Environmental Engineering Reference
In-Depth Information
larger volume and heat content than spent uranium fuel itself. Reprocessing creates large volumes
of low and intermediate waste as well as high-level waste in liquid form and increases the difficul-
ties and dangers of interim waste management (Wohlstetter et al. 1979, 5, 11).
Many countries reprocess spent fuel or contract with France or Great Britain to do it, taking
back the resulting plutonium and high-level waste. However, “an increasing backlog of plutonium
from reprocessing is developing in many countries” and “it is doubtful that reprocessing makes
economic sense in the present environment of cheap uranium” (Vandenbosch and Vandenbosch
2007, 247). Fears about development of a “plutonium economy” that might accelerate proliferation
of nuclear weapons materials and technologies, along with the lack of economic incentives for
reprocessing spent fuel, led President Jimmy Carter in April 1977 to postpone indefinitely further
government support for development of commercial reprocessing technology in the United States
(Sailor 1999, 111; Executive Office of the President 1977, 506-507).
Decommissioning nuclear facilities involves removal and disposal of all radioactive components
and materials and cleanup of any radioactivity that remains in buildings or on-site. Radioactive
surface material accumulated inside pipes and heat exchangers or on floors and walls must be
removed. Chemical, physical, electrical, and ultrasonic processes are used to decontaminate
equipment and surfaces, and liquid and solid waste materials are collected, packaged, and shipped
to licensed low-level radioactive waste disposal sites. Spent fuel, reactor fuel assemblies, reac-
tor vessels, primary heat exchange loops, and equipment that cannot be decontaminated must
be secured in wet or dry temporary storage under or above ground while awaiting transport to
a permanent high-level radioactive waste repository. Spent fuel may be submerged under about
three meters of water for five to ten years in specially designed and structurally reinforced pools
to shield radiation and allow further cooling (Ruff 2006, 4). A longer-term temporary alternative
is dry cask storage in rugged containers made of steel or steel-reinforced concrete, eighteen or
more inches thick, sometimes lined with lead as a radiation shield (USNRC 2002).
Three decommissioning strategies are currently in use in the United States.
1. Immediate dismantlement, or DECON, of equipment, structures, and portions of a facility
containing radioactive contaminants shortly after a nuclear facility closes. Normally reac-
tor fuel is removed from such a facility and the remaining structures are allowed to cool
as radioactivity decays for many months before the rest of the facility is dismantled.
2. After reactor fuel is removed, a nuclear facility may be maintained and monitored in a
condition that allows radioactivity to decay and cool for a period of years in SAFSTOR,
or “delayed DECON,” after which it is dismantled.
3. In a process referred to as ENTOMB, after reactor fuel is removed, a nuclear facility may
be permanently encased on-site in a structurally sound material such as concrete, which
is maintained and monitored until radioactivity decays to safe levels.
A combination of the first two strategies may also be used, in which some portions of a facility
are dismantled or decontaminated while other parts are left in SAFSTOR. This strategy is often
used where multiple generating units built at different times occupy a single site and complete
decommissioning of one unit is deemed undesirable until all units have ceased operations
(US NRC 2002).
Until the United States builds a permanent radioactive waste repository, high-level radioac-
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