Comparison of the Chernobyl and Fukushima nuclear accidents


The following table compares the nuclear accidents at the Chernobyl and Fukushima Daiichi nuclear power plants, the only INES level 7 nuclear accidents to date.
Plant NameChernobyl
Fukushima Daiichi
LocationSoviet Union Japan
Date of the accidentApril 26, 1986March 11, 2011
INES Level77
Plant commissioning date19771971
Years of operation before the accident9 years
40 years
Electrical outputplant : 3700 MWe
reactors : 925 MWe 		plant : 4546 MWe
reactors : 439 MWe, 760 MWe, 1067 MWe
Type of reactorRBMK-1000 graphite moderated, 2nd generation reactor without containmentBWR-3 and BWR-4 reactors with Mark I containment vessels
Number of reactors4 on site; 1 involved in accident6 on site; 4 involved in accident; one of the four reactors was empty of fuel at the time of the accident.
Amount of nuclear fuel in affected reactors1 reactor - 210 tons 4 reactors - 854 tons, 59 tons in Unit 1 spent fuel pool
Cause of the accidentProximate cause was human error and violation of procedures. The unsafe reactor design caused instability at low power due to a positive void coefficient and steam formation. When an improper test was conducted at 1:00 am at low power, the reactor became prompt critical. This was followed by a steam explosion that exposed the fuel, a raging fire, and a core meltdown. The fire lasted for days to weeks, and there is controversy over whether it was the fuel burning, nuclear decay heating or whether the graphite moderator that made up most of the core was involved. See Chernobyl Disaster, Note 1, for more discussion.The plants were not designed with consideration of such a large tsunami. Subsequent review did not lead to mitigation. A major earthquake and tsunami caused the destruction of power lines and backup generators. Once the plants were without external power and the generators were flooded, a catastrophic decay heat casualty ensued, leading to major reactor plant damage including meltdowns and explosive loss of reactor containment.
Maximum level of radiation detected300 Sv/h shortly after the explosion in vicinity of the reactor core.530 Sv/h inside Unit 2 containment vessel in 2017 according to Japan Times.
Radioactivity releasedAccording to IAEA, total release was. in iodine-131 equivalentAs of 2014, a peer reviewed estimate of the total was 340-780 PBq, with 80% falling into the Pacific Ocean. Radiation continues to be released into the Pacific via groundwater.
Area affectedAn area up to away contaminated, according to the United Nations.Radiation levels exceeding annual limits seen over to northwest and to south-southwest, according to officials.
Exclusion Zone Area30 km20 km extending north-west to 45 km in the downwind direction to Iitate, Fukushima
Population relocated335,000 154,000
Population returned-122,000
Direct fatalities from the accidentTwo immediate trauma deaths; 28 deaths from Acute Radiation Syndrome out of 134 showing symptoms; four from an industrial accident ; 15 deaths from radiation-genic thyroid cancers ; as many as 4000 to 90000 cancer related deaths.-
Current statusAll reactors were shut down by 2000. The damaged reactor was covered by a hastily built steel and concrete structure called the sarcophagus. A New Safe Confinement structure was installed in November 2016, from which the plant will be cleaned up and decommissioned.Cold shutdown declared on 16 December 2011, but decommissioning is likely to take 30 to 40 years. All fuel rods in reactor 4 pool removed. Fukushima disaster cleanup is ongoing.

Radioactive contamination discharge

Report datePlacePeriodAmount
Source
12 April 2011Chernobyl25 April – June 19865,200,000NISA
12 April 2011Fukushima11 March – 5 April 2011630,000NSC
12 April 2011Fukushima11 – 17 March 2011370,000NISA
April 2011Fukushima4 April 2011154NSC
25 April 2011Fukushima24 April 201124NSC
6–7 June 2011Fukushima11 – 17 March 2011770,000NISA>
7 June 2011Fukushima11 – 17 March 2011840,000NISA, press printing
17 August 2011Fukushima3–16 August 20110.07Government
23 August 2011Fukushima12 March - 5 April 2011630,000NISA