Fukushima gets worst crisis rating. But how much radiation has been released?

Based on new estimates of the radiation that has been released, Fukushima now has the worst score on the IAEA's accident rating scale. But much about the reactors, and their future, is still unknown.

Tokyo Electric Power Co./AP
This April 10 photo released by Tokyo Electric Power Co. (TEPCO) shows orange colored floats suspending 'silt fence,' that was installed under water to help prevent contaminated water from spreading outside the Fukushima Daiichi nuclear power plant's bay. The tsunami-crippled nuclear complex is still leaking radiation after its cooling systems were knocked out by the March 11 tsunami, and the government on April 11 urged even more people living around the complex to leave within a month, citing concerns about long-term health risks from radiation as the crisis wears on.

Japan on Tuesday raised its assessment of the severity of the situation at the crippled Fukushima Daiichi nuclear plant to 7 – the worst score possible on the accident rating scale overseen by the International Atomic Energy Agency.

That does not mean the Fukushima crisis has suddenly become more dire. Japanese nuclear regulators said they moved the rating up from its previous position of 5 due to new assessments of the total amount of radiation released from the plant since it was pulverized by an earthquake and tsunami on March 11.

So far the Fukushima accident has resulted in a release of about one-tenth of the amount of radiation that escaped from Chernobyl, the worst civilian nuclear disaster to date. Japanese officials said there was a small chance that Fukushima could eventually exceed Chernobyl’s emissions if workers are not able to soon restore the site’s crippled cooling systems.

IN PICTURES: Japan's 9.0 earthquake

“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.

Does the increase in the accident rating mean that the Japanese government and Tokyo Electric Power Company (TEPCO) now have a better idea of the extent of damage at the plant, and where radioactive releases have gone? After all, over the last month residents of the region have complained that they have received confusing and sometimes contradictory information. On Monday, for instance, Japan finally began urging the evacuation of residents of “hot spots” marked by high radiation levels outside the original 12-mile evacuation zone.

Well, officials surely are developing a more accurate picture of the effects of the nuclear accident by the day. But much remains unknown, from the condition of partially melted fuel in the damaged reactors, to why hot spots such as Iitate were affected by greater deposition of radioactive material. What Japan has now is more of an outline of the incident – an outline that will be filled in gradually as the months go by, workers gain greater access to damaged areas, and scientists collect more and more radiation measurements from the environment.

That is why it is premature to make any recommendations about improved safety procedures in the US and elsewhere, according to one former head of the US Nuclear Regulatory Commission.

“After Three Mile Island and after Chernobyl, it took several years of analyzing what happened before one could really reach a conclusion about what could have been done to prevent it, and we are a long way away from having that kind of knowledge about the Japanese systems,” said former NRC chief John Ahearne in an interview posted on the website of the Council on Foreign Relations.

The preliminary nature of authorities’ knowledge about Fukushima can be seen in the fact that different Japanese nuclear regulatory agencies on Tuesday issued different estimates for the total amount of radiation the crippled plant has emitted so far.

Japan’s Nuclear and Industrial Safety Agency estimated that 370 thousand terabecquerels of radioactive iodine-131 and cesium-137 have been released from Fukushima since March 11. Meanwhile, Japan’s Nuclear Security Council put the total release of radioactive material at 630 thousand terabecquerels.

At a joint press conference Tuesday the two agencies agreed that the Fukushima accident was a 7 on the IAEA scale. But officials stressed that the increase in the rating was not a signal for the public to panic.

“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,” said Prime Minister Naoto Kan.

IN PICTURES: Japan's 9.0 earthquake

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