• 한국산업정보학회논문지
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• 제25권5호
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• pp.31-39
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• 2020

후쿠시마 원전사고의 교훈으로 사고단계별 다양한 방사선 탐사 수단을 이용하여 포괄적인 환경방사선을 측정하는 것이 효율적인 사고대응과 위험관리를 위하여 바람직하다. 본 연구에서는 드론 등의 무인기를 이용한 환경방사선 탐사 기술 현황으로 분광분석이 가능한 고분해능의 방사선 검출기 2대를 활용한 환경방사선 탐사시스템을 개발하고, 이를 무인기에 장착하여 직접 사고현장에 적용함으로써 그 성능을 평가하였다. 최종적으로 다양한 비행고도에서의 탐사결과를 지상 1m 높이에서의 선량률로 환산하기 위한 보정인자를 도출함으로써 성공적인 현장 적용성 평가 결과를 도출할 수 있었다.

• Journal of Radiation Protection and Research
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• 제42권1호
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• pp.42-47
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• 2017

Background: One of the most urgent issues following the accident at the Fukushima Daiichi nuclear power plant (FDNPP) was the remediation of the land, in particular, for residential area contaminated by the radioactive materials discharged. In this study, the effect of decontamination on reduction of ambient dose equivalent outdoors and indoors was evaluated. The latter is essential for residents as most individuals spend a large portion of their time indoors. Materials and Methods: From December 2012 to November 2014, thirty-seven Japanese single-family detached wooden houses were investigated before and after decontamination in evacuation zones. Outdoor and indoor dose measurements (n = 84 and 114, respectively) were collected based on in situ measurements using the NaI (Tl) scintillation surveymeter. Results and Discussion: The outdoor ambient dose equivalents [$H^*(10)_{out}$] ranged from 0.61 to $3.71{\mu}Sv\;h^{-1}$ and from 0.23 to $1.32{\mu}Sv\;h^{-1}$ before and after decontamination, respectively. The indoor ambient dose equivalents [$H^*(10)_{in}$] ranged from 0.29 to $2.53{\mu}Sv\;h^{-1}$ and from 0.16 to $1.22{\mu}Sv\;h^{-1}$ before and after decontamination, respectively. The values of reduction efficiency (RE), defined as the ratio by which the radiation dose has been reduced via decontamination, were evaluated as $0.47{\pm}0.13$, $0.51{\pm}0.13$, and $0.58{\pm}0.08$ ($average{\pm}{\sigma}$) when $H^*(10)_{out}$ < $1.0{\mu}Sv\;h^{-1}$, $1.0{\mu}Sv\;h^{-1}$ < $H^*(10)_{out}$ < $2.0{\mu}Sv\;h^{-1}$, and $2.0{\mu}Sv\;h^{-1}$ < $H^*(10)_{out}$, respectively, indicating the values of RE increased as $H^*(10)_{out}$ increased. It was found that the values of RE were $0.53{\pm}0.12$ outdoors and $0.41{\pm}0.09$ indoors, respectively, indicating RE was larger outdoors than indoors. Conclusion: Indoor dose is essential as most individuals spend a large portion of their time indoors. The difference between outdoors and indoors should be considered carefully in order to estimate residents' exposure dose before their returning home.

• 방사성폐기물학회지
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• 제14권4호
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• pp.423-434
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• 2016

인접 국가인 일본의 후쿠시마 원전에서 극한 자연재해로 인한 중대사고가 발생하면서, 국내에서 중대사고 및 확률론적 안전성 평가 (PSA, Probabilistic Safety Assessment)에 대한 중요성이 재인식되었다. 국내에서는 원전의 소외결말을 평가하는 3단계 PSA에 대한 연구개발이 최근까지 거의 이루어지지 않았다. 본 논문에서는 국외 3단계 PSA 전산코드 중, 미국의 MACCS2 (MELCORE Accident Consequence Code System 2), 유럽의 COSYMA (COde SYstem from Maria) 그리고 일본의 OSCAAR (Off-Site Consequence Analysis code for Atmospheric Releases in reactor accidents)에 대한 간략한 분석과 미국의 MACCS2에 대한 단점 및 한계점 분석을 수행하였다. 국내 외 전문가들에 의해 공통적으로 지적되어 온 MACCS2의 한계점은 다수호기사고와 사용후핵연료 저장조로부터의 방출 모사의 불가능, 그리고 대기확산모델을 단순 가우시안 플륨모델을 기본으로 한다는 것이며, 이중 일부는 MACCS2업데이트 버전을 통해 개선되어 왔다. Food chain 모델의 모사의 제한, 해양 및 수계 확산모델의 부재, 제한된 범위의 경제영향평가 등 또한 개선되어야 할 사항이다. 기술보고의 결과는 국내 3단계 PSA 관련 기술 개발을 위한 기초자료로 활용될 수 있을 것으로 기대된다.

• Journal of Radiation Protection and Research
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• 제41권3호
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• pp.216-221
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• 2016

Background: Very fine radiation-induced aerosol particles are produced in intense radiation fields, such as high-intensity accelerator rooms and containment vessels such as those in the Fukushima Daiichi nuclear power plant (FDNPP). Size measurement of the aerosol particles is very important for understanding the behavior of radioactive aerosols released in the FDNPP accident and radiation safety in high-energy accelerators. Materials and Methods: A combined technique using wire screens and imaging plates was developed for size measurement of fine radioactive aerosol particles smaller than 100 nm in diameter. This technique was applied to the radiation field of a proton accelerator room, in which radioactive atoms produced in air during machine operation are incorporated into radiation-induced aerosol particles. The size of $^{11}C$-bearing aerosol particles was analyzed using the wire screen technique in distinction from other positron emitters in combination with a radioactive decay analysis. Results and Discussion: The size distribution for $^{11}C$-bearing aerosol particles was found to be ca. $70{\mu}m$ in geometric mean diameter. The size was similar to that for $^7Be$-bearing particles obtained by a Ge detector measurement, and was slightly larger than the number-based size distribution measured with a scanning mobility particle sizer. Conclusion: The particle size measuring method using wire screens and imaging plates was successfully applied to the fine aerosol particles produced in an intense radiation field of a proton accelerator. This technique is applicable to size measurement of radioactive aerosol particles produced in the intense radiation fields of radiation facilities.

• Journal of Radiation Protection and Research
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• 제45권4호
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• pp.154-162
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• 2020

Background: Several studies have reported that wild mushrooms contain high amounts of radioactive cesium (137Cs). After the Fukushima Daiichi Nuclear Power Plant Accident, a significantly high concentration of 137Cs has been detected in wild mushrooms, and their consumption may be the cause of the chronic internal exposure of local consumers to radioactivity. Therefore, an accurate evaluation of the internal radioactivity resulting from mushroom ingestion is needed. Materials and Methods: The 137Cs elution rate through the cooking and digestion stages was evaluated using in vitro experiments. The edible mushroom Pleurotus djamor was taken as a sample for the experiments. The mushrooms were cultivated onto solid media containing 137Cs. We evaluated the internal dose based on the actual conditions using the elution rate data. For various cooking methods, the results were compared with those of other wild edible mushrooms. Results and Discussion: From the elution experiment through cooking, we proved that 25%-55% of the 137Cs in the mushrooms was released during soaking, boiling, or frying. The results of a simulated digestion experiment after cooking revealed that almost all the 137Cs in the ingested mushrooms eluted in the digestive juice, regardless of the cooking method. The committed effective dose was reduced by 20%-75% when considering the dissolution through the cooking process. Conclusion: We found that cooking lowers 137Cs concentration in mushrooms, therefore reducing the amount of radioactivity intake. Besides, since there were differences between mushroom types, we demonstrated that the internal exposure dose should be evaluated in detail considering the release of 137Cs during the cooking stages.

• Nuclear Engineering and Technology
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• 제47권3호
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• pp.240-252
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• 2015

In the original licensing application for the prototype fast-breeder reactor, MONJU, the event progression during an unprotected loss of flow (ULOF), which is one of the technically inconceivable events postulated beyond design basis, was evaluated. Through this evaluation, it was confirmed that radiological consequences could be suitably limited even if mechanical energy was released. Following the Fukushima-Daiichi accident, a new nuclear safety regulation has become effective in Japan. The conformity of MONJU to this new regulation should hence be investigated. The objectives of the present study are to conduct a preliminary evaluation of ULOF for MONJU, reflecting the knowledge obtained after the original licensing application through CABRI experiments and EAGLE projects, and to gain the prospect of in-vessel retention for the conformity of MONJU to the new regulation. The preliminary evaluation in the present study showed that no significant mechanical energy release would take place, and that thermal failure of the reactor vessel could be avoided by the stable cooling of disrupted-core materials. This result suggests that the prospect of in-vessel retention against ULOF, which lies within the bounds of the original licensing evaluation and conforms to the new nuclear safety regulation, will be gained.

• Journal of Radiation Protection and Research
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• 제46권1호
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• pp.14-23
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• 2021

Background: For radiological protection and control, the International Commission on Radiological Protection (ICRP) provides the nominal risk coefficients related to radiation exposure, which can be extrapolated using the excess relative risk and excess absolute risk obtained from the Life Span Study of atomic bomb survivors in Hiroshima and Nagasaki with the dose and dose-rate effectiveness factor (DDREF). Materials and Methods: Since it is impossible to directly estimate the radiation risk at doses less than approximately 100 mSv only from epidemiological knowledge and data, support from radiation biology is absolutely imperative, and thus, several national and international bodies have advocated the importance of bridging knowledge between biology and epidemiology. Because of the accident at the Tokyo Electric Power Company (TEPCO)'s Fukushima Daiichi Nuclear Power Station in 2011, the exposure of the public to radiation has become a major concern and it was considered that the estimation of radiation risk should be more realistic to cope with the prevailing radiation exposure situation. Results and Discussion: To discuss the issues from wide aspects related to radiological protection, and to realize bridging knowledge between biology and epidemiology, we have established a research group to develop low-dose and low-dose-rate radiation risk estimation methodology, with the permission of the Japan Health Physics Society. Conclusion: The aim of the research group was to clarify the current situation and issues related to the risk estimation of low-dose and low-dose-rate radiation exposure from the viewpoints of different research fields, such as epidemiology, biology, modeling, and dosimetry, to identify a future strategy and roadmap to elucidate a more realistic estimation of risk against low-dose and low-dose-rate radiation exposure.

• Journal of Radiation Protection and Research
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• 제47권4호
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• pp.204-213
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• 2022

Background: The accident at the Fukushima Daiichi nuclear power plant increased the level of anxiety related to the radioactive contamination of various foods sourced in Japan. Particularly, after the accident, the detection of artificial radionuclides in locally produced foods raised food safety concerns. In this study, the radioactivity concentrations and annual ingestions of ⁴⁰K and ¹³⁷Cs in food products commonly and frequently consumed by the general public were investigated, and the annual effective dose of each was evaluated. Materials and Methods: The 2016-2018 data from the Radiation Safety Management Report released by the Korea Nuclear Safety Technology Center was referenced for the evaluation of the amounts of ⁴⁰K and ¹³⁷Cs contained in food. Using the food-ingestion survey mentioned above as a reference, we selected 62 foods to include in our radioactivity concentration and dose assessment. We also developed a questionnaire and evaluated the responses from the subjects who answered the questionnaire. Results and Discussion: The radioactivity concentration of ¹³⁷Cs was found to be close to or below the level of minimum detectable activity. Additionally, the annual ingestion of 62 foods was 294.77 kg/yr, the effective doses from ⁴⁰K and ¹³⁷Cs were 136.4 and 0.163 μSv/yr, respectively. Conclusion: Thus, the findings confirmed that the effective dose from ⁴⁰K and ¹³⁷Cs in food tends to be lower than the effective dose limit of 1 mSv/yr suggested by the International Commission on Radiological Protection (ICRP) Publication 60. The questionnaire developed in this study is expected to be useful for estimating the annual effective dose status of Korean adults who consume foods containing ⁴⁰K and ¹³⁷Cs.

• Nuclear Engineering and Technology
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• 제56권3호
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• pp.803-811
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• 2024

Nuclear accidents such as Fukushima Daiichi have highlighted the potential of passive safety systems to replace or complement active safety systems as part of the overall prevention and/or mitigation strategies. In addition, passive systems are key features of Small Modular Reactors (SMRs), for which they are becoming almost unavoidable and are part of the basic design of many reactors available in today's nuclear market. Nevertheless, their potential to significantly increase the safety of nuclear power plants still needs to be strengthened, in particular the ability of computer codes to determine their performance and reliability in industrial applications and support the safety demonstration. The PASTELS project (September 2020-February 2024), funded by the European Commission "Euratom H2020" programme, is devoted to the study of passive systems relying on natural circulation. The project focuses on two types, namely the SAfety COndenser (SACO) for the evacuation of the core residual power and the Containment Wall Condenser (CWC) for the reduction of heat and pressure in the containment vessel in case of accident. A specific design for each of these systems is being investigated in the project. Firstly, a straight vertical pool type of SACO has been implemented on the Framatome's PKL loop at Erlangen. It represents a tube bundle type heat exchanger that transfers heat from the secondary circuit to the water pool in which it is immersed by condensing the vapour generated in the steam generator. Secondly, the project relies on the CWC installed on the PASI test loop at LUT University in Finland. This facility reproduces the thermal-hydraulic behaviour of a Passive Containment Cooling System (PCCS) mainly composed of a CWC, a heat exchanger in the containment vessel connected to a water tank at atmospheric pressure outside the vessel which represents the ultimate heat sink. Several activities are carried out within the framework of the project. Different tests are conducted on these integral test facilities to produce new and relevant experimental data allowing to better characterize the physical behaviours and the performances of these systems for various thermo-hydraulic conditions. These test programmes are simulated by different codes acting at different scales, mainly system and CFD codes. New "system/CFD" coupling approaches are also considered to evaluate their potential to benefit both from the accuracy of CFD in regions where local 3D effects are dominant and system codes whose computational speed, robustness and general level of physical validation are particularly appreciated in industrial studies. In parallel, the project includes the study of single and two-phase natural circulation loops through a bibliographical study and the simulations of the PERSEO and HERO-2 experimental facilities. After a synthetic presentation of the project and its objectives, this article provides the reader with findings related to the physical analysis of the test results obtained on the PKL and PASI installations as well an overall evaluation of the capability of the different numerical tools to simulate passive systems.

• Journal of Radiation Protection and Research
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• 제40권4호
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• pp.223-230
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• 2015

공공수역 내 방사성물질 분포특성 파악을 위하여 춘천시 의암호 퇴적물 내 인공방사성핵종인 $^{134}Cs$, $^{137}Cs$, $^{239+240}Pu$과 자연방사성동위원소인 $^{210}Pb$을 분석하였고, 퇴적물 내 유기물의 특성을 파악하기 위하여 총 유기탄소(total organic carbon, TOC)를 분석하였다. 의암호 퇴적물 내 $^{134}Cs$ 농도는 4지점 모두 minimum detectable activity(MDA) 미만으로 나타났으며, $^{137}Cs$ 농도는 $MDA{\sim}8.79Bq{\cdot}kg^{-1}-dry$으로 나타났다. 표층 내 $^{137}Cs$의 농도는 $2.4{\sim}4.2Bq{\cdot}kg^{-1}-dry$의 범위를 나타냈고, St. 4에서 최소값, St. 3에서 최대값을 보였다. 의암호 퇴적물 내 $^{239+240}Pu$ 농도는 $0.049{\sim}0.47Bq{\cdot}kg^{-1}-dry$의 농도를 보였고, St. 2에서 최소값이, St. 3에서 최대값이 나타났다. $^{239+240}Pu$과 $^{137}Cs$ 농도의 상관관계 (r)는 0.54~0.97로 이들 두 핵종의 퇴적물 내 거동과 기원이 유사한 것으로 사료된다. $^{134}Cs$의 농도가 MDA 미만으로 검출된 점과 $^{239+240}Pu/^{137}Cs$의 평균값 0.041이 과거 대기 핵실험기원의 농도 비와 비슷한 값이 나타나는 점으로 의암호 퇴적물 내 인공방사성동위원소 ($^{134}Cs$, $^{137}Cs$, $^{239+240}Pu$)의 기원은 후쿠시마 사고가 아닌 과거 핵실험에 인한 낙진의 영향으로 사료된다. 의암호 퇴적물 내 $^{210}Pb$의 결과를 이용하여 퇴적물의 퇴적률을 산출한 결과, St. 2에서 $0.31{\pm}0.06cm{\cdot}y^{-1}$의 퇴적률을 나타냈으며, 이는 $^{137}Cs$의 퇴적물 내 peak를 1963년으로 가정하였을 때 측정된 퇴적률, $0.41{\pm}0.05cm{\cdot}y^{-1}$와 불확도($2{\sigma}$)의 범위에서 유사한 값으로 나타내었다. 의암호 퇴적물 내 TOC는 0.20~13.01%의 값이 나타났으며, 퇴적물 내 TOC와 $^{137}Cs$의 상관관계는 St. 1에서 다른 지점에 비해 높게 나타났다.