Japan Raises Nuclear Disaster to Chernobyl Level

Japan upgraded its month-old nuclear emergency to a maximum seven on an international scale of atomic crises Tuesday, placing it on a par with the Chernobyl disaster a quarter-century ago.

The reassessment to a "major accident" with "widespread health and environmental effects" was based on the total radiation released, which officials said was one-tenth of the 1986 accident in the then Soviet Union.

As workers continued their struggle to stabilize the charred reactors, Japan was rocked by more aftershocks from the 9.0-magnitude quake on March 11 that sent a massive tsunami barreling into the northeast coast.

By the latest count the disaster, the country's worst post-war crisis, had killed more than 13,000 people and left over 14,000 others missing. Around 150,000 people are still in emergency shelters.

In the latest of a series of quakes in recent days, a powerful 6.3-magnitude tremor struck Fukushima prefecture Tuesday afternoon, forcing the temporary evacuation of nuclear plant workers and rattling buildings in Tokyo.

"About a week ago, we believed that the biggest threat at the plant was a new hydrogen explosion," said a senior government official, who asked not to be named. "But now when we take a big-picture view of the plant, the biggest threat is definitely aftershocks and tsunamis."

Japan has experienced more than 400 major aftershocks stronger than 5.0 in magnitude since March 11.

The reassessment on the UN's International Nuclear Events Scale (INES) came as Japan prepared to evacuate more people living near the plant, extending the 20-kilometer (12-mile) exclusion zone to take in several towns further afield.

Level seven accidents on the INES scale involve a "major release of radioactive material with widespread health and environmental effects requiring implementation of planned and extended countermeasures".

Each level on the scale indicates a roughly 10-fold increase in severity.

The previous rating of five had placed the unfolding disaster at the tsunami-hit Fukushima plant northeast of Tokyo on the same level as the 1979 Three Mile Island accident in the US state of Pennsylvania.

Despite the upgrade, nuclear safety agency official Hidehiko Nishiyama said there were marked differences between the Chernobyl and Fukushima accidents.

"In Chernobyl, there was acute exposure to a high level of radiation, and 29 people died from it. This is not the case in Fukushima," he said.

The longer-term death toll from the Chernobyl accident, in what is now Ukraine, ranges from a UN estimate in 2005 of 4,000 fatalities to tens or even hundreds of thousands suggested by non-governmental groups.

The official also said that while in the Chernobyl accident the reactor had exploded, "in Fukushima... the reactors themselves have stayed intact, although we are seeing some leakage".

However, an official for operator Tokyo Electrical Power Co. (TEPCO) said that "the radiation leak has not stopped completely and our concern is that it could eventually exceed Chernobyl", media reports said.

Nuclear experts looking at Fukushima have said that partial meltdowns took place when reactor cooling systems failed, causing a series of explosions that leaked radioactive material into the atmosphere.

Tens of thousands of residents were evacuated from the 20-kilometer exclusion zone and people in a further 10-kilometer band have been advised to stay indoors.

On Monday the government said it would order several other communities further afield to leave due to concerns over long-term exposure to radiation, but that a uniform extension of the zone was not appropriate.

Emergency crews at the plant have battled around the clock to bring the disaster under control and on Monday the government said the danger of a large leak of radioactive materials was becoming "significantly smaller".