332 ENVIRONMEN'IAL ENGINEERINGAdditional Sources of Reactor WasteThe increasingly widespread use of radionuclides in research, medicine, and industry
has created a lengthy list of potential sources of radioactive waste. This list ranges
from laboratories using a few isotopes, to medical and research laboratories where
large quantities of many different radioisotopes are used (and often wasted), to a
growing list of industrial uses like well logging.
Liquid scintillation counting has become an important biomedical tool and pro-
duces large volumes of mixed hazardous and radioactive waste (MLLW): organic
solvents like toluene that are contaminated, usually with tritium or C-14, but have a
low specific radioactivity. The RCRA prohibits landfill disposal of the solvents in an
LLW site, and there is considerable public opposition to incineration of any radioactive
material, no matter how low the specific activity. MLLW incinerators are operated at
two U.S. Department of Energy sites.
Naturally occurring radionuclides like those listed in Table 16- 10 may pose threats
to public health. As may be seen in Table 16-4, by far the largest fraction of background
ionizing radiation comes from radon (Rn-222). Rn-222 is a member of the uranium
decay series and is thus found ubiquitously in rock. Chemically, Rn-222 is an inert gas,
like helium, and does not become chemically bound. When uranium-bearing minerals
or rock are crushed or machined, Rn-222 is released; there is even a steady release of
able 16-10. Some Radionuclides of Concern
Isotope Qpe of emission Half-lifeCosmic ray production
H-3
Be-10Si-32C-14C1-36Rock and building materials
Rn-222
Uranium + daughters
Thorium + daughters
K-40Atmospheric fallout and
radioactive waste
C-14
0-137
Sr-90
1-131
H-3Beta
Beta
Beta
Beta
BetaAlpha
Alphahetdgamma
Alphahetalgamma
BetaBeta
Beta
Beta
Beta
Beta12 years
2.5 x 106years
5730 years
650 years
3 10,000 years3.8 days1.3 x lo9 years5730 years
30 years
29 years
8.3 days
12 years