Sources of Tritium cont'd - hdbk1132990104

DOE-HDBK-1132-99

reactions between incoming cosmic rays and elemental nitrogen. In its

simplest form, this type of reaction can be written as

N +

C +

(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

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-

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