Management of Commercially Generated Radioactive Waste - U.S. ...

4.6 DECOMMISSIONING OF RETIRED FACILITIES
4.69
Portions of fuel cycle facilities become contaminated with radionuclides during their
use. Upon retirement these facilities become a waste that must be managed. Management of
this waste is commonly termed decommissioning. Various alternatives are available for
decommissioning retired fuel cycle facilities, as discussed in DOE/ET-0028, Section 8.0.
Much of this information was extrapolated from results of detailed studies of the techno-
logy, safety, and costs of decommissioning nuclear facilities that have been performed at
PNL for the NRC (see Schneider and Jenkins 1977, Smith et al. 1978, Smith and Polentz 1978,
Jenkins et al. 1979). In this Statement we assume that dismantlement is required and have
chosen one of two basic decommissioning modes: either immediate dismantlement, or safe
storage with deferred dismantlement.
In immediate dismantlement, all radioactive contamination above regulatory limits is
removed from the facility to an approved disposal or storage site shortly after the facility
is shut down. Depending on further uses of the site, noncontaminated portions of the
facility remaining after dismantlement may be demolished and removed or they may be used for
other purposes.
In safe storage with deferred dismantlement, the facility is prepared at shutdown to
be left in place for an extended time before it is dismantled. The purpose of this defer-
ment is to allow some of the radionuclides to decay so that radiation exposure during the
decommissioning will be reduced. Consideration has been given to both passive safe storage
and hardened safe storage methods. These methods differ in the strength and complexity of
the barriers installed and in the amount of maintenance and surveillance required during
the time of deferment. This time period is termed the continuing care period.
Among the techniques used in decommissioning are chemical decontamination, mechanical
decontamination, equipment deactivation and removal, and isolation of contaminated areas.
Chemical decontamination is often carried out during the initial stages of a decommissioning
operation to reduce radiation levels and remove relatively mobile contamination. Decontami-
nation solutions may include corrosive acids, complexants, detergents, and high-pressure
water or steam. These liquids are generally concentrated by evaporation, and the concen-
trated waste is then immobilized for disposal or storage.
Mechanical decontamination is required to remove residual radioactive contamination
from structural surfaces. These activities are minimal when the facility is being prepared
for safe storage but are extensive during dismantlement. Contaminated steel structural com-
ponents or liners may be removed by sectioning in place with plasma torches, arc saws, or
explosives. Contaminated concrete can be removed with explosives, by drilling and rock-
splitting, or by jackhammering.
Equipment deactivation is done during preparation for safe storage and equipment is
removed at the time of dismantlement. Deactivation involves removing bulk quantities of
process materials or other hazardous substances, closing valves or installing blank