春雨直播app

On March 11, 2011, the Great East Japan Earthquake triggered a severe nuclear accident at the Fukushima Daiichi Nuclear Power Station (F1NPS), operated by the Tokyo Electric Power Company. The tsunami caused by the earthquake flooded and destroyed the nuclear reactor cooling systems, and the resulting blackout caused meltdowns in three reactor cores. The release of radionuclides into the atmosphere occurred due to these meltdowns and led to hydrogen gas explosions in mid-March 2011. Subsequently, in April 2011, highly contaminated water from the housing of reactor cores and turbines was released into the open water through the port of the F1NPS.
 
Radionuclides released into our environment dispersed globally through the atmosphere within a few weeks. Radioactive concentrations in the atmosphere decreased rapidly as the materials were deposited on land and sea surfaces, due to the short residence time of radioactive materials in the atmosphere. However, the dispersion of contaminated water in the ocean continues even ten years after the accident in 2011 because the speed of the ocean currents is approximately two orders of magnitude slower than the speed of winds in the atmosphere. The residence time of dissolved radionuclides in the ocean surface water is approximately 10-20 years.
 
For example, radiocesium, which is relatively soluble in seawater, flows into the vicinity of the 1FNPS and travels eastward across the North Pacific via the Kuroshio Extension. Approximately three years later, it reaches the west coast of the United States, then moves northward. Six years later, it passes through the Gulf of Alaska into the eastern Bering Sea, and two years after that, some of it flows into the Arctic Ocean while some returns from the western Bering Sea to the northwest Pacific. Such transport and diffusion of radionuclides at the hemispheric level have attracted the interest of several countries. To fully understand these processes, it is necessary to consistently link information across various temporal and spatial scales from a scientific perspective.
 
In this book, seven oceanographers reviewed over 300 papers published mainly in the 10 years since the accident and added new analytical results to the knowledge gained, engaged in repeated discussions, and scientifically summarized the dynamics of radionuclides resulting from an accident in the ocean. Each referenced paper provides a detailed discussion of the various issues it addresses, but it is important to provide an overview from an oceanographic perspective, which may not be possible to obtain from individual papers alone.
 
We hope this book provides an opportunity to reconsider what happened in the ocean after the accident, identify the challenges that arose, and determine what perspectives should guide future monitoring efforts to protect and utilize clean oceans.
 

(Written by OTOSAKA Shigeyoshi, Associate Professor, Atmosphere and Ocean Research Institute / 2024)