Residents have been told to evacuate the vicinity near the nuclear reactors damaged in Japan March 10 as a result of the historic earthquake and tsunami. The concern is radiation emanating from damaged reactors at the Fukushima Dai-ichi power plant, where several of the six reactors have been compromised. James F. Stubbins, professor and head of nuclear, plasma, and radiological engineering at Illinois, discussed radiation in an interview with Jeff Unger, of the U. of I. News Bureau.
How is radiation exposure measured and what are the exposure limits?
Radiation comes from the decay of certain isotopes produced in the nuclear fission process. The amount or activity of the radiation is measured in Sieverts (SV) and often reported in mSV or milliSieverts. A milliSievert is one-thousandth of a Sievert.
Workers at nuclear plants wear dosimeters to record the amount of radiation dose they receive while working. The normal limit for the whole-body dose for radiation workers should be less than 500 mSV per year.
What is background radiation and what are typical medical exposures?
Background radiation in Illinois is about 3 mSV per year, excluding medical treatment exposure. Two mSV per year is from radon exposure. The remainder is from cosmic rays, and carbon-14 and potassium-40, which are present in foods that are ingested. Natural background radiation in Denver is twice as high as it is in Illinois because of the thinner atmosphere in Denver. A flight from New York to Los Angeles exposes those in the plane to about 0.04 mSV per flight. A chest X-ray or chest CAT scan is about 0.1 mSV and a full-body CAT scan is about 10 mSV.
How would radiation releases disperse around the Japanese plants?
So far the radioactivity probably has been released with the steam to relieve pressure inside the reactor. When this is done, some of the radioactive material can be carried out with the steam. It appears that two radioactive isotopes, iodine-131 and cesium-137, have been released.
Many of the other radioisotopes are still contained in the fuel inside the pressure vessel or in the spent fuel pools. This radioactivity would not be released unless there are further problems cooling the fuel.
Why is the discussion concentrating on iodine (I-131) and cesium (Cs-137)?
Iodine-131 has an eight-day half-life and can be released in significant quantities from a damaged nuclear reactor core. Cesium-137 is released in a particulate form as compared to the vapor form of iodine-131 from a damaged nuclear reactor. Cesium-137 has a
30-year half-life. Workers are protected from inhaling cesium-137 by wearing particulate face-mask respirators. Potassium iodide is a non-prescription drug that can be used to protect the thyroid gland from an expected exposure to considerably higher levels of radiation. But it does not protect other parts of the body. The Illinois Department of Public Health issued a news release March 16 recommending that Illinois residents should not take potassium iodide at this time.
