A suspected breach in the core at one reactor at a stricken Fukushima nuclear plant could mean more serious radioactive contamination:

The Globe and Mail: March 25, 2011

Japanese officials revealed Friday — a situation the prime minister called “very grave and serious.”

A somber Prime Minister Naoto Kan sounded a pessimistic note at a briefing hours after nuclear safety officials said they suspected a breach at the Fukushima Dai-ichi plant that would be a major setback in the urgent mission to stop the facility from leaking radiation.

Radiation spike threatens Japan's water supply:

“The situation today at the Fukushima Dai-ichi power plant is still very grave and serious. We must remain vigilant,” Kan said. “We are not in a position where we can be optimistic. We must treat every development with the utmost care.”

The uncertain situation halted work at the nuclear complex, where dozens had been trying feverishly to stop the overheated plant from leaking dangerous radiation. The plant has leaked some low levels of radiation, but a breach could mean a much larger release of contaminants.

The uncertain situation halted work Friday at the Fukushima Dai-ichi nuclear complex, where dozens had been working feverishly to stop the overheated plant from leaking dangerous radiation, officials said.

Suspicions of a possible breach were raised when two workers waded into water 10,000 times more radioactive than normal and suffered skin burns when the water splashed over their protective boots, the Nuclear and Industry Safety Agency said.

However, though damage cannot be ruled out, the cause remained unclear, spokesman Hidehiko Nishiyama told reporters.

“It is possible there may be damage somewhere in the reactor,” he said, adding later that there was no data suggesting there were any cracks and that a leak in the plumbing or the vents could be to blame.

The confusion was yet another setback to the urgent task of gaining control of the Fukushima nuclear plant 220 kilometres northeast of Tokyo two weeks after a magnitude-9 quake triggered a tsunami that engulfed the facility and knocked out its crucial cooling system.

The plant has been releasing radiation, with elevated levels of radiation turning up in raw milk, seawater and 11 kinds of vegetables, including broccoli, cauliflower and turnips.

Radiation from Fukushima exceeds Three Mile Island March 25, 2011

Fukushima No. 1 nuclear plant, crippled by the Great East Japan Earthquake of March 11, has discharged more radiation than the infamous Three Mile Island nuclear plant in the United States, according to calculations by the central government.

It has already reached a level 6 serious accident on the International Nuclear and Radiological Event Scale (INES).

Separately, calculations made by experts place the level of soil contamination in some locations at levels comparable to those found after the Chernobyl accident in 1986.

With the Fukushima plant continuing to release radiation, there is the danger that the contaminated land will be unusable for many years.

To calculate the spread of radiation using the System for Prediction of Environmental Emergency Dose Information, the Nuclear Safety Commission of Japan estimates the discharge rate for radioactive iodine per hour from the Fukushima plant based on radiation measurements taken at various locations.

Using those figures to make a simple calculation of the amount of discharge between 6 a.m. March 12 and midnight Wednesday results in figures between 30,000 and 110,000 terabecquerels. Tera is a prefix meaning 1 trillion.

The INES defines a level 7 major accident such as Chernobyl as one in which radiation of more than several tens of thousands of terabecquerels is released.

The Fukushima accident is already at a level 6, which is defined as having a radiation discharge of several thousands to several tens of thousands of terabecquerels.

The discharge of radioactive iodine at the Chernobyl accident was said to be about 1.8 million terabecquerels. The Three Mile Island accident, which was considered the second-worst accident until now, had only a limited discharge of radioactive iodine into the outside atmosphere, but was classified as a level 5 accident because of the considerable damage done to the core.

In a provisional assessment made March 18 by the Nuclear and Industrial Safety Agency, the situation at the No. 1 to No. 3 reactors at Fukushima was classified as a level 5 accident, but if estimates of the radiation discharged should progress, there could be the possibility of a revision in that assessment.

Meanwhile, calculations of soil contamination by experts have already produced results that are at the same level as for Chernobyl.

Cesium-137 levels of 163,000 becquerels per kilogram of soil was detected in Iitate, Fukushima Prefecture, about 40 kilometers northwest of the Fukushima plant, on March 20. That was the highest figure in the prefecture.

According to Tetsuji Imanaka, an associate professor of nuclear engineering at the Kyoto University Research Reactor Institute, if the Iitate figure was converted to one square meter, the figure would be 3.26 million becquerels.

After the Chernobyl accident, residents who lived in regions with cesium levels of 550,000 becquerels ore more per square meter were forcibly moved elsewhere.

"Iitate has reached a contamination level in which evacuation is necessary," Imanaka said. "Radiation is still being released from the Fukushima plant. The areas of high contamination can be considered to be on par with Chernobyl."

Residents who were forced to move after the Chernobyl accident were believed to have been exposed to an average of about 50 millisieverts of radiation.

However, a study of the health of residents who lived for many years on contaminated land found that the incidence of leukemia among adults did not increase.

The increase in thyroid gland cancer was believed due to internal radiation exposure among children who drank milk contaminated by radioactive iodine when they lived in areas close to Chernobyl.

The accumulated radiation level at Iitate as of Thursday afternoon was 3.7 millisieverts.

Shigenobu Nagataki, professor emeritus at Nagasaki University, who specializes in radiation medicine, said, "Because there were no other health problems after the Chernobyl accident besides thyroid gland cancer among children, it is unlikely (that the situation in Fukushima) would lead immediately to health problems. In areas where high levels of contamination were detected, measures should be considered after holding sufficient discussions with residents based on the data that is available."

Meanwhile, in Vienna, Yukiya Amano, the director-general of the International Atomic Energy Agency, told The Asahi Shimbun that while the situation at the Fukushima No. 1 plant was still serious, it was too early to compare it to Chernobyl.

Asked about radiation found in agricultural produce and drinking water, Amano said, "The circumstances are serious based on the standards used in Japan."

However, touching upon analyses and predictions about radiation contamination that have related the Fukushima incident to Chernobyl, Amano said, "The studies are being conducted based on very limited data and are very extreme."

Amano also referred to debate in other nations about their own nuclear energy policy.

"There is no change to the fact that nuclear power is a stable and clean form of energy," he said, indicating his hope that other nations would respond in a calm manner.