Method of Estimation of Internal Dose Using Environmental Samples

Abstract

On March 11, 2011, the nuclear accident at the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) occurred as a consequence of the massive earthquake and subsequent tsunami that struck East Japan. The accident caused the release of a large amount of radionuclides into the environment, forming radioactive plume. It is reported that the abundance ratio of radionuclides in the soil is different in the North Western and Southern directions.

This study considers the difference of the abundance ratio of radionuclides in the soil using the air dose rate monitoring result data, path of movement of the radioactive plume and rainfall information around the FDNPP, and estimates internal dose using environmental samples.

From the air dose rate monitoring result, it was found that the dose rate in the North Western area was higher than that in the Southern area. Moreover, the radioactive plume reached the North Western area and deposited in the soil. The ratio of iodine and cesium in the North Western area is 3.68 and in the Southern area is 15.2. The difference of abundance ratio of radionuclides in the soil is because of the difference in the deposition of particle matter and gaseous substance. The dry deposition of particle matter is difficult compared with that of the gaseous substance. Furthermore, in the Southern area, there was more rainfall since the arrival of the radioactive plume than that in the North Western area. Therefore, the abundance ratio in the North Western area is higher than that in the Southern area.

In this study, internal doses are estimated; approximately 0.20 mSv effective dose by cesium was found in the North Western area, and approximately 7.43 mSv thyroid equivalent dose by iodine and 0.011 mSv effective dose by cesium ware found in the Southern area. In these results, the estimations are close, similar to the result of WBCs for evacuee and residents.