Introduction to Health Physics: Fourth Edition - Ruang Baca FMIPA UB

INTERNAL RADIATION SAFETY 599
Figure 11-3. Tank for storing high-level liquid radioactive waste. (Reproduced from Roecker JH. Radioactive
Waste Management at Hanford, 4th rev. Hanford, WA: US Department of Energy; 1979.)
centuries. The potential hazards from high-level nuclear waste are twofold. The
greatest threat is from indiscriminate release of the fission product waste to the biosphere.
If this were to happen, successive bioconcentration of radionuclides by plants
and animals in the food web could lead to unacceptably high levels of radioactivity
in our food supply, which, in turn, could lead to an unacceptably high internal dose.
The second threat, of smaller magnitude than the first, is the external radiation
from the radioactive waste. After extensive research directed toward new treatment
methods that would remove these threats, it was found that the internal exposure
pathway can be blocked by immobilizing the radioactivity in such a manner as to
make it unavailable to the biosphere. This is accomplished by the process of vitrification,
whereby the radioactive atoms are chemically incorporated into the chemical
structure of glass beads, and become part of the glass itself. When this happens, the
only way that the radionuclides can get into the biosphere is by dissolution of the
glass, which would require time periods measured in geological terms rather than
in historical time units. Thus, even if the glass were to escape from its containment
into the environment, the radioactivity would remain locked in the glass and would
not be available for uptake by flora or fauna. If an animal were to swallow one of
these glass beads, the bead would pass through its gastrointestinal (GI) tract and
be eliminated. Of course, the GI tract would be irradiated during passage of the
bead, but the animal would not absorb any radioactivity from the bead and irradiation
of the GI tract would cease when the bead passes out of it. Experience with
thorium and obsidian, a naturally occurring volcanic glass, in the Morro do Ferro
(Mountain of Iron) in Brazil proves that glass is stable over geologic time periods.
Having thus assured that the HLRW will not enter into the biosphere, the second
task is to isolate the radioactive beads so that they do not irradiate people or other