Updated April 5

• The power plant has dumped about 11,000 tons of water (11 million liters) of radioactive water into the ocean to make room for storage containers holding water that is even more radioactive.

• Japan reported finding radioactive fish that exceeds regulatory limits, although based on the levels found so far, you would need to eat 16 kilograms of the tainted fish meat in a year to get sick. But fish and seaweed could concentrate radioactive particles to levels higher than those in the surrounding waters, so monitoring will be crucial to assess the impact on marine life. Shellfish and other bottom feeders would be the ones most likely to suffer long-term contamination as radioactive particles settle on the sediment.

• Japan has established a fishing exclusion zone of 20 kilometers around the plant, which could be extended depending on the amount of radioactivity found.

Updated March 28

• Water leaking from at least one of the reactors shows high levels of radioactivity, suggesting a potential core breach that could make the plant even more radioactive. Clean-up remains challenging because high radioactiviity prevents workers from staying too long near the reactors.

• In a meltdown, the reactor cores will not detonate like a nuclear bomb. Any explosions would likely be the result of a build-up of steam pressure.

Updated Saturday, March 19

• Radiation 5 to 7 times the legal limit has been detected in milk and spinach in parts of the country near the plant. The Japanese government said that drinking one glass of contaminated milk every day for an entire year would expose a person to the radiation equivalent to one CT scan. Radioactive iodine was also detected in Tokyo's drinking water, although at levels considered safe.

• Workers have connected a cable to feed power to two of the crippled reactors, with the hope of restarting the water pumps that cool the cores.

Updated Friday, March 18

• The Fukushima Daiichi power plant has six nuclear reactors. Their status ranges from being stable to having varying degrees of core meltdown.

• Of greatest concern are the spent fuel rods stored at reactor Nos. 3 and 4. They are not contained in the same kind of vessel as active fuel rods. If left exposed to air, they may catch fire or explode, spreading radioactive particles into the air.

• Workers at the plant are trying to keep all fuel rods under water, which cools the rods (thereby preventing fires and explosions) and blocks radiation.

• The most damaging radiation are gamma rays and x-rays; energetic alpha rays (streams of helium nuclei) and beta rays (electrons) can also damage cells. These rays are emitted during the decay of certain versions of uranium, iodine, cesium and other elements.

• Wearing masks and respirators prevent the ingestion of radioactive particles.

• Currently, there is no radiation danger to residents of the U.S. Although higher-than-normal radiation may well be detectable in the U.S., the amount poses no health risk. Unless a large explosion sends radioactive material high into the atmosphere, most of the fallout from Japan will not make it across the Pacific Ocean.

• Residents of the U.S. do not need to take iodine pills to prevent radiation-induced thyroid cancer. In fact, overuse of potassium iodide can lead to thyroid problems, especially among children.

• Most of the radioactive particles are expected to fall out over the western Pacific Ocean. Quantities will be so diffuse at that point that they're not likely to make fish there unsafe to eat.

For complete coverage, see our in-depth report "The Japan Earthquake and Tsunami."

3 Comments

1. 1. Carl.R.Larson 06:32 PM 3/20/11

   So here, it says that radiation levels are nowhere near high enough to pose a health risk.
   
   What I'm wondering is, what is the risk that the plants could actually have a partial meltdown, say, next week... and *then* pose a significant health risk?

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2. 2. shinpanstone 10:30 AM 3/21/11

   Milk and spinach in parts of the country near the plant already contaminated ,but it doesn't have serious effects. So, we shouldn't refuse those products.
   If we didn't buy those products, people who live in town near the plant would be damaged more than now.

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3. 3. eco-steve 05:07 AM 3/29/11

   As mercury shows, the problem with diffuse radiation pollution in sea water is that the food chain concentrates trace elements. Are there enough dosimeters in Japan to safely test all fish catches to ensure public health? Plutonium is a highly dangerous substance, even in great dilution.

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