60 © The Containment of Undergruund Nuclear Explosions Figure 4-1—The Typical Bimodai Curvefor Fission-Product Yield ry jt Table 4-1—Common Radionuclides Invoived ina Nuclear Explosion Radionuclide Trittum eee Krypton-85 200, Leas lodine-131 62... 0. eee, years years years years years years 12.3 years 109 years 8 days 5 2 days 24 hours oO Xenon-133 2.0.0... ee, lodine-132 0.02... eee N The type of release is also important in predicting what radionuclides will be present. For example. atmospheric tests release all radionuclides created. Prompt, massive ventings have released a nonnegitgible fraction of the radionuclides created Lutetime, minorseeps,like those since 1970. release only the mostvolatile radionuclides. In an underground 3 Percent fission yield Hait-Life Uranium-238 ..0. 0.2, 4,500.000,000 Plutonium-239 ©0000. ee eee 24.300 Carbon-14 ce . 5.800 Radium-226 ....0. 0... eee 1,620 Cesium-137 ......0.....0.00.004.. a 30 Strontium-90 20... 28 explosion, radionuclides also separate (called “‘tracuionation’’) according to their chemical or physical 8 @po. RS r > » TT characteristics. Refractory particles «partuwles that 346. «106 «1'18~=—«130—«s42”—=i«'5CG Mass number Products of a nuclear explosion occur predominantly in two major groups of nuclides. SOURCE: Modified from Lapp and Andrews, Prentice-Hall, Inc., 1972. An individual radioactive species follows the half-life rule of decay—that is. half of the nuclei disintegrate in a characteristic time. called a *‘halflife."” However, a mixture of fission products has a more complicated decay pattern. The general rule of thumb for a nuclear explosion is that the total activity decreases by a factor of 10 for every sevenfold increase in time. In other words, if the gammaradiation | hour after an explosion has an intensity of 100 units, then 7 hours later it will have an intensity of 10. Consequently. the time after the explosion has a dramatic effect on the amount of radioactivity. A 1 kiloton explosion in the atmosphere will produce 41 billion curies 1 minute after determination, but this will decrease to 10 million curies in just 12 hours. do not vaporize during the nuclear explosion) settle out fast underground, while more volatile elements that vaporize easily condenselater. This has a strong effect on radioactive gases that seep siowls through the soil from an underground exniesion in an underground explosion, nearly all the reactive materials are filtered out through the soil woiumn and the only elements that come up through che sail io the aunosphere are the noble gases. pnmurls Knpton and xenon. CRITERIA FOR CONDUCTING Although every attempt is made to present the accidental release of radioactive Mulerul to the atmosphere. several safety programy are varned oul for each test. These programs ure designed to minimize the likelihood and extent of cadiauon exposure offsite and to reduce risks to people should an accidental release of radioactive matenal occur The Environmental Protection Agencs monttors the population around the test site and has established plans to protect people should an accident occur. EPA’s preparations are aimed toward reducing the whole-body exposure of the off-site populace and to minimizing thyroid doseto offsite residents, particu-