• 방사성폐기물학회지
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• 제18권3호
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• pp.347-354
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• 2020

Site characterization for decommissioning Kori Unit 1 is ongoing in South Korea after 40 years of successful operation. Kori Unit 1's containment building is assumed to be mostly radioactively contaminated, and therefore radiation exposure management and detailed contamination investigation are required for decommissioning and dismantling it safely. In this study, site-specific Derived Concentration Guideline Levels (DCGLs) were derived using the residual radioactivity risk evaluation tool, RESRAD-BUILD code. A conceptual model of containment building for Kori Unit 1 was set up and limited occupational worker building inspection scenario was applied. Depending on the source location, the maximum contribution source and exposure pathway of each radionuclide were analyzed. The contribution of radionuclides to dose and exposure pathways, by source location, is expected to serve as basic data in the assessment criteria of survey areas and classification of impact areas during further decommissioning and decontamination of sites.

• 대한방사선기술학회지:방사선기술과학
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• 제43권5호
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• pp.343-351
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• 2020

This study analyzed dose reduction and quality of images through dose reduction tools and shielding board to protect sensitive eye lens in radiation during orbit CT examinations for clinical data use. During CT scans of the phantom, surface dose (CT scanner dosimetry phantom, ion chamber-3 times) and quality of image (radiosurgery head phantom, visual assessment-2 times, HU standard deviation) were evaluated using X-care which is dose reduction tools and bismuth shielding board. The results of experiments of eight conditions showed a relatively reduced dose in all other conditions compared to when no conditions were set. In particular, the area corresponding to the ophthalmic part reduced the surface dose by up to 45.7 %. The visual evaluation of images by specialists and the quality evaluation of images analyzed by HU standard deviation were clinically closest to the use of X-care and shielding board (1 cm in height). Therefore, it is believed that the use of shielding board in a suitable location with dose reduction tools while investigating the optimal radiation dose will reduce the exposure dose of sensitive lens at radiation while maintaining the quality of the images with high diagnostic value.

• Safety and Health at Work
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• 제12권2호
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• pp.174-183
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• 2021

Background: Toluene diisocyanate (TDI) is a highly reactive chemical that causes sensitization and has also been associated with increased lung cancer. A risk assessment was conducted based on occupational epidemiologic estimates for several health outcomes. Methods: Exposure and outcome details were extracted from published studies and a NIOSH Health Hazard Evaluation for new onset asthma, pulmonary function measurements, symptom prevalence, and mortality from lung cancer and respiratory disease. Summary exposure-response estimates were calculated taking into account relative precision and possible survivor selection effects. Attributable incidence of sensitization was estimated as were annual proportional losses of pulmonary function. Excess lifetime risks and benchmark doses were calculated. Results: Respiratory outcomes exhibited strong survivor bias. Asthma/sensitization exposure response decreased with increasing facility-average TDI air concentration as did TDI-associated pulmonary impairment. In a mortality cohort where mean employment duration was less than 1 year, survivor bias pre-empted estimation of lung cancer and respiratory disease exposure response. Conclusion: Controlling for survivor bias and assuming a linear dose-response with facility-average TDI concentrations, excess lifetime risks exceeding one per thousand occurred at about 2 ppt TDI for sensitization and respiratory impairment. Under alternate assumptions regarding stationary and cumulative effects, one per thousand excess risks were estimated at TDI concentrations of 10 - 30 ppt. The unexplained reported excess mortality from lung cancer and other lung diseases, if attributable to TDI or associated emissions, could represent a lifetime risk comparable to that of sensitization.

• 한국콘텐츠학회논문지
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• 제18권1호
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• pp.232-240
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• 2018

본 연구는 자동노출제어장치의 감도변화에 따른 흡수선량의 변화와 히스토그램을 이용하여 검출기 성능평가 방법을 제안하고자 하였다. 실험방법은 두개부, 복부, 골반부위 별로 검출기 감도 S200, S400, S800, S1000의 흡수선량을 측정하여 검출기의 정확성을 평가하였다. 또한 영상의 히스토그램 분석을 통하여 검출기의 감도별 동적범위를 평가하였다. 그 결과 부위 별 흡수선량은 감도가 S200에서 S1000으로 높게 설정될수록 흡수선량이 단계적으로 감소하였다. 감도 별 히스토그램을 분석한 결과 두개부는 감도가 높게 설정될수록 히스토그램의 양단의 정보량이 상실되는 결과를 보였다. 복부와 골반부는 감도가 높게 설정될수록 히스토그램의 첫부분의 정보량이 상실되는 언더플로우 현상을 보였다. 결론적으로 검출기가 감도의 변화는 정확하게 구현해 내었으나 검출기 성능저하로 인한 자동노출제어장치의 감도변화에 따른 영상의 동적범위는 제대로 구현해내지 못한다는 것을 알 수 있었고 검출기의 성능평가 시 흡수선량과 히스토그램을 통한 평가가 유용하다는 것을 알 수 있었다.

• Nuclear Engineering and Technology
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• 제52권9호
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• pp.2085-2091
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• 2020

The license for Kori-1, the first commercial reactor in Busan, Korea, was terminated in June 2017; therefore, preparations are being made for its decommissioning. Because the radioactivity of Bio-shield varies greatly throughout the structure, the doses received by the workers depend on the location, order, and duration of dismantling operations. Thus, a model for evaluating the worker external dose during the dismantling of the Kori-1 bio-shield was developed, and work scenarios for dose assessment were designed. The Dose evaluation code VISIPLAN was used for dose assessment. The dose rate around the bio-shield was evaluated and the level of exposure to the operator was evaluated according to the work scenario. The maximum annual external dose was calculated as 746.86 mSv for a diamond wire saw operator under dry cutting conditions, indicating that appropriate protective measures, such as changing dismantling sequence, remote monitoring, shield installation, and adjustment of work team are necessary for the safe dismantling of the bio-shield. Through these protective measures, it was found that the worker's dose could be below the dose limit.

• 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.

• 한국방사선학회논문지
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• 제16권3호
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• pp.351-356
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• 2022

전립선암의 방사선치료 시 사용되는 세기조절방사선치료와 부피적회전방사선치료시 발생하는 광중성자선량을 측정하여, 암 발생률을 평가하며 기초자료를 제공하고자 하였다. Rando phantom에 중성자 측정용 광자극발광선량계를 복부와 갑상선에 위치시킨 상태에서 발생하는 광중성자선량을 측정하였다. 연구결과 세기조절방사선치료(7 portal)가 부피적회전방사선치료보다 복부와 갑상선 위치에서 모두 높게 측정되었다. ICRP 103의 명목위험계수를 이용하여 암 발생확률을 평가하였을 때, 세기조절방사선치료시 대장과 갑상선의 피폭으로 인한 암발생확률은 1,000명 당 9.9명 이었으며, 부피적회전방사선치료시는 1,000명 당 3.5명이었다. ALARA(As low as reasonably archievable)원칙에 의거하여 방사선치료계획 수립에 있어서 정상장기들의 피폭선량의 최소화를 위한 가이드라인이 되리라 사료된다.

• 한국산학기술학회논문지
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• 제4권3호
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• pp.223-229
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• 2003

ICRP-60 신권고에 맞게 수정된 방사선피폭선량 계산프로그램인 K-DOSE 60을 4개 발전소 (고리, 월성, 울진, 영광)에 적용하여 주변주민 최대개인피폭선량을 평가하였다 핵종, 장기, 경로별로 결정변수값들을 도출한 결과, 경로는 성인의 경우 농작물, 유아의 경우 우유가, 핵종은 ³H, /sup 133/Xe, /sup 60/Co (고리 1,2발전소), /sup 14/C, /sup 41/Ar(월성 1,2발전소)로 나타났으며, 모든 장기에 대한 피폭선량차이가 매우 작았다. "출력 대 입력" 변동에 근거한 민감도 분석결과, 핵종의 화학적 형태가 타 입력변수들보다 10² factor만큼 높은 민감도를 보였으며, 전이/농축계수에 의한 민감도는 섭취량이나 방출량의 그것에 비하여 상대적으로 매우 낮았다. PCC를 이용한 상관성 민감도의 경우는 4가지 입력변수 모두 0.97 이상의 높은 상관성을 보였다.

• Journal of Radiation Protection and Research
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• 제46권4호
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• pp.184-193
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• 2021

Background: The radionuclides released by the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident 9 years ago are still being monitored by various research teams and the Japanese government. Comparison of different surveys' results could help evaluate the exposure doses and the mechanism of radiocesium behavior in the urban environment in the area. In this study, we clarified the relationship between land use and temporal changes in the ambient dose rates (air dose rates) using big data. Materials and Methods: We set a series of 1 × 1 km² meshes within the 80 km zone of the FDNPP to compare the different survey results. We then prepared an analysis dataset from all survey meshes to analyze the temporal change in the air dose rate. The selected meshes included data from all survey types (airborne, fixed point, backpack, and carborne) obtained through the all-time survey campaigns. Results and Discussion: The characteristics of each survey's results were then evaluated using this dataset, as they depended on the measurement object. The dataset analysis revealed that, for example, the results of the carborne survey were smaller than those of the other surveys because the field of view of the carborne survey was limited to paved roads. The location factor of different land uses was also evaluated considering the characteristics of the four survey methods. Nine years after the FDNPP accident, the location factor ranged from 0.26 to 0.49, while the half-life of the air dose rate ranged from 1.2 to 1.6. Conclusion: We found that the decreasing trend in the air dose rate of the FDNPP accident was similar to the results obtained after the Chernobyl accident. These parameters will be useful for the prediction of the future exposure dose at the post-accident.

• 대한방사선기술학회지:방사선기술과학
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• 제46권2호
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• pp.131-139
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• 2023

High-dose I-131 used for the treatment of thyroid cancer causes localized exposure among radiology technologists handling it. There is a delay between the calibration date and when the dose of I-131 is administered to a patient. Therefore, it is necessary to directly measure the radioactivity of the administered dose using a dose calibrator. In this study, we attempted to apply machine learning modeling to measured external dose rates from shielded I-131 in order to predict their radioactivity. External dose rates were measured at 1 m, 0.3 m, and 0.1 m distances from a shielded container with the I-131, with a total of 868 sets of measurements taken. For the modeling process, we utilized the hold-out method to partition the data with a 7:3 ratio (609 for the training set:259 for the test set). For the machine learning algorithms, we chose linear regression, decision tree, random forest and XGBoost. To evaluate the models, we calculated root mean square error (RMSE), mean square error (MSE), and mean absolute error (MAE) to evaluate accuracy and R² to evaluate explanatory power. Evaluation results are as follows. Linear regression (RMSE 268.15, MSE 71901.87, MAE 231.68, R² 0.92), decision tree (RMSE 108.89, MSE 11856.92, MAE 19.24, R² 0.99), random forest (RMSE 8.89, MSE 79.10, MAE 6.55, R² 0.99), XGBoost (RMSE 10.21, MSE 104.22, MAE 7.68, R² 0.99). The random forest model achieved the highest predictive ability. Improving the model's performance in the future is expected to contribute to lowering exposure among radiology technologists.