Anyone knows about the nuclear accident happened on March 2011, as a consequence of the Tsunami generated by the 9.0 Richter scale earthquake, the 5th strongest ever recorded.
By now the nuclear threat level is 7 (INES – International Nuclear Event Scale), same level of the Chernobyl disaster.

Here an extract of what you can find about the INES scale:

Threat levels

7 – Major accident
6 – Serious accident
5 – Accident with wider consequences
4 – Accident with local consequences
3 – Serious incident
2 – Incident
1 – Anomaly
0 – Deviation (no safety significance)

Threat levels details

Level 7: Major accident

Impact on people and environment
Major release of radio­active ­material with widespread health and environmental effects requiring implementation of planned and extended ­countermeasures
There have been two such events to date:

  • Chernobyl disaster, 26 April 1986. A power surge during a test procedure resulted in a criticality accident, leading to a powerful steam explosion and fire that released a significant fraction of core material into the environment, resulting in a death toll of 56 as well as estimated 4,000 additional cancer fatalities among people exposed to elevated doses of radiation. As a result, the city of Chernobyl (pop. 14,000) was largely abandoned, the larger city of Pripyat (pop. 49,400) was completely abandoned, and a 30 km exclusion zone was established.
  • Fukushima I nuclear accidents, a series of events beginning on 11 March 2011. Rated level 7 on 11 April 2011 by the Japanese government’s nuclear safety agency.[2][3] Major damage to the backup power and containment systems caused by the 2011 Tōhoku earthquake and tsunami resulted in overheating and leaking from some of the Fukushima I nuclear plant’s reactors. Each reactor accident was rated separately; out of the six reactors, three were rated level 5, one was rated at a level 3, and the situation as a whole was rated level 7.[4] An exclusion zone of 20 km was established around the plant as well as a 30 km voluntary evacuation zone[5] .

Level 6: Serious accident

Impact on people and environment
Significant release of radioactive material likely to require implementation of planned countermeasures.
There has been only one such event to date:

  • Kyshtym disaster at Mayak, Soviet Union, 29 September 1957. A failed cooling system at a military nuclear waste reprocessing facility caused a steam explosion that released 70–80 tons of highly radioactive material into the environment. Impact on local population is not fully known. This is the only accident to go over 5 on the scale besides Chernobyl and Fukushima.[6]

Level 5: Accident with wider consequences

Impact on people and environment
Limited release of radioactive ­material likely to require i­mplementation of some planned­ countermeasures.
Several deaths from ­radiation.
Impact on radiological barriers and control
Severe damage to reactor core.
Release of large quantities of radioactive material within an installation with a high probability of significant public exposure. This could arise from a major criticality accident or fire.
Examples:

Level 4: Accident with local consequences

Impact on people and environment
Minor release of radioactive material unlikely to result in implementation of planned countermeasures other than local food controls.
At least one death from radiation.
Impact on radiological barriers and control
Fuel melt or damage to fuel ­resulting in more than 0.1% release of core inventory.
Release of significant quantities of radioactive material within an installation with a high ­probability of significant public exposure.
Examples:

Level 3: Serious incident

Impact on people and environment
Exposure in excess of ten times the statutory annual limit for workers.
Non-lethal deterministic health effect (e.g., burns) from radiation.
Impact on radiological barriers and control
Exposure rates of more than 1 Sv/h in an operating area.
Severe contamination in an area not expected by design, with a low probability of ­significant public exposure.
Impact on defence-in-depth
Near accident at a nuclear power plant with no safety provisions remaining.
Lost or stolen highly radioactive sealed source.
Misdelivered highly radioactive sealed source without adequate procedures in place to handle it.
Examples:

Level 2: Incident

Impact on people and environment
Exposure of a member of the public in excess of 10 mSv.
Exposure of a worker in excess of the statutory annual limits.
Impact on radiological barriers and control
Radiation levels in an operating area of more than 50 mSv/h.
Significant contamination within the facility into an area not expected by design.
Impact on defence-in-depth
Significant failures in safety ­provisions but with no actual ­consequences.
Found highly radioactive sealed orphan source, device or transport package with safety provisions intact.
Inadequate packaging of a highly radioactive sealed source.
Examples:

Level 1: Anomaly

Impact on defence-in-depth
Overexposure of a member of the public in excess of statutory ­annual limits.
Minor problems with safety components with significant defence-in-depth remaining.
Low activity lost or stolen radioactive source, device or transport package.

(Arrangements for reporting minor events to the public differ from country to country. It is difficult to ensure precise consistency in rating events between INES Level-1 and Below scale/Level-0)

Examples:

  • Gravelines (Nord, France), 8 August 2009; during the annual fuel bundle exchange in reactor #1, a fuel bundle snagged on to the internal structure. Operations were stopped, the reactor building was evacuated and isolated in accordance with operating procedures.[10]
  • TNPC (Drôme, France), July 2008; leak of 6,000 litres (1,300 imp gal; 1,600 US gal) of water containing 75 kilograms (170 lb) of uranium into the environment.

Level 0: Deviation

No safety significance.

Examples:

Out of scale

There are also events of no safety relevance, characterized as “out of scale”.[14]

    Examples:

    • 17 November 2002, Natural Uranium Oxide Fuel Plant at the Nuclear Fuel Complex in Hyderabad, India: A chemical explosion at a fuel fabrication facility.[15]
    • 29 September 1999: H.B. Robinson, United States: A tornado sighting within the protected area of the nuclear power plant (NPP).[16][17][18]
    • 5 March 1999: San Onofre, United States: Discovery of suspicious item, originally thought to be a bomb, in nuclear power plant.[19]

The main worry, for me but I guess also for many people around the world, are health consequences on the local and global population, here what can be found in the Fukushima Accident wiki page:

Long-term health consequences

The situation remains in the acute phase for detection of human health effects, according to the World Health Organization. Still, the WHO has stated that the basis for continuing public health studies over the next 20 years need to be put in place.[390] Studies on the effects of the Chernobyl nuclear disaster suggest that longer-term studies are justified. A study published in the journal Environmental Health Perspectives, “The Chernobyl Accident 20 Years On,” found that the most prominent health issue resulting from Chernobyl is thyroid cancer for people exposed to radiation as children; in neighboring Belarus, such reports were initially greeted with skepticism by scientists, but the link has been established. Adverse psychological consequences have been firmly established in the Ukraine and Belarus, including negative stress outcomes and addiction. Less certain, but worthy of increased attention, are possible genetic effects of radiation, which have been established; the precise health effects are still under study. Also less clear is the level of increased risk for leukemia and birth defects, although increases here have been observed.[391] Another study, “Thyroid Cancers in Ukraine Related to the Chernobyl Accident,” states that across the sample population there exists an increased risk of thyroid cancer 20 years after the initial exposure. This risk was not uniform for the whole sample and was most varied conditional on geographical distance from the plant at the time of exposure. The study also found that there is no evidence indicating that this increased cancer risk for those who lived in the area at the time of the accident is decreasing at all over time.[392]