Page 132 - Radiochemistry and nuclear chemistry

118 Radiochemistry and Nuclear Chemistry

Effluents may also come from large radiotracer users (especially hospitals). In most cases
these releases are well known and the area concerned ('contaminated') identified. From a
global standpoint, compared to natural radioactivity, these releases are minor, but they do
add to the our "natural" radiation background, as discussed in Chapters 18 and 22.
Usually one distinguishes between "near field" and "far field" effects of radioactivity
releases. Near field effects are observed close to the release source, as for example the
nuclear power plant or nuclear waste storage facility. The dissolution of nuclear waste by
rain or ground water is a typical near field problem. As the source is known, it can be
controlled and its environment monitored. If the radioactivity exceeds permitted levels,
access to the contaminated area can be restricted. Far field effects involve the behavior of
radionuclides which have spread out of such a restricted area, caused either by nuclear
power accidents and weapons tests or by leakage from nuclear power plants.
In this paragraph we briefly describe some of the largest anthropogenic sources causing
far field effects, i.e. nuclear weapons tests and nuclear power plant accidents. The cause
of the releases is discussed in Chapter 19. Chapter 22 discusses both near and far field
effects in further detail, particulary with regard to chemical properties: liquid releases from
nuclear power plants, dissolution of solidified nuclear waste and of fall-out particles, migra-
tion in the environment, and possible consequences.

5.10.1. Nuclear weapons

Nuclear weapons were tested in the atmosphere up to 1990, with total releases up to 2 x
1020 Bq fission products, as well as some lesser amounts of Pu isotopes; cf. Table 22.2.
Most of the debris injected into the troposphere had a mean residence time of ~-30 d,
causing fall-out mostly in the neighborhood of the test area. Some of the debris passed
through the tropopause and entered the stratosphere where it was carried by winds around
the globe at approximately the latitude of the release. The residence time in the stratosphere

TABLE 5.4. Events leading to large injections of radionuclides into the atmosphere

Source Country Time Radioactivity Important
Bq nuclides
Hiroshima Japan 1945 4 x 1016 Fiss.prod.
& Nagasaki Actinides

Atmospheric USA - 1963 2 x 102o Fiss. prod.
weapons tests USSR Actinides

Windscale UK 1957 1 • 1015 1311
Chelyabinsk USSR 1957 8 X 1016 Fiss. prod.
(Kysthym) 9OSr ' 137Cs
Harrisburg USA 1979 I x 1012 Noble gases, 131I
Chernobyl USSR 1986 2 x 1018 137Cs