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Author: Marvin S. Fertel
The debate over managing high-level radioactive waste is really about extending proven technology and successful practices.
Nuclear power plants are valuable producers of electricity that do not cause harm to the environment by discharging greenhouse gases or other regulated air pollutants into the atmosphere. In addition, nuclear energy is unique among major sources of electricity in that its primary by-products—used uranium fuel rods—remain safely contained on the sites where they have been used in nuclear reactors.
Nevertheless, the question of how the nuclear industry manages its highly radioactive used fuel rods is perceived to be extremely difficult, a problem yet to be solved. Despite the significant environmental benefits of nuclear electricity, public concerns about the management of high-level radioactive waste abound, based largely on a lack of information about the nature of these materials and the care with which they are managed.
In January 2012, President Obama’s Blue Ribbon Commission on America’s Nuclear Future (BRC) completed nearly two years of deliberations on this very question. The commission’s recommendations provide a sound policy for moving forward (BRC, 2012), even though a policy is, in fact, already well established. The current policy includes proven technical solutions to the safe management of used fuel elements and the storage of used reactor fuel at plant sites. Strict licensing requirements and oversight of used fuel facilities by the U.S. Nuclear Regulatory Commission (NRC) provide another layer of protection for public safety and the environment. Nevertheless, over the long term, consolidated storage, followed by ultimate disposal or advanced treatment of the fuel, would be preferable to the present policy.
The Nature of Used Nuclear Fuel
When considering policy approaches to managing used nuclear fuel, it is important to understand the physical nature of the material. To generate electricity, nuclear energy facilities use small, ceramic, uranium-oxide pellets as fuel. These pellets (about the size of a fingertip) are loaded into long, thin metal fuel rods, which are then grouped into bundles called fuel assemblies. A typical fuel assembly is about 12 feet long (Figure 1). Inside the reactor, uranium atoms in the pellets split in a process known as fission. The heat generated from this process is used to produce steam, which drives the turbines that produce electricity.
Over time, fissionable uranium in the fuel is consumed, and the radioactive by-products of the fission process accumulate inside the rods. Every 18 to 24 months, the reactor is shut down, and as much as one-third of the uranium fuel—the oldest fuel assemblies—is removed and replaced (Figure 2).
The used fuel assemblies are highly radioactive and will remain that way for several thousand years while the natural process of radioactive decay takes place. Nuclear fuel and other high-level radioactive wastes contain elements that present a potential radiation hazard to the public and environment if not handled properly. However, this hazard diminishes over time, often declining significantly in the first few hundred years and thereafter much more gradually.
Throughout the decay process, the used fuel remains solid, compact, and relatively small in volume. All of the used fuel rods from 50 years of electricity production by America’s nuclear energy facilities could be stacked seven yards deep on one football field.
Safeguarding and Disposing of Used Nuclear Fuel
The primary question for policy makers is determining the best way for the federal government to safeguard and dispose of used nuclear fuel. There are two parts to this question: (1) steps that must be taken by industry now to protect the environment from radioactive materials in the fuel and (2) steps that must be taken by future generations to safeguard the materials, which will remain highly radioactive for thousands of years.
Answers to both parts of the question are well known. Protection for the near term and foreseeable future is provided by storage pools and dry-container storage technology. Protection in the distant future will be provided by a geologic repository. Over the past several decades, much of the debate about used nuclear fuel has centered on the question of where a future repository will be located, rather than on the viability and safety of accepted storage and disposal methods.
Used Fuel Storage Systems
There are three primary safety considerations for managing used nuclear fuel: (1) radiation protection and containment; (2) ensuring that fuel assemblies do not overheat; and (3) preventing an unintended nuclear chain reaction (a “criticality accident”).
When used fuel is first removed from a reactor, the used fuel assemblies are placed in steel-lined, concrete pools of water inside the power plant structures. The depth of the water is typically maintained at about 20 feet above the top of the fuel assemblies to provide radiation shielding for people working directly above the enclosed pool.
This volume of water, in combination with heat exchangers through which the water is circulated, also keeps the fuel cool, thus preventing damage to the fuel assemblies from overheating. Finally, the racks in which the fuel is placed at the bottom of the pools are specially engineered and configured to preclude the possibility of nuclear criticality.
These steel-lined concrete pools are extremely robust and are designed to protect the fuel under even the most severe conditions—a design philosophy that proved itself in extraordinary fashion during the 2011 earthquake and tsunami at Fukushima Daiichi, Japan. There were seven used fuel pools at the Daiichi site, containing approximately 10,000 used fuel assemblies (TEPCO, 2010). All of the pools maintained their integrity and protected the fuel assemblies throughout the event, even though some of them were located in reactor buildings that suffered catastrophic damage from hydrogen explosions associated with the reactor accidents (Figure 3).
The heat load associated with reactor fuel drops dramatically over time. After about five years in storage, used fuel has cooled enough for it to be removed from the pools. In the 1960s and 1970s, U.S. commercial reactors were designed with pools that had limited storage capacity under the assumption that the federal government would remove the cooler assemblies for transportation either directly to a geologic repository for disposal or to a reprocessing or recycling facility where the radioactive by-products would be separated from reusable constituents prior to disposal.
However, in the 1980s, it became apparent that the U.S. Department of Energy’s (DOE’s) disposal program was well behind schedule and that this commitment would not be met before the pools reached their maximum storage capacity. This was true even though companies had expanded capacity by modifying storage racks in the pools.
Dry Storage Container Systems
The challenge of providing more capacity was met through the development of dry storage container technology, which has extended safe storage capacity at commercial reactor sites beyond the estimated operating period of the reactors. The first dry-container storage systems were placed in service at the Surry Nuclear Power Station in Virginia in 1986 (GTS, 2012). These above-ground systems—like the steel-lined pools—incorporate safety features to protect public health.
The foremost safety feature is the extremely rugged containers, which are made of steel, steel-reinforced concrete, or steel-enclosed concrete 18 or more inches thick—all materials that have been proven to be effective radiation shields. A typical container is about 20 feet tall and 11 feet in diameter and weighs more than 360,000 pounds when fully loaded. The makers of dry-container systems design and test them to ensure that they prevent the release of radioactivity even under extreme conditions—such as earthquakes, tornadoes, hurricanes, floods, and sabotage.
At the Fukushima Daiichi site when the earthquake and tsunami struck, there were nine loaded dry-cask systems, containing approximately 400 used fuel assemblies. None of the containers was damaged (TEPCO, 2010).
The containers and their enclosures, which involve no moving parts, dissipate heat given off by the used fuel assemblies through natural circulation cooling. The containers are sealed and tested for leakage to a high standard to ensure that the used fuel assemblies are maintained in a benign inert-gas environment. The internal structures inside the containers are engineered with the same precision as the racks in the pools to ensure that no unintended nuclear criticality can occur (Figure 4).
Dry-storage containers can hold 24 to 87 used fuel assemblies—depending on the specific fuel type and the container design. To date, more than 1,500 dry casks have been loaded at 56 reactor sites in 30 states in the United States. Of the approximately 237,000 fuel rod assemblies that have been discharged from commercial reactors during the U.S. industry’s 50-year history, approximately 65,000 have been removed from pools and loaded into dry-container systems. About 6,500 assemblies are loaded into 150 containers each year. By 2020, more than 2,600 dry storage systems will have been loaded at 75 locations in 33 states (GTS, 2012).
Industry’s Safety Record
The storage systems described above have a stellar safety record, and no harmful radioactivity has been released to the environment. The industry’s commitment to safety has been recognized by NRC, which oversees the operation of U.S. nuclear energy facilities. NRC’s regulations originally called for dry-container storage systems to be licensed for 20 years, with an option for a 20-year renewal. Considering the extensive experience that has been gained since the first dry-container systems were put into service, in 2011 NRC regulations were amended to provide for a 40-year license, with an option for a 40-year renewal (NRC, 2011).
In 2010, NRC stated that used fuel generated at any reactor “can be stored safely and without significant environmental impacts for at least 60 years beyond the licensed life for operation.” Given that 70 percent of U.S. reactors are already licensed for operation for up to 60 years, NRC has expressed confidence that it is safe to store used nuclear fuel at reactor sites for as long as 120 years—even though it is unlikely that fuel will remain at a site for that long (NRC, 2010).
When dry-container storage systems were originally loaded, it was not intended that they would remain at reactor sites indefinitely. In fact, 75 percent of the containers in service today were specifically designed to be transportable, as are new systems that will be loaded in the future. Storage systems that were not originally designed for transport would either have to be modified to make them transportable or unloaded at reactor sites where the used fuel could be transferred to a transportable system. In the latter case, the inner canisters, which hold the fuel rods, would be removed from the storage package and transferred to transportation packages designed to provide the same high level of protection during shipment.
Transport for Interim Storage or Reprocessing
Although the specific location to which containers will be shipped is not yet known, the types of facilities that will be needed at the other end are well understood. A strong, long-standing international scientific consensus supports disposal of nuclear waste in a geologic repository as the ultimate, permanent solution. In addition, many experts believe there is a benefit to recycling used fuel to separate the radioactive by-products from reusable constituents prior to disposal; this is already being done in the United Kingdom and France.
Transporting used fuel away from reactor sites to consolidated storage locations for longer term storage prior to disposal or recycling is under consideration in the United States. In fact, a U.S. Senate subcommittee in April approved a fiscal year 2013 budget for DOE that included language supporting consolidation of used nuclear fuel at one or more storage sites.
According to a survey by Bisconti Research Inc./GfK Roper in February 2012, 64 percent of Americans believe that storing used nuclear fuel at reactor sites is safe, but three-quarters of U.S. adults surveyed agreed that it would be preferable to store used nuclear fuel at one or two consolidated storage facilities. The public was evenly split on whether the government’s nuclear fuel management program should be managed by a corporate-style board of directors or a federal agency. However, a strong majority—86 percent—believe that America’s nuclear energy industry should develop recycling technology to take advantage of the energy that remains in uranium fuel rods after they are removed from a reactor (NEI, 2012a).
An Integrated Plan for Managing Used Nuclear Fuel
The remainder of this article focuses on consolidated storage, potential recycling, and geologic disposal, which are vital components of an integrated approach to managing used nuclear fuel. However, it should be noted that the dry-container storage systems in use today will also be an important component of the permanent solution.
Dual-Purpose and Transportation, Aging, and Disposal Containers
In 2008, while DOE was studying a potential geologic repository at Yucca Mountain in Nye County, Nevada, scientists developing the repository and industry designers of dry-container storage systems collaborated to develop a storage system design that could be both transported to and disposed of in the repository (DOE, 2008). This system—known as a transportation, aging, and disposal (TAD) container—was under licensing review by NRC when the Yucca Mountain project was terminated in 2010 for policy, not technical reasons.
Although work on TAD containers was never completed, the program demonstrated the utility of a system by which radioactive by-products in used fuel could be packaged, in reactor pools, in containers that would never have to be reopened. At the same time, the industry sought to qualify dual-purpose systems that were already loaded for disposal in Yucca Mountain. Based on substantial technical analysis (EPRI, 2008), the nuclear energy industry filed contentions in the Yucca Mountain licensing process seeking to amend the repository license to allow for the disposal of fuel loaded in dual-purpose systems.
Although the Yucca Mountain project was terminated by the Obama administration before the potential of disposable dry-storage containers could be realized, it is possible that the next effort to design a repository could capitalize on this potential. If direct disposal of dry-container storage systems were pursued, it would mean that one element of the infrastructure for permanent isolation of radioactive by-products of nuclear energy is already in use today.
Even though it is feasible for industry to safely store used nuclear fuel at reactor sites for more than 100 years, this may not be the most practical approach. When the storage of used fuel is co-located with an operating reactor, the additional costs for storage are not significant. However, when a reactor is shut down and the used fuel must be maintained on the site in dry-cask systems as a stand-alone facility—as is the case at some U.S. locations (GTS, 2012)—the costs are high. In addition, the land upon which this facility sits remains unavailable for future use by nearby communities. Even where used fuel is co-located with operating reactors, efficiencies—beginning with the development of a common monitoring, inspection, and security infrastructure—could be gained by moving the fuel to consolidated locations.
For these reasons, BRC has recommended “prompt efforts to develop one or more consolidated storage facilities” (BRC, 2012). In a letter dated April 23, 2012, to Senators Dianne Feinstein and Lamar Alexander, BRC co-chairs Lee Hamilton and Brent Scowcroft wrote that proposed legislation in the U.S. Senate to develop consolidated storage “incorporates several key recommendations of the Blue Ribbon Commission on America’s Nuclear Future and is a positive step toward the goal of creating an integrated nuclear waste management system in the United States.” The nuclear energy industry supports the proposed legislation and has also recommended to Congress and DOE that consolidated storage be implemented in a timely manner.
There are international precedents for the success of consolidated storage. Sweden and Switzerland operate independent facilities for dry-container storage (NWTRB, 2009), and Spain recently selected a site for a similar facility (Frayer, 2012; Reuters, 2011; WNN, 2012).
In 2006, NRC granted a license to Private Fuel Storage LLC for a commercial consolidated storage facility in Utah that would be capable of storing approximately two-thirds of all U.S. commercial used fuel (NRC, 2006). In the face of state opposition, the Utah facility has yet to be developed, but other states and communities have expressed interest in hosting such a facility, in part because of the economic development that is expected to accrue to host communities.
Geologic Disposal for Permanent Isolation
A long-standing consensus among scientific organizations worldwide supports the disposal of used fuel and high-level radioactive waste underground in a specially designed repository. In such a facility, a combination of engineered and natural features would isolate the radioactive by-products deep beneath the earth’s surface for the thousands of years it will take for the level of radioactivity to decay to the point at which it no longer presents a health or environmental hazard. More than a dozen nations are pursuing this approach. Finland (Figure 5), Sweden, and France are expected to complete construction of geologic repositories in 2020, 2023, and 2025, respectively (NWTRB, 2011).
In the United States, from 1982 to 2010, one of the most exhaustive scientific programs ever undertaken was focused on a potential geologic repository site at Yucca Mountain in Nevada. This effort resulted in a comprehensive safety analysis that showed the proposed repository would protect public health and safety for one million years, with radiation exposures from the repository expected to be equal to a fraction of natural background radiation—well below regulatory limits (DOE, 2008). This safety analysis was under review by NRC when DOE terminated the Yucca Mountain project for policy reasons.
Nevertheless, the scientific work that was completed on the Yucca Mountain project provides a powerful indicator of the safety benefits of geologic disposal. Similar safety analyses are under review by regulatory authorities in Sweden and Finland (and will be initiated in the near future in France). Each of these projects is moving forward with strong support from local communities.
In fact, the concept of geologic disposal is already being successfully demonstrated in Carlsbad, New Mexico, at the Waste Isolation Pilot Plant (WIPP), an operating repository for long-lived radioactive waste. In 1999, WIPP began receiving shipments of radioactive by-products from U.S. Department of Defense programs containing some of the same long-lived radioactive constituents found in used fuel. So far, the facility has received more than 9,000 shipments of radioactive waste for disposal in salt formations more than 2,000 feet below the earth’s surface (DOE, 2007, 2010, 2011).
Billions of dollars have been spent worldwide studying and refining approaches to geologic repositories. In 2001, the U.S. National Academy of Sciences concluded: “After four decades of study, geologic disposal remains the only scientifically and technically credible long-term solution available” (National Research Council, 2001). Similarly, in 2003, the International Atomic Energy Agency concluded, “In a generic way, it can be stated with confidence that deep geological disposal is technically feasible and does not present any particularly novel rock engineering issues. The existence of numerous potentially suitable repository sites in a variety of host rocks is also well established” (IAEA, 2003).
Clearly, the relevant question about geologic disposal facilities is not whether, but when and where they will be developed. In the United States, until the time and place have been agreed upon, used fuel storage technology will continue to protect public health and safety.
Recycling to Enhance Disposal and Energy Production
There is broad agreement that disposal in a geologic repository represents the ultimate solution to the permanent isolation of long-lived radioactive by-products of nuclear fission. However, there are two schools of thought about the form in which these by-products should be disposed.
The approach pursued in most countries, including the United States thus far, is the direct disposal of used fuel. This would permanently isolate radioactive by-products but would not take advantage of the vast energy content remaining in the fuel. For this reason, several countries, including the United Kingdom and France, recycle or reprocess used fuel to separate the radioactive by-products for disposal and reuse the fissionable uranium and plutonium to make new fuel elements.
Although the United States does not recycle reactor fuel—and there are significant questions about whether it is economical to do so—DOE is sponsoring ongoing research to improve recycling methods that could make this option more attractive. Depending on future uranium supplies and advances in recycling technologies, the United States may turn to this course of action. Doing so would provide additional supplies of energy and make possible the development of tailored waste forms that would enable more efficient use of geologic repository capacity.
The Federal Government’s Obligation
Despite industry’s outstanding safety and security record and considerable progress around the world toward implementing geologic disposal, the public and policy makers in the United States continue to raise concerns about the management of used nuclear fuel. This is due, in part, to the federal government’s failure to develop sustainable spent fuel management solutions.
In 1982, the Nuclear Waste Policy Act codified the federal government’s obligation to remove used nuclear fuel from reactor sites and dispose of its radioactive by-products in a geologic repository. As required by this law, the government entered into contracts with the owners of America’s commercial nuclear energy facilities to begin removing used fuel from reactor sites by 1998.
To date, the government remains unable to meet this legal requirement, and billions of dollars paid by the industry into a Nuclear Waste Trust Fund have been diverted to help balance the federal budget. Inaction also has undermined confidence in the overall management of used nuclear fuel. Even though this lack of confidence does not reflect shortcomings in the industry’s ongoing safe management of nuclear materials or NRC’s oversight of the program, it is vitally important that action be taken to reform the federal program so a permanent solution can be developed.
The President’s Blue Ribbon Commission has recommended reform of the DOE program, including the creation of an independent program management entity with unrestricted access to the Nuclear Waste Fund. The commission also recommended a new consent-based process for selecting both a consolidated storage site and a repository site. If implemented, these measures would help resolve the impasse (BRC, 2012). The U.S. industry strongly supports the BRC recommendations and looks forward to prompt action by the president and Congress to enact the necessary reforms (NEI, 2012b).
The storage of used nuclear fuel is among the best understood and most effectively managed responses to the environmental challenges associated with electricity production. For several decades, the nuclear energy industry has successfully used dry-container storage technology to ensure that public health and safety are protected—today and for the foreseeable future. The debate over high-level radioactive waste is, in reality, about how to extend proven technology and successful practices so future generations will enjoy the same level of protection, as well as the benefits of nuclear energy.
There are promising opportunities for the development of a repository, perhaps complemented by advanced recycling technologies. The recent recommendations of the President’s Blue Ribbon Commission provide an excellent policy platform for developing short- and long-term approaches to satisfy the federal government’s commitment to the nuclear energy industry and consumers of electricity produced by America’s 104 reactors.
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