• 설비공학논문집
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• 제21권11호
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• pp.606-612
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• 2009

Interzonal air movements are important to characterize overall ventilation performance of complicated multi-zone buildings. Tracer gas techniques are widely used to measure ventilation rates, ventilation effectiveness, and interzonal air movements. Depending on the number of gases used, they are divided into single and multi tracer gas methods. This paper deals with the comparison of the tracer gas methods in measuring air exchange rate between rooms. Experiments have been conducted in a simple two-room model with known airflow rates. In multi-gas procedure, the concentration decays of two tracer gases, i.e SF6 and R134a are measured after simultaneous injections in each room. The single tracer gas method is also applied by injecting SF6 gas with a time lag between two rooms. The data reduction procedures are developed to obtain the interzonal airflow rate using the matrix inversion, and various data manipulation methods are tested, such as data shift, interpolation, and smoothing. Uncertainty for each airflow rate is investigated depending on the parameters based on the setting values.

• Nuclear Engineering and Technology
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• 제46권4호
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• pp.547-556
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• 2014

Korea expects a shortage in storage capacity for spent fuels at reactor sites. Therefore, a need for more metal and/or concrete casks for storage systems is anticipated for either the reactor site or away from the reactor for interim storage. For the purpose of interim storage and transportation, a dual purpose metal cask that can load 21 spent fuel assemblies is being developed by Korea Radioactive Waste Management Corporation (KRMC) in Korea. At first the gamma and neutron flux for the design basis fuel were determined assuming in-core environment (the temperature, pressure, etc. of the moderator, boron, cladding, $UO_2$ pellets) in which the design basis fuel is loaded, as input data. The evaluation simulated burnup up to 45,000 MWD/MTU and decay during ten years of cooling using the SAS2H/OGIGEN-S module of the SCALE5.1 system. The results from the source term evaluation were used as input data for the final shielding evaluation utilizing the MCNP Code, which yielded the effective dose rate. The design of the cask is based on the safety requirements for normal storage conditions under 10 CFR Part 72. A radiation shielding analysis of the metal storage cask optimized for loading 21 design basis fuels was performed for two cases; one for a single cask and the other for a $2{\times}10$ cask array. For the single cask, dose rates at the external surface of the metal cask, 1m and 2m away from the cask surface, were evaluated. For the $2{\times}10$ cask array, dose rates at the center point of the array and at the center of the casks' height were evaluated. The results of the shielding analysis for the single cask show that dose rates were considerably higher at the lower side (from the bottom of the cask to the bottom of the neutron shielding) of the cask, at over 2mSv/hr at the external surface of the cask. However, this is not considered to be a significant issue since additional shielding will be installed at the storage facility. The shielding analysis results for the $2{\times}10$ cask array showed exponential decrease with distance off the sources. The controlled area boundary was calculated to be approximately 280m from the array, with a dose rate of 25mrem/yr. Actual dose rates within the controlled area boundary will be lower than 25mrem/yr, due to the decay of radioactivity of spent fuel in storage.

• Journal of Radiation Protection and Research
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• 제42권3호
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• pp.158-165
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• 2017

Background: Nuclear facilities in South Korea have generally adopted pressurized ion chambers to measure ambient gamma ray exposure rates for monitoring the impact of radiation on the surrounding environment. The rates assessed with pressurized ion chambers do not distinguish between natural and man-made radiation, so a further step is needed to identify the cause of abnormal variation. In contrast, using NaI(Tl) scintillation detectors to detect gamma energy rates can allow an immediate assessment of the cause of variation through an analysis of the energy spectra. Against this backdrop, this study was conducted to propose a more effective way to monitor ambient gamma exposure rates. Materials and Methods: The following methods were used to analyze gamma energy spectra measured from January to November 2016 with NaI detectors installed at the Korea Atomic Energy Research Institute (KAERI) dormitory and Hanbat University. 1) Correlations of the variation of rates measured at the two locations were determined. 2) The dates, intervals, duration, and weather conditions were identified when rates increased by $5nSv{\cdot}h^{-1}$ or more. 3) Differences in the NaI spectra on normal days and days where rates spiked by $5nSv{\cdot}h^{-1}$ or more were studied. 4) An algorithm was derived for automatically calculating the net variation of the rates. Results and Discussion: The rates measured at KAERI and Hanbat University, located 12 kilometers apart, did not show a strong correlation (coefficient of determination = 0.577). Time gaps between spikes in the rates and rainfall were factors that affected the correlation. The weather conditions on days where rates went up by $5nSv{\cdot}h^{-1}$ or more featured rainfall, snowfall, or overcast, as well as an increase in peaks of the gamma rays emitted from the radon decay products of $^{214}Pb$ and $^{214}Bi$ in the spectrum. This study assumed that $^{214}Pb$ and $^{214}Bi$ exist at a radioactive equilibrium, since both have relatively short half-lives of under 30 minutes. Provided that this assumption is true and that the gamma peaks of the 352 keV and 1,764 keV gamma rays emitted from the radionuclides have proportional count rates, no man-made radiation should be present between the two energy levels. This study proved that this assumption was true by demonstrating a linear correlation between the count rates of these two gamma peaks. In conclusion, if the count rates of these two peaks detected in the gamma energy spectrum at a certain time maintain the ratio measured at a normal time, such variation can be confirmed to be caused by natural radiation. Conclusion: This study confirmed that both $^{214}Pb$ and $^{214}Bi$ have relatively short half-lives of under 30 minutes, thereby existing in a radioactive equilibrium in the atmosphere. If the gamma peaks of the 352 keV and 1,764 keV gamma rays emitted from these radionuclides have proportional count rates, no man-made radiation should exist between the two energy levels.

• 한국식품저장유통학회지
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• 제11권3호
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• pp.304-312
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• 2004

감귤의 수확 후 저장, 유통과정에서 부패 억제 및 품질유지 효과를 얻기 위하여 환경친화적 방법으로서 중-고온 예조처리의 적용 가능성을 확인하고자, 조생종 온주 감귤의 열풍처리에 따른 저장 중 품질특성 변화를 살펴보았다. 45$^{\circ}C$에서 2, 4, 6시간 동안 열풍을 가한 다음, 충분히 냉각시킨 감귤을 통기성 천공 LDPE 필름에 포장하여 5$^{\circ}C$에서 3주, 18$^{\circ}C$에서 1주간저장하면서 호흡률, 과실내부 기체조성,pH, 산도, 가용성 고형분 함량, 과피 표면색, 생체 중량 감소율, 경도, 부패과 발생률, 관능특성 등을 평가하였다. 열풍처리 직후 초기 호홉률은 처리구 모두 무처리구와 비교하여 높았으나 처리시간과는 유의적 상관성이 없었고, 저장 중처구 감귤의 호흡률은 감소하여 21일째는 무처리구와 유사한 수준을 나타내었다. 과실내부 기체조성은 처리구간에 유의적인 차이를 보이지 않았으며, 과즙의 pH, 산도, 가용성 고형분 함량 및 과실의 생체 중량감소와 경도, 과피 표면색 역시 열처리에 의해 거의 영향을 받지 않았다. 한편 부패과 발생률에 있어서는 4시간 이상의 처리구가 꼭지 썩음 현상과 곰팡이 발생정도, 검은 썩음병인 표피 흑변 정도에서 저장 중 낮은 수준을 나타내었다. 그러나 외관품질 및 체감품질에 대한 관능평가에서는 열풍처리구와 무처리구 사이에서의 유의적인 차이를 발견할 수 없었다. 결론적으로 45$^{\circ}C$, 4-6시간의 제한적 열풍처리는 조생 온주 감글의 저장 중 부패과 발생률을 현저히 감소시킴으로서 수확 후 품질유지에 효과적인 중-고온 예조처리 조건임을 확인할 수 있었다.

• Journal of Radiation Protection and Research
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• 제44권4호
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• pp.128-148
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• 2019

Massive environmental monitoring has been conducted continuously since the Fukushima Daiichi Nuclear Power accident in March of 2011 by different monitoring methods that have different features together with migration studies of radiocesium in diverse environments. These results have clarified the characteristics of radiological environments and their temporal change around the Fukushima site. At three months after the accident, multiple radionuclides including radiostrontium and plutonium were detected in many locations; and it was confirmed that radiocesium was most important from the viewpoint of long-term exposure. Radiation levels around the Fukushima site have decreased greatly over time. The decreasing trend was found to change variously according to local conditions. The air dose rates in environments related to human living have decreased faster than expected from radioactive decay by a factor of 2-3 on average; those in pure forest have decreased more closely to physical decay. The main causes of air dose rate reduction were judged to be radioactive decay, movement of radiocesium in vertical and horizontal directions, and decontamination. Land-use categories and human activities have significantly affected the reduction tendency. Difference in the air dose rate reduction trends can be explained qualitatively according to the knowledge obtained in radiocesium migration studies; whereas, the quantitative explanation for individual sites is an important future challenge. The ecological half-lives of air dose rates have been evaluated by several researchers, and a short-term half-life within 1 year was commonly observed in the studies. An empirical model for predicting air dose rate distribution was developed based on statistical analysis of an extensive car-borne survey dataset, which enabled the prediction with confidence intervals. Different types of contamination maps were integrated to better quantify the spatial data. The obtained data were used for extended studies such as for identifying the main reactor that caused the contamination of arbitrary regions and developing standard procedures for environmental measurement and sampling. Annual external exposure doses for residents who intended to return to their homes were estimated as within a few millisieverts. Different forms of environmental data and knowledge have been provided for wide spectrum of people. Diverse aspects of lessons learned from the Fukushima accident, including practical ones, must be passed on to future generations.

• 대한환경공학회지
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• 제37권7호
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• pp.387-395
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• 2015

본 논문에서는 Graphical Statistic Analysis (GSA) 방법을 이용하여 유기성 폐자원의 최종생분해도와 다중 분해속도를 평가하였다. GSA에 의한 최종생분해도는 돈분뇨 69%, 젖소 생분뇨 45%, 도축폐기물 66%를 나타냈고 음식물류 폐기물과 음폐수는 각각 79%와 87%이었으며, 1차 슬러지와 폐활성 슬러지는 각각 68%와 39%이었다. 유기성 폐자원의 분해양상을 정확히 표현하기 위하여 사용된 다중분해속도해석(Multi k Analysis) 방법을 이용해 평가한 결과 돈분뇨는 $k_1$ ($0.116day^{-1}$)의 속도로 평균 31일 안에 전체 생분해성 유기물 중 빠르게 분해되는 분율($S_1$)인 89%가 분해되었으며, 느리게 분해되는 $S_2$의 분율은 11%로써 $k_2$ ($0.004day^{-1}$)의 속도로 남은 기간 동안 분해되었다. 젖소 생분뇨는 $k_1$ ($0.074day^{-1}$)의 속도로 평균 29일 안에 분해되었으며 $S_1$의 분율은 91%이었다. 도축폐기물과 1차 슬러지는 $k_1$ ($0.095day^{-1}$)의 같은 속도로 분해되었으며, $S_1$은 각각 89%와 85%를 보였다. 음식물류 폐기물과 음폐수는 15일의 운전기간 동안 $S_1$은 각각 89%와 93%로 기질의 대부분이 분해되었으며 $k_1$은 각각 $0.195^{-1}$과 $0.184^{-1}$로 대단히 빠른 속도로 분해되었다. 폐활성 슬러지는 $k_1$ ($0.054day^{-1}$)의 속도로 28일 동안 분해되었으며 $S_1$은 80%를 보였다. 따라서 Multi k Analysis 방법을 이용해 유기성 폐자원의 분해 속도와 분해 양상을 토대로 최소 HRT를 산정할 수 있으며, 본 대상시료를 활용한 바이오가스화 시설의 최적 설계인자 도출이 가능하다.

• 한국환경농학회지
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• 제14권1호
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• pp.7-14
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• 1995

하천 수질관리 모델인 QUAL2E를 남강에 적용한 결과는 다음과 같다. 1. 모델변수의 민감도 분석 결과는 BOD, DO의 경우 BOD decay rate constant, 영양염류인 경우 Org-N oxidation rate constant, $NH_3-N$ oxidation rate constant, Org-P decay rate constant가 각 수질인자에 중요한 변수로 작용하였다. 2. 모델보정 결과를 보면 실측치와 예측치의 상관성은 DO, BOD의 경우 r=0.93, 0.94로 높은 상관성을 보였으며 영양염류인 경우는 질산성 질소가 r=0.61이었으나, 그 외는 r=0.90 이상으로 나타났다. 3. 모델검증 결과는 보정시보다 상관성이 떨어졌으나 DO, $NO_3-N$의 경우 r=0.68, 0.45로 낮고 그 외는 r=0.75이상으로 높은 편으로 나타났다. 4. 유량과 부하량의 변화에 대하여 하류 40.5 Km 이후의 BOD 농도변화는 적었으나, 하수종말처리장 건설이후 유량과 부하량을 변화시켜 수질농도를 예측한 결과 하류 40.5 Km 이후는 함안천의 영향을 받을 것으로 예측되었다.

• 환경생물
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• 제19권1호
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• pp.59-69
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• 2001

본 연구는 자연수중의 미생물을 식종원으로 하는 TOC-HANDAI법과 OECD 생분해법을 활용하여 자연수 환경내에서 환경호르몬물질인 비스페놀 A와 노닐페놀의 생분해성을 비교평가하였다. TOC-HANDAI법에 의한 BPA분해는 73-78% 이었고 OECD법은 이보다 다소 높은 77-81%를 나타내었다. 두 방법을 통한 BPA의 분해양상은 대체로 2단계를 거쳐 진행되었다. 즉 초기 1주일 이내에는 분해반응속도(k$_1$)가 0.24-0.34day$^{-1}$로 아주 빠르게 분해되었고, 그 후에는 아주 완만한 분해양상을 나타내었다(k$_2$는 0.02-0.05 $day^{-1}$). 이는 BPA가 자연수계에서 TOC로 약 20-25%가 중간생성물로 잔존하고 있음을 시사해 주고 있으며, 이 중간대사물이 완만한 분해과정에 기여하고 있다. 수계 환경에 따라 분해율이 현저하게 차이를 보이지만 노닐페놀은 20-48% 정도 밖에 분해되지 않는 난분해성 환경호르몬 물질임을 알 수 있다. 한편, 금강수계내 조사대상 하천과 대청호수의 조사지점에서 BPA는 모두 불검출되었다. 그러나 공단폐수 종말처리장 유입수에서 평균 25 ppb가 검출되었다.

• 한국식품과학회지
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• 제29권4호
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• pp.758-763
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• 1997

당도와 ascorbic acid함량이 높은 우수한 신선 과일인 생대추를 장기간 저장하기 위하여 숙도 및 저장온도에 따른 무등품종 대추의 호흡특성, 저장 중 품질변화를 측정하였다. 녹숙 대추와 적숙 대추의 숙도에 따라서 호흡속도는 차이가 없어서 non-climacteric특성으로 간주될 수 있었고, 호흡의 온도의존성에서도 숙도간에 차이가 없었다. 적숙 대추가 녹숙 대추에 비해서 단위과중이 약간 크며, 가용성 고형분 농도와 ascorbic acid 함량이 약간 높았다. 대추는 저장 중 조직의 연화가 먼저 나타난 후 부패가 진행되었다. 대추의 저장 중 연화 및 부패의 진행은 녹숙대추의 경우가 적숙대추에 비해서 늦어서 장기저장을 위해서는 녹숙대추를 저장하는 것이 유리하였다. 저장 중 녹숙 대추의 표면색택은 붉은 색으로 착색이 진행되고 가용성 고형분은 증가하고, 총산과 ascorbic acid 함량은 감소하였다. $-2^{\circ}C,\;0^{\circ}C,\;5^{\circ}C,\;10^{\circ}C,\;20^{\circ}C$에서의 녹숙 대추의 저장실험에서는 $-2^{\circ}C$에서는 저온장해가 발생하였고, $5^{\circ}C$ 이상의 온도에서는 온도가 높을수록 품질변화와 부패가 빨라서, $0^{\circ}C$가 저장적온으로 판단되었다. 저장적온인 $0^{\circ}C$에서 대추는 40일정도 밖에 신선한 상태로 저장될 수 없어서 보다 장기간의 저장이 가능한 포장 기법의 적용이 필요한 것으로 평가되었다.

• Bulletin of the Korean Chemical Society
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• 제23권2호
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• pp.281-285
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• 2002

The photophysical properties and the singlet oxygen generation efficiencies of meso-tetraphenyl-trithiasapphyrin $(S_3TPS)$ and meso-tetmkis(p-methoxy phenyl)-trithiasapphy rin ((p-MeO)-$S_3TPS$) have been investigated, utilizing steady-state and time-resolved spectroscopic methods to elucidate the possibility of their use as photosensitizers for photodynamic therapy (PDT). The observed photophysical properties were compared with those of other porphyrin-like photosensitizers in geometrical and electronic structural aspects, such as extended ${\pi}$ conjugation, structural distortion, and internal heavy atoms. The steady-state electronic absorption and fluorescence spectra were both red-shifted due to the extended ${\pi}$-conjugation. The fluorescence quantum yields were measured as very small. Even though intersystem crossing rates were expected to increase due to the increment of spin orbital coupling, the triplet quantum yields were measured as less than 0.15. Such characteristics can be ascribed to the more enhanced internal conversion rates compared with the intersystem crossing rates. Furthermore, the triplet state lifetimes were shortened to -1.0 ${\mu}s$ as expected. Therefore, the singlet oxygen quantum yields were estimated to be near zero due to the fast triplet state decay rates and the inefficient energy transfer to the oxygen molecule as well as the low triplet quantum yields. The low efficiencies of energy transfer to the oxygen molecule can be attributed to the lower oxidation potential and/or the energetically low lying triplet state. Such photophysical factors should be carefully evaluated as potential photosensitizers that have extended ${\pi}$-conjugation and heavy core atoms synthesized for red-shifted absorption and high triplet state quantum yields.