Published on Portside (https://portside.org)
Nuclear
Power Plant? Or Storage Dump for Hot Radioactive Waste?
Robert Alvarez
Thursday, August 11, 2016
Bulletin of the Atomic Scientists
In addition
to generating electricity, US nuclear power plants are now major
radioactive waste management operations, storing concentrations of
radioactivity that dwarf those generated by the country's nuclear weapons
program. Because the proposed Yucca Mountain nuclear waste repository remains
in limbo, and other permanent storage plans are in their infancy, these wastes
are likely to remain in interim storage at commercial reactor sites for the
indefinite future. This reality raises one issue of particular concern—how to
store the high-burnup nuclear fuel used by most US utilities. An Energy
Department expert panel has raised questions that suggest neither government
regulators nor the utilities operating commercial nuclear power plants
understand the potential impact of used high-burnup fuel on storage and
transport of used nuclear fuel, and, ultimately, on the cost of nuclear waste
management.
Spent
nuclear power fuel accumulated over the past 50 years is bound up in more than
241,000 long rectangular assemblies containing tens of millions of fuel rods [1]. The
rods, in turn, contain trillions of small, irradiated uranium pellets. After
bombardment with neutrons in the reactor core, about 5 to 6 percent of the
pellets are converted to a myriad of radioactive elements [2] with
half-lives ranging from seconds to millions of years. Standing within a
meter of a typical spent nuclear fuel assembly guarantees a lethal radiation
dose in minutes.
Heat from the radioactive decay in spent nuclear fuel [3] is
also a principal safety concern. Several hours after a full reactor core is
offloaded, it can initially give off enough heat from radioactive decay [4] to
match the energy capacity of a steel mill
furnace [5]. This is hot enough to melt and ignite the fuel’s
reactive zirconium cladding [6] and
destabilize a geological disposal site [7] it is
placed in. By 100 years, decay heat and radioactivity drop substantially but
still remain dangerous. For these reasons, the US Government Accountability Office (GAO) informed the
Congress in 2013 [8] that spent nuclear
fuel is “considered one of the most hazardous substances on Earth.”
US
commercial nuclear power plants use uranium fuel that has had the percentage of
its key fissionable isotope—uranium 235—increased, or enriched, from what is
found in most natural uranium ore deposits. In the early decades of commercial
operation, the level of enrichment allowed US nuclear power plants to operate
for approximately 12 months between refueling. In recent years, however, US
utilities have begun using what is called high-burnup fuel. This fuel generally
contains a higher percentage of uranium 235, allowing reactor operators to
effectively double the amount of time the fuel can be used, reducing the
frequency of costly refueling outages. The switch to high-burnup fuel has been
a major contributor to higher capacity factors and lower operating costs in the
United States over the past couple of decades.
While this
high-burnup trend may have improved the economics of nuclear power, the
industry and its regulator, the Nuclear Regulatory Commission (NRC), have taken
a questionable leap of faith that could, according to the Electric Power
Research Institute, “result in severe economic penalties and in operational
limitations to nuclear plant operators.” Evidence is mounting that spent
high-burnup fuel poses little-studied challenges to the temporary used-fuel
storage plans now in place and to any eventual arrangement for a long-term
storage repository.
High burnup
significantly boosts the radioactivity in spent fuel and its commensurate decay heat [9]. Of
particular concern is the effect of high-burnup fuel on the cladding that
contains it in the fuel assemblies used in commercial reactors. Research shows
that under high-burnup conditions, that cladding may not be relied upon as the
primary barrier to prevent the escape of radioactivity, especially during
prolonged storage in the "dry casks" that are the preferred method of
temporary storage for spent fuel. Resolution of these problems remains elusive.
For
instance, research shows that in regard to high-burnup waste the fuel cladding
thickness of used fuel is reduced and a hydrogen-based rust forms on the
zirconium metal used for the cladding, and this thinning can cause the cladding to become brittle and fail [10]. In
addition, under high-burnup conditions, increased pressure between the uranium
fuel pellets in a fuel assembly and the inner wall of the cladding that
encloses them causes the cladding to thin and elongate [11]. And the
same research has shown that high burnup fuel temperatures make the used fuel more vulnerable to damage [12] from
handling and transport; cladding can fail when used fuel assemblies are removed
from cooling pools, when they are vacuum dried, and when they are placed in
storage canisters.
The NRC and
the nuclear industry do not have the necessary information to predict when
storage of high-burnup fuel may cause problems. To err on the side of caution,
high-burnup fuel might have to be left in cooling pools for 25 years—as opposed
to the current three to five years for lower burnup spent fuel— to allow
cladding temperatures to drop enough to reduce risks of cladding failure before
the fuel is transferred to dry storage. Also, the cooling pools at US
commercial reactors are rapidly filling, with more than 70 percent of the
nation's 77,000 metric tons of spent fuel in reactor pools, of which roughly a
fourth is high burnup. So far, a small percentage of high-burnup used fuel
assemblies are sprinkled amid lower burnup fuel in dry casks at reactor sites.
But by 2048—the Energy Department's date for opening a permanent geologic
disposal site—the amount of spent fuel could double, with high burnup waste
accounting for as much as 60 percent of the inventory.
What’s
next? In 2014, the NRC adopted a "continued storage" rule that
recognized the strong likelihood of long-term surface storage of used nuclear
fuel—but that rule basically ignored high-burnup spent fuel. Under the rule,
the agency currently permits dry storage casks to accommodate a uniform loading
of spent fuel below a certain level of use in reactors. The average burnup for
the US reactor fleet is measured by the amount of energy produced, expressed in
gigawatt days per metric ton of uranium; at present, used fuel assemblies are
allowed to go up to 62 gigawatt days per metric ton.
Accordingly,
a few high burnup assemblies, with higher decay heat, may be mixed with lower
burnup assemblies in a storage canister. But there is little guidance on how
this can be done without exceeding NRC peak temperature requirements. NRC’s
current regulatory guidance concedes that “data is not currently available”
supporting the safe transportation of high burn
spent nuclear fuel [13]. Owners of the
shuttered Maine Yankee and Zion reactors [14] are
not taking a chance and have packaged high burnup spent fuel as it were damaged
goods, stored in double-shell containers instead of single-shell, to allow for
safer transport.
The impacts
of decay heat from high-burnup spent fuel on the internal environment of
commercial dry casks are virtually impossible to monitor, according to a 2014
NRC-sponsored study, “because of high temperatures, radiation, and
accessibility difficulty.” The uncertainties of storing a mix of high- and
low-burnup spent fuel in a canister are compounded by the lack of data on the
long-term behavior of high-burnup spent fuel. This problem was highlighted by
the Nuclear Waste Technical Review Board, an expert panel that provides
scientific oversight for the Energy Department on spent fuel disposal. That
panel said there is little to no data to support dry storage and transport for
spent fuel with burnups greater than 35 gigawatt days per metric ton of
uranium. In a May 2016 letter to the Energy Department, the board raised
elemental questions that should have been answered before the NRC and reactor
operators took this leap of faith: “What could go wrong? How likely is it? What
are the consequences?” The board provided no answers to those questions.
It will
take the Energy Department at least a decade to complete a study involving
temperature monitoring in a specially designed dry cask containing high burnup
fuel. Meanwhile, as high-burnup inventories increase, the higher amounts of
radioactivity and decay heat associated with high-burnup fuel assemblies are
putting additional stress on cooling pool storage systems.
This is
happening at a time when concerns over spent fuel pool storage conditions are
increasing. “As nuclear plants age, degradations of spent fuel pools … are
occurring at an increasing rate,” a study by Oak Ridge National Laboratory [15]concluded
in 2011. “During the last decade, a number of NPPs [nuclear power plants] have
experienced water leakage from the SFPs [spent fuel pools] and reactor
refueling cavities.” As a result of increasing high burnup loadings, spent
nuclear pool storage systems are likely to require upgrading, which will
certainly drive up costs at a time when age and deterioration are of growing
concern.
These
concerns were given greater prominence in May of this year by a National
Academy of Sciences panel established by Congress to review the response of the NRC to the
Fukushima nuclear accident [16]. In its report, the
panel warned the NRC about terrorist attacks for the second time since 2004 and
urged the agency to “ensure that power plant operators take prompt and
effective measures to reduce the consequences of loss-of-pool-coolant events in
spent fuel pools that could result in propagating zirconium cladding
fires.” Allison Macfarlane [17], then
chair of the U.S. Nuclear Regulatory Commission (NRC), noted in April, 2014
that “land interdiction [from a spent nuclear fuel pool fire at the Peach
Bottom Reactor in Pennsylvania] is estimated to be 9,400 square miles with a
long term displacement of 4,000,000 persons.”
Down the
road, it is likely that spent nuclear fuel will have to be repackaged to
mitigate decay heat into smaller containers ahead of final disposal. High-burnup fuel will only complicate
the process [18], and increase costs, currently estimated
in the tens of billions of dollars. Depending on the geologic medium, a
maximum of four assemblies for high burnup, as opposed to the dozens in current
storage casks, would be permitted after 100 years of decay; larger packages
containing no more than 21 assemblies might have to be disposed if there is
forced ventilation for 50 to 250 years—driving up repository costs [19].
The basic
approach undertaken in this country for the storage and disposal of spent
nuclear fuel needs to be fundamentally revamped. Instead of waiting for
problems to arise, the NRC and the Energy Department need to develop a
transparent and comprehensive road map identifying the key elements of—and
especially the unknowns associated with—interim storage, transportation,
repackaging, and final disposal of all nuclear fuel, including the high-burnup
variety. Otherwise, the United States will remain dependent on leaps of faith
in regard to nuclear waste storage—leaps that are setting the stage for large,
unfunded radioactive waste “balloon mortgage” payments in the future.
Robert
Alvarez is a senior scholar at the Institute for Policy Studies, Robert Alvarez
served as senior policy adviser to the Energy Department's secretary and deputy
assistant secretary for national security and the environment from 1993 to
1999. During this tenure, he led teams in North Korea to establish control of
nuclear weapons materials. He also coordinated the Energy Department's nuclear
material strategic planning and established the department's first asset
management program. Before joining the Energy Department, Alvarez served for
five years as a senior investigator for the US Senate Committee on Governmental
Affairs, chaired by Sen. John Glenn, and as one of the Senate's primary staff
experts on the US nuclear weapons program. In 1975, Alvarez helped found and
direct the Environmental Policy Institute, a respected national public interest
organization. He also helped organize a successful lawsuit on behalf of the
family of Karen Silkwood, a nuclear worker and active union member who was
killed under mysterious circumstances in 1974. Alvarez has published articles
in Science, the Bulletin of Atomic Scientists, Technology Review, and The
Washington Post. He has been featured in television programs such as NOVA and
60 Minutes.
Source URL: https://portside.org/2016-08-22/nuclear-power-plant-or-storage-dump-hot-radioactive-waste
Links:
[1] https://www.eia.gov/nuclear/spent_fuel/
[2] http://fissilematerials.org/library/ornl12.pdf
[3] https://inldigitallibrary.inl.gov/sti/4781584.pdf
[4] http://pbadupws.nrc.gov/docs/ML0220/ML022000232.pdf
[5] https://en.wikipedia.org/wiki/Induction_furnace
[6] http://www.nap.edu/openbook.php?record_id=11263&page=38
[7] http://www.nap.edu/openbook.php?record_id=11263&page=39
[8] http://www.gao.gov/assets/660/653731.pdf
[9] http://www.environmental-defense-institute.org/publications/Alvarez%20Memo%20re-%20High%20Burnup%20Nuclear%20Fuel.%2012-17-2013%20rev.%202docx.pdf
[10] http://www.nrc.gov/reading-rm/doc-collections/commission/secys/2012/2012-0034scy.pdf
[11] http://indico.ictp.it/event/a07178/session/60/contribution/35/material/0/0.pdf
[12] https://www.inmm.org/AM/Template.cfm?Section=29th_Spent_Fuel_Seminar&Template=/CM/ContentDisplay.cfm&ContentID=4383
[13] http://www.nrc.gov/reading-rm/doc-collections/isg/isg-11R3.pdf
[14] http://www.energy.gov/sites/prod/files/2016/05/f31/Shutdown_Sites_Report_Sept2015_web.pdf
[15] http://pbadupws.nrc.gov/docs/ML1204/ML12047A184.pdf
[16] http://www.nap.edu/catalog/21874/lessons-learned-from-the-fukushima-nuclear-accident-for-improving-safety-and-security-of-us-nuclear-plants
[17] http://www.nrc.gov/reading-rm/doc-collections/commission/comm-secy/2013/2013-0030comvtr.pdf
[18] https://curie.ornl.gov/system/files/documents/not%20yet%20assigned/STAD_Canister_Feasibility_Study_AREVA_Final_1.pdf
[19] http://www.energy.gov/sites/prod/files/2013/08/f2/RepositoryReferenceDisposalConcepts.pdf
[20] https://thebulletin.org/donate
[2] http://fissilematerials.org/library/ornl12.pdf
[3] https://inldigitallibrary.inl.gov/sti/4781584.pdf
[4] http://pbadupws.nrc.gov/docs/ML0220/ML022000232.pdf
[5] https://en.wikipedia.org/wiki/Induction_furnace
[6] http://www.nap.edu/openbook.php?record_id=11263&page=38
[7] http://www.nap.edu/openbook.php?record_id=11263&page=39
[8] http://www.gao.gov/assets/660/653731.pdf
[9] http://www.environmental-defense-institute.org/publications/Alvarez%20Memo%20re-%20High%20Burnup%20Nuclear%20Fuel.%2012-17-2013%20rev.%202docx.pdf
[10] http://www.nrc.gov/reading-rm/doc-collections/commission/secys/2012/2012-0034scy.pdf
[11] http://indico.ictp.it/event/a07178/session/60/contribution/35/material/0/0.pdf
[12] https://www.inmm.org/AM/Template.cfm?Section=29th_Spent_Fuel_Seminar&Template=/CM/ContentDisplay.cfm&ContentID=4383
[13] http://www.nrc.gov/reading-rm/doc-collections/isg/isg-11R3.pdf
[14] http://www.energy.gov/sites/prod/files/2016/05/f31/Shutdown_Sites_Report_Sept2015_web.pdf
[15] http://pbadupws.nrc.gov/docs/ML1204/ML12047A184.pdf
[16] http://www.nap.edu/catalog/21874/lessons-learned-from-the-fukushima-nuclear-accident-for-improving-safety-and-security-of-us-nuclear-plants
[17] http://www.nrc.gov/reading-rm/doc-collections/commission/comm-secy/2013/2013-0030comvtr.pdf
[18] https://curie.ornl.gov/system/files/documents/not%20yet%20assigned/STAD_Canister_Feasibility_Study_AREVA_Final_1.pdf
[19] http://www.energy.gov/sites/prod/files/2013/08/f2/RepositoryReferenceDisposalConcepts.pdf
[20] https://thebulletin.org/donate
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