The following is a brief description of different methods of radioactive
waste disposal, but one should consult 10CFR20 and 10CFR35 for details.
Decay in Storage
Although 10CFR20 does not spell out the conditions of the decay-in-
storage method, 10CFR35.92 describes this method in detail. Radionuclides
with half-lives less than 120 days usually are disposed of by this method.
These radionuclides are allowed to decay in storage and monitored before
disposal. If the radioactivity of the waste cannot be distinguished from back-
ground, it can be disposed of in the normal trash after removal or defacing
of all radiation labels. Note that the requirement for 10 half-lives decay is
eliminated from the revised 10CFR35. This method is most appropriate for
shortlived radionuclides such as 99mTc,^123 I,^201 Tl,^111 In,^67 Ga and^131 I. Radioac-
tivities should be stored separately according to half-lives for convenience
of timely disposal of each radionuclide.
Release into Sewerage System
The NRC permits radioactive waste disposal into the sewerage system pro-
vided the radioactive material is soluble or dispersible in water and the
quantity disposed monthly does not exceed the maximum permissible limits
set in 10CFR20. Disposal depends on the total volume and flow rate of
water used but is limited to 1 Ci (37 GBq) of^14 C, 5 Ci (185 GBq) of^3 H, and
1 Ci (37 GBq) of all other radionuclides annually. Excreta from humans
undergoing medical diagnosis or treatment with radioactive material are
exempted from these limitations. However, items contaminated with
radioactive excreta (e.g., linen, diapers, etc., contaminated with urine or
feces) are not exempted from these limitations. To adopt this method of
radioactive disposal, one must determine the total volume and the flow of
sewer water in the institution and the number of users of a specific radionu-
clide so that for each individual user, a limit can be set for sewer disposal
of the radionuclide in question.
Transfer to Authorized Recipient
This method of transfer to an authorized recipient is adopted for longlived
radionuclides and usually involves transfer of radioactive wastes to autho-
rized commercial firms that bury or incinerate at approved sites or
facilities.
Although the columns of the^99 Mo–99mTc generators may be decayed to
background for disposal to normal trash, a convenient method of disposing
of this generator is to return them to the vendors, who let them decay and
later dispose of them. Normally, the used generator is picked up by the
authorized carrier when a new one is delivered.
Radiation Protection 281