

• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.2
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• pp.173-180
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• 2013

Compacted graphite iron(CGI), also known as vermicular graphite iron, is a metal which is gaining popularity in applications that require either greater strength, or lower weight than cast iron. Recently compacted graphite iron has been used for diesel engine blocks. Considering that using in exhaust manifold of the diesel engine, CGI340 was conducted the heat treatment during 1 hour to 96 hours from 873 to 1273 K. Mechanical characteristics were evaluated. The obtained results are as follows; The tensile strength of the heat treated specimens showed overall lower tensile strength than that of the base metal. Tensile strength decreases with increasing of heat treatment time, and the higher heat treatment temperature and the longer time, were more reduced. The fatigue limit by the ultrasonic fatigue test was approximately 130 MPa of base metal, 100 MPa of 1173 K (96 hrs) specimen, respectively. The hardness decreases with increasing heat treatment time, and the higher the heat treatment temperature was lowered hardness distribution. In CGI340, average hardness of nodular graphite was 120 Hv, average hardness of vermicular graphite was 114 Hv. This showed lower hardness than the base structure ferrite. The nodular graphite and vermicular graphite according to the heat treatment temperature and time didn't have a consistent change. However, the grain size of base structure grew with increasing of heat treatment time.

• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.2
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• pp.165-172
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• 2013

Power generating unit structures are designed and built to meet standard to secure its safety for expected life time. As the structures have been exposed to combined environment, degradation of structure material is accelerated and it can cause unexpected damage; evaluating precise mechanical properties of weak site like welded area is an essential research area as it is directly connected to safety issues. Existing measuring technique like tensile test requires specific size in testing specimen yet it is destructive method which is hard to apply on running structures. To overcome above mentioned limitation, IIT is getting limelight as it is non-destructive and simple method. In this study, latest technique is introduced to evaluate tensile property and residual stress by analyzing stress field occurs under the indenter while IIT is performed. Test on welded area, the weak site of nuclear structures have been practiced and confirmed that IIT can be usefully applied to evaluate integrity in industry.