Fukushima is no Chernobyl, IAEA says as level raised

Though Japan has raised the severity level of the Fukushima nuclear accident to that of the Chernobyl disaster, nuclear experts say the two incidents are vastly different.

On Tuesday, Japanese officials declared the crisis at the Fukushima plant a "major accident," and changed its severity rating from 5 to 7 -- the highest level on an international scale overseen by the International Atomic Energy Agency.

But a senior official with the IAEA said the rating change does not mean the Japan situation is comparable to Chernobyl.

"This is a totally different accident," the IAEA's Denis Flory told a news conference.

He said the amount of radiation released at Chernobyl in 1986 was far higher.

Japanese officials say the radiation from the Fukushima plant has so far amounted to just a tenth of that emitted in the Chernobyl disaster.

The severity level change was prompted by new assessments of the cumulative amount of radiation leaked from the plant. Officials were quick to insist that the rating change didn't signal that the crisis was worsening; only that the event as a whole is worse than previously thought.

According to the IAEA's scale, a "major accident" signifies that the radiation leaks could cause widespread effects on the environment and health.

"This reconfirms that this is an extremely major disaster. We are very sorry to the public, people living near the nuclear complex and the international community for causing such a serious accident," said Chief Cabinet Secretary Yukio Edano.

And Edano told reporters there was no "direct health damage" so far from the crisis.

"The accident itself is really serious, but we have set our priority so as not to cause health damage," he said.

Nevertheless, if the work to stabilize the plant does not meet with success soon, radiation levels could eventually exceed Chernobyl's emissions, officials warned.

Continuing aftershocks following the 9.0-magnitude earthquake on March 11 have slowed work on restoring the cooling systems at the reactors, which are critical to cooling the still-overheated nuclear fuel rods.

The latest aftershock had magnitude of 6.3, which prompted plant operator Tokyo Electric Power Co., or TEPCO, to temporarily pull back some workers. The aftershock also caused a fire to break out at the plant, but engineers quickly extinguished the blaze.

As well, the water that was pumped into the damaged reactors to cool them has left huge pools of contaminated, radioactive water that has also slowed down further repairs.

In a national television address, Prime Minister Naoto Kan urged the public not to panic and to focus on recovering from the disaster.

"Right now, the situation of the nuclear reactors at the Fukushima plant has been stabilizing step by step. The amount of radiation leaks is on the decline," he said. "But we are not at the stage yet where we can let our guards down."

Officials from Japan's Nuclear and Industrial Safety Agency said one of the reasons they raised the threat level to 7 is the cumulative amount of radioactive particles released into the atmosphere since the March 11 accident. Other factors included damage to the plant's buildings and accumulated radiation levels for its workers.

Reports say 21 plant workers have been affected by minor radiation sickness. No radiation-linked deaths have been reported.

"We have refrained from making announcements until we have reliable data," said NISA spokesman Hidehiko Nishiyama said.

"The announcement is being made now because it became possible to look at and check the accumulated data assessed in two different ways," he said, referring to measurements from NISA and Japan's Nuclear Security Council.

NISA and the NSC have been measuring emissions of radioactive iodine-131, which has a relatively short half-life of only a few days, 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, they decided that the equivalent of about 500,000 terabecquerels of radiation from iodine-131 had been released into the atmosphere since the crisis began.

That exceeds the Level 7 threshold of the International Nuclear and Radiological Event Scale of "several tens of thousands of terabecquerels" of iodine-131.

To put that into perspective, the Chernobyl incident released 5.2 million terabecquerels into the air -- about 10 times that of the Fukushima plant, the Japanese government said.

With reports from the Associated Press