Search

Nuclear energy has been gaining momentum recently as one of the solutions to tackle climate change. However, significant environmental and health-risk concerns remain associated with potential accidents. Despite significant preventive efforts, we must acknowledge that accidents may happen and, therefore, develop strategies and technologies for mitigating their consequences. In this paper, we review the Fukushima Dai-ichi Nuclear Power Plant accident, synthesize the time series and accident progressions across relevant disciplines, including in-plant physics and engineering systems, operators' actions, emergency responses, meteorology, radionuclide release and transport, land contamination, and health impacts. In light of the latest observations and simulation studies, we identify three key factors that exacerbated the consequences of the accident: (1) the failure of Unit 2 containment venting, (2) the insufficient integration of radiation measurements and meteorology data in the evacuation strategy, and (3) the limited risk assessment and emergency preparedness. We propose new research and development directions to improve the resilience of nuclear power plants, including (1) meteorology-informed proactive venting, (2) machine learning-enabled adaptive evacuation zones, and (3) comprehensive risk-informed emergency planning while leveraging the experience from responses to other disasters.

The gamma component of air radiation dose rates is a function of the amount and spread of radioactive nuclides in the environment. These radionuclides can be natural or anthropogenic in origin. The field of view describes the area of radionuclides on, or below, the ground that is responsible for determining the air dose rate, and hence correspondingly the external radiation exposure. This work describes Monte Carlo radiation transport calculations for the field of view under a variety of situations. Presented first are results for natural 40K and thorium and uranium series radionuclides distributed homogeneously within the ground. Results are then described for atmospheric radioactive caesium fallout, such as from the Fukushima Daiichi Nuclear Power Plant accident. Various stages of fallout evolution are considered through the depth distribution of 134Cs and 137Cs in soil. The fields of view for the natural radionuclides and radiocaesium are different. This can affect the responses of radiation monitors to these nuclides if the detector is partially shielded from the ground within its field of view. The field of view also sets the maximum reduction in air dose rates that can be achieved through local decontamination or remediation measures. This maximum efficiency can be determined quickly from the data presented here for the air dose rate versus the spatial extent of radioactive source on the ground., Comment: 6 pages, 6 figures, Author Accepted Manuscript for Proceedings of the 2015 International Symposium on Radiological Issues for Fukushima's Revitalized Future

Land topography can affect air radiation dose rates by locating radiation sources closer to, or further from, detector locations when compared to perfectly flat terrain. Hills and slopes can also shield against the propagation of gamma rays. To understand the possible magnitude of topographic effects on air dose rates, this study presents calculations for ambient dose equivalent rates at a range of heights above the ground for varying land topographies. The geometries considered were angled ground at the intersection of two planar surfaces, which is a model for slopes neighboring flat land, and a simple conical geometry, representing settings from hilltops to valley bottoms. In each case the radiation source was radioactive cesium fallout, and the slope angle was varied systematically to determine the effect of topography on the air dose rate. Under the assumption of homogeneous fallout across the land surface, and for these geometries and detector locations, the dose rates at high altitudes are more strongly affected by the underlying land topography than those close to ground level. At a height of 300m, uneven topographies can lead to a 50% change in air dose rates compared to if the ground were uniformly flat. However, in practice the effect will more often than not be smaller than this, and heterogeneity in the source distribution is likely to be a more significant factor in determining local air dose rates., Comment: 7 pages, 8 figures, corrected problem with column formatting + latex tweaks, for presentation at the Joint International Conference on Mathematics and Computation, Supercomputing in Nuclear Applications and the Monte Carlo Method (M&C + SNA + MC 2015), Nashville, USA

A letter to the editor of the Journal of Environmental Radioactivity on the article: E. Gasser, A. Nachab, A. Nourreddine, Ch. Roy, and A. Sellam, `Update of 40K and 226Ra and 232Th series $\gamma$-to-dose conversion factors for soil', J. Environ. Radioactiv. 138, 68-71 (2014), DOI: 10.1016/j.jenvrad.2014.08.002., Comment: Author accepted manuscript, Journal of Environmental Radioactivity (2015), 9th Jan 2015, 2 pages, 1 figure