On a Field Investigation and Open Data Analysis to Identify Diffusion Sources of Radioactive Substance

Abstract

Abstract-After the Fukushima No. 1 nuclear power plant disaster due to the huge earthquake, spreading contamination is a serious fear for Japanese society. In this paper, a field investigation is described to understand the contamination in the west part of Japan, which is in a region approximately a thousand km from the east power plant. Based on the contamination origin found in the investigation, open data is analyzed to identify important factors for spreading radioactive substance in terms of relationship between air dose rate and weather conditions. Based on the analysis, a detection rule or algorithm for the contamination origin is summarized to develop a detection system for radiation warning. Air dose rate is observed on each public monitoring point. The nearest weather observation station for each public monitoring point concerning air dose rate is also identified to analyze the relationship between air dose rate and weather conditions.According to the analysis, rainfall is an effective trigger to drop radioactive substance, such as contaminated airborne particles, to the ground. However, long-term rainfall, e.g., over half of a day, also has an effect to clean the air and ground. The most serious factor is wind direction from spreading origins of the particles in terms of air dose rate. In addition, consistent wind from a spreading origin can bring the particles without rainfall. On the other hand, wind speed seems not to be a big factor of increase of air dose rate, although the speed could multiply the effect of wind consistency on a spike of the dose rate.