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Sources of Tritium - hdbk1132990103
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The Relative Abundance of Tritium


DOE-HDBK-1132-99
reactions between incoming cosmic rays and elemental nitrogen. In its
simplest form, this type of reaction can be written as
6
14
1
12
3
N +
n
C +
H.
(1)
7
0
6
1
Tritium is also produced in the sun as a sub-set of the proton-proton chain of
fusion reactions. Although a steady stream of tritium near the surface of the
sun is ejected out into space (along with many other types of particles) on the
solar wind, much larger streams are ejected out into space during solar flares
and prominences. Being much more energetic than its solar wind counterparts,
tritium produced in this manner is injected directly into the earth' upper
s
atmosphere as the earth moves along in its orbit. Regardless of the method of
introduction, however, estimates suggest that the natural production rate for
tritium is about 4 x 106 Ci/yr, which, in turn, results in a steady-state, natural
production inventory of about 7 x 10  7 Ci.
Tritium is also introduced into the environment through a number of man-made
sources. The largest of these, atmospheric nuclear testing, added
approximately 8 x 109 Ci to the environment between 1945 and 1975.
Because the half-life of tritium is relatively short, much of the tritium produced
in this manner has long since decayed. However, tritium introduced into the
environment as a result of atmospheric testing increased the natural
background levels by more than two orders of magnitude, and, in spite of its
relatively short half-life, the natural background levels of tritium in the
environment will not return to normal until sometime between the years 2020
and 2030.
Tritium levels in the environment cannot truly return to background levels,
however, because of a number of additional man-made sources. Tritium is
also produced as a ternary fission product, within the fuel rods of nuclear
reactors, at a rate of 1-2 x 10  4 Ci/1,000 MW(e). (Although much of the tritium
produced in this manner remains trapped within the matrix of the fuel rods,
estimates suggest that recovery of this tritium could reach levels of 1 x 10 6
Ci/yr.) Light-water and heavy-water moderated reactors produce another 500-
I-88


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