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Background on the Nuclear Emergency in Japan

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The disaster at the Fukushima Daiichi nuclear power station in Japan is a sobering reminder that nuclear power is inherently dangerous.

UPDATE MAY 2011 -- While the disaster at the Fukishima Daiichi reactor remains uncontrolled, the crisis is no longer making front-page news. We will continue to blog about nuclear policy in the United States, but we do not plan to further update the information below, which can serve as a record of our take on the events as they unfolded.

 

*Update on March 25, 2011*

After more than two weeks, the situation at the stricken reactors in Japan remains unstable.

Yesterday, Japanese officials announced that workers found a large crack in a nuclear reactor containing extremely dangerous plutonium, and widened the evacuation zone around the plant. Two workers were hospitalized for severe radiation burns.   

Serious radiation levels appear to be escaping the plant. Officials found radiation levels dangerous to infants  in Tokyo's drinking water. Austrian researchers managing an international network of radiation detectors believe thatsignificant amounts of radioactive iodine and cesium are escaping the plant.

Japan's Prime Minister Naoto Kan told the nation, "The situation today at the Fukushima Dai-ichi power plant is still very grave and serious."

*Status of events as of 11 AM Pacific, March 16 2011*

The nuclear crisis at Fukushima threatens to expose large numbers of people to radioactive contaminants, harming public health. Radiation has already escaped the reactor complex, and has been detected in food from farms up to 90 miles away from the reactor site.

The Japanese government has evacuated everyone within about 13 miles of the plant, and told everyone within 20 miles to stay indoors. The U.S. and other governments have advised their citizens to evacuate to a distance of 50 miles or more.

Over the past week, the New York Times reports that authorities have made "a series of rapid and at times confusing pronouncements on the crisis," making reliable and timely information hard to come by. However, on March 15, the The Institute for Science and International Security in the United States ranked the disaster a 6 on a 7-point scale of severity -- making it the worst nuclear emergency since Chernobyl in 1986.

There are two primary sources of potential radiation leaks; the reactor cores involved in power generation, and the storage pools where the reactor operator stores used nuclear fuel rods.

Spent Fuel Storage Pools

There are 6 reactor units at the stricken Fukushima Daiichi Nuclear Power  Station. [The New York Times is posting ongoing updates about the status of each reactor and its associated spent fuel pool here.] Each unit stores used fuel rods in deep pools located above ground in the secondary containment building of the reactor. Importantly, these pools do not have the same level of protective shielding as the fuel rods within the reactor core itself. And some of the buildings have suffered damage from hydrogen explosions, which may have left pools open to the atmosphere.

In order to keep the spent nuclear fuel from overheating, the pools have to be constantly cooled. If the rods overheat, they could boil off the water in the pool. Alternately, if damage to the reactor building penetrated the pool itself, water could leak out. Should the fuel rods become exposed to open air, they could catch fire, spreading radioactive smoke into the atmosphere.

That would be "worse than a meltdown," David Lochbaum of the Union of Concerned Scientists told reporters at theNew York Times. If a fire occurred, the smoke would loft radioactive material higher into the atmosphere, causing contamination over a potentially wide area, depending on prevailing winds.

According to analysis by Robert Alvarez, a senior scholar at the Institute for Policy Studies and former Senior Policy Advisor to the Secretary and Deputy Assistant Secretary for National Security and the Environment at the U.S. Department of Energy during the Clinton administration, a single spent fuel pool can contain 3 to 8 times more radioactive material than the reactor core at Chernobyl.

Brookhaven National Laboratory studied the consequences of a severe spent fuel pool accident at a closed U.S. reactor in a 1997 report prepared for the U.S. Nuclear Regulatory Commission. In the most severe case, if the fuel rods rapidly caught fire after water completely drained from the spent fuel pool, an accident could:

  • Contaminate up to 2,790 square miles of land, making it unfit for human habitation,
  • Cause as many as 143,000 cancer fatalities over time, in a radius of 500 miles from the accident site, and
  • Cause property damage up to $780 billion (in 2011 dollars).

On March 17 2011, the chair of the U.S. nuclear regulatory commission testified before Congress with the opinion that the spent fuel pool at the Number 4 reactor had run out of water.

On March 18 2011, the Los Angeles Times reported that U.S. nuclear experts believe that the spent fuel pool at reactor number 4 has a breach in its walls or floor, reducing its ability to retain water. Given the high levels of radiation at the reactor site, it may be extremely difficult to fix the containment structure.

The spent fuel pool at the number 3 reactor may pose an even greater threat. On Thursday, the New York Times reported:

[...] authorities reached for ever more desperate and unconventional methods to cool damaged reactors, deploying helicopters and water cannons in a race to prevent perilous overheating in the spent rods of the No. 3 reactor.[...] it is the only one at the site loaded with a mixed fuel known as mox, for mixed oxide, which includes reclaimed plutonium. Western nuclear engineers have said that the release of mox into the atmosphere would produce a more dangerous radioactive plume than the dispersal of uranium fuel rods at the site."

Reactor Cores

At Fukushima Daiichi reactors 1, 2 and 3, nuclear reactions were underway, generating power, when the earthquake and tsunami struck on March 11. The reactors shut down automatically during the quake.

However, even after a reactor shuts down, the cooling systems must remain active in order to circulate fresh water and keep the reactor core from overheating, which could cause fuel to melt and potentially release radioactive material into the atmosphere. (For a more detailed explanation, see these articles from the New York Times.)

Apparently the combination of loss of power, a tsunami flooding the backup generators, and human error caused the primary and backup cooling systems to fail at each reactor.

Pressure levels inside several of the reactors began to rise beyond safe levels. Plant operators declared an emergency situation and began to vent the extra pressure.

In a last-ditch effort to cool the three reactors at Fukushima Daiichi, operators began a plan to pump seawater containing boron into the reaction chamber to cool the fuel rods and quench any fission reactions. But the effort was fraught with technical difficulties. Water levels have dropped to dangerous levels at times, and fuel rods began to melt down – increasing the risk of a breach of reactor containment and an uncontrolled release of radioactive material.

Somehow, hydrogen gas built up in two buildings housing reactor vessels. The gas exploded, blowing the roofs off of the buildings and causing unknown damage inside. Two other explosions have apparently damaged the primary containment structure housing the reactor vessel inside reactors 2 and 3.

As of noon pacific time on March 19, the New York Times reported that:

[...]engineers linked a power cable to the crippled Fukushima Daiichi Nuclear Power Station early Saturday as they struggled to restart systems designed to prevent overheating and keep radiation from escaping. [...] Officials have cautioned, however, that restoring electricity to the reactor would prove fruitless if the pumps were not working. In that case, a new cooling system would be needed, leading to more delays [...]

Engineers are starting the power cord effort with Reactor No. 2 because its outer building has not blown off, thus making it hard to spray in water the way they can with Nos. 1, 3 and 4, according to NHK, Japan’s national broadcaster, which cited power company officials.  

The plan was to lay a 1.5-kilometer power cable between Reactor Nos. 1 and 3 to get to No. 2. If they can hook it up, it will theoretically be able to power all six reactors. The main hazard was the exposure of workers.

This crisis is not likely to end anytime soon. Even if the workers manage to extinguish the fires, cool the spent fool storage pools and successfully restart the cooling systems, the reactors could be damaged enough to require ongoing venting of steam from the reactor cores, leading to ongoing releases of an unknown quantity of radioactive material into the atmosphere, potentially for months into the future.

The Earthquake and Tsunami

On March 11, 2011, Japan suffered an earthquake off the northeastern coast of the main island, Honshu. The earthquake was a 9.0 on the Richter scale, the strongest ever recorded in Japan, and one of the strongest earthquakes recorded on the planet in the last century. Following the quake, a tsunami flooded nearby coastal areas, causing widespread destruction.

The damage affected several nuclear power plants in the country.  Eleven separate reactors shut down automatically in the incident. Fukushima Daiichi was not the only facility to suffer problems. Backup cooling systems at Fukushima Daini Nuclear Power Station, 10 miles away, also failed at 3 out of 4 reactors -- although workers appear to have kept the crisis there from spiraling out of control.