||RADIOSTRONTIUM ISOTOPES IN JAPAN AFTER THE FUKUSHIMA NUCLEAR ACCIDENT
Fukushima Daiichi Nuclear Power Plant accident in Japan released and dispersed a significant amount of radionuclides (~520 PBq) in the environment. Shortly after the accident, volatile nuclides e.g. 137Cs, 131I and 132Te were detected in the Northern Hemisphere and elevated dose rates were observed in most of Japan.Contamination of radiostrontium isotopes, as they have intermediate volatility, was was delayed. Measurement of radiostrontium is a time consuming process since it involves a complex sample preparation and analytical separation required to produce reliable data. Five years after the accident, a few numbers of scientific publications and official reports have been published revealing the presence of radiostrontium - that originated from the Fukushima accident and dispersed into the environment.The estimated 90Sr (89Sr) emission into the atmosphere was 0.14 PBq (2.0 PBq) and 0.1-2.2 PBq into the Pacific Ocean. A significant part of the 90Sr (89Sr) - about 8.6 PBq (70 PBq) - remained in the stagnant water in the area of the nuclear plant. In the vicinity of the plant, ground water contamination has been reported but could not be clarified. While comparing with deposition monitoring results of 2011 to 2010, statistically there is a significant increase of 90Sr in 16 of the 47 prefectures. Especially for the evacuation zone, the radiostrontium deposition rates in Japan did not reach the levels caused by nuclear weapon tests or the Chernobyl accident. On the other hand, the discovery of radiostrontium deposition hot spots cannot be ruled out.Compared to other nuclear facilities, liquid discharge into the Atlantic Ocean and the Techa River (Russia), the radiostrontium contamination of the Pacific Ocean is at least two or three times lower. Considering uncertainties and overestimation, maximum range of the average annual effective dose originating from radiostrontium is ~20 µSv year-1. This dose is negligible when compared to the effective dose generated by natural radiation (decay series of 238U and 232Th, 40K).
II INTERNATIONAL CONFERENCE ON RADIOECOLOGICAL CONCENTRATION PROCESSES(50 years later)