Storage of Spent Nuclear Fuel

 Regardless of how long spent fuel is stored, eventually it will have to be moved from reactor sites.¹

After nuclear fuel has been used for five to six years to furnish the power to produce electricity, the spent (or used) fuel, which is still highly radio-active, must be stored on the reactor site until it can be moved to a geological disposal site. The disposal site selected in the United States was Yucca Mountain, located in a remote desert region of the Nevada Nuclear Weapons Test Site. However, after 20 years of study, a cost of $10 billion, and the submission of a licensing application to the Nuclear Regulatory Commission (NRC), which was nearing completion of its review, President Obama directed the U.S. Department of Energy (DOE), the responsible federal agency, to cancel the project. That decision is being appealed in the courts, and the outcome is still not clear.

At the direction of the president, DOE then created the Blue Ribbon Commission on America’s Nuclear Future (the BRC or the Commission) to study what to do next with regard to the disposal of nuclear waste, which is currently stored at nuclear power plant sites, either in spent fuel storage pools or in concrete-shielded canisters or dry casks. In January 2012, the Commission completed its review and delivered its final report, Report to the Secretary of Energy (BRC, 2012).

One of the BRC’s recommendations, in the absence of a waste disposal site, was the creation of one or more centralized, “interim” (or consolidated), spent-fuel storage facilities, which would not have been necessary had the Yucca Mountain Project been opened by 2017, as planned. The Commission believes that some communities and states might be willing to accept the presence of interim storage facilities for spent nuclear fuel based on a volunteer, consensus process. However, given that there is no plan for a permanent repository and that a consensus-based process for the siting of interim storage facilities was tried in the past and failed (Kadak and Yost, 2010), the prospects for success are not high.

Lawsuits brought by utilities for breach of contract when DOE did not begin accepting spent fuel from nuclear plant sites in 1998, as required by law, have further complicated the issue. If DOE does not start accepting spent fuel until 2020, the estimated liability to U.S. taxpayers could be as high as $20.8 billion (BRC, 2012). To date, taxpayers have paid $2 billion to nuclear utilities to compensate them for the costs of storing spent fuel. Thus, the overall cost, so far, for canceling the Yucca Mountain Project has been more than $12 billion, and it increases with every year of delay (BRC, 2012). For their part, nuclear utilities are anxious to have the spent fuel removed from their sites, especially in places where the reactors have been decommissioned, leaving only spent fuel storage pools or casks on the site.

The purpose of this article is to describe the current status of spent fuel storage and the challenges associated with interim storage of unknown duration at existing nuclear plant sites.

What is Spent (Used) Fuel?

In the course of generating electricity, nuclear plants create small amounts of highly radioactive waste in the form of spent nuclear fuel, which constitutes a significant hazard to human safety if not properly stored and disposed. Because of the radioactivity and extreme longevity of spent nuclear fuel, its management is a major policy challenge for virtually every country in the world that generates nuclear power. According to the National Academy of Sciences (National Research Council, 1990), the best way to dispose of nuclear waste is in a geologic repository. This is also the common conclusion of all nations with nuclear power plants.

Figure 1

Two types of nuclear reactors are used in the United States, pressurized-water reactors and boiling-water reactors, to generate steam to power the turbines and electric generators that produce electricity. Fuel rods comprise the “used fuel” that is stored at reactor sites in used-fuel storage pools and in dry storage systems. Figure 1 shows typical fuel-rod assemblies for pressurized and boiling-water-reactors.

Characteristics of Spent Nuclear Fuel

Spent nuclear fuel has the following characteristics:

• Small volume and mass. The energy released from nuclear reactions is about one million times greater than from the burning of fossil fuels; consequently, only small quantities of spent nuclear fuel are generated.
• Fuel value. Existing reactors recover slightly less than 1 percent of the energy value of the initial mined uranium. Advanced breeder reactors could recover most of the energy value of the uranium by appropriate recycling of the spent fuel and the use of depleted uranium from the uranium enrichment process. Although recycling spent fuel is not economical today, this may change in the future.
• Radioactive decay. As radioactive materials decay to non-radioactive materials, they generate heat. Over time, both radioactivity and heat generation from spent fuel decrease. Therefore, the longer spent fuel is stored on reactor sites, the less complex the design of a permanent (or interim) repository can be, because the heat load, which is a limiting design constraint, will be much lower. Figure 2 shows the reduction in decay heat over time.

Figure 2

Options for Spent Fuel Storage

Two options are available for storing spent fuel—wet storage in pools of water and dry storage in canisters or casks. However, for the first five years after discharge from a reactor, spent fuel assemblies generate too much heat to be safely stored in dry canisters or casks. During those years, they require active cooling in storage pools to prevent damage to the fuel. The two options are briefly described below.

Wet Storage. Spent-fuel pools are 40-foot deep, water-filled, and typically lined with stainless steel. Submerged holding racks are capable of safely storing spent-fuel assemblies after they have been removed from a reactor (Figure 3). The water and the concrete sides and floor of the pool shield reactor workers from radiation from the spent fuel, and pumps actively remove decay heat generated from the fuel-rod assemblies.

Figure 3

When the current generation of reactors was being built, fuel storage pools were intended to provide only short-term cooling until the assemblies could be sent to a storage or reprocessing site. As a result, storage pools were constructed with only a small storage capacity (typically enough for about one-and-one-third of the assemblies in a core). However, the ban on reprocessing spent fuel in the 1970s and the failure to build a national repository by 1998 made storage in spent-fuel pools the de facto policy of the United States.

In response, reactor operators were forced to retrofit their storage pools in an effort to increase their capacity. By using more densely packed storage racks and adding neutron absorbers, utilities were able to expand their waste-storage potential. Ultimately, however, the pools became filled to capacity even with more densely packed storage racks. To make room for more spent fuel and enable the plants to keep operations going, the storage racks had to be moved to dry storage systems.

Since 1986, more and more fuel storage pools have approached their maximum holding capacity (Figure 4). By 2017, all but one site (which was constructed with sufficient pool storage capacity to accommodate all of the spent fuel produced during the reactor’s lifetime) will be at capacity, necessitating the greater use of dry storage.

Figure 4

 Dry Storage. By the end of 2011, the United States commercial nuclear waste inventory had reached approximately 65,000 metric tons of heavy metal (MTHM). This represents about 224,000 fuel assemblies. Roughly 50,000 MTHM are held in spent fuel pools. The remaining 15,000 MTHM have been placed in casks that are collectively referred to as “dry storage.” Roughly 2,200 MTHM are produced each year by existing nuclear reactors.

In the early 1980s, in response to the overcrowding of storage pools, the nuclear industry began to explore other temporary storage techniques. Spent fuel assemblies that have decayed sufficiently, thereby emitting less heat, can be transferred to dry storage systems consisting either of thick-walled metal casks bolted closed with metallic seals or thin-walled canisters surrounded by a metal or concrete outer shell for shielding. Both casks and canisters are passively cooled by ambient air. To date, utilities have transferred 13,000 MTHM of spent fuel to above-ground dry storage systems.

Spent fuel canisters are filled with inert helium gas to prevent degradation by oxidation. They are then seal welded and placed in concrete cylinders fitted with inner metal liners (which provide radiation shielding) or in separate metal enclosures.

Canisters loaded with spent fuel are moved to dry-storage facilities, referred to as independent spent fuel storage installations (ISFSIs) on the utilities’ sites. ISFSIs are large, parking-lot-type concrete pads surrounded by protective fencing and under continuous security surveillance.

Figure 5

Typical storage casks can be stored in either vertical or horizontal systems (Figures 5, 6, and 7). Cask systems are popular among reactor operators because of their inherent flexibility. For one thing, they allow for the modular expansion of storage capabilities. For another, licensed “dual-purpose” casks can be used for both storage and transportation of nuclear waste. Some cask vendors have even developed “multiple-purpose containers” they hope will be suitable for storage, transport, and disposal.

Figure 6

 Figure 7

Storage-only casks, which are not suitable for transportation, require repackaging prior to shipment. The easiest way to do this is by first placing the casks back into spent fuel pools and transferring the spent fuel from the storage-only canister into a canister suitable for transportation. However, this is not always possible, because some plants, including the spent fuel storage pools, have been decommissioned. Therefore, either alternative dry transfer systems will have to be developed or NRC will have to grant special exemptions for spent fuel in storage-only canisters.

Dry-storage systems for spent fuel (i.e., ISFSIs) are licensed by NRC according to Title 10, Part 72 of the Code of Federal Regulations (10 CFR 72) (Federal Register, 2009; NRC, 2008). Approximately 22 percent of domestic spent fuel is in dry storage at 44 plant sites. Figure 8 shows existing and likely future locations for storage of commercial spent nuclear fuel.

Figure 8

Dry cask storage of nuclear waste is considered safe. NRC estimates that the per-cask risk of failure-induced fatalities is equal to 1.8 x 10^-12 in the first year of operation and 3.2 x 10^-14 per year for each subsequent year of storage (NRC, 2007).

Under current regulations, NRC licenses commercial dry-storage systems initially for 20 years. However, NRC recently authorized an exemption to the regulation and renewed the license for a dry-storage system at the Surry Nuclear Power Station in Virginia for an additional 40 years (a total of 60 years). On September 15, 2009, NRC proposed changing the initial licensing and license renewal periods from 20 to 40 years (Federal Register, 2009).

Centralized Interim Storage

The siting of a centralized regional interim storage facility will be more difficult today than in the past, because we have no clear exit strategy for the spent fuel that is “temporarily” stored. Under the Nuclear Waste Policy Act (NWPA), as amended in 1987, Congress authorized volunteer efforts by a “nuclear waste negotiator” to site a monitored, retrievable, interim storage facility (NWPA, 1983, 1987). The effort failed, however, partly because of political opposition and partly because of congressional interference in the process once siting decisions were near.

Despite the BRC’s optimism, there are no indications of fundamental changes in the politics of siting interim facilities or in the willingness of states and local communities to accept such a facility. Some have suggested that co-locating a reprocessing plant and an interim storage facility, which would provide jobs and an economic boost to the area, might be a differentiator. But that remains to be seen.

The NWPA, as amended in 1987, forbids DOE from building an interim waste storage facility until Yucca Mountain obtains an operating license (NWPA, 1987). This legislative restriction will have to be removed to allow the construction of an interim facility independent of progress on a repository site. Of course, this would make the siting of an “interim” facility even more difficult.

Efforts by private utilities to build a regional interim storage facility, such as the private fuel storage (PFS) project in Utah, which, after a 10-year licensing process, was granted an NRC license, have been stymied by national and state political opposition. Nevertheless, because the PFS site already has an NRC license, it should be considered a near-term option.

Even if another volunteer site could be found, the licensing process for that site could also last 10 years, plus 3 to 5 years for construction, before any spent fuel could be accepted by the facility. In addition, a transportation infrastructure would have to be constructed for shipping casks of spent fuel to the facility. The process could be expedited if construction and permits could be pursued concurrently.

Another option would be to site an interim facility on land at an existing federal facility that already has the requisite security and infrastructure. DOE, for example, operates many national laboratories, and the military has many bases across the country that might meet these requirements.

In December 2008, DOE issued a report to Congress on the regulatory issues associated with the creation of a large, independent site for centralized interim storage and concluded that it would take six years to complete such a facility—three years for licensing and three years for construction (DOE, 2008). Thus, 2015 is the earliest date that operations could begin. However, given that the PFS facility took more than 10 years to obtain a license and fight its way through legal battles, DOE’s estimates are considered optimistic. If an existing site were used, operations might begin sooner, but significant political and regulatory issues would have to be resolved.

Taxpayer Obligation

To cover the costs utilities have incurred in building their own dry cask storage facilities, nuclear utilities have been paying 0.1 cent per kilowatt-hour for electricity generated by nuclear plants. By the end of 2010, $16 billion had been collected (BRC, 2012). When interest is added and expenditures are subtracted, a balance of $27 billion remains to fund repository development.

Even though this money does not really exist, because it has been used to help fund the federal government, and even though DOE did not, as mandated by law and by contract, open the high-level waste repository by 1998, the taxpayer obligation for utilities remains. By 2020, this obligation is estimated to total $20.8 billion. By that time, most utilities will have built their own ISFSIs, for which the government will have to pay under court decisions. Thus, the total liability to the government from the unspent, but unavailable, fund and payments to utilities for failing to remove spent fuel from reactor sites comes to $49.1 billion (BRC, 2012).

Decommissioned Nuclear Plant Sites (Orphaned Waste)

Currently, 104 commercial nuclear reactors are operating in the United States, and 14 have been permanently shut down. Of the 14 facilities that have been shut down, 4 are located at sites with other operating reactors. The other 10 decommissioned reactors are located at 9 sites that have no operating reactors; and all 9 of them have stranded spent fuel stored on site. Figure 9 shows the Yankee Atomic Nuclear Plant site with the reactor gone and the spent fuel in the background. As more reactors are shut down in the future, the number of stranded storage sites will increase considerably, raising the cost, not only for utilities, but also ultimately for U.S. taxpayers.

Figure 9

The marginal cost of storing spent fuel on a site with ongoing nuclear operations is relatively low, because most of the operations and maintenance costs for storage can be integrated with existing site operations with little additional overhead. However, at sites with no current nuclear operations, the cost of spent fuel storage is about $8 million dollars per year per site (Kadak and Yost, 2010). Thus, the high cost of maintaining spent fuel on sites with no ongoing reactor operations is a primary economic incentive for consolidating spent fuel at a central facility or on sites with working reactors.

One option would be to co-locate decommissioned spent fuel at an existing decommissioned plant ISFSI in a community willing to host spent fuel from other plants. The chances of success would depend on the willingness of the community and state to accept such a solution. In addition, this might be a near-term test case for finding volunteer sites in communities that understand the issues related to spent fuel storage and past nuclear operations.

Transportation

Regardless of how long spent fuel is stored, it will eventually have to be moved from the reactor sites either to offsite interim storage facilities, to used fuel processing facilities for recycling, or to a waste disposal site. Transportation regulations are largely focused on the integrity of the casks that contain the used fuel. These casks are designed to withstand a series of accidents without releasing radioactive materials.

Figure 10

Figure 10 shows a full-scale crash test conducted by Sandia National Laboratories in 1977. In this test, a locomotive traveling at approximately 80 miles per hour crashed broadside into a used fuel transportation cask. As Figure 10 shows, the cask and the dummy fuel inside it performed in accordance with regulatory requirements.

Economics

The most recent capital-cost estimate for a centralized ISFSI of 40,000 MTHM is about $560 million; this includes design, licensing, and construction of the storage pad, cask-handling systems, and rail infrastructure (locomotive, rail cars, transport casks, etc.) (EPRI, 2009). Annual operating costs during loading are estimated at $290 million per year, including the costs of dual-purpose canisters and storage overpacks, which will provide shielding for the canisters once they are placed on the interim storage pads.

It will take 20 years to fully load an ISFSI of this size, and a period of “unloading” and eventual decommissioning will be necessary after storage. The interim period of “caretaking” is estimated to cost about $4 million per year, about half the caretaking costs of a decommissioned reactor (Kadak and Yost, 2010).

Technical Basis for Long-Term Storage

The length of time an interim storage facility will be used cannot be known, because there is no firm plan to build a repository or reprocessing plant. However, some have suggested that it could be as long as 300 years. Given that it might be a very long time, the U.S. Nuclear Waste Technology Review Board (NWTRB) was asked to assess the technology basis for long-term storage.

Based on its assessment, the study board concluded that the technical basis for the spent fuel currently being discharged (high utilization, burnup fuels) is not well established and that the possibility of degradation mechanisms, such as hydriding, will require more study. The NWTRB recommended periodic examinations of representative amounts of spent fuel to ensure that degradation mechanisms are not in evidence and to confirm the presence of the helium cover gas (NWTRB, 2010). The industry and DOE have embarked on a research program to address these issues (EPRI, 2010).

Conclusions

As a result of political decisions, spent fuel in the United States will have to be stored either at reactor sites or in regional interim storage facilities. Given the political difficulties of finding a state and community willing to host either an interim storage facility or a waste repository, predictions of success or timing cannot be made. Here is what we do know:

1.  Storage at reactor sites will be necessary for a minimum of 10 more years.
2.  According to NRC, spent fuel can be safely stored in dry casks for at least 60 years, and evidence may show that it can be stored for even longer.
3.  Building an interim storage facility is currently not permitted by law. Therefore, legislative action will be necessary before such a storage facility can be considered.
4.  Once an interim facility has been identified and licensed, transportation to the site will require considerable additional time and investment.
5.  Until DOE removes the spent fuel from operating and decommissioned sites, the cost to taxpayers for the government’s failure to build a repository will continue to grow.
6.  The top priority for ending this costly financial obligation completely is to remove spent fuel from decommissioned sites. The obligation would continue for operating sites, however, until DOE removes all of the spent fuel, as obligated by contracts with utilities.

References

BRC (Blue Ribbon Commission on America’s Nuclear Future). 2012. Report to the Secretary of Energy. Available online at http://brc.gov/sites/default/files/documents/brc_ finalreport _jan2012.pdf.

DOE (U.S. Department of Energy). 2008. Report to Congress on the Demonstration of the Interim Storage of Spent Nuclear Fuel from Decommissioned Nuclear Power Reactor Sites. Available online at http://pbadupws.nrc.gov/docs/ML0834/ML083450160.pdf.

EPRI (Electric Power Research Institute). 2009. Cost Estimate for an Away-From-Reactor Generic Interim Storage Facility (GISF) for Spent Nuclear Fuel. Technical Update 1018722. May 2009. Palo Alto, Calif.: EPRI.

EPRI. 2010. Used Fuel and High-Level Radioactive Waste Extended Storage Collaboration Program. November 2009 Workshop Proceedings. Palo Alto, Calif.: EPRI.

Federal Register. 2009. 10 CFR Part 72 License and Certificate of Compliance Terms. 74FR47126. September 15, 2009.

Kadak, A.C, and K. Yost. 2010. Key Issues Associated with Interim Storage of Used Nuclear Fuel. MIT-NFC-TR-123. December. Cambridge, Mass.: Massachusetts Institute of Technology.

National Research Council. 1990. Rethinking High-Level Radioactive Waste Disposal: A Position Statement of the Board on Radioactive Waste Management. Washington, D.C.: National Academy Press.

NRC (U.S. Nuclear Regulatory Commission). 2007. A Pilot Probabilistic Risk Assessment of a Dry Cask System at a Nuclear Power Plant.  NUREG-1864. Available online at http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/ sr1864/sr1864.pdf.

NRC. 2008. Title 10, Code of Federal Regulations, Part 72, Energy: Licensing Requirements for the Independent Storage of Spent Nuclear Fuel and High-Level Radioactive Waste, and Reactor-Related Greater than Class C Waste. Washington, D.C.: U.S. Government Printing Office. Office of Federal Register National Archives and Records Administration, as amended June 9, 2008 (10 CFR 72).

NRC. 2012.  Locations of Independent Spent Fuel Storage Installations. Available online at http://www.nrc.gov/waste/spent-fuel-storage/locations. html.

NWPA (Nuclear Waste Policy Act). 1983. Nuclear Waste Policy Act of 1982, 42 U.S.C. 10101, P.L. 97-425; Nuclear Waste Policy Act Amendments of 1987. Available online at http://epw.senate.gov/nwpa82.pdf.

NWPA (Nuclear Waste Policy Act as Amended) 1987. P.L. 100-203-December 22, 1987, Part E: Nuclear Waste Technical Review Board. Available online at http://www.nwtrb.gov/mission/1987aa.pdf.

NWTRB (Nuclear Waste Technology Review Board). 2010. Evaluation of the Technical Basis for Extended Dry Storage and Transportation of Used Nuclear Fuel. December. Available online at http://www.nwtrb.gov/reports/eds_rpt.pdf.

 FOOTNOTES

 ¹ This paper does not necessarily represent the positions of the U.S. Nuclear Waste Technology Review Board.