|Fig. 1: Chernobyl contamination zone after the accident.  (Source: Wikimedia Commons)|
Many research works have been conducted to study the impacts of Chernobyl and Fukushima nuclear disasters including the environmental hazard, released radiation dose, political impact and food safety issues. Previous reports have investigated the backgrounds and causes, and introduced some of the consquences. [1-3] Yet only a few of studies have summarized the differences between these two accidents. In this report, I will make a comparison of these two nuclear disasters.
Both of Chernobyl and Fukushima nuclear disasters have been rated as a Major Accident as INES 7 by the International Atomic Energy Agency (IAEA).  The Chernobyl nuclear accident happened on 26 April 1986 was mainly due to the inappropriate reactor operation at low power level and the flawed engineering of the reactor core. This mistake led to RBMK-1000 reactor thermal destruction, and finally resulted in the released radionuclides from the explosion.  An additional continuous release of radionuclides occurred over 10 days due to the graphite fire after the initial peak release. 
Fukushima Daiichi nuclear power plant (NPP) accident happened on 11 March 2011 was caused by the 9.0 magnitude Tohoku Earthquake. The tsunami resulting from the earthquake shut down the diesel generators and the main cooling system, causing a series of nuclear meltdowns and hydrogen-air chemical reactions. Thus highly radioactive materials were released surrounding the plant.  The Chernobyl releases were uncontrolled and continuous, with peak releases in the very beginning. The Fukushima releases happened in pulses over a time span of more than a week. And based on a chemical transport model (CMAQ) estimation, which roughly reproduced the observed spatiotemporal variations of Cs-137 deposition rates for Fukushima, 22% of the radionuclides were deposited over land and around 80% were transported offshore. 
|Fig. 2: .Estimation of first year radiation dose for area surrounding Fukushima Daiichi nuclear accident. [8,9] (Courtesy of the NNSA. Source: Wikimedia Commons ; Courtesy of Dylan Sarkisian.)|
With model simulations and assumptions, the total activity released in Chernobyl was estimated as 5.3 × 1018 Bq.  The total activity released in Fukushima accident was 10% to 15% of the Chernobyl value (5.2 × 1017 Bq).  For the contamination area, some papers defined it as the zone with activity density over 1.85 × 105 Bq/m2. The contamination zone around Chernobyl was 29400 km2, and around Fukushima was 1700 km2.  For the Fukushima accident, more than 75% of the contaminated areas were forested, 10% were rice paddy fields, 10% were other agricultural areas and 5% were urban areas. The contaminated areas in Belarus were 43% agricultural areas, 39% forested and 2% rivers and lakes.  Figs. 1 and 2 show the affected areas for the two accidents.
Both the Chernobyl and Fukushima accidents caused severe radionuclide contamination over the entire northern hemisphere. Important radionuclides such as I-131, Cs-137, Sr-90 and Pu-239 + Pu-240 were monitored and data collected around two accidents origins over a long time period. The data show that maximum radionuclide concentrations in air after the accidents of Chernobyl was much higher than the accident of Fukushima (around two orders higher). 
Another set of data which clearly shows the difference between these two accidents is the effects on workers at the plant sites. On the first day of the Chernobyl accident, the maximum doses for emergency workers was 16 Gy. For clean-up, the mean exposure of 18700 workers and liquidators was 170 mSv.  For Fukushima accident, the reported data on the exposure of workers has not been reviewed by international organizations and thus might need corrections in the future. Based on the released data, 146 workers received doses over 100 mSv, 6 received over 250 mSv, 2 in the control rooms received over 600 mSv, and 2 received skin exposure of 2-3 Sv while standing in highly contaminated water.  The data shows that the exposure of workers in the Fukushima accident is much lower than in the Chernobyl accident.
In summary, the Chernobyl and Fukushima accidents had different causes and consequences. The Chernobyl accident was mainly due to operation mistake while Fukushima accident resulted from and earthquake. The Chernobyl accident had more severe consequences than Fukushima because more radionuclides was released during the accident and larger area was contaminated. Also the dose exposure of the workers was significantly higher in Chernobyl accident.
© Jiechen Wang. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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 "Annex J: Exposures and Effects of the Chernobyl Accident," in Sources and Effects of Ionizing Radiation, Vol II: Effects (United Nations, 2000), p. 460.