Japan raised the severity level of the crisis at its crippled nuclear plant Tuesday to rank it on par with the 1986 Chernobyl disaster, citing cumulative radiation leaks that have contaminated the air, tap water, vegetables and seawater.
Japanese nuclear regulators said the rating was being raised from 5 to 7 — the highest level on an international scale overseen by the International Atomic Energy Agency — after new assessments of radiation leaks from the Fukushima Dai-ichi plant since it was disabled by the March 11 tsunami.
The new ranking signifies a "major accident" that includes widespread effects on the environment and health, according to the Vienna-based IAEA.
"Our preparations for how to measure (the radiation leakage) when such a tsunami and earthquake occurred were insufficient and, as a result, we were late in disseminating information internationally," said a senior official in Prime Minister Naoto Kan's office.
Hidehiko Nishiyama, a deputy director-general of the Nuclear and Industrial Safety Agency (NISA), said the decision to raise the severity of the incident from level 5 to 7 — the same as the Chernobyl disaster in Ukraine in 1986 — was based on cumulative quantities of radiation released.
"Even before this, we had considered this a very serious incident so, in that sense, there will be no big change in the way we deal with it just because it has been designated level 7," an agency official said.
Continued aftershocks following the 9.0-magnitude megaquake on March 11 have impeded work in stabilizing the Fukushima plant — the latest a 6.3-magnitude one Tuesday that prompted plant operator Tokyo Electric Power Co., or TEPCO, to temporarily pull back workers.
The aftershock caused a fire to break out at the plant, but engineers later extinguished the blaze.
However, the operator of the stricken facility appears to be no closer to restoring cooling systems at the reactors, critical to lowering the temperature of overheated nuclear fuel rods.
The official in Kan's office said that the prime minister would instruct plant operator Tokyo Electric Power (TEPCO) to set target dates for when it would halt the radiation leakage as well as restore the cooling systems.
No radiation-linked deaths have been reported since the earthquake struck, and only 21 plant workers have been affected by minor radiation sickness, according to Chief Cabinet Secretary Yukio Edano.
'Nowhere near' Chernobyl
A level 7 incident means a major release of radiation with a widespread health and environmental impact, while a 5 level is a limited release of radioactive material, with several deaths, according to the International Atomic Energy Agency (IAEA).
Several experts said the new rating exaggerated the severity of the crisis, and that the Chernobyl disaster was far worse.
"It's nowhere near that level. Chernobyl was terrible — it blew and they had no containment, and they were stuck," said nuclear industry specialist Murray Jennex, an associate professor at San Diego State University in California.
"Their (Japan's) containment has been holding, the only thing that hasn't is the fuel pool that caught fire."
The blast at Chernobyl blew the roof off a reactor and sent large amounts of radiation wafting across Europe. The accident contaminated vast areas, particularly in Ukraine and neighboring Belarus, led to the evacuation of well over 100,000 and affected livestock as far away as Scandinavia and Britain.
Nevertheless, the increase in the severity level heightens the risk of diplomatic tension with Japan's neighbors over radioactive fallout. China and South Korea have already been critical of the operator's decision to pump radioactive water into the sea, a process it has now stopped.
"Raising the level to a 7 has serious diplomatic implications. It is telling people that the accident has the potential to cause trouble to our neighbors," said Kenji Sumita, a nuclear expert at Osaka University.
NISA and the NSC have been measuring emissions of radioactive iodine-131 and cesium-137, a heavier element with a much longer half-life. Based on an average of their estimates and a formula that converts elements into a common radioactive measure, the equivalent of about 500,000 terabecquerels of radiation from iodine-131 has been released into the atmosphere since the crisis began.
That well exceeds the Level 7 threshold of the International Nuclear and Radiological Event Scale of "several tens of thousands of terabecquerels" of iodine-131. A terabecquerel equals a trillion becquerels, a measure for radiation emissions.
The government says the Chernobyl incident released 5.2 million terabecquerels into the air — about 10 times that of the Fukushima plant.