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Abstract: The EMRAS-2 Urban Areas Working Group, which is supported by the IAEA, has designed a variety of accidental scenarios to test and improve the capabilities of the models used for an evaluation of radioactive contamination in an urban environment. A variety of models including a Korean model, METRO-K, are used for predictive results on the hypothetical scenarios. This paper describes the predictive results of METRO-K for the hypothetical scenarios designed in the Working Group. The external dose resulting from the air contamination of Co-60 was evaluated, and its contribution was analyzed with time as a function of the location of a receptor and precipitation conditions at the time of the contamination event. As a result, the external doses showed a distinctive difference with the locations to be evaluated and the precipitation conditions. Moreover, the contribution of contaminated surfaces for external doses was strongly dependent on the locations to be evaluated and the precipitation conditions. These results will provide essential information to assist the decision-making of appropriate countermeasures in an emergency situation of a radioactively contaminated urban environment. [Copyright &y& Elsevier]

Abstract: This paper specifically discusses an atmospheric dispersion modeling and health risk assessment for Cs-137 to assess the potential and actual effects on human health from an inhalation event due to a radiological terrorist attack in the Seoul metropolitan area, Korea. The source term was assumed to be 5TBq of Cs-137, introduced into the central part of Seoul’s metropolitan area by a terrorist attack. Atmospheric dispersion models can be used to support the decision making and risk assessments when terrorist attacks have happened in an urban area. The concepts of Gaussian plume modeling and computational fluid dynamics modeling were used to calculate the Cs-137 concentration in the air. Mortality risk and morbid risk coefficients for the inhalation of contaminated air were used to assess the human health risk. The mortality and morbidity are 1.12E−2 and 1.64E−2, respectively in case of the Gaussian plume, while 6.23E−3 and 9.13E−3 in case of the computational fluid dynamics model. The results of the modeling are dependent on the terror scenarios and dispersion models. Accordingly, the optimization process is needed for final decision making. [Copyright &y& Elsevier]

Abstract: This paper specifically discusses a water quality modeling and health risk assessment for cesium-137 to assess the potential and actual effects on human health from drinking water contaminated by a radiological terrorist attack in the Seoul metropolitan area, Korea. With respect to the source term caused by a terrorist attack, it was assumed that 50TBq of cesium-137 was introduced into the Paldang Lake which is a single water resource for the Seoul metropolitan area. EFDC (Environmental Fluid Dynamics Code) model was used to calculate the hydrodynamic and water quality for the model domain, Paldang Lake. Mortality risk and morbid risk coefficients caused by the ingestion of tap water were used to assess a human health risk due to cesium-137. The transport of cesium-137 in the Paldang water system was mainly dependent on the flow streamlines and the effect of the dilution from the other branches. The mortality and morbidity risks due to the drinking water contamination by cesium-137 were 4.77×10−7 and 6.92×10−7, respectively. Accordingly, it is very important to take appropriate countermeasures when radiological terrorist attacks have occurred at water resources to prevent radiological risks by radionuclides. [Copyright &y& Elsevier]

The influence of predictive contamination to agricultural products due to the wet processes as well as dry processes from radioactive air concentration during a nuclear emergency is comprehensively analyzed. The previous dynamic food chain model DYNACON considering Korean agricultural and environmental conditions, in which the initial input parameter was radionuclide concentrations on the ground, is improved so as to evaluate radioactive contamination to agricultural products from either radioactive air concentrations or radionuclide concentrations on the ground. As for the results, wet deposition is a more dominant mechanism than dry deposition in contamination on the ground. While, the contamination levels of agricultural products are strongly dependent on radionuclide and precipitation when the deposition of radionuclides occurs. It means that the contamination levels of agricultural products are determined from which is the more dominant process between deposition on the ground and interception to agricultural plants. [Copyright &y& Elsevier]

This paper describes an investigation which was done on prematurely failed pins used in die-casting dies for aluminum engine blocks. To investigate the causes of the failures, static and fatigue strength evaluations of the pin materials and the deterioration degree of the strength due to exposure to high temperatures were evaluated. SEM observations of the fracture surfaces of broken pins revealed that the fractures were the fatigue failure type caused by thermal stresses upon thermal expansion and cooling during the repeated die-casting process. A solidification analysis of the die-casting process was conducted to determine the temperature distribution of the dies and pins, and a coupled thermal-structure analysis was carried out using the temperature distribution information to determine the magnitude of the thermal stress in the pin. The maximum thermal stresses were used to predict the fatigue lifetime of the pin. The result of this investigation reveals that cooling holes at the center of the pin were machined with some degree of eccentricity, leading to a concentration of the thermal stress at the thin part and, ultimately resulting in a premature failure. Appropriate machining of a cooling hole in the die pins must be carried out in order to avoid premature failures of these components. • Pins used in die-casting dies for aluminum engine blocks prematurely failed. • Fracture surfaces of broken pins are the fatigue failure caused by thermal stress. • Coupled thermal-structure analysis was carried out to determine the thermal stress • Cooling holes with eccentricity caused a concentration of the thermal stress. [ABSTRACT FROM AUTHOR]

The fission product inventory for a loss-of-coolant accident (LOCA) analysis is generally evaluated based on the average burnup of the fuel at the end of life regardless of the variation of the actual burnup with time. In this study, we analyze the variation of the fission product inventory based on the accident occurrence cycle and the degree of fuel meltdown, which reflect the axial burnup of the fuel at the beginning, middle, and end of the cycle (BOC, MOC, and EOC). The fuel assembly for the Hanul unit 6, which is an OPR1000-type pressurized water reactor (PWR) in Korea, was chosen as an analysis model for the source-term assessment. The burnup cross-section library was generated using the TRITON module of the SCALE6.1 code system, and the depletion calculations were carried out using ORIGEN-ARP. The first scenario, which is referred to as CASE (I), is applied with an average burnup at the EOC, which is a commonly recommended conservative assumption in accident analyses. The CASE (II) scenario includes various cases that consider the accident occurrence cycle and fuel meltdown from the top to the bottom of the core at the BOC, MOC, and EOC. As a result, the inventory of the main nuclides gradually decreased as the reactor core operation was performed. In addition, the activity intensity for the main fission products of CASE (II) was shown to be higher than that of CASE (I) in the range above a fuel meltdown of approximately 30%. Therefore, this study concludes that not all of the results obtained by the CASE (I) assumption are guaranteed to be more conservative than those obtained by CASE (II). [ABSTRACT FROM AUTHOR]