Steady- and transient-state analyses of fully ceramic microencapsulated fuel loaded reactor core via two-temperature homogenized thermal-conductivity model

Lee, Yoonhee,Cho, Nam Zin Elsevier 2015 Annals of nuclear energy Vol.76 No.-

<P><B>Abstract</B></P> <P>Fully ceramic microencapsulated (FCM) fuel, a type of accident-tolerant fuel (ATF), consists of TRISO particles randomly dispersed in a SiC matrix. In this study, for a thermal analysis of the FCM fuel with such a high heterogeneity, a two-temperature homogenized thermal-conductivity model was applied by the authors. This model provides separate temperatures for the fuel-kernels and the SiC matrix. It also provides more realistic temperature profiles than those of harmonic- and volumetric-average thermal conductivity models, which are used for thermal analysis of a fuel element in VHTRs having a composition similar to the FCM fuel, because such models are unable to provide the fuel-kernel and graphite matrix temperatures separately.</P> <P>In this study, coupled with a neutron diffusion model, a FCM fuel-loaded reactor core is analyzed via a two-temperature homogenized thermal-conductivity model at steady- and transient-states. The results are compared to those from harmonic- and volumetric-average thermal conductivity models, i.e., we compare <I>k<SUB>eff</SUB> </I> eigenvalues, power distributions, and temperature profiles in the hottest single-channel at steady-state. At transient-state, we compare total powers, reactivity, and maximum temperatures in the hottest single-channel obtained by the different thermal analysis models. The different thermal analysis models and the availability of fuel-kernel temperatures in the two-temperature homogenized thermal-conductivity model for Doppler temperature feedback cause significant differences as revealed by comparisons.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Fully ceramic microencapsulated fuel-loaded core is analyzed via a two-temperature homogenized thermal-conductivity model. </LI> <LI> The model is compared to harmonic- and volumetric-average thermal conductivity models. </LI> <LI> The three thermal analysis models show ∼100pcm differences in the <I>k<SUB>eff</SUB> </I> eigenvalue. </LI> <LI> The three thermal analysis models show more than 70K differences in the maximum temperature. </LI> <LI> There occur more than 3 times differences in the maximum power for a control rod ejection accident. </LI> </UL> </P>

Determination of Dimensional Profile and Heat Input of Welded Joint with Average Temperature

Jiangchao Wang 한국정밀공학회 2019 International Journal of Precision Engineering and Vol.20 No.4

With the proposal of the average temperature concept, the target of this study is to determine the appropriate dimensional profile and heat input for butt welded joints. Meanwhile, inherent deformation as the cause of welding distortion was examined to confirm the dimensional profile and heat input of welded joints for reliable welding experiments. First, butt welding experiment and measurement of out-of-plane welding distortion were conducted. The effect of length and width of welded joint on longitudinal shrinkage force was numerically considered and examined with a series of thermal elastic plastic finite element computations, where the mechanism of this behavior was clarified with average temperature. The case of heat input increasing was also examined with average temperature, which can be considered as the identical heat input for plate width decreasing. Moreover, the difference between theoretical and computational approaches to evaluate longitudinal shrinkage force was perfectly clarified with the concept of average temperature, and dimensional profile and heat input of butt welded joints were suggested.

몇몇 조경수목의 만개일 예측을 위한 기본온도 설정

김재순,정명일,한승원,장하경,정현환 한국인간·식물·환경학회 2013 인간식물환경학회지 Vol.16 No.5

한국에 자생하는 몇몇 조경용 수목의 만개일과 기온자료를 활용하여 생물계절에 따른 기본온도와 생장도일(Growing Degree Day, GDD)을 추정하였다. 2011~2012년 조경수목의 만개일를 조사하였으며 수원기상대의 온도자료를 사용하여 일평균온도에서 기본온도를 차감한 생장도일을 계산하였다. 기준온도 설정을 위하여 0.1℃ 단위로 생장도일을 계산하여 2011~2012년 생장도일의 표준편차가 적은 온도를 기본온도로 설정하였다. 그 결과 식물의 기본온도는 진달래, 박태기나무, 팥꽃나무는 1.9℃, 공조팝나무 0℃, 장구밥나무 1.2℃로 나타났으며 만개기의 생장도일은 진달래 324.10±96.32℃, 박태기나무와 팥꽃나무 506.90±84.99℃, 공조팝나무 853.65±59.61℃, 장구밥나무 2112.70±11.74℃이다. 계산된 생장도일을 이용하여 홍릉수목원에서의 예측만개일과 실제만개일 비교 시 진달래의 예측만개일의 45%, 박태기나무의 35% 수준으로 일치하였다. 팥꽃나무는 박태기나무와 만개일이 유사하므로 비슷한 예측 정확도를 보일 것이라 생각된다. This study used the data of full blooming date and temperature of landscape woody plants to estimate the base temperature and Growing Degree Day(GDD) according to plant phenology. The full blooming date of landscape woody plants from 2011 to 2012 was investigated, and the GDD was calculated by deducting the base temperature from daily mean temperature using the temperature data of Suwon Regional Meteorological Office. To set up the reference temperature, the GDD is calculated in the unit of 0.1℃, setting the temperature with low standard deviation of GDD from 2011 to 2012 as the base temperature. As a result, the base temperature of plants is 1.9℃ for Rhododendron mucronulatum Turcz., Cercis chinensis Bunge. and Daphne odora Thunb., 0℃ for Spiraea cantoniensis Lour., and 1.2℃ for Grewia parviflora Bunge.. The GDD of the full bloom stage is 324.10±96.32℃d for R. mucronulatum Turcz., 506.90±84.99℃d for C. chinensis Bunge. and D. odora Thunb., 853.65±59.61℃d for S. cantoniensis Lour., and 2112.70±11.74℃d for G. parviflora Bunge. The comparison of predicted full bloom date and actual full bloom date in Hongreung Arboretum using the calculated GDD showed that 45% of the predicted fullbloom date for R. mucronulatum Turcz. matched the actual full bloom date, 35% for C. chinensis Bunge.. D. odora Thunb. has similar full bloom date with C. chinensis Bunge., and thus may show similar prediction accuracy.

Steady- and Transient-State Analyses of Fully Ceramic Microencapsulated Fuel with Randomly Dispersed Tristructural Isotropic Particles via Two-Temperature Homogenized Model-II: Applications by Coupling with COREDAX

이윤희,BUM HEE CHO,조남진 한국원자력학회 2016 Nuclear Engineering and Technology Vol.48 No.3

In Part I of this paper, the two-temperature homogenized model for the fully ceramicmicroencapsulated fuel, in which tristructural isotropic particles are randomly dispersed in afine lattice stochastic structure, was discussed. In this model, the fuel-kernel and siliconcarbide matrix temperatures are distinguished. Moreover, the obtained temperature profilesare more realistic than those obtained using other models. Using the temperature-dependentthermal conductivities of uranium nitride and the silicon carbide matrix, temperaturedependenthomogenized parameters were obtained. In Part II of the paper, coupled withthe COREDAX code, a reactor core loaded by fully ceramic microencapsulated fuel in whichtristructural isotropic particles are randomly dispersed in the fine lattice stochastic structureis analyzed via a two-temperature homogenized model at steady and transient states. Theresults are compared with those from harmonic- and volumetric-average thermalconductivity models; i.e., we compare keff eigenvalues, power distributions, and temperatureprofiles in the hottest single channel at a steady state. At transient states, we compare totalpower, average energy deposition, and maximumtemperatures in the hottest single channelobtained by the differentthermal analysismodels. The different thermal analysis models andthe availability of fuel-kernel temperatures in the two-temperature homogenized model forDoppler temperature feedback lead to significant differences

농업용수 활용을 위한 비피압지하수관정 수온의 시계열 변동특성

박승기,정남수 한국농촌계획학회 2016 농촌계획 Vol.22 No.1

There is a need to analyze unconfined groundwater behavior since the demand of groundwater use has been increasing. While unconfined groundwater temperature is tend to be affected by air temperature, it is hard to find an empirical study in South Korea. In this research, we try to determine the relationship between daily average air temperature and daily average groundwater temperature by time-sequential analysis of groundwater monitoring wells in Galshin basin in Yesan-Gun, Chungcheongnam-Do. In addition, models to estimate groundwater temperature from air temperature were developed. In this research 101-day moving average method with measured air temperature is used to estimate groundwater temperature. To verify the developed model, estimated values of average groundwater temperature with 101 moving average are compared to the measured data from September 10 2007 to September 9 2008. And, Nash-Stucliff Efficiency and Coefficient of Determination were 0.970 and 0.976, therefore it was concluded that the model allowing groundwater temperature estimation from air temperature is with reasonable applicability.

우리나라 강수량과 일평균기온의 시·공간적 특성변화 분석

이원현,홍성현,김영규,정은성 한국방재학회 2011 한국방재학회논문집 Vol.11 No.4

This study analyzed the recent changed temporal and spatial variations of precipitation and daily average temperature in the South Korea. 65 weather stations were grouped, based on their latitudes and longitudes and the recent variable temporal and spatial variations of each latitude and longitude were derived, quantitatively. In addition, the Mann-Kendall trend analysis was used to determine the tendency (upward/downward/no trend) of rainfall and temperature. From these analyses, it was shown that the precipitation of zone 1 (33°-34°) has increased by 7% and the rate of increase showed 5%∼18% as the latitude went up. During summer, the rate of precipitation increase has increased as the latitude went up. Due to the rapid increase of summer, the rate of precipitation increase has increased as the longitude went up. On the whole, average temperature has been increased as the latitude went up. The Mann-Kendall trend analysis derived that the temperature of South Korea has increased except zone 2 (34°-35°)and summer period and the precipitation on latitude 36°∼38° and longitude 126°∼130° has increased during summer. Since this study showed the recent climate change trend in detail, it will be a preliminary data for the research of climate change adaptation. 본 연구는 1991년 이전부터 관측을 시작한 65개 기상청 관측소의 강수량과 평균기온 자료를 이용하여 2000년 이전으로 대표되는 과거 자료와 2001년 이후로 대표되는 최근 자료를 계절별로 분석하여 시·공간적 특성을 분석하였다. 관측소를 위도, 경도별로 각각 분류하여 강수량과 일평균기온의 특성을 2000년 이전과 이후에 대해 비교하였다. 또한 증감 여부를 확인하기 위해 가장 많이 사용되는 Mann-Kendall 경향성 분석 기법을 적용하였다. 위도별 분석 결과 일평균강수량의 경우 33°∼34°(제주도)에서는 7%이상의 증가율을 보였고 남부지방에서 북부지방으로 위도가 올라갈수록 증가율이 5%∼18%까지 증가하였다. 여름의 경우 계절별로 살펴보면, 위도가 증가함에 따라 강수량의 증가율도 증가하였다. 경도별 분석 결과 130°∼131°(울릉도)에서 평균적으로 30%이상의 증가율을 보였고 서에서 동쪽으로 갈수록 증가율의 추이가 여름철의 증가 경향으로 인해 증가한다는 것을 알 수 있다. 평균 기온은 위도가 39°∼40° 가을철과 겨울철의 기온차가 최대 1.0℃ 이상 증가하는 추이를 보이고 있으며 경도가 129°∼130°에서 특징적으로 기온이 상승했다. 또한 경향성 분석결과 일평균기온의 경우 일부 지역(34°∼35°)과 여름철을 제외하면 전국적으로 봄, 가을, 겨울에 증가하는 경향이 나타났으며, 강수량의 경우 여름철에 36°∼38°, 126°∼130° 지역에 집중적으로 증가하는 경향을 보였다. 본 연구의 결과는 최근 우리나라 기후변화 경향을 구체적으로 제시하고 있으므로 기후변화 대비 적응 연구의 기초자료로 활용될 수 있다.

Analytical Prediction of Flow Stress on Aluminum Alloy/ Self-Reinforced Polypropylene Laminated Sheet Material Considering Temperature-Dependent Material Constants

박으뜸,이병언,강동식,김정,강범수,송우진 한국정밀공학회 2016 International Journal of Precision Engineering and Vol.17 No.4

A flow stress model is developed prior to a material formability evaluation using analytical analysis. However, some existing models do not consider the effects of temperature on the flow stress, while others utilize a complicated process to predict the temperaturedependent behavior. Previously, the modified Hollomon and modified Ludwik models were proposed as flow stress models that incorporate the effects of temperature, but that involve relatively simple processes. However, in those models, the material constants are formulated as temperature-dependent linear equations only. In this study, material constant equations (the yield stress, strength coefficient, and work hardening exponent) based on the modified Ludwik model are obtained for a laminated sheet composed of an aluminum alloy and self-reinforced polypropylene (SRPP); these expressions are then examined in detail using nonlinear regression analysis. Newly modified models are created, in which the material constants are modeled using combinations of quadratic and exponential temperature-dependent equations. Then, the previous and newly modified models are evaluated by comparing their average maximum absolute errors and R-squared errors against experimental data. Hence, the best-fitted flow stress models are determined. Models comprising a combination of quadratic equations, or a combination of exponential (yield stress) and quadratic equations, yield the greatest accuracy.

Steady- and Transient-State Analyses of Fully Ceramic Microencapsulated Fuel with Randomly Dispersed Tristructural Isotropic Particles via Two-Temperature Homogenized Model-I: Theory and Method

이윤희,BUM HEE CHO,조남진 한국원자력학회 2016 Nuclear Engineering and Technology Vol.48 No.3

As a type of accident-tolerant fuel, fully ceramic microencapsulated (FCM) fuel was proposedafter the Fukushima accident in Japan. The FCM fuel consists of tristructural isotropic particlesrandomly dispersed in a silicon carbide (SiC) matrix. For a fuel element with such highheterogeneity, we have proposed a two-temperature homogenized model using the particletransport Monte Carlo method for the heat conduction problem. This model distinguishesbetween fuel-kernel and SiC matrix temperatures. Moreover, the obtained temperatureprofiles are more realistic than those of other models. In Part I of the paper, homogenizedparameters for theFCM fuel in which tristructural isotropic particles are randomly dispersedin the fine lattice stochastic structure are obtained by (1) matching steady-state analyticsolutions of the model with the results of particle transport Monte Carlo method for heatconduction problems, and (2) preserving total enthalpies in fuel kernels and SiC matrix. Thehomogenized parameters have two desirable properties: (1) they are insensitive to boundaryconditions such as coolant bulk temperatures and thickness of cladding, and (2) they areindependent of operating power density. By performing the Monte Carlo calculations withthe temperature-dependent thermal properties of the constituent materials of the FCM fuel,temperature-dependent homogenized parameters are obtained.

공기유동에 대한 고온상태의 비원형 도과내에서의 열전달 및 압력강하의 측정

이동렬 한국마린엔지니어링학회 2001 한국마린엔지니어링학회지 Vol.25 No.3

Measurement of average of heat transfer and friction coefficients were obtained with air flowing through electrically heated ducts having square, rectangular(aspect ration, 5), and triangular cross section for range of surface temperature from $540^{\circ}$to $1780^{\circ}$ R and Reynolds number from 1000 to 330,000. The results indicates that the effect of heat flux on correlations of the average heat transfer and friction coefficients is similar to that obtained for circular tubes in previous investigation and was nearly eliminated by evaluating the physical properties and density of the air a film temperature halfway between the average surface and fluid bulk temperatures, With the Nusselt and Reynolds numbers on the hydraulic diameter of the ducts, the data for the noncircular ducts could be represented by the same equations obtained in the previous investigation for circular tubes. Correlation of the average difference between the surface corner and midwall temperatures for the square duct was in agreement with predicted values from a previous analysis. However, for the rectangular and triangular ducts, the measured corner temperature was greater by approximately 20 and 35 percent, respectively, than the values predicted by analysis.

WARM FEELING EVALUATION OF HEAT STORAGE FABRIC USING AN INFRARED THERMOGRAPHY CAMERA

Jung Soon Lee,Myoung-Ok Kim 글로벌지식마케팅경영학회 2015 Global Fashion Management Conference Vol.2015 No.06

Clothing comfort indicates the comfortableness of the in varying environmental situations while wearing specific clothing. Various factors affect clothing comfort such as skin moisture perception and heat transmission characteristics via clothing; however, cool and warm touch are the most important factors (Kwon, Yi, & Sung,1999; Hong & Kim, 2007; Manshahia & Das, 2014). The thermal comfort of clothing is perceived through sensory receptors on the skin surface and is highly related to a cool and warm touch. An infrared thermography camera detects infrared-ray-form energy, a type of electromagnetic wave radiated from the subject's surface that assesses the intensity of radiant heat. The changing intensity then presents a real-time infrared thermal distribution using various colors. The advantages of an infrared thermography camera are the ability to use a non-contacting method to measure temperature distribution and analyze temperatures. Therefore, an infrared thermography camera is widely used in material characteristic assessment, boiler heat distribution analysis, process control, and building insulation assessments that indicate system deficiencies. This technique has also recently been used in human-body-related temperature measurements with potential for application to medical fields that include breast cancer examinations, joint muscle disorders, and body reactions under specific conditions. The most significant advantage of infrared thermography cameras to evaluate heat conductivity according to wearing conditions are its inexpensive price, ease-of-use and visual representation of surface heat dispersion on clothing that maintains body temperature and helps dissipate sweat(B. Lee, Hong, & Y. Lee, 2010; Lee, K. Hong, & S. A. Hong, 2007). This technique is also used in a quantitative analysis of thermal sensation when wearing clothes (Choi & Lee, 2008). This study helps develop a method to evaluate the warm feeling of fabrics using an infrared thermal image of a small test specimen. An infrared thermal image helped develop5 types of fabrics for heat storage fabric; consequently, the average temperature difference of the human palm when the fabric is on or off was used for the scale of the fabrics’ warm feeling. The relationshipbetween this average temperature difference on the palm surface Qmax, and warmth keep-ability rate was examined. Fabric had a significant average temperature difference in the infrared thermal image with alow Qmax value and was evaluated with high values in the warmth keep-ability rate. Infrared thermography camera was shown to be effective in the fabric's warm feeling evaluation.