News Brief, 3/30/11
Plutonium Found in Soil
Soil samples collected from five locations around the Fukushima Daiichi site were found to contain trace amounts of plutonium. These trace amounts are in roughly the same quantities as the amounts left behind by nuclear weapons tests conducted prior to 1980, and are not considered a threat to human health, according to JAIF. Only two of the sites are believed to contain plutonium originating in the troubled reactors, with the rest being the result of the nuclear weapons tests. It is not known from which reactor the observed plutonium might have come, or how it was deposited in the soil. A companion post will discuss this, and the health effects of plutonium.
Contaminated water has accumulated in the basements and turbine rooms of units 1-3, and the basement of unit 4. Efforts are underway to clean up and store this water, preventing it from entering the environment, and allowing crews to continue servicing the electrical connections in the basement of each reactor.
Each reactor building additionally has a trench outside it which is concrete-encased, and holds cables and piping for its associated reactor. The trenches outside units 1-4 have flooded with contaminated water. The trenches do not flow to the ocean, and are currently being sandbagged so that they do not overflow and carry radionuclides elsewhere. TEPCO has released a nuclide analysis of trench 1 (http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110330e2.pdf) which shows that the trench contains low levels of fission products, and no uranium or plutonium. Dose rates at the surface of this trench are around 0.4 milliSievert per hour. Dose rates at Unit 2’s trench are high, at 1000 milliSieverts per hour. This high dose rate indicates that the water has been in contact with molten fuel for some time. The pathway through which this water made it to the trench is not known at this time.
Measurements have been taken of seawater 30 km from the facility, and have indicated that only fission products, in small quantities, have made their way to the sea. These quantities, in amounts shown here (http://www.tepco.co.jp/en/press/corp-com/release/betu11_e/images/110330e7.pdf) are far too low to impact human health. Fish from the region have been tested, and a have shown levels of Cs-137 at or just above the level of detection. These levels are below those of concern for fish consumption. Experts from the National Research Insitute’s Fisheries Research group say that it’s too early to draw conclusions, as the situation may change rapidly, but that the situation should improve as the radionuclides decay and dilute in seawater.