Research on radionuclide migration in coastal waters under nuclear leakage accident
Introduction
The development of nuclear power is a strategic requirement for energy development in China, being an effective way to counteract the environmental pollution crisis and optimize energy structure. Nuclear power also has its own developmental limitations, and once a nuclear accident occurs, it will have a great impact on public safety. The tsunami, having been triggered by the earthquake in the Northeast Pacific region in March 2011 caused a nuclear leakage accident at Fukushima-Daichi nuclear power plant (Hirose, 2011), which is yet another far-reaching nuclear leakage event (after the Three Mile Island accident in the United States and Chernobyl accident (Renjie, 1987; Koo et al., 2014) in the former Soviet Union). In this nuclear accident, the Japanese government did not predict the scope of radionuclide diffusion in a scientific and timely manner. The emergency area classification was not clear, exposing many problems (Xu et al., 2012) such as slow response, confused deployment, and improper disposal. The nuclear power plants of China are distributed in coastal areas. If a nuclear accident occurs, it will seriously threaten the safety of residents in the nearby sea areas, pollute the marine ecological environment. Hence it became an important issue to deal with marine nuclear pollution effectively. At present, the second AP1000 unit in the world (a third-generation nuclear power unit) was successfully connected to the grid (Brief news, 2018) in August 2018. AP1000 is recognized as an advanced third-generation nuclear power technology (Anonymous, 2018) in the world, and its safety factor has increased by an order of magnitude. Nevertheless, the possibility of a nuclear leakage accident cannot completely be ruled out. The unit is very close to the Yellow Sea (a semi-enclosed sea area). Once a nuclear leakage accident occurs, the consequences will be very serious. After the Fukushima accident, foreign scholars have conducted a series of studies on the transport of radionuclides in the ocean. Inoue et al. (2012) analyzed the observation data of radionuclides in coastal waters of Japan before and after the accident. The results showed that the radionuclide concentration increased rapidly after the accident, and began to decrease in June 2011, because the radionuclides were brought to the distant sea. Nakano et al. (Nakano and Povinec, 2012) predicted the long-term transport path of Cs-137 by establishing a global radionuclide transport model with a resolution of 2.0° × 2.0°. The Japanese scholar Kawamura H et al. (Kawamura et al., 2017) simulated the oceanic dispersion of Cs-137 by atmospheric and oceanic dispersion simulations. The mean Cs-137 concentrations of the multiple models relatively well agreed with the observed concentrations in the coastal and offshore oceans during the first few months after the Fukushima disaster. Perianez R et al. (Perianez et al., 2019) applied a number of marine radionuclide dispersion models (both Eulerian and Lagrangian) to simulate Cs-137 releases from Fukushima Daiichi nuclear power plant accident in 2011 over the Pacific at oceanic scale. Domestic scholars have also conducted a lot of numerical research. He et al. (2012) used the Miami Isopycnic Coordinate Ocean Model (MICOM) to simulate the long-distance transport of radionuclides in the ocean. The results showed that different emission scenarios and meteorological data had no significant effect on the migration path of radionuclides in the surface and subsurface. Zhao Chang et al. (Chang, 2013) used the Princeton Ocean Model (POM) to establish a global radionuclide transport model, which carried out a long-term simulation of Cs-137, predicting the migration path for 30 years. The results indicated that radionuclides migrated to the US west coast after four or five years and spread to the entire North Pacific after eight or nine years. Wang Hui et al. (Wang et al., 2012) simulated and predicted the radionuclide transportation of Fukushima for ten years using a North Pacific circulation model with a resolution of 1/8° × 1/8°. Zhang Junli et al. (Zhang et al., 2003) established a depth-averaged and two-dimensional diffusion model for the Dapeng'ao waters, and studied the diffusion of radionuclides which is in the wastewater of nuclear power plants. Qiao Qingdang et al. (Qiao et al., 2015) established an overall scheme of nuclear accident assessment system for marine environmental problems through the analysis of radionuclide transport model at home and abroad. At present, studies on radionuclide migration in the ocean are mostly focused on the global scale, and there are few studies on the radionuclide diffusion in coastal waters. Based on Haiyang AP1000 nuclear power unit and real-time meteorological data, therefore, it is necessary to establish a high-precision radionuclide diffusion model in coastal waters to analyze the radionuclide migration path, and study the influence of tide and decay on radionuclide concentration. It can provide a reference for emergency response after a nuclear leakage accident.
Section snippets
Research object
AP1000 is recognized as an advanced third-generation nuclear power technology. The AP1000 unit of Haiyang Nuclear Power Plant has successfully completed the 168-h and full-power operation test on October 22, 2018, and has officially been put into commercial operation. Haiyang nuclear power plant is located in the Yellow Sea coast, which is a semi-enclosed sea area. The coastal areas near of the nuclear power plant are mostly tourist and residential areas. Therefore, the Haiyang nuclear power
Source item model
In order to achieve fast response, the activity of fission products can be estimated using a simplified model (Wang, 2003). For a radionuclide whose irradiation time is much longer than its half-life, the product can reach equilibrium, and the core accumulation is as shown in equation (1).Where, A is the activity, 1 × 1012Bq; Y is the fission yield of radionuclides, %; P is the reactor thermal power, MWt.
If the radionuclide half-life is significantly longer than the irradiation time, the
Hydrodynamic field in coastal waters of China
Based on the hydrodynamic model (in section 3.1) and the boundary in coastal waters of China (in section 3.3), hydrodynamic results in coastal waters of China were calculated. The surface flow field of Kuroshio in summer is shown in Fig. 4(a) and the temperature of section 35°N in the Yellow Sea is shown in Fig. 4(b).
As can be seen from Fig. 4, the simulated result of the surface flow field well depicts the whole Kuroshio path from the east of Taiwan to the south of Japan, and its velocity
Conclusion
A climatic hydrodynamic model was established in coastal waters of China. Then a hydrodynamic model, based on the real-time meteorological data, was established for the coastal waters of nuclear power plant. Based on Lagrangian and Euler methods, radionuclide diffusion models were established in coastal waters of nuclear power plant, respectively. The reliability of models were verified. Hydrodynamic characteristics and radionuclide migration principle were analyzed for coastal waters of
Acknowledgment
The research is supported by the National Key Project of Research and Development Plan (2016YFC1402501).
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