6 on site; 4 (and spent fuel pools) involved in accident; one of the four reactors was empty of fuel at the time of the accident.
Amount of nuclear fuel in affected reactors
1 reactor—190 tonnes (t, metric tons = 210 U.S. short tons): spent fuel pools not involved in incident[4]
4 reactors—854 tonnes (t, metric tons): 81 t in Unit 1 reactor, 111 t in Unit 2 reactor, 111 t in Unit 3 reactor, 0 t in Unit 4 reactor (defueled), 59 t in Unit 1 spent fuel pool (SFP), 119 t in Unit 2 SFP, 104 t in Unit 3 SFP, and 269 t in Unit 4 SFP[a]
Cause of the accident
Proximate 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 concurrently occurring with the ground sinking. 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.[citation needed]
300 Sv/h shortly after the explosion in vicinity of the reactor core.[8]
530 Sv/h inside Unit 2 containment vessel in 2017 according to Japan Times.[9]
Radioactivity released
According to IAEA, total release was 14 EBq (14,000 PBq).[10] 5.2 EBq (5,200 PBq) in iodine-131 equivalent [11][12]
As of 2014, a peer reviewed estimate of the total was 340–780 PBq, with 80% falling into the Pacific Ocean.[13] Radiation continues to be released into the Pacific via groundwater.
An area up to 500 kilometres (310 mi) away contaminated, according to the United Nations.[14][15][16]
Radiation levels exceeding annual limits seen over 60 kilometres (37 mi) to northwest and 40 kilometres (25 mi) to south-southwest, according to officials.[citation needed]
Two immediate trauma deaths; 28 deaths from Acute Radiation Syndrome out of 134 showing symptoms; four from an industrial accident (helicopter crash); 15 deaths from radiation-genic thyroid cancers (as of 2005);[20] as many as 4000 to 90000 cancer related deaths.[21]
1 confirmed cancer death attributed to radiation exposure by the government for the purpose of compensation following opinions from a panel of radiologists and other experts, medical sources pending for long-term fatalities due to the radiation.
Current status
All 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.
^183.3 kg/assembly;[5] 400 assemblies in reactor 1, 548 assemblies in reactors 2&3, 0 assemblies in reactor 4, total of 1496 assemblies in reactors 1-4;[5][6] 292 assemblies in Unit 1 spent fuel pool (SFP), 587 assemblies in Unit 2 SFP, 514 assemblies in Unit 3 SFP, 1331 assemblies in Unit 4 SFP, total of 2724 assemblies in spent fuel pools 1-4.[7]
^Three Mile Island, Chernobyl, and Fukushima, A comparison of three nuclear reactor calamities reveals some key differences. IEEE. 1 November 2011. doi:10.1109/MSPEC.2011.6056644.
^Steinhauser, Georg; Brandl, Alexander; Johnson, Thomas E. (2014). "Comparison of the Chernobyl and Fukushima nuclear accidents: A review of the environmental impacts". Science of the Total Environment. 470–471: 800–817. Bibcode:2014ScTEn.470..800S. doi:10.1016/j.scitotenv.2013.10.029. PMID24189103.
^Archived 14 September 2011 at the Wayback Machine(in German). ZAMG, 22 March 2011, archived from Original on 20 April 2011, retrieved on 20 April 2011.
^Archived 27 February 2012 at the Wayback Machine(in German). In: www.zamg.ac.at. Zentralanstalt für Meteorologie und Geodynamik, 2 April 2011, archived from Original on 20 April 2011, retrieved on 2 April 2011.
^ abcdArchived 30 January 2012 at the Wayback Machine. JAIF / NHK, 26 April 2011, archived from Original on 27 April 2011, retrieved on 27 April 2011.
^ abcdeArchived 28 March 2012 at the Wayback Machine. NISA/METI, 12 April 2011, archived from Original on 12 April 2011, retrieved on 12 April 2011.
^Archived 19 April 2012 at the Wayback Machine. In: Atoms in Japan. JAIF, 5 September 2011, archived from Original, retrieved on 20 December 2011.
^Archived 30 January 2012 at the Wayback Machine. Kantei, 15 September 2011, archived from Original, retrieved on 17 December 2011. Spent fuel pool measurement on page 205, 207, 210 and 214; total release on page 449. [dead link]
^Archived 30 January 2012 at the Wayback Machine. JAIF / NHK, 18 August 2011, archived from Original, retrieved on 21 August 2011. Converted from 200 MBq/h in a two-week period.
