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Tritium Primer
DOE-HDBK-1079-94
BIOLOGICAL PROPERTIES
A pure HT exposure is considered as a combination of a lung exposure from the HT and a
whole body exposure from HTO. The HTO comes from the conversion of HT dissolved in the
blood. The whole body dose can be determined as outlined above by analysis for HTO in the
urine. Because the effective dose equivalents from the lung and whole body exposures are
about equal, the total effective dose can be obtained conservatively by multiplying the HTO
whole body dose by 2. However, in general, this is too conservative because a release of pure
tritium gas with less than 0.01% HTO is highly unlikely. With only a slight fraction (~0.1%)
of HTO in the air, the total effective dose is essentially the HTO whole body dose determined
by bioassay.
As noted above, tritium-labeled molecules in the skin result from contact with metal surfaces
contaminated with HT. This form is associated with a longer half-life. Lung exposure to
airborne metal tritides may also cause unusual patterns of tritium concentrations in body water
because of the slow release of tritium to the blood stream. If such exposures are possible at the
facility, it is good practice to follow the elimination data carefully and to look for organically
bound tritium in the urine.
The results of the bioassay measurements and their contribution to the worker's dose and
general health must be shared with the worker in a timely fashion.
Dose Reduction
The committed dose following an HTO exposure is directly proportional to the biological
half-life, which in turn is inversely proportional to the turnover rate of body water. This rate
varies from individual to individual. Such things as temperature, humidity, work, and drinking
habits may cause rate variations. Although the average biological half-life is 10 days, it can be
decreased by simply increasing fluid intake, especially diuretic liquids such as coffee, tea, beer,
and wine. Even though the half-life may be easily reduced to 4 to 5 days in this way, a
physician must be consulted before persons are placed on a regimen that might affect their
health. Chemical diuretics require medical supervision because the resultant loss of potassium
and other electrolytes can be very serious if they are not replaced. Such drastic measures can
result in a decrease in half-life to 1 to 2 days. Even more drastic is the use of peritoneal dialysis
or a kidney dialysis machine, which may reduce the half-life to 13 and 4 hours, respectively.
Such extreme techniques should be used only in life-threatening situations involving potential
committed dose equivalents that would exceed about 100 rem without any treatment. Based
on a 10-day half-life, the committed dose for an intake of 1 mCi of HTO is approximately
63 mrem.
Individuals whose urine concentrations exceed established limits should stop work that involves
possible exposure to radiation, whether from tritium or other sources. Work restrictions are
suggested or imposed to make certain that the annual dose limits for workers are not exceeded.
The operating group may impose stricter limits on their staff than those imposed by the health
physics group. Depending on the number of workers available and the importance of the work
to be done, doses can be managed to safe levels (from 5 to 100 Ci/L in urine).
Rev. 0
Page 19
Tritium


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