With a half-life of 30, years, Cs-137 gives off penetrating radiation, as it decays. Once in the environment, it mimics potassium as it accumulates in biota and the human food chain for many decades. When it enters the human body, about 75 percent lodges in muscle tissue, with perhaps the most important muscle being the heart. Studies of chronic exposure to Cs-137 among the people living near Chernobyl show an alarming rate of heart problems, particularly among children. As more information is made available, we now know that the Fukushima Dai-Ichi site is storing 10,833 spent fuel assemblies (SNF) containing roughly 327 million curies of long-lived radioactivity About 132 million curies is cesium-137 or nearly 85 times the amount estimated to have been released at Chernobyl.
The overall problem we face is that nearly all of the spent fuel at the Dai-Ichi site is in vulnerable pools in a high risk/consequence earthquake zone. The urgency of the situation is underscored by the ongoing seismic activity around NE Japan in which 13 earthquakes of magnitude 4.0 - 5.7 have occurred off the NE coast of Honshu in the last 4 days between 4/14 and 4/17. This has been the norm since the first quake and tsunami hit the site on March 11th of last year. Larger quakes are expected closer to the power plant.
Last week, Tokyo Electric Power Company (TEPCO) revealed plans to remove 2,274 spent fuel assemblies from the damaged reactors that will probably take at least a decade to accomplish. The first priority will be removal of the contents in Pool No. 4. This pool is structurally damaged and contains about 10 times more cesium-137 than released at Chernobyl. Removal of SNF from the No. 4 reactor is optimistically expected to begin at the end of 2013. A significant amount of construction to remove, debris and reinforce the structurally-damaged reactor buildings, especially the fuel- handling areas, will be required.
