The slow motion events occurring at Japan's (or GE's) Fukushima reactor cannot be sugar-coated. It is a doomsday scenario unfolding.
Nuclear reactors are not the same as coal/oil/gas electricity plants. Unlike conventional plants, they cannot be turned off. So while brave workers were tending to Units 1, 2 and 3 reactors, attempting against all odds to keep the reactor from overheating, the fuel pool at Unit 4 was left untended; without makeup water to cool them, the fuel rods overheated. Above 1800 oF, an exothermic reaction, a fire, took place with the zirconium cladding around the uranium pellets. Zirconium burned, forming zirconium oxide and hydrogen gas, which then exploded and released radioactive cesium, a semi-volatile metal, to the atmosphere.
Near the plant, the radiation levels dangerously escalated to 400 milliseiverts/hour (or 40 rems/hour in U.S. parlance). Considering background is on the order of 1 milliseivert per YEAR, this means a yearly background dose every 9 seconds. Put plainly, workers at the Fukushima reactors are putting their lives in immediate jeopardy.
What is a fuel pool?
Each year a commercial reactor operates, approximately 30 tons of fuel are irradiated. Every year or year and a half, this fuel is moved to a fuel pool for safe storage. Under 20 feet of circulating and replenished water, the fuel is stored. Water shields the radioactivity and cools the fuel, which still gives off heat. If water is not resupplied, which apparently was the case at unit 4, the water levels decline, the fuel is uncovered and it overheats, leading to a hydrogen explosion.
How much cesium-137 is contained in a fuel pool?
The amount of cesium contained in the fuel pool is typically measured in curies or becquerels, but these assessments are meaningless unless you are a physicist. An easier way to look at it is in relation to the atomic bomb dropped on Hiroshima at the end of World War II, where 100,000 Japanese where killed. Cesium is a semi-volatile material that has been detected in the air downwind of the Fukushima reactors. How many Hiroshima bombs worth of cesium-137 are contained in the fuel pool?
In work for the State of Nevada, we estimated that 10 tons of irradiated (what the industry calls "spent") nuclear fuel was equivalent to 240 times the amount of cesium-137 released by the Hiroshima bomb. Ten tons is the amount of irradiated fuel that would be contained in a shipping container or cask used to transport the fuel. Why so much more cesium than the Hiroshima bomb? Because an atomic explosion occurs in milliseconds, but a nuclear reactor operates continuously for years. Many more fissions means much more fission products, including cesium You do the math. If Unit 4 operated for 35 years and produced 30 tons of irradiated fuel per year and each ton is equivalent to 24 times the amount of cesium-137 produced by the Hiroshima bomb, then each fuel pool could contain on the order of 24,000 times the amount of cesium-137 produced by the Hiroshima bomb, if all the produced irradiated fuel remains in the fuel pool..
This is not to say all this material will be released to the atmosphere or ocean. This is the maximum cesium-137 possible inventory at each Fukushima reactor. Each fuel pool at each Fukushima reactor also contains approximately the same amount of strontium-90 and other cancer causing materials. In addition to the fuel pools at each Fukushima reactor, a larger common fuel pool sits at ground level between two reactors in a building with windows. The damage the tsunami caused to this independent fuel pool has not been discussed by the media.
Iodine, cesium and other radionuclides can be carried downwind and inhaled. Radionuclides that land in the sea may be taken up by fish and eaten. When these cancer-causing materials are taken into the body by inhalation or ingestion, they concentrate in different organs. Cesium concentrates in muscle, strontium (like calcium) in bones, iodine in the thyroid. Once in the body, these radioactive materials continue to decay, releasing harmful gamma and beta radiation. Plutonium, also present, gives off alpha radiation. Rearranging the DNA in the human body leads to cancer. To put this in another way, a BWR reactor boils water to produce electricity by generating cancer-causing materials.
Take this out of the nuclear realm. Imagine another harmful poison, botulism. Imagine a botulism reactor, reproducing botuli fast enough to produce heat and steam to turn turbines. Then imagine having to contain these billions of botuli so the public is not harmed. This is essentially the friendly atom that has now come full circle in Japan and that the Nuclear Regulatory Commission will relicense for an additional 20 years at Vermont Yankee and at 30 other Fukushima-type reactors in the United States. Fortunately, the State of Vermont has taken matters into its own hands and has decided not to allow Vermont Yankee to run past 2012..