Environmental Engineering FOURTH EDITION

Radioactive Waste 333

Rn-222 from undisturbed rock outcrops. Buildings that are insulated to prevent exces-

sive heat loss often have too little air circulation to keep the interior purged of Rn-222;

thus concentrations of Rn-222 in homes and commercial buildings with restricted

circulation can become quite high. Rn-222 itself has a short half-life, but decays to

shorter and longer-lived metallic radionuclides (see Table 16-9). The combined dose

from radon and its radioactive progeny can be significant when radon is inhaled.

Coal combustion, copper mining, and phosphate mining release isotopes of

uranium and thorium into the environment. K-40, C-14, and H-3 are found in many

foodstuffs. Although atmospheric nuclear testing was discontinued about 30 years ago,

radioactive fallout from past tests continues to enter the terrestrial environment.

MOVEMENT OF RADIONUCLIDESTHROUGH THE ENVIRONMENT

Aradionuclide is an environmental pollutant because of a combination of the following
properties:

0 Half-life

0 Chemical nature and properties: a radioactive isotope will behave chemically and

0 Abundance

0 Nature of the radioactive emissions

biochemically like stable (nonradioactive) isotopes of the same element.

Like any other waste material, radioactive wastes may contaminate air, water, soil,
and vegetation, and this contamination may affect public health adversely. Figure 16-6
shows the pathways of contamination from a hypothetical source. Doses of radia-
tion from environmental contamination are usually classified by pathway, that is, as
inhalation dose, ingestion dose, and immersion dose.
Radionuclides released and transported through the air that people breathe enter
the human body by the atmospheric dispersion and inhalation pathway. The NRC
prescribes strict containment of almost all airborne radionuclides, although there can
be accidental releases. However, atmospheric releases of Kr-85, Xe134, radioiodine,
and tritium from boiling water reactors are planned, since these are gases and cannot
be completely trapped, as are some gaseous radionuclide releases from fuel repro-
cessing plants. During the period 1945-1955 there were deliberate releases of 1-131
from defense reprocessing facilities. Today, the greatest amount of radioactivity from
planned releases is the venting of Rn-222 to the air.
The atmospheric pathway has received considerable attention because of the
analogies between radioactive emissions and the more ordinary gaseous air pollutants
generated by industries, automobiles, diesel trucks, etc. Chapters 18 and 19 discuss
air pollution dispersion and meteorology; most of that discussion is equally applicable
to airborne radioactive gases and particles. Airborne radionuclides can also enter the
ingestion or food-chain pathway through deposition on the soil and on vegetation. The
accident at the Chernobyl nuclear reactor, discussed previously, which released a very
large quantity of radioactive material into the air, resulted in radioactively contaminated