• Journal of the Korean Society of Safety
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• v.16 no.4
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• pp.29-38
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• 2001

The purpose of this paper is to evaluate the structural integrity of a reactor pressure vessel subjected to the pressurized thermal shock(PTS) during the transient events, such as main steam line break(MSLB) and small break loss of coolant accident(SBLOCA). For postulated surface or subsurface cracks, variation curves of stress intensity factor are obtained by using the three different methods, including ASME section XI code anlysis, the finite element alternating method and the finite element method. From the stress intensity factor curves, the maximum allowable nil-ductility transition temperatures(RT/NDT/) are determined by the tangent criterion and the maximum criterion for various crack configurations and two initial transient events. As a result of the analysis, it is noted that axial cracks have smaller maximum allowable RT$_{NDT}$ values than same-sized circumferential cracks for both the transient events in the case of the tangent criterion. Axial cracks have smaller RT$_{NDT}$ values than same-sized circumferential cracks for MSLB and circumferential cracks have smaller values than axial cracks for SBLOCA in the case of the maximum criterion.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.12 no.3
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• pp.271-279
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• 1999

본 연구에서는 국내에서 가장 취약할 것으로 예상되는 원자력 발전소에 가압열충격 사고를 유발할 수 있는 주증기관 파단사고를 가정하여 열수력 해석과 파괴역학 해석을 수행하였다. 원전수명관리연구의 일환으로 계통열수력 해석 및 혼합열유동 해석에 의하여 구한 냉각제의 온도와 압력의 이력 및 용기의 재질성분으로부터 용기의 응력확대계수와 파괴인성치를 계산하고 이들을 비교하여 균열의 진전여부를 판단하여 형상계수가 1/6인 표면균열이 견딜 수 있는 최대 기준무연성천이온도를 결정하였다.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.10a
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• pp.108-111
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• 2007

It's important to measure quantitative properties about thermal-nano variation conduct of polymer for producing high quality components using NIL process. NanoScale indents can be used ad cells for molecular electronics and drug deliver, slots for integration into nanodevices, and defects for tailoring the structure and properties. In this study, it's to evaluate mechanical characteristic of polymer such as PMMA and PC at high temperature for manufacture of nano/micro size of polymer using indenter at high temperature. At high temperature mechanical properties of polymer have extreme variation. Because heating the polymer, it becomes softer than room temperature. In this case it is especially important to study for mechanical properties of polymer at high temperature.

• Computational Structural Engineering
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• v.9 no.2
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• pp.153-161
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• 1996

In this paper, theory of fracture mechanics for the pressurized thermal shock is investigated and numerical procedure for the evaluation of the pressure vessel under pressurized thermal shock is developed. For the given material properties, transient history such as temperature and pressure, and postulated flaw, the stress distribution is obtained to calculate stress intensities for a wide range of assumed crack sizes. The stress intensities are compared with the material fracture toughness values corresponding to the chemical compositions and the distribution of the nil ductility transition temperature, to determine the crack growth during the transient. Plant-specific calculations have been performed for several transients and the evaluation results are discussed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.7
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• pp.1089-1096
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• 1997

In this paper, Rancho Seco transient which is reported as a typical pressurized thermal shock event is postulated to be occuring in the Kori unit 1 plant, the oldest nuclear power plant in Korea. For the given material properties, transient history such as temperature and pressure, and postulated flaw, the stress distribution is obtained to calculate stress intensities for a wide range of assumed crack sizes. The stress intensities are compared with the fracture toughness, which is determined using the material properties and the distribution of the nil ductility transition temperature, to determine if cracking is expected to occur during the transient. The allowable operating year for the transient is determined and the evaluation results are discussed.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.5
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• pp.457-465
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• 2000

An experiment was carried out to evaluate the thermal performance of the wire-coil inserts method. Tested were the smooth tubes with the wire-nil inserts of various pitch and helix angle combinations. Test fluids were the 50%-solution of the ethylene glycol and the Hue water. Heat transfer coefficient and friction factors were deduced from the measured values of temperatures, flowrates and pressure drops. A unified dimensionless correlation for the heat transfer coefficients was developed as a function of the pitch to diameter ratio, the Reynolds number and the Prandtl number. An exergy analysis was performed to evaluate an optimal operating condition with the wire-coil inserts.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.12
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• pp.1403-1410
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• 2011

Creep characteristic is an important failure mechanism when evaluating engineering materials that are soft material as polymers or used as mechanical elements at high temperatures. One of the popular thermo-elastic polymers, Polymethyl methacrylate(PMMA) which is used broadly for engineering polymer, as it has excellent mechanical and thermal properties compared to other polymers, was studied for creep characteristic at various level of stresses and temperatures. From the experimental results, the creep limit of PMMA at room temperature is 85 % of tensile strength. which is higher than that of PE (75%)at room temperature. Also the creep limits decreased to nil linearly as the temperatures increased, up to $120^{\circ}C$ of the melting point($267^{\circ}C$). Also the first and third stage among the three creep stages were non-existent nor were there any rupture failure which occurred for many metals at high temperatures.

• KSBB Journal
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• v.22 no.6
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• pp.433-437
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• 2007

A constant desire has been to fabricate nanopatterns for biochip and the Ultraviolet-nano imprint lithography (UV-NIL) is promising technology especially compared with thermal type in view of cost effectiveness. By using this method, nano-scale to micro-scale structures also called nanopore structures can be fabricated on large scale gold plate at normal conditions such as room temperature or low pressure which is not possible in thermal type lithography. One of the most important methods in fabricating biochips, immobilizing, was processed successfully by using this technology. That means immobilizing proteins only on the nanopore structures based on gold, not on hardened resin by UV is now possible by utilizing this method. So this selective nano-patterning process of protein can be useful method fabricating nanoscale protein chip.

• Journal of Ginseng Research
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• v.12 no.1
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• pp.1-10
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• 1988

Panax ginseng seedlings were grown at various temperature regimes from 15 to $30^{\circ}C$ for 19 days under dark and the linear relationship between various regrowth efficiencies and thermal stress indices, cumulative superoptimum temperatures corrected with factors. Gross growth efficiency(shoot weight l root weight loss) was 37.5 % at the optimum temperature $15^{\circ}C$/$15^{\circ}C$, and 12.3% at the highest temperature, $30^{\circ}C$/$30^{\circ}C$ while net growth efficiency (shoot weight + Sm)l(root loss-Rm), which corrected by maintenance respiration for shoot(Sm) and root(Rm) was 39.6% and 16.7 at optimum and highest temperature respectively. All growth efficiencies showed negative correlations (p = 0.001) with all thermal stress indices and negative(p = 0.001) with shoot growth(St). When growth temperature difference in a day was nil or above $15^{\circ}C$ growth efficiency decreased greatly. Thermal stress indices showed negative correlation with root dry matter loss(RDL) but positive with Rm. St showed positive correlation with RDL. Thermal stress appeared to inhibit substrate supply for shoot growth resulting in the extremely low growth efficiency comparing with other crops that seems to be main rate limiting factor of slow growth, Thus it is necessary that growth efficiency and thermal stress must be elucidated in terms of metabolic pathway.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.11
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• pp.2219-2227
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• 2002

In a nuclear power plant, reactor pressure vessel (RPV) is the primary pressure boundary component that must be protected against failure. The neutron irradiation on RPV in the beltline region, however, tends to cause localized damage accumulation, leading to crack initiation and propagation which raises RPV integrity issues. The objective of this paper is to estimate the integrity of RPV under hot leg leaking accident by applying the finite element analysis. In this paper, a parametric study was performed for various crack configurations based on 3-dimensional finite element models. The crack configuration, the crack orientation, the crack aspect ratio and the clad thickness were considered in the parametric study. The effect of these parameters on the maximum allowable nil-ductility transition reference temperature ($(RT_{NDT})$) was investigated on the basis of finite element analyses.