Earticle

Background: South Korea’s extensive nuclear energy capabilities, driven by 25 operational nuclear power plants (NPPs), have been instrumental in supporting industrial development. However, concerns among antinuclear activists regarding the potential risks associated with nuclear accidents have emerged. To address these concerns, this study evaluated the long-term radiological effects of a nuclear accident on individuals living near an NPP site. In particular, this study focused on the most likely type of accident, a loss of coolant accident (LOCA), assuming that it occurs in a single unit because of the rarity of simultaneous accidents across multiple units. Materials and Methods: The source terms from the LOCA comprising 131I, 134Cs, 137Cs, and 90Sr were computed using the Radiological Assessment System for Consequence AnaLysis code, and these were fed into the GENII code, which computed the annual individual effective doses and cancer incidences at various distances and directions from the NPP. Results and Discussion: The effective dose contributions from food ingestion, ground exposure, and soil particle ingestion were 86.4%, 13.5%, and 0.01%, respectively, in children and adults. Food, particularly vegetables and meat, had the greatest impact on effective doses. Regarding individuals exposed at distances of 3, 16, and 30 km from the NPP, adults received annual effective doses of 98, 19, and 12 mSv, respectively, whereas children received doses of 56, 10, and 6.6 mSv, respectively. Comparison of the computed cancer incidence with South Korea’s past 8-year data resulted in a radiation exposure contribution to cancer of 0.012%, which was significantly below the NPP safety goal of 0.1%. Conclusion: This study suggests that radiation exposure from nuclear accidents has minimal impact on cancer incidence. Therefore, restrictions on vegetable and meat consumption should be implemented after accidents to mitigate the long-term health effects of radiation exposure.

Introduction of the Lagrangian atmospheric dispersion model was considered insteadof the existing Gaussian atmospheric dispersion models for the level 3 probabilistic safety assessmentto reduce uncertainty in the atmospheric dispersion. The objective of the present study was toanalyze atmospheric dispersion behavior, surface deposition, and atmospheric dispersion models. The study was performed using RASCAL computer code, which employs Gaussian plume modeland Gaussian puff model and HYSPLIT computer code, which employs Lagrangian model. Forthe analysis, long-term station blackout accident was assumed. Released radionuclides includedparticle type 137Cs and gaseous type 131I, which are dispersed widely and extensively for nuclearaccident case. Radionuclide emission rate by time resulting from State-of-the-Art Reactor ConsequenceAnalyses project was used as a source term. The atmospheric dispersion behavior and surfacedeposition was analyzed for two case dates, which include a date with average wind speed ofmore than 3 m·s-1 and a date with wind speed of less than 3 m·s-1. For both 137Cs and 131I, atmosphericdispersion directions were roughly similar among three models. However, deposition concentrationof 131I compared with 137Cs was higher by about 100 folds for the Gaussian models andby about 1,000 folds for the Lagrangian model. For 137Cs, deposition concentrations were higherfor Gaussian plume model, Gaussian puff model, and Lagrangian model, in that sequence. For131I, deposition concentrations were generally higher for the Lagrangian model. The difference inthe deposition concentrations can be attributed to differences in the atmospheric concentration byatmospheric dispersion model and dry deposition velocity of released radionuclides. Therefore, it isrequired to study the physico-chemical characteristics of the released radionuclides for more realisticprediction of surface deposition concentration in applying the Lagrangian model instead of theexisting Gaussian plume models in the level 3 PSA. This study results is expected to contribute asan important base data for more realistic prediction of atmospheric

After the Fukushima nuclear power plant accident in March 2011, the importance ofevaluating the consequence of the accident is increasing. Accordingly, in South Korea, the law onsubmission of accident management plans including severe accidents was revised in June 2016 toassess accident management capability through probabilistic safety assessment. In this study, werecognized the necessity of verifying the results of the level 3 probabilistic safety assessment andcompared the accident consequence through probabilistic and deterministic methods to confirmthe similarity. In this study, the offsite accident consequence was evaluated for the severe accidentscenario of the US Surry nuclear power plant. For each accident scenario, the radiation source termand the meteorological data of the site of Surry nuclear power plant were used. For the probabilisticconsequence assessment, the WinMACCS computer code was used. For the deterministicconsequence assessment, the RASCAL computer code was used. As a result of the offsiteconsequence assessment, the ratio of the result of the RASCAL computer code to the WinMACCScomputer code was evaluated. In the case of LTSBO, it was 0.53~4.24 times. In the case of STSBO,it was 0.57~3.73 times. In the case of ISLOCA, it was 0.24~2.39 times. In the case of TISGTR, itwas 0.16~1.08 times. These differences were due to the differences in the radiation source term,meteorological data, and exposure modeling methods. The results of offsite consequence assessmentwere evaluated at the same order. It was 0.16 times in minimum, 4.24 times in maximum. Therefore,it is expected that the validity and reliability of probabilistic safety assessment can be judgedeconomically. The results of this study can be used as a basis for establishing a domestic level 3probabilistic safety assessment system.