Radioactive material has been released from the Fukushima containment vessels as the result of deliberate venting to reduce gaseous pressure, deliberate discharge of coolant water into the sea, and accidental or uncontrolled events. Junichi Matsumoto, acting head of TEPCO's Nuclear Power & Plant Siting Division, acknowledged the seriousness of the Fukushima accident at a [12 April] press conference stating, "although the details of the [Chernobyl and Fukushima] accidents are different, from the standpoint of how much radiation has been released, [Fukushima] is equal to or more serious than Chernobyl."
Using Japanese Nuclear Safety Commission
numbers, Asahi Shimbun
reported that by 24 March the accident might have emitted 30,000 to 110,000 TBq
The highest reported radiation dose rate outside was 1000 mSv/h on 16 March.
On 29 March, at times near Unit 2, radiation monitoring was hampered by a belief that some radiation levels may be higher than 1000 mSv/h, but that "1,000 millisieverts is the upper limit of their measuring devices".
The maximum permissible dose for Japanese nuclear workers was increased to 250 mSv/year, for emergency situations after the accidents.
TEPCO has been criticized in providing insufficient safety equipment for its workers, including accusations of a lack of monitoring and decontamination equipment, and for giving the most dangerous work to subcontractors.
The Japanese Ministry of Health, Labour and Welfare announced that levels of radioactivity exceeding legal limits had been detected in milk produced in the Fukushima area and in certain vegetables in Ibaraki. On 23 March, Tokyo drinking water exceeded the safe level for infants, prompting the government to distribute bottled water to families with infants.
Seawater near the discharge of the plant elevated levels of iodine-131 were found on 22 March, which had increased to 3,355 times the legal limit on 29 March.[citation needed
] Also concentrations far beyond the legal limit were measured for caesium-134 and caesium-137 were more than 100 times above the limit.[citation needed
The severity of the nuclear accident is provisionally
rated 7 on the International Nuclear Event Scale
(INES). This scale runs from 0, indicating an abnormal situation with no safety consequences, to 7, indicating an accident causing widespread contamination with serious health and environmental effects. Prior to Fukushima, the Chernobyl disaster
was the only level 7 accident on record, while the Three Mile Island accident
was a level 5 accident.
The Japan Atomic Energy Agency
initially rated the situation at Unit 1 below both of these previous accidents; on 13 March it announced it was classifying the event at level 4, an "accident with local consequences".
On 18 March it raised its rating on Units 1, 2 and 3 to Level 5, an "accident with wider consequences". It classified the situation at Unit 4 as a level 3 "serious incident".
Several parties disputed the Japanese classifications, arguing that the situation was more severe than they were admitting at the time. On 14 March, three Russian experts stated that the nuclear accident should be classified at Level 5, perhaps even Level 6.
One day later, the French nuclear safety authority ASN said that the Fukushima plant could be classified as a Level 6.
as of 18 March , the French nuclear authority
—and as of 15 March, the Finnish nuclear safety authority
—estimated the accidents at Fukushima to be at Level 6 on the INES.
On 24 March, a scientific consultant for noted anti-nuclear environmental group Greenpeace
, working with data from the Austrian ZAMG
and French IRSN
, prepared an analysis in which he rated the total Fukushima accident at INES level 7.
The Asahi Shimbun
newspaper reported on 26 March that the accident might warrant level 6, based on its calculations.
The Wall Street Journal stated that Japan's NISA would make any decision on raising the level.
INES level 6, or "serious accident", had only been applied to the Kyshtym disaster
(Soviet Union, 1957), while the only level 7 was Chernobyl (Soviet Union, 1986). Previous level 5 accidents included the Windscale fire
(United Kingdom, 1957); the Lucens reactor
(Switzerland, 1969); Three Mile Island (United States, 1979); and the Goiânia accident
Assessing "seriousness" as partial or full meltdown at a civilian plant, The New York Times reported on 3 April that based on remote sensing, computer "simulations suggest that the number of serious accidents has suddenly doubled, with three of the reactors at the Fukushima Daiichi complex in some stage of meltdown." The Times counted three previous civilian meltdowns, from World Nuclear Association
information: Three Mile Island; Saint-Laurent Nuclear Power Plant
(France, 1980, INES level 4); and Chernobyl.
On 11 April, the Japanese Nuclear and Industrial Safety Agency (NISA) temporarily raised the disaster at Fukushima Daiichi to Level 7 on the INES scale, by considering the whole event and not considering each reactor as an individual event per se (rated between 3 and 5). This would make Fukushima the second Level 7 "major accident" in the history of the nuclear industry; having said that, radiation released as a result of the events at Fukushima was, as of 12 April, only approximately 10% of that released as a result of the accident at Chernobyl (1986), also rated as INES Level 7.
said Fukushima has 20 times the potential to be released than Chernobyl. Hot spots are being found 60 to 70 kilometres away from the reactor (further away than they were found from Chernobyl), and the amount of radiation in many of them is the amount that caused areas to be declared no-man's-land for Chernobyl.