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***Please note, this is taken right from the NRC site.
To learn more on this topic, please refer to www.NRC.gov
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decon | entomb | safstor
Decommissioning Methods
In the NRC's original decommissioning studies (NUREG/CR-0130 for PWRs and NUREG/CR-0672 for BWRs), three alternatives
were defined: DECON (decontamination/dismantlement as rapidly after reactor shutdown as possible to achieve termination of the nuclear license); SAFSTOR (a period of safe storage of the stabilized and
defueled facility followed by final decontamination/dismantlement and license termination); and ENTOMB (immediate removal of the highly activated reactor vessel internals for disposal and relocation of
the remainder of the radioactively contaminated materials to the reactor containment building, which is then sealed. With sufficient time, the radioactivity on the entombed materials will have decayed to
levels that permit termination of the nuclear license). However, because current regulations require decommissioning to be complete within 60 years, ENTOMB may not be a viable option.
Changes in the industrial and regulatory situation in the United States since the late 1970s have forced revisions to
the scenarios of the NRC's original decommissioning alternatives. The most recently revised decommissioning scenarios are described for PWRs in NUREG/CR-5884 and for BWRs in NUREG/CR-6174. There are two
principal changes in the revised scenarios. One is the delay of major decommissioning actions for at least 5 to 7 years following reactor shutdown because of a Department of Energy (DOE) requirement to
cool the spent fuel in the reactor pool to avoid cladding failures in dry storage. The other is the assumption that decommissioning will be complete within 60 years, as required by current regulations.
This delay results in an increase in decommissioning costs during the short safe storage period while the spent fuel pool continues to operate. Changes in cumulative occupational radiation doses also
result from the decommissioning scenario changes.
The basic concept of the three alternatives remains unchanged. However, because of the accumulated inventory of spent
fuel in the reactor storage pool and the requirement for at least 5 years of storage for the spent fuel before transfer to DOE for disposal, the timing and steps in the process for each alternative have
been adjusted to reflect present conditions and possibilities. For the DECON alternative, it is assumed that the owner has strong incentives to decontaminate and dismantle the retired reactor facility as
promptly as possible [i.e., future availability and cost of low-level radioactive waste (LLW) disposal and the need to reuse or dispose of the site, necessitating transfer of the stored spent fuel from
the pool to a dry storage facility on the reactor site]. Although continued storage of spent fuel in the pool would be acceptable, the modified Part 50 license could not be terminated until the pool was
emptied. It is also assumed that an acceptable dry transfer system would be available to remove the spent fuel from the dry storage facility and place it into licensed transport casks when the time came
for DOE to accept the spent fuel for disposal. Similar assumptions are made for the SAFSTOR and ENTOMB alternatives for convenience of analysis, even though extended use of the spent fuel pool might be
more cost-effective for SAFSTOR.
DECON
DECON is the decommissioning method in which the equipment, structures, and portions of the facility and site
containing radioactive contaminants are removed or decontaminated to a level that permits the property to be released for unrestricted use shortly after cessation of operations. It is the only
decommissioning alternative that leads to termination of the facility license and release of the facility and site for unrestricted use shortly after cessation of facility operations. DECON activities
are expected to require about 9 years for large light-water reactors; less time should be required for smaller facilities.
Because DECON operations are expected to be completed within a few years following shutdown, radiation exposures to
workers generally are higher than for decommissioning methods that allow for radioactive decay by delaying or extending the work over a longer period. DECON also requires larger commitments of money and
commercial waste disposal site space than do other decommissioning methods. The principal advantage of DECON is that the site is available for unrestricted use promptly.
Non radioactive equipment and structures need not be dismantled or removed for termination of the NRC license and
release for unrestricted use. Once the facility's radioactive structures are decontaminated to levels permitting unrestricted use of the facility, non radioactive facilities may either be put to some
other use or demolished at the owner's discretion. [NRC has issued proposed amendments to 10 CFR Part 20 containing radiological criteria for decommissioning of NRC-licensed nuclear facilities (FR 59,
43200, August 22, 1994). Currently, NRC uses, on a case-by-case basis, criteria and practices contained in Regulatory Guide 1.86 and in a letter to Stanford University from J. Miller, Office of Nuclear
Reactor Regulation, NRC, dated April 21, 1982.]
DECON, as defined by NUREG/CR-5884 and NUREG/CR-6174, comprises four distinct periods of effort: (1) preshutdown
planning/engineering and regulatory reviews, (2) plant deactivation and preparation for storage (no dismantling activities are conducted during this period that would affect the safe operation of the
spent fuel pool), (3) plant safe storage with concurrent operations in the spent-fuel pool until the pool inventory is zero, and (4) decontamination and dismantlement of the radioactive portions of the
plant, leading to license termination. Because of the delays in development of the federal waste management system, it may be necessary to continue operation of a dry fuel storage facility on the reactor
site after the reactor systems have been dismantled and the reactor nuclear license terminated. However, these latter storage costs are considered operations costs under 10 CFR 50.54(b)(b) and are not
considered part of decommissioning.
SAFSTOR
SAFSTOR is the decommissioning method in which the nuclear facility is placed and maintained in a condition that
allows the safe storage of radioactive components of the nuclear plant and subsequent decontamination to levels that permit release for unrestricted use. SAFSTOR was initially conceived of as having
three successive stages: (1) a short period of preparation for safe storage (expected to be up to 2 years after final reactor shutdown); (2) a variable safe storage period of continuing care consisting
of security, surveillance, and maintenance during which much of the reactor's radioactivity decays; and finally, (3) a relatively short period of decontamination (NUREG-0586). In NUREG/CR-5884 and
NUREG/CR-6174, SAFSTOR is described as five distinct periods of effort, with the initial three periods identical to those of DECON. The fourth period is extended safe storage (50 years) with no fuel in
the reactor storage pool, and the fifth period is decontamination and dismantlement of the radioactive portions of the plant.
The radioactive or contaminated material must be decontaminated or removed, packaged, and disposed of at a regulated
disposal facility. After it has been determined that residual radioactivity is at acceptable levels, the license will be terminated and the facility can be released for unrestricted use. After
termination of the NRC license, disassembly or demolition of nonradioactive facilities would be performed at the owner's discretion.
SAFSTOR may be used as a means of satisfying requirements for protection of the public while minimizing the initial
commitments of time, money, radiation exposure, and waste disposal capacity. SAFSTOR may also have some advantage where there are other operational nuclear facilities at the same site or where a shortage
of radioactive waste disposal capacity occurs. The disadvantages of SAFSTOR are that the site is unavailable for other uses for an extended time; maintenance, security, and surveillance are required
until the final decontamination is complete; and few, if any, personnel familiar with the facility are available at the time of decontamination (up to 60 years after plant shutdown).
ENTOMB
ENTOMB is the alternative in which radioactive contaminants are encased in a long-lasting material, such as concrete.
The entombed structure is maintained and surveillance is performed until the radioactivity decays to a level permitting release of the property for unrestricted use. ENTOMB also comprises five distinct
periods of effort, with the initial three periods identical to those of DECON (NUREG/CR-5884 and NUREG/CR-6174). The fourth period is preparation for entombment, when all of the radioactive materials are
consolidated within the containment building and entombed. The fifth period is entombed storage for an extended time, between 60 and 300 years.
ENTOMB is intended for use where the residual radioactivity will decay to levels permitting unrestricted release of
the facility within reasonable time periods (100 years). However, a few radioactive isotopes produced in nuclear reactors have long half-life periods (Section 7.3.1) that prevent the release of the
facilities for unrestricted use within the foreseeable lifetime of any man-made structure. ENTOMB would be a viable alternative only for facilities where radioactive isotopes would be expected to decay
to safe levels within the expected lifetime of the entombment structure. This condition likely would not pertain to nuclear power reactors. In addition, the use of the ENTOMB alternative contributes to
problems associated with increased numbers of sites dedicated to "interim" storage of radioactive materials for long periods of time.
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