Safe reactor decommissioning, especially for damaged Fukushima Daiichi (1F) nuclear power plants, is vital for environmental safety. Key challenges include remotely cleaning radiation hotspots and ...cutting fuel debris within the damaged primary containment vessel. However, submicron radioactive Aerosol Particles (APs) can be generated, thus necessitating effective aerosol control and removal to avoid radioactive environmental pollution and reduce radiation exposure risks during 1F decommissioning. Flue gases containing submicron APs that result in environmental pollution can also generated from other industrial works, e.g., coal, mining and chemical sectors. Conventional water spray is difficult to scavenge these small APs. Although previous studies showed the effectiveness of charged droplets on accelerating aerosol removal, the charging configuration is also important to scavenging performance. Hence, this study performs aerosol scavenging experiments in our UTARTS facility with varying induction electrode designs. Experimental results show the saturation of scavenging efficiency at high voltage and indicate the importance of charging polarity. Moreover, proper configurations of electrode position, geometry and material are studied and discussed. Our findings can be beneficial for the improvement of spray system for aerosol removal to mitigate radioactivity release and minimize contaminated water production and have implications for gas purification in various environmental and chemical industries.
•Electro-charged spray aerosol removal experiments are conducted at UTARTS facility.•Various electrode models are developed for improving aerosol removal efficiency.•A saturated aerosol removal efficiency is found around 10–15 kV.•Charging polarity is significant for system effectiveness at different situations.•Effects of electrode design and configuration are studied for improving spray system.
•Numerical study on aerosol spray removal is conducted using Euler-Lagrange method.•Reliability of the method are validated by experimental results in UTARTS facility.•Characteristics of droplets and ...gas flow during spraying are investigated.•Virtual spray nozzles are designed for improving performance on aerosol removal.•Obtained understanding is beneficial to ensure safe decommissioning of 1F NPPs.
During decommissioning of the Fukushima Daiichi (1F) nuclear power plants, retrieving the solidified debris inside the reactors is a critical issue. Debris must be segmented using cutting techniques for retrieval by robots. However, these processes will generate submicron radioactive aerosol particles. Water spray system is considered as a useful technique for removing these aerosols. To investigate the optimization of the spray system for 1F decommissioning, this study conducts numerical simulations using Euler-Lagrange approach in STAR-CCM +. The evaluations focus on aerosol removal processes within our UTARTS facility under varying spray configurations. Our simulations consider the particle-laden gas and spray droplets in the continuous Eulerian phase and dispersed Lagrangian phase, respectively. Numerical models for aerosol scavenging through various mechanisms, including inertial impaction, diffusion, and interception, are developed and implemented. The characteristics of droplets and gas flow during spraying are investigated. With validation from experimental results, simulations incorporating newly designed virtual spray nozzles are analyzed for improved scavenging performance. The study suggests that an optimized combination of spray configurations may exist. The results from this study are expected to be beneficial for the improvement of spray system designs to efficiently scavenge aerosols during 1F decommissioning, thereby mitigating radioactivity release and minimizing the production of contaminated water.
The Fukushima accident has had a tremendous impact on Japan and the rest of the world in the areas of public health, economy, and nuclear energy policy. Thus, international consensus has been reached ...that inherent tolerance of nuclear fuel to severe accidents needs to be increased significantly to prevent accidents or to mitigate their consequences. In this respect, several countries have started to develop accident-tolerant fuel (ATF) that can tolerate loss of active cooling for a considerably longer time period than current fuels, while maintaining or improving performance during normal operations and operational transients and also enhancing fuel safety for beyond-design-basis events. The Korea Atomic Energy Research Institute is also developing ATF: surface-coated Zr cladding and metal-ceramic hybrid cladding for the purpose of suppressing hydrogen generation during severe accidents, and microcell UO
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pellets to enhance the retention of highly radioactive and corrosive fission products such as Cs and I, where all UO
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grains are enveloped by thin cell walls that act as chemical traps or physical barriers for the movement of fission products. When the screening of developing fuel materials has been performed through various out-of-pile tests, irradiation tests of the selected materials will be carried out in a research reactor to demonstrate their enhanced accident tolerance.
The Fukushima accident in March 2011 caused by the massive earthquake and tsunami led to hydrogen explosion, core meltdown, and the subsequent release of huge radioactivity both into the atmosphere ...and the Pacific Ocean. In the case of volatile fission products such as 137Cs and 131I, the release fraction of the core inventory of the units 1–3 into the atmosphere is estimated to be 1.2–6.6% and 1.1–7.9%, respectively. As for gaseous fission product 133Xe, it is estimated that nearly 100% of the core inventory might have been released into the atmosphere. In addition, about 16% of the 137Cs inventory flowed into the sea when the contaminated water used for cooling the decay heat of the units 1–3 overflowed the reactors. Therefore, even though almost three years have passed since the accident, it is still having a tremendous impact not only on Japan but all over the world as well.
This paper reviews the Fukushima accident from the viewpoint of radioactivity release and dispersion in the environment and its effect on public health, economy, energy policy, international relationship, and LWR fuel development.
•Radioactivity release into the environment by the Fukushima accident is reviewed.•Radioactivity distribution in Japan and around the world is reviewed.•Impacts of the accident on public health, economy and energy policy are described.
General description of Chernobyl accident is given in the review. The accident causes are briefly described. Special attention is paid to radiation situation after the accident and radiation ...measurements problems. Some data on Chernobyl disaster are compared with the corresponding data on Fukushima accident. It is noted that Chernobyl and Fukushima lessons should be taken into account while developing further measures on raising nuclear industry safety.
► The short comparative analysis of accidents at Chernobyl and Fukushima is given. ► We note the great effect of β-radiation on the radiation situation at Chernobyl. ► We discuss the problems of radiation measurements under these conditions. ► The impact of shelter on the radiation situation near Chernobyl NPS is described.
The estimation of radioactivity release following an accident in a nuclear power plant is crucial due to its short and long-term impacts on the surrounding population and the environment. In the case ...of any accidental release, the activity needs to be estimated quickly and reliably to effectively plan a rapid emergency response and design an appropriate evacuation strategy. The accurate prediction of incurred dose rate during normal or accident scenario is another important aspect. In this article, three different non-linear estimation techniques, extended Kalman filter, unscented Kalman filter, and cubature Kalman filter are proposed in order to estimate release activity and to improve the prediction of dose rates. Radionuclide release rate, average wind speed, and height of release are estimated using the dose rate monitors data collected in proximity of the release point. Further, the estimates are employed to improve the prediction of dose rates. The atmospheric dispersion phenomenon of radioactivity release is modelled using the Gaussian plume model. The Gaussian plume model is then employed for the calculation of dose rates. A variety of atmospheric and accident related scenarios for single source and multiple sources are studied in order to assess the efficacy of the proposed filters. Statistical measures have been used in order to validate the performance of the proposed approaches.
A stepwise sequential assimilation algorithm is proposed based on an optimisation approach for recursive parameter estimation and tracking of radioactive plume propagation in the early stage of a ...radiation accident. Predictions of the radiological situation in each time step of the plume propagation are driven by an existing short-term meteorological forecast and the assimilation procedure manipulates the model parameters to match the observations incoming concurrently from the terrain. Mathematically, the task is a typical ill-posed inverse problem of estimating the parameters of the release. The proposed method is designated as a stepwise re-estimation of the source term release dynamics and an improvement of several input model parameters. It results in a more precise determination of the adversely affected areas in the terrain. The nonlinear least-squares regression methodology is applied for estimation of the unknowns. The fast and adequately accurate segmented Gaussian plume model (SGPM) is used in the first stage of direct (forward) modelling. The subsequent inverse procedure infers (re-estimates) the values of important model parameters from the actual observations. Accuracy and sensitivity of the proposed method for real-time forecasting of the accident propagation is studied. First, a twin experiment generating noiseless simulated “artificial” observations is studied to verify the minimisation algorithm. Second, the impact of the measurement noise on the re-estimated source release rate is examined. In addition, the presented method can be used as a proposal for more advanced statistical techniques using, e.g., importance sampling.
•Inverse model parameter re-estimation based on optimisation approach.•Extraction of information from incoming measurements.•Recursive predictions of the most adversely impacted areas.•Sensitivity study on the noise of measurements.
This paper analyzes the role of nuclear power of China's energy structure and industry system. Comparing with other renewable energy the nuclear power chain has very low greenhouse gas emission, so ...it will play more important role in China's low-carbon economy. The paper also discussed the necessity of nuclear power development to achieve emission reduction, energy structure adjustment, nuclear power safety, environmental protection, enhancement of nuclear power technology, nuclear waste treatment, and disposal, as well as nuclear power plant decommissioning. Based on the safety record and situation of the existing power plants in China, the current status of the development of world nuclear power technology, and the features of the independently designed advanced power plants in China, this paper aims to demonstrate the safety of nuclear power. A nuclear power plant will not cause harm either to the environment and nor to the public according to the real data of radioactivity release, which are obtained from an operational nuclear plant. The development of nuclear power technology can enhance the safety of nuclear power. Further, this paper discusses issues related to the nuclear fuel cycle, the treatment, and disposal strategies of nuclear waste, and the decommissioning of a nuclear power plant, all of which are issues of public concern.
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