Current Topics about the Radiological Consequences by the Chernobyl Accident

Basic radiological factors of the Chernobyl accident are reviewed such as radioactivity discharge, the size of contaminated area, radiation dose, radiation risk assessment etc. Roughly estimating, 50-60 % of I and 30-50 % of Cs in the reactor core were released into the environment, which correspond to 40-50 MCi and 2-4 MCi, respectively, as the activities at the time of the accident. The total area in 13 European countries with the Cs contamination more than 1 Ci/km amounts to 190,000 km. The collective thyroid dose for the entire populations in the most affected three countries (Belarus, Ukraine and Russia) is estimated 1.6 × 10 person-Gy. The collective effective dose (excluding thyroid dose) for 5.16 million people living in the main contaminated territories in three countries is estimated 4.26 × 10 person-Sv during 10 years after the accident. Using these collective doses together with radiation risk coefficients of ICRP (1990), 13,000 thyroid cancer and 2,100 other cancer deaths are expected among the corresponding populations. Other articles in this report indicate the followings. About 4,400 cases of radiation-induced thyroid cancer were observed in Belarus by the end of 2000. There are also observed some increasing tendencies of other cancers among inhabitants in the contaminated areas and liquidators. Health deteriorations and mental retardations are observed among the children living in the contaminated areas and having received irradiation in utero. All these findings suggest the necessity of well organized epidemiological studies before giving conclusions about the health consequences of the Chernobyl accident as well as applicability of ICRP radiation risks to the related populations. An interesting map is shown representing dose rate around the Chernobyl NPP on June 1, 1986. Using the dose rate in this map for reconstructing radiation dose for evacuees, the possibility of acute radiation sickness was confirmed among a substantial part of evacuees from some villages within the 30 km zone.