Particles of Shadow Carried by the Sea Breeze - Memories of the South Wind that Enveloped the Fukushima Daini Nuclear Power Plant (2011)

Particles of Shadow Carried by the Sea Breeze - Memories of the South Wind that Enveloped the Fukushima Daini Nuclear Power Plant (2011)

In March 2011, as the severe accident at the Fukushima Daiichi Nuclear Power Plant progressed, an increase in radiation levels was also observed at the Fukushima Daini Nuclear Power Plant, located approximately 12 km to the south. The background to this was the possibility that the SR valve operation at Unit 2 of the Daiichi Nuclear Power Plant released high-pressure steam to the outside, and that the radioactive materials contained in the steam were carried by the southerly winds toward the Daini Nuclear Power Plant. This phenomenon was not merely a matter of distance, but was caused by a complex combination of the unique topography of Hamadori, sea breezes, and the weather conditions at the time of the earthquake.

Along the Fukushima coast, sea breezes from the Pacific Ocean vary greatly during the day, with southerly winds tending to prevail, especially in early spring. For several days after the earthquake, analysis by the Japan Meteorological Agency showed that southerly winds were blowing from the Daiichi Nuclear Power Plant toward the Daini Nuclear Power Plant. Hamadori, located between the sea and mountains, has limited wind paths, and zonal air currents tend to form along the topography. Therefore, radioactive materials were concentrated and carried in a specific direction, and the effect was manifested in the form of a slight increase in radiation levels around the No. 2 nuclear power plant.

This case showed how fragile the idea of safety by distance is in nuclear accidents: a short distance of 12 km is a boundary that can be easily crossed with a single change in wind direction, indicating that the second nuclear power plant could be involved in a crisis as an extension of the first nuclear accident. Fortunately, the Daini plant suffered no serious damage and remained stable, but if serious trouble had occurred simultaneously at both plants, a chain reaction crisis that could have resulted in the loss of functions throughout the entire Hamadori area could have been anticipated.

Furthermore, the southerly winds made evacuation orders and monitoring assessments in the vicinity of the Daiichi Nuclear Power Plant difficult. Post-accident investigations confirmed that radioactive materials were also moving southward in the direction of Iwaki City, revealing the reality that topography and weather conditions can drastically change the distribution of contamination. The minute changes in radiation levels observed at the No. 2 nuclear power plant are important clues to deciphering the way the accident at the No. 1 nuclear power plant spread, and quietly illustrate the harsh fact that the natural forces of wind can determine the fate of local communities.