Fukushima Daiichi and Chernobyl: Comparison of radioactivity release and contamination

Abstract

The Fukushima Daiichi accident on March 11, 2011 became the most serious accident that can be compared only with the Chernobyl accident on April 26, 1986. The radioactivity composition released by these two accidents was different each other, depending the reactor type and the accident process. Chernobyl was a power surge accident at one reactor, while Fukushima was loss-of-coolant accidents at three reactors. In the case of Chernobyl, the radioactivity composition of the initial release caused by an explosion due to the power surge was similar to that contained in the reactor core, and then the graphite fire of the moderator continued about ten days. According to the USSR report presented to IAEA in August 1986, the total release of ¹³¹I and ¹³⁷Cs was estimated to be 2.710¹⁷ and 3.710¹⁶ Bq, respectively. Meanwhile, in the case of Fukushima, the large amount of volatile radionuclides was released into the environment when the integrity of containment, the last protecting shield was destroyed during the course of pressure increases inside containments as well as hydrogen explosions after the core melt-downs. According to the press release from the Nuclear Safety Commission on April 12, the released amount of ¹³¹I and ¹³⁷Cs was estimated to be 1.510¹⁷ and 1.210¹⁶ Bq, respectively. From these figures, the similar level of radioactivity release occurred for volatile radionuclides although the Chernobyl case was a little larger than the Fukushima. Regarding refractory radionuclides such as ⁹⁰Sr and ⁹⁵Zr, the released estimates of 8.110¹⁵ and 1.410¹⁷ Bq were given for ⁹⁰Sr and ⁹⁵Zr for Chernobyl, respectively, while, according to the Japanese government report to IAEA in June, they were 1.410¹⁴ and 1.710¹³ Bq for Fukushima, respectively. The amount of ⁹⁰Sr and ⁹⁵Zr released by the Fukushima accident was estimated 1/60 and 1/8000 of the Chernobyl accident, respectively. In our presentation discussion will be given for uncertainties of the above values as well as a comparison of radiation situation in the contaminated areas between Fukushima and Chernobyl.