Thirty-two days after disaster struck, Japan finally admits Fukushima is in same league as Chernobyl

Published on Tuesday 12 April 2011 14:57

Japan has ranked its nuclear crisis at the highest possible severity on an international scale, taking it to the same level as the 1986 Chernobyl disaster.

Raising the threat level on the International Nuclear Event Scale at the Fukushima plant by two notches from five up to seven is an open acknowledgement that the nuclear accident is the second-worst in history after Chernobyl in what is now Ukraine.

The threat increase was recorded on the international scale overseen by the International Atomic Energy Agency (IAEA) and reflects concerns about long-term health risks as radioactive material continues to be emitted into the air, soil and seawater.

The decision to raise the threat level was made after radiation of a total up to 630,000 terabequerels - a unit of radioactivity - had been estimated at the stricken plant.

It was not clear when that level had been reached at the earthquake and tsunami hit nuclear reactors, but it has subsequently dropped to less than one terabequerel an hour, reports said.

The Japanese authorities insisted that upping the severity did not signal any new health dangers.

According to the Vienna-based IAEA, the new ranking signifies a major accident that includes widespread effects on the environment and people's health.

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The upgraded status did not mean radiation from the plant was worsening, but rather reflected concern about long-term health risks as it continues to spew into the atmosphere. Workers are still trying to restore disabled cooling systems at the plant, and radioactive isotopes have been detected in tap water, fish and vegetables.

In Scotland, traces of radioactive Iodine from Fukushima have been observed in Glasgow (370 becquerels per cubic metre), Lerwick (849 becquerels per cubic metre) and Caithness (500 becquerels per cubic metre).

Experts have said those levels of radioactivity are not high enough to be harmful to health.

In Japan, level seven signifies a "major accident" with "wider consequences" than the previous level, officials said.

"We have upgraded the severity level to seven as the impact of radiation leaks has been widespread from the air, vegetables, tap water and the ocean," said Minoru Oogoda of Japan's Nuclear and Industrial Safety Agency, the government's nuclear watchdog.

The IAEA said previous level five ratings had been provided separately for accidents at Reactors 1, 2 and 3 but had now been combined as a single event. Another affected unit, Reactor 4, has retained its level-three rating, it said.

Japanese officials said the leaks from the Fukushima plant so far amount to a tenth of the radiation emitted from Chernobyl, but about ten times the amount needed to reach the level 7 threshold.They acknowledged the emissions could eventually exceed Chernobyl's, but said the chance was very small.

The deaths of 31 men were blamed on high exposure to radiation and numerous cancer cases have been blamed on the Russian disaster. So far there have been no Japanese deaths due to radiation.

However, industry regulators have also acknowledged that a more severe nuclear accident is a distinct possibility until cooling systems are restored - a process likely to take months.

Seven levels of severity

1 Anomaly A breach of operating limits at a nuclear facility.

2 Incident The overexposure of a worker at a power reactor in Atucha in Argentina in 2005 was classed as an "incident".

3 Serious incident The release of a large quantity of radioactive material at Sellafield, Cumbria, in 2005 fell into this category.

4 Accident with local consequences Fatal overexposure to radiation of workers at the Tokaimura nuclear plant in Japan was classed at Level 4, as was the melting of a channel of fuel in a reactor at Saint Laurent des Eaux, France, in 1980.

5 Accident with wider consequences The Three Mile Island incident in Pennsylvania in 1979 fell into this category. The partial meltdown was the biggest nuclear accident in US history.

6 Serious accident A release of radioactive material caused by the explosion of a high activity waste tank was classed as a "serious accident". The explosion took place at Kyshtym, Russia, in 1957.

7 Major accident The Chernobyl disaster of 1986 in what is now Ukraine was classed as a category 7 event. An explosion and fire released large quantities of radiation that spread over much of Western Russia and Europe.