Dry Cask Storage Booming for Spent Nuclear Fuel

A combination of spent fuel pools reaching capacity, security concerns, and mostly nonexistent policies regarding long-term consolidated storage of nuclear waste is making dry cask storage the only way forward for most nations with nuclear power reactors.

Around the world, demand for dry cask storage facilities for spent nuclear fuel (SNF) is on the rise. Few countries are making any meaningful progress on facilities for permanent storage of this nuclear waste—only Sweden and Finland are expected to see underground repositories for radioactive waste completed in the 2020s; plans for “permanent” storage facilities nearly everywhere else are stalled. Meanwhile, as other nations, especially in Asia, ramp up their nuclear capacity, the need for spent fuel storage continues to increase—all of which is good news for companies developing dry cask technologies.

One sign of the growing market: Privately held Holtec International is building a new plant in Camden, N.J., for both SNF containers and its small modular reactor business that will have a full-time staff of 395 on opening day—anticipated in mid-2018. Thereafter, Holtec estimates the local craft labor employment in the plant to approach 2,000 in the first five years of operation. Professional employment at the center is expected to increase to 1,000. The company already has three existing fabrication facilities.

AREVA TN (formerly Transnuclear), a division of state-owned French multinational AREVA Inc., another major cask supplier, sees Asia as the market with the biggest growth in dry storage, as that region continues to build new reactors that will eventually require dry storage or reprocessing systems.

AREVA told POWER it sees the U.S. market remaining steady with reorders until the Department of Energy (DOE) makes a decision on the way forward with consolidated storage. “This decision will drive new technologies that offer innovative and cost-effective solutions that can accommodate different types of canisters that can easily be retrieved and transported. The establishment of a national consolidated dry storage location will also require transportation expertise and equipment,” Jean C. Tullier, AREVA TN’s marketing and communications manager, said.

From Wet to Dry Storage

Roughly one-third of the fuel in a nuclear reactor is removed and replaced with fresh fuel at each refueling. The removed “spent” fuel then is placed into deep pools of water at the reactor site, where it continues to generate heat and radiation (Figure 1). Although spent fuel pool designs vary somewhat by country, facility, and era, according to the U.S. Nuclear Regulatory Commission (NRC), pools at U.S. plants “are robust constructions made of reinforced concrete several feet thick, with steel liners. The water is typically about 40 feet deep, and serves both to shield the radiation and cool the rods.”

1. Cooling in the pool. This spent nuclear fuel pool is at the closed 860-MW Caorso Nuclear Power Plant in Caorso, Italy, which used low-enriched uranium as fuel. The plant operated from 1978 to 1990, when it was closed following a 1987 referendum. Courtesy: Simone Ramella/Wikipedia

When rods have cooled sufficiently—after at least one year, but typically several years—they can be removed for transportation to a reprocessing or long-term storage site. The NRC says fuel is typically cooled at least five years in a pool before transfer to casks. The NRC has authorized transfer as early as three years; the industry norm is about 10 years, it says.

Spent fuel at many U.S. and other plants has stayed in pools for much longer than anticipated. Even with reconfiguration of the pools to accommodate more rods, eventually, they reach capacity.

Because the U.S. does not permit commercial reprocessing of fuel, as some nations do and as China is planning for, and because prospects for a permanent waste storage facility get bleaker with each passing year, onsite dry storage has become the de facto next and final step in the U.S. storage plan. The NRC formally recognized onsite dry cask storage as safe from short to indefinite timeframes with its August 2014 Continued Storage of Spent Nuclear Fuel Rule. And that is one reason the market for onsite dry cask storage is sure to grow.

A report by authors from Oak Ridge National Laboratory projects that the number of SNF canisters in dry storage will roughly double in the next 10 years (from more than 1,850 in 2013) and will exceed 10,000 by 2050 in the U.S. alone. An October 2014 report by the U.S. Government Accountability Office (GAO) found that in 2013, about 70% of SNF was stored in pools and the remaining 30% in dry storage. As reactors reach the end of their operating licenses, the volume of SNF will increase.

Cask designs vary by manufacturer, but some of the main variants involve purpose (some designs can be used both for transportation and storage), orientation (vertical or horizontal), materials (stainless steel is most common, though cast iron is also used), and siting (above ground on a cement pad or subsurface).

Dry cask storage has been used in North America, Europe, and Asia. The first casks used in the U.S. were loaded in 1986 at the Surry Nuclear Power Plant in Virginia. As of September 2014, the NRC, which offers both a site-specific and a general license for dry storage cask systems, said spent fuel was being housed in dry storage at more than 50 sites under general licenses and at 15 sites with specific licenses. However, Maureen Conley in the NRC’s Office of Public Affairs told POWER that the commission hasn’t received a site-specific license application “in many years.”

The NRC also licenses cask designs; not all vendors have applied for or received NRC licenses. In addition to Holtec and AREVA TN, vendors with currently approved designs are General Nuclear Systems Inc. (only used at Surry), NAC International Inc., and Energy Solutions Inc. Conley confirmed that reactors with operating licenses may use any of the dry storage systems certified by the NRC as long as they do an analysis showing their site meets the parameters of the approval. Some sites use casks of multiple designs or from multiple vendors.

Security Concerns Push Dry Cask Storage

In addition to the absence of permanent storage sites and crowded spent fuel pools, two events within a decade underscored the need for more secure “interim” storage options: the terrorist attacks of September 11, 2001, and the disaster at the Fukushima Daiichi power plant in 2011.

The NRC notes that after 9/11, it required plant operators to take “several measures aimed at mitigating the effects of a large fire, explosion, or accident that damages a spent fuel pool. These were meant to deal with the aftermath of a terrorist attack or plane crash; however, they would also be effective in responding to natural phenomena such as tornadoes, earthquakes or tsunami.” These measures included:


■ Controlling the configuration of fuel assemblies in the pool to enhance the ability to keep the fuel cool and recover from damage to the pool.

■ Establishing emergency spent fuel cooling capability.

■ Staging emergency response equipment nearby so it can be deployed quickly.


In December 2014, more than three years after the site experienced catastrophic damage from the Great East Japan earthquake and tsunami, Tokyo Electric Power Co. (Tepco), the plant’s operator, finished removing 1,331 spent fuel rods and 204 unused assemblies from Daiichi Unit 4 and had placed them in a cask container for transportation to an undamaged Unit 6 pool on the site. (Because Unit 4 had been under routine maintenance at the time of the disaster, all 1,535 fuel assemblies were in the pool.) Tepco expects to remove fuel from Units 1, 2, and 3 by fall of this year. It started with Unit 4 because the hydrogen explosion that blew the roof off the reactor building made that pool the most critical to remediate. (A video at http://on.fb.me/1Drgd3M tracks the stages of the fuel removal process.)

In Japan, concern about the safety of SNF pools persists, especially as onsite pools fill up and completion of a planned Japanese fuel reprocessing center in Rokkasho is looking unlikely.

A June 2014 report in the Nikkei Asian Review noted that Japan’s pools have been criticized as being vulnerable to natural disaster or terrorist attack. The Japanese Economy, Trade and Industry Ministry, the publication said, plans to provide incentives for using dry cask storage as soon as after one year of in-pool cooling. In addition to offering better safety in the event of a disaster, the story noted that maintenance costs for dry cask storage are reportedly 60% lower than for pool storage. Japan, the article said, currently has two dry cask sites “storing 240 tons combined, or roughly 1% of the total amount of spent fuel in the country.”

According to a paper by Xuegang Liu of the Division of Nuclear Chemistry and Engineering, The Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing (“Spent Nuclear Fuel Management in China,” NAPSNet Special Reports, Aug. 5, 2014), because China has chosen to use a closed-cycle fuel path, it has less need for long-term SNF storage. The author notes that “Dry cask storage has only been implemented for CANDU spent fuel at the Qinshan Phase III NPP, because of the low thermal density of CANDU spent fuel and the lack of plans to reprocess spent CANDU fuel, which is made of natural uranium. Dry cask storage is also a possibility for use in storing fuel from high temperature gas cooled pebble-bed reactors, and dry casks are being designed for this purpose.”

In China, although the disposition of SNF varies based upon reactor type, used fuel is typically stored in pools, which have capacity for about 10 years’ worth of fuel. According to the Chinese academic paper, “The construction of the dry storage facility in Qinshan Phase III started in 2008. The first two concrete MACSTOR-400 dry storage modules were completed in 2009. There are plans to construct 18 MACSTOR-400 modules at a rate of 2 modules every 5 years.”

New Cask Designs Promise Added Safety

More U.S. dry cask facilities are on the way, including at Ameren Missouri’s Callaway Energy Center, which expects construction of its dry cask storage system to be completed this summer. Holtec International is supplying engineering, site construction, security, fabrication, and pool-to-pad loading services for the Callaway project, which is an underground storage facility that was developed after the 9/11 attacks. All equipment for the HI-STORM UMAX system will be domestically fabricated at the Holtec Manufacturing Division facility in Turtle Creek, Pa.

The Callaway site will have an initial installed capacity of 1,776 fuel assemblies, according to a December Holtec update (Figure 2). The pool-to-pad loading “dry run” is scheduled for March-April 2015, with first loading scheduled to begin in early May. Ameren Missouri says the site is designed to store fuel from the plant’s 40-year operating license plus the 20-year extension it expects to receive.

2. Buried casks. The Cavity Enclosure Canisters (CECs), shown here with biological lids placed on each silo, provide an all-welded steel enclosure for storage of the multipurpose canisters (MPC) and were manufactured at Holtec Manufacturing Division near Pittsburgh, Pa. Each CEC will hold one MPC-37 canister (with a capacity of 37 fuel assemblies), giving the Callaway site an initial installed capacity of 1,776 fuel assemblies. Courtesy: Holtec International

Holtec also was chosen in December to provide the HI-STORM UMAX system for SNF from the shuttered San Onofre Nuclear Generating Station (SONGS) on the Southern California coast. Transfers of SNF from pools to the dry casks could begin in 2017.

Among Holtec’s technology advances that contribute to the safe storage of SNF is the underground configuration (UMAX), resulting in “virtually zero radiation dose to the public, a low profile, and full protection of the stored spent fuel from man-made and extreme environmental events,” VP of Corporate Business Development Joy Russell told POWER. Another is Metmic-HT, developed for criticality control. “This material provides superb heat transfer over previous materials, allowing spent fuel to be moved more rapidly from wet to dry storage and with its lower weight permits additional shielding material to be added to the dry storage system,” Russell explained.

AREVA TN also has landed recent new U.S. business. In December it announced a contract with Exelon for the supply of its NUHOMS dry shielded canisters and horizontal storage modules for the Limerick Generating Station in Pennsylvania as well as a long-term contract with FirstEnergy Nuclear Operating Co. to provide dry fuel storage equipment and related services. AREVA TN will supply its NUHOMS dry fuel storage systems (Figure 3), in use at more than 30 U.S. plant sites, to the Davis Besse and Beaver Valley nuclear power plants. This includes the first order of AREVA TN’s next-generation, NUHOMS Extended Optimized Storage (EOS) canisters and horizontal storage modules (Figure 4).

3. Diagram of a NUHOMS storage site. Courtesy: AREVA TN
4. A new home for old fuel. AREVA TN’s new NUHOMS EOS dry fuel storage canister features an advanced large-capacity basket that uses high-strength, low-alloy materials for improved thermal performance. Courtesy: AREVA TN

AREVA TN will manage the fuel-loading campaigns for the Davis Besse and Beaver Valley plants as part of the contracts. The used fuel loading is scheduled to begin in 2017 with additional services planned for 2019. The NUHOMS canisters will be manufactured near Pittsburgh, Pa.

AREVA TN says the NUHOMS EOS system has the best demonstrated shielding in the industry. The stainless steel canisters feature redundant welded lids, state-of-the-art precision welding procedures, low-risk horizontal transfer processes, and a “massive concrete module” for housing (which provides additional radiation shielding).

The company says that additional design improvements of the EOS system include increased heat rejection, increased thickness of basket conductors for improved emissivity, the ability to store damaged fuel assemblies (which saves the cost of “canning”), options for an inspection port built into the EOS concrete module for ease and effectiveness of long-term aging management, and a corrosion-proof option for use in marine environments. AREVA says this new model is the highest seismically qualified dry fuel storage system in the world. The horizontal, above-ground storage configuration makes the canisters easy to access and monitor long-term and less costly to maintain than underground systems, it says.

Is one dry cask design inherently better than another? As with most technologies—especially new ones and new models—only time and site-specific operating experience will tell. The NRC doesn’t weigh in on that question. Conley noted that, “All systems that we have approved meet our regulations for protecting public health and safety and the environment. We do not recommend one over another.”

Although previous generations of dry casks have not been without problems (including weld-related issues and two instances of water seeping into casks that were noted in 2013, which didn’t affect the SNF), the NRC’s August decision signals its overall confidence in the technology as well as in its oversight of the facilities. In fact, the NRC recently approved a 40-year license renewal for Exelon Generation’s dry cask independent spent fuel storage installation (ISFSI) at the Calvert Cliffs nuclear power plant in Lusby, Md., the fifth such extension. ISFSI licenses contain conditions requiring periodic inspections of the casks and their components to ensure potential aging effects are identified and managed.

Public Acceptance of Dry Storage Lags

There are 71 independent spent fuel storage facilities in the U.S., but that doesn’t mean that new ones are easily accepted. Last fall, neighbors of the Pilgrim Nuclear Power Station in Plymouth, Mass., appealed a Zoning Board decision that Entergy, which owns the plant, did not need a special permit to begin construction of a dry cask storage facility. And on the other coast, there has been opposition to onsite storage of fuel from the shuttered SONGS plant.

Entergy’s Vermont Yankee Nuclear Power Station, which went permanently offline at the end of December, will also use dry cask storage for its SNF after initial cooling in the facility’s spent fuel pools. After cooling in the spent fuel pool for seven years, the 3,880 SNF assemblies are to be stored in 58 dry casks located at two ISFSIs on plant property, although the second pad has not yet been built. Vermont Yankee was frequently a target of opposition during its 42-year operating life, and opponents to onsite storage continue to use legal challenges to the NRC’s environmental analysis that found onsite storage safe.

The October GAO report found that the DOE, which is legally responsible for interim and long-term SNF storage (which would be some type of dry storage), should implement a “coordinated outreach strategy” to better inform the public about federal SNF issues in order to successfully develop consolidated interim storage sites. “Without a better understanding of spent nuclear fuel management issues, the public may be unlikely to support any policy decisions about managing spent nuclear fuel,” the report said. ■

Gail Reitenbach, PhD is POWER’s editor.