TOKYO -- Japan's nuclear safety agency raised the severity rating of the country's nuclear crisis Friday from Level 4 to Level 5 on a seven-level international scale, putting it on par with the Three Mile Island accident in Pennsylvania in 1979.
Ryohei Shiomi, a spokesman for the nuclear safety agency, said Friday that the agency raised the rating of the Fukushima Dai-ichi nuclear crisis on the International Nuclear Event Scale. The scale defines a Level 4 incident as having local consequences and a Level 5 incident as having wider consequences.
The hallmarks of a Level 5 emergency are severe damage to a reactor core, release of large quantities of radiation with a high probability of "significant" public exposure or several deaths from radiation.
A partial meltdown at Three Mile Island also was ranked a Level 5. The Chernobyl accident of 1986, which killed at least 31 people with radiation sickness, raised long-term cancer rates, and spewed radiation for hundreds of miles (kilometers), was ranked a Level 7.
France's Nuclear Safety Authority has been saying since Tuesday that the crisis in northeastern Japan should be ranked Level 6 on the scale.
The fuel rods at all six reactors at the stricken Fukushima Dai-ichi complex contain plutonium - better known as fuel for nuclear weapons. While plutonium is more toxic than uranium, other radioactive elements leaking out are likely to be of greater danger to the general public.
Only six percent of the fuel rods at the plant's Unit 3 were a mixture of plutonium-239 and uranium-235 when first put into operation. The fuel in other reactors is only uranium, but even there, plutonium is created during the fission process.
This means the fuel in all of the stricken reactors and spent fuel pools contain plutonium.
Other developments in the crisis overnight:
ATTEMPTS TO COOL REACTORS: Military fire trucks spray seawater for a second day on the stricken Fukushima Dai-ichi nuclear complex in a desperate attempt to prevent its fuel from overheating and spewing dangerous radiation. A U.S. military fire truck joins six Japanese vehicles, but is apparently driven by Japanese workers. Japanese air force says some water appears to be reaching its target.
_ IAEA CALLS ACCIDENT "EXTREMELY SERIOUS." The head of the U.N.'s International Atomic Energy Agency says authorities are "racing against the clock" to cool the complex and calls the accident "extremely serious."
_ NEW POWER LINE NEARLY COMPLETE: The nuclear plant's operator, Tokyo Electric Power Co., hopes to finish laying a new power line to the plant on Friday to allow operators to restore cooling systems. But it is not clear if the cooling systems will still function.
_ MOMENT OF SILENCE: Tsunami survivors observe a minute of silence at the one-week mark since the quake, which struck at 2:46 p.m. Many are bundled up against the cold at shelters in the disaster zone, pressing their hands together in prayer. The twin disasters have left thousands dead and missing. Hundreds of thousands are staying in schools and other shelters, as supplies of fuel, medicine and other necessities run short.
_ IMPACT ON ECONOMY: The yen backs away from historic highs and Japanese shares rise after the Group of Seven major industrialized nations promises coordinated intervention in currency markets to support recovery from the disaster. The G-7 pledge comes a day after the yen soared to an all-time high against the dollar, possibly threatening Japanese exports. Japanese automakers, meanwhile, seek alternative parts suppliers to replace those knocked out by the earthquake, which forced most of the country's car production to a halt.