Danger Posed by Radioactivity in Japan Hard to Assess

The different radioactive materials being reported at the nuclear accidents in Japan range from relatively benign to extremely worrisome. 

The central problem in assessing the degree of danger is that the amounts of various radioactive releases into the environment are now unknown, as are the winds and other atmospheric factors that determine how radiation-emitting materials will disperse around the stricken plants.
Still, the properties of the materials and their typical interactions with the human body give some indication of the threat.

“The situation is pretty bad,” said Frank N. von Hippel, a nuclear physicist who advised the Clinton White House and now teaches international affairs at Princeton. “But it could get a lot worse.”

In Vienna on Saturday, the International Atomic Energy Agency said Japanese authorities had informed it that iodine pills would be distributed to residents around the Fukushima Daiichi and Daini plants in northeast Japan. Both have experienced multiple failures in the wake of the huge earthquake and tsunami that struck Friday.
In the types of reactors involved, water is used to cool the reactor core and produce steam to turn the turbines that make electricity. The water contains two of the least dangerous radioactive materials now in the news — radioactive nitrogen and tritium. Normal plant operations produce both of them in the cooling water, and they are even released routinely in small amounts into the environment, usually through tall chimneys.

Nitrogen is the most common gas in the earth’s atmosphere, and at a nuclear plant the main radioactive form is known as nitrogen-16. It is made when speeding neutrons from the reactor’s core hit oxygen in the surrounding cooling water. This radioactive form of nitrogen does not occur in nature.

The danger of nitrogen-16 is an issue only for plant workers and operators because its half-life is only seven seconds, after which it decays back into natural nitrogen. A half-life is the time it takes half the atoms of a radioactive substance to disintegrate.
The other radioactive material often in the cooling water of a nuclear reactor is tritium. It is a naturally occurring radioactive form of hydrogen, sometimes known as heavy hydrogen. It is found in trace amounts in groundwater throughout the world. Tritium emits a weak form of radiation that does not travel very far in the air and cannot penetrate the skin.
It accumulates in the cooling water of nuclear reactors and is often vented in small amounts to the environment. Its half-life is 12 years.

The big worries on the reported releases of radioactive material in Japan center on radioactive iodine and cesium.

“They imply some kind of core problem,” said Thomas B. Cochran, a senior scientist in the nuclear program of the Natural Resources Defense Council, a private group in Washington.
The active core of a nuclear reactor splits atoms in two to produce bursts of energy and, as a byproduct, large masses of highly radioactive particles. The many safety mechanisms of a nuclear plant focus mainly on keeping these so-called fission products out of the environment.
Iodine-131 has a half-life of eight days and is quite dangerous to human health. If absorbed through contaminated food, especially milk and milk products, it will accumulate in the thyroid and cause cancer. Located near the base of the neck, the thyroid is a large endocrine gland that produces hormones that help control growth and metabolism.

Dr. von Hippel of Princeton said the thyroid danger was gravest in children. “The thyroid is more sensitive to damage when the cells are dividing and the gland is growing,” he said.
Fortunately, an easy form of protection is potassium iodide, a simple compound typically added to table salt to prevent goiter and a form of mental retardation caused by a dietary lack of iodine.
If ingested promptly after a nuclear accident, potassium iodide, in concentrated form, can help reduce the dose of radiation to the thyroid and thus the risk of cancer. In the United States, the Nuclear Regulatory Commission recommends that people living within a 10-mile emergency planning zone around a nuclear plant have access to potassium iodide tablets.
Over the long term, the big threat to human health is cesium-137, which has a half-life of 30 years.
At that rate of disintegration, John Emsley wrote in “Nature’s Building Blocks” (Oxford, 2001), “it takes over 200 years to reduce it to 1 percent of its former level.”

It is cesium-137 that still contaminates much of the land in Ukraine around the Chernobyl reactor. In 1986, the plant suffered what is considered the worst nuclear power plant accident in history.
Cesium-137 mixes easily with water and is chemically similar to potassium. It thus mimics how potassium gets metabolized in the body and can enter through many foods, including milk. After entering, cesium gets widely distributed, its concentrations said to be higher in muscle tissues and lower in bones.
The radiation from cesium-137 can throw cellular machinery out of order, including the chromosomes, leading to an increased risk of cancer.

The Environmental Protection Agency says that everyone in the United States is exposed to very small amounts of cesium-137 in soil and water because of atmospheric fallout from the nuclear detonations of the cold war.
The agency says that very high exposures can result in serious burns and even death, but that such cases are extremely rare. Once dispersed in the environment, it says, cesium-137 “is impossible to avoid.”
 
This article has been revised to reflect the following correction:

Read more...

Cuba Gives 15-Year Prison Term to American

A Cuban court sentenced an American government contractor, Alan Gross, to 15 years in prison for crimes against the state, Cuban state television reported Saturday.
Mr. Gross, 61, was detained in December 2009 while on a U.S.A.I.D. mission in Cuba designed to weaken the government. Cuban authorities said that Mr. Gross was distributing satellite telephone equipment, which could be sued to access the Internet, to Jewish groups in Cuba. Those groups have denied having anything to do with him.

The prosecution was seeking a 20-year sentence.
A panel of judges found that the evidence “demonstrated the participation of the North American contractor in a subversive project of the U.S. government that aimed to destroy the Revolution through the use of communications systems out of the control of authorities,” the Associated Press reported Saturday.

The United State National Security Council spokesman, Tommy Vietor, criticized the ruling and called again for Mr. Gross to be released. “Today’s sentencing adds another injustice to Alan Gross’s ordeal,” he said. “He has already spent too many days in detention and should not spend one more.”

Mr. Gross’ detention has been a point of contention between the United States and the Cuban government, even as President Obama has loosened restrictions on travel for groups like scholars and artists and pledged renewed engagement with the Cuban people.
Most political observers have said they expect Mr. Gross to be released on humanitarian grounds. 

He has lost some 90 pounds while in detention, and his daughter had a double mastectomy after a cancer diagnosis last year.

Read more...

Japan Floods Nuclear Reactor Crippled by Quake in Effort to Avert Meltdown

TOKYO — Japanese officials took the extraordinary step on Saturday of flooding a crippled nuclear reactor with seawater in a last-ditch effort to avoid a nuclear meltdown, as the nation grappled simultaneously with its worst nuclear mishap and the aftermath of its largest recorded earthquake. 

A radiation leak and explosion at the Fukushima Daiichi Nuclear Power Station on Saturday prompted the government to expand an evacuation order to affect 170,000 people in the plant’s vicinity. And the plant’s operator issued an emergency notice early Sunday morning that a second reactor at the same aging plant was also experiencing critical failures of its cooling system and that rising pressure there risked a new explosion.
The government said radiation emanating from the first reactor appeared to be decreasing after the blast Saturday afternoon destroyed part of the facility, and they said that they had filled it with sea water to prevent full meltdown of the nuclear fuel. That step would only be taken in extreme circumstances because ocean water is likely to permanently disable the reactor.

The Japanese Nuclear and Industrial safety agency said as many as 160 people may have been exposed to radiation around the plant, and Japanese news media said three workers at the facility were suffering from full-on radiation sickness.
Even if Japan manages to avoid large, uncontrolled releases of radiation that would result from a meltdown, the problems at the Fukushima facility already amounted to the worst nuclear accident in Japan’s history and perhaps the biggest malfunction at a nuclear plant since the Chernobyl disaster 25 years ago, the worst ever.
The handling of the crisis and vulnerability of Japan’s extensive nuclear facilities to earthquakes and tsunamis will also add to long-simmering grass-roots resistance against nuclear power within Japan, where people have learned to doubt the industry’s reliability as well as anodyne official statements about safety.
Even before the explosion on Saturday, officials said they had detected radioactive cesium, which is created when uranium fuel is split, an indication that some of the nuclear fuel in the reactor was already damaged — a situation sometimes referred to as a partial meltdown. How much damage the fuel suffered remained uncertain, though safety officials insisted repeatedly through the day that radiation leaks outside the plant remained small.

Although officials said the leaks did not pose a major health risk, they also told the International Atomic Energy Agency that they were making preparations to distribute iodine, which helps protect the thyroid gland from radiation exposure, to people living near Daiichi and a second nuclear plant that suffered damage in the quake, called Daini, about 10 miles away.
Worries about the safety of the two plants were worsened on Saturday because government officials and executives of Tokyo Electric Power, which runs the plant, gave confusing accounts of the causes of the dramatic midday explosion and the damage it caused. Late Saturday night, officials said that the explosion occurred in a structure housing turbines near the No. 1 reactor at the plant rather than inside the reactor itself.

The blast, apparently caused by a sharp buildup of pressure or of hydrogen when the reactor’s cooling system failed after the quake, destroyed the concrete structure surrounding the reactor but did not collapse the critical steel container inside, they said. They said that raised the chances they could continue cooling the core, and prevent the release of large amounts of radioactive material and avoid a full core meltdown at the plant.

“We’ve confirmed that the reactor container was not damaged,” Japan’s chief cabinet secretary, Yukio Edano, said in a news conference on Saturday night. “The explosion didn’t occur inside the reactor container. As such there was no large amount of radiation leakage outside. At this point, there has been no major change to the level of radiation leakage outside, so we’d like everyone to respond calmly.” 

 Mr. Edano said that, in addition to filling the reactor with seawater, Tokyo Electric Power workers also added boric acid to the containment vessel on Saturday night to poison the nuclear chain reaction. Mr. Edano said that the operation could “prevent criticality.”

He said radioactive materials had leaked outside the plant before the explosion, but that the explosion did not worsen the leak and that, in fact, measured levels of radioactive emission had been decreasing. He did not specify the levels of radiation involved.
Naoto Sekimura, a professor at Tokyo University, told NHK, Japan’s public broadcaster, that “only a small portion of the fuel has been melted. But the plant is shut down already, and being cooled down. Most of the fuel is contained in the plant case, so I would like to ask people to be calm.”

Japanese nuclear safety officials and international experts said that because of crucial design differences, the release of radiation at the Fukushima plant would most likely be much smaller than at Chernobyl even if the Fukushima plant had suffered a complete core meltdown, which they said it had not.

But the vulnerability of nuclear plants to earthquakes was also underscored by continuing problems at the cooling system of reactors at the second nearby plant, Daini, which prompted a evacuation of 30,000 from surrounding communities. Together, the authorities sought to move about 200,000 people around the two plants, a massive logistical task at a time when rescue workers also sought to help people trapped on injured in the earthquake.
After a full day of worries about leaking radiation at the Daiichi plant after its cooling systems malfunctioned, Tokyo Electric Power said an explosion occurred “near” the No. 1 reactor at Daiichi around 3:40 p.m. Japan time on Saturday. It said four of its workers were injured in the blast.



The decision to flood the reactor core with seawater, experts said, was an indication that Tokyo Electric and Japanese authorities had probably decided to scrap the plant, because the salt water would corrode its delicate metal innards. “This plant is almost 40 years old, and now it’s over for that place,” Olli Heinonen, the former chief inspector for the I.A.E.A., and now a visiting scholar at Harvard, said on Saturday.
Mr. Heinonen lived in Japan in the 1980s, monitoring its nuclear industry, and visited the stricken plant many times. Based on the reports he was seeing, he said he believed that the explosion was caused by a hydrogen formation, which could have begun inside the reactor core. “Now, every hour they gain in keeping the reactor cooling down is crucial,” he said.

But he was also concerned about the presence of spent nuclear fuel in a pool inside the same reactor building. The pool, too, needs to remain full of water, to suppress gamma radiation and prevent the old fuel from melting. If the spent fuel is also exposed — and so far there are only sketchy reports about the condition of that building — it could also pose a significant risk to the workers trying to prevent a meltdown in the core.
Both the Daiichi and Daini plants were shut down by Friday’s earthquake. But the loss of power in the area and damage to the plant’s generators from the subsequent tsunami crippled the cooling systems, which need to function after a shutdown to cool down nuclear fuel rods.
Malfunctioning cooling systems allowed pressure to build up beyond the design capacity of the reactors. Early Saturday, officials had said that small amounts of radioactive vapor were expected to be released into the atmosphere to prevent damage to the containment systems and that they were evacuating tens of thousands of people living around the plants as a precaution.

Those releases apparently did not prevent the buildup of hydrogen inside the plant, which ignited and exploded Saturday afternoon, government officials said. They said the explosion itself did not increase the amount of radioactive material being released into the atmosphere. But safety officials also urged people who were not evacuating but still lived relatively near the plants to cover 

David Lochbaum, who worked at three reactors in the United States similar to the Fukushima design, and who was later hired by the Nuclear Regulatory Commission to teach its personnel about that technology, said that from pictures he had seen of the stricken plant, the explosion appeared to have occurred in the turbine hall, and not the reactor vessel or the containment that surrounds the vessel.  

The technology used at Fukushima is called a boiling-water reactor, in which the reactor, inside a containment, sends its steam out of containment to a turbine. The turbine converts the steam’s energy into rotary motion, which turns a generator and makes electricity.
But as the water goes through the reactor, some water molecules break up into hydrogen and oxygen. A system in the turbine hall usually scrubs out those gases. Hydrogen is also used in the turbine hall to cool the electric generator. Hydrogen from both sources has sometimes escaped and exploded, he said, but in this case, there is an additional source of hydrogen: interaction of steam with the metal of the fuel rods. Operators may have vented that hydrogen into the turbine hall.

Earlier Saturday, before the explosion, a Japanese nuclear safety panel said the radiation levels were 1,000 times above normal in a reactor control room at the Daiichi plant. Some radioactive material had also seeped outside, with radiation levels near the main gate measured at eight times normal, NHK quoted nuclear safety officials as saying.
The emergency at the Daiichi plant began shortly after the earthquake struck on Friday afternoon. Emergency diesel generators, which had kicked in to run the reactor’s cooling system after the electrical power grid failed, shut down about an hour after the earthquake. There was speculation that the tsunami had flooded the generators and knocked them out of service.
For some time after the quake, the plant was operating in a battery-controlled cooling mode. Tokyo 
Electric said that by Saturday morning it had also installed a mobile generator at Daiichi to ensure that the cooling system would continue operating even after reserve battery power was depleted. Even so, the company said it needed to conduct “controlled containment venting” in order to avoid an “uncontrolled rupture and damage” to the containment unit.

Why the controlled release of pressure did not succeed in addressing the problem at the reactor was not immediately explained. Tokyo Electric and government nuclear safety officials also did not explain the precise sequence of failures at the plant.
Daiichi and other nuclear facilities are designed with extensive backup systems that are supposed to function in emergencies to ensure the plants can be shut down safely.
At Daiichi, a pump run by steam, designed to function in the absence of electricity, was adding water to the reactor vessel, and as that water boiled off, the steam was being released. Such water is usually only slightly radioactive, according to nuclear experts. As long as the fuel stays covered by water, it will remain intact, and the bulk of the radioactive material will stay inside. But if fresh water cannot be pumped into the containment vessel and the cooling water evaporates, the nuclear fuel is exposed, which can result in a meltdown.

Japan, with no substantial coal or oil, relies heavily on nuclear power, which generates just over one-third of the country’s electricity. Its plants are designed to withstand earthquakes, which are common, but experts have long expressed concerns about safety standards, particularly if a major quake hit close to a reactor.

Read more...