There are really two problems, both of them extremely serious because of the toxic nature of the radioactive waste materials in nuclear fuel rods, and because of the enormity of the amounts of these wastes in the rods. Each reactor generates hundreds of pounds of super-toxic plutonium-239, strontium-90, cesium-137, and iodine-131 each year. The most toxic and serious of these is plutonium; it has a half-life of 24,000 years, that is only half of its radioactivity is gone after that time. It's "lifetime" - the time that it takes to reduce its radioactivity by 1000 - is 240,000 years. Plutonium is an "alpha" emitter; a microgram of it in your lungs will almost guarantee that you will get lung, bone, or some other internal cancer. Strontium-90 and cesium-137 are gamma and beta emitters which are absorbed in bones and muscles and cause cancer. Iodine-131 is a beta and gamma emitter which is absorbed in the thyroid gland and causes thyroid cancer.

1. Meltdown: The nuclear reactors themselves, even though they were shut down at the time of the earthquake, need constant pressurized cooling. The earthquake disrupted local power and there was likely damage as well to various control systems. Without local power, neither the main pumps nor the Emergency Core Cooling Systems (ECCS) of the reactors will not run. TEPCO ran the ECCS pumps on battery power until the batteries died and/or other failures took place, but there were times when they were not running, some water boiled away and the fuel rods overheated, and some hydrogen gas was formed, vented, and exploded in several of the reactors.

The explosions further damaged the pumping equipment, compounding the problems. Eventually TEPCO started pumping seawater into the reactors. If they are not able to keep the reactor fuel rods cool or cover them over in some way, they will either catch fire or melt through the floor of their containment, hit groundwater, and create a giant and powerful steam explosion, spewing the waste skyward. This is a "meltdown" or "China Syndrome."

TEPCO has acknowledged that core melting has occurred. Estimates vary as to how much, some as high as 70% for one of the reactors (#1).

2. Burning spent fuel pools: In each of the 6 reactor buildings there are thousands of spent fuel rods which were replaced in regular replacement cycles. The reactors have been operating for about 40 years. The spent fuel rods need to be continuously cooled, although not to the same extent as the active reactor rods. The earthquake and subsequent hydrogen explosions have disrupted - and at least one of the units, destroyed - the cooling systems of these spent fuel pools. Without continuously pumping of cool water, some of the fuel rods are physically hot enough to boil off the water in the pools and then catch fire. This has already apparently happened in Fukushima units 3 and 4. Burning fuel rods are what caused the vast radiological pollution and harm from the Chernobyl reactors.

Two weeks into the disaster, TEPCO lost control of the reactors, the radiation was too high for personnel to be there for any significant length of time, the waste pools were boiling away, radioactive smoke is coming from the facility, probably from a waste pool fire, and some of the fuel rods in the reactors had already partially melted. Since then, they have used water cannons to attempt to refill the waste pools, and local power has been restored, but no one knows whether the reactor fuel and spent fuel ponds can be brought under control.

One of more of the hydrogen explosions spread high-level waste directly, in smoke and large particles, from the spent fuel rods high in the sky and to the surrounding countryside; high readings of these contaminants have been found more than a mile away.

At last accounting, there was still highly radioactive smoke and steam coming from units 3 and 4, indicating burning fuel and water exposure to cracked fuel rods. The building surrounding unit 3 was blown apart by a hydrogen or steam explosion, and there is radioactive smoke streaming out of the reactor. It is feared that the core of unit 3 has cracked and that one or more of the containment vessels around one or more of the reactors are leaking.

The radioactive pollution from the Fukushima reactors has reached monumental proportions. The public water system of Tokyo, 135 miles from the plant, is contaminated with iodine-131. Crops are radioactive from fallout. TEPCO has been pumping 200 tons of seawater into the plant each day, and the wastewater, being pumped back into the ocean, is contaminated with radioactive waste from the damaged fuel rods. There have been other large discharges of radiation-contaminated water to the ocean, and ocean water near the facility is contaminated at levels thousands of times above normal radiation levels. Additionally, Unit 2 had a crack in its water containment pit, and it was leaking large amounts of extremely highly radioactive water into the ocean. Plutonium has been detected in soil samples, which means that it is in the air and water as well.

The problem is made more difficult by the nature of the pollutants: they are very toxic (that is, they cause cancer if ingested or inhaled), long-lived, and are made up of fine dust particles. This radioactive dust pollution is being carried by the prevailing winds and jet stream eastward towards Hawaii and the continental United States, Canada, and Mexico. Radioactive fallout has already detected in rainwater in the US. Water and air samples all over the US have been found to contain radioactive particles from Fukushima, and several milk and vegetable samples as well.

To give you an idea of the scale of radioactive fallout pollution that may come from Fukushima: The amount of plutonium (by far the most dangerous radioactive poison in the fuel rods) in the Hiroshima and Nagasaki bombs was less than 20 lbs in each one. The amount of plutonium in the fuel rods of a reactor is at least 400 lbs per year of operation, and the reactors have been operating for 40 years, so that release of any significant fraction of the rods would be literally thousands of pounds of radioactive poisons, the amount of pollution from hundreds of atomic bombs.

There are some things that you can do to limit the amount of damage that this kind of pollution causes.

1. To prevent absorption of environmental iodine, stock up and take Atlantic kelp or potassium iodide tablets, or eat some Atlantic seaweed each day. The RDA of iodine is 150 mcg (micrograms) per day. If you decide not to eat seaweed for extra iodine, take double that amount, about 300 mcg, in kelp or iodine tablets or capsules each day, in divided doses (one AM, one PM).

2. To prevent absorption of environmental strontium and cesium, eat some Atlantic seaweed each day and take calcium and potassium supplements. The RDA of calcium is 1000-1500 mg per day. Take this amount in supplementation each day, in divided doses. Take 1000-2000 mg of potassium citrate, depending on the amount of high-potassium foods you consume (orange and tomato juice, whole grains, bananas).

3. To prevent absorption of plutonium and other radioactive heavy metals, use a heavy metal chelator (such as MSM) and an absorbent (such as chlorella or spirulina). Buy powdered MSM, marked "Opti-MSM" (because other products taste terrible), and take 1/2 to 1 teaspoon of it (about 2000-4000 mg) mixed with spring or distilled water at each meal. Buy chlorella in tablets, capsules, or powder, and take a teaspoon of it or 3000 mg, about 20 minutes before each meal.

4. To protect your liver and increase its ability to filter and excrete radioactive heavy metals, take N-Acetylcysteine (NAC) 2000-3000 mg per day, in divided doses.

5. Do not eat dairy products. Please focus on eating as low as possible on the food chain (avoiding meat and processed food when possible). Wash leafy greens, vegetables, fruit, and beans thoroughly.

6. Since unit 3, and at times unit 4, appear to be on fire, think about staying inside as much as possible, preferably in areas which have filtered air. You might consider buying an air filter (HEPA) for your home as well, and avoid bringing outside dust into your home.

References:

Passwater, R. N-Acetylcysteine (NAC): An Old Nutrient Attracts New Research, http://www.healthy.net/scr/article.aspx?id=575

Reliene R, Pollard JM, Sobol Z, Trouiller B, Gatti RA, Schiestl RH.
N-acetyl cysteine protects against ionizing radiation-induced DNA damage but not against cell killing in yeast and mammals, http://www.ncbi.nlm.nih.gov/pubmed/19427509

MSM for Detoxification, http://www.healingdaily.com/oral-chelation/MSM-for-detoxification.htm