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-