Dry-Cask Storage: How Germany Led the Way

Abstract

With Yucca Mountain dead, the United States needs an alternative home for its nuclear waste. It would do well to look to Germany, which invented interim dry-cask storage and still relies on the technology today to store its spent fuel safely.

With the abandonment of Yucca Mountain as the future location of the first U.S. underground spent-fuel repository, the country now finds itself $13.5 billion poorer and with no national disposal policy. 1 Not so long ago, Germany found itself in a similar position. It had a partially built underground repository that it had shut down, in part for political reasons, and the only alternative it had was to store its excess and accumulating spent fuel in dry casks at its reactor sites. Although U.S. utilities are unhappy that the federal government has not fulfilled its commitment to take spent fuel off their sites as promised in the 1982 Nuclear Waste Policy Act, it looks as if they have no other option than the current situation for some decades to come. Fortunately, there is no need to panic: Dry-cask storage is safe, and Washington is reimbursing utilities for dry-cask storage-related expenses.

Germany invented the dry spent-fuel storage cask, and the first such casks in the United States came from Germany, shipped to the Surry Nuclear Power Plant in Virginia after it received the first U.S. license to build a dry-cask storage facility in 1986. 2 The cast-iron casks were made by the German company Gesellschaft für Nuklear Service (or Company for Nuclear Services, known by its German acronym GNS), which Klaus Janberg, a co-author of this article, ran from 1980 to 2000. Eventually, GNS lost market share and was forced to abandon the United States in the 1990s due to cheaper competitors. Nevertheless, the history of how this technology was first developed and promoted in Germany, and how it made possible Germany's transition from a failed national policy of reprocessing to interim storage in dry casks, is of value as the United States looks for a new solution for its own nuclear waste–and as reprocessing of U.S. spent fuel is being actively promoted by many Republicans and some Democrats in Congress.

Dreams of plutonium breeder reactors.

Until India's nuclear test in 1974, nuclear energy proponents–led by the U.S. Atomic Energy Commission–assiduously promoted the idea of a global “plutonium economy,” in which chain-reacting plutonium produced by fast reactors, also known as breeder reactors, would replace low-enriched uranium fuel. In anticipation of this transition, in the 1970s, West Germany built an experimental civilian spent-fuel reprocessing plant to recover plutonium from spent fuel and a small experimental breeder reactor, both located in Karlsruhe in the country's southwest region. This was a part of the German nuclear program that began in 1957, when the first German research reactor, Garching I, went critical. The country built 31 more power reactors, mostly light water reactors (LWRs), and with the passage of the 1960 Atomic Energy Act, the federal government took responsibility for the final disposal of the country's radioactive waste. This was done in exchange for a small charge per kilowatt-hour on electricity generated by nuclear power plants (an arrangement that was adopted in the United States in 1982).

During the first oil embargo in the early 1970s, Germany's Socialist-Liberal governing coalition became convinced–like many other national governments–that nuclear power should be expanded. It promoted a plan in which fast reactors would be phased in as quickly as possible because of the concern that supplies of low-cost natural uranium would soon run out–an assumption that later proved to be incorrect. The plan envisioned that the plutonium in spent fuel discharged by LWRs would be recovered through reprocessing to provide start-up fuel for the fast reactor fleet.

In 1977, Germany strengthened its commitment to reprocessing by establishing a policy that no new operating licenses would be issued for nuclear reactors unless they had reprocessing contracts for their spent fuel. At this point, however, the reprocessing plant that the German government wanted to build was not yet even in the design stage. In the meantime, Germany's nuclear utilities needed to store their accumulating spent fuel somewhere. U.S. nuclear utilities also had faced this problem and decided to increase the capacity of the storage pools at their reactor sites by reracking them to fit more spent fuel. In Germany, that decision was not made because such a retrofit would have constituted a major license change necessitating public hearings at a time when German public sentiment regarding nuclear power was turning negative. The fear was that licensing hearings would put the continued operation of Germany's power reactors at risk. So Germany's nuclear operators needed another option.

Aggravating the situation was the size of Germany's spent fuel pools, which were small because they were built within reactor containment buildings to protect them from aircraft impacts and attacks with anti-tank weapons. At that time, there were frequent crashes of German Air Force jets and the Red Army Faction, a notorious German terrorist group, was attacking U.S. Army vehicles and personnel, sometimes with rocket-propelled grenades. The small German reactor pools could store only three to five years' worth of spent fuel, which was completely insufficient for the amount of time it would take before a licensed German reprocessing facility could begin operating.

In the 1970s, there were no casks available except for a concrete cask used in Canada to store small spent-fuel assemblies from that country's heavy water reactors. There were spent-fuel transport casks for LWR fuel, but they were not intended for storage.

To deal with this problem, Germany's nuclear utilities decided in 1976 to build a 1,500-ton-capacity interim spent-fuel storage pool at Ahaus, about 10 kilometers from the Dutch border, and a second 3,000-ton intake pool for the planned German reprocessing plant at Gorleben Nuclear Park in Lower Saxony where all of Germany's fuel-cycle facilities were to be concentrated. Gorleben is located roughly 145 kilometers from Hamburg and only about 3 kilometers from the border of the former East Germany. The Gorleben facilities were to be located atop a salt dome within which solidified radioactive waste from reprocessing would be deposited permanently.

Deutsche Gesellschaft für Wiederaufarbeitung von Kernbrennstoffen (or German Company for Spent Nuclear Fuel Reprocessing, known by its acronym DWK) was established by Germany's nuclear utilities to build and operate the Gorleben reprocessing complex. DWK also was interested in pursuing the option of transport and storage casks for spent fuel. In the 1970s, there were no casks available except for a concrete cask used in Canada to store small spent-fuel assemblies from that country's heavy water reactors. There were spent-fuel transport casks for LWR fuel, but they were not intended for storage. These transport casks were made of steel, and their manufacture required costly, time-consuming welding. So DWK was quite interested when GNS approached it in the late 1970s with the idea of building what became the CASTOR, or Cast Iron Cask for Transport and Storage. The cast-iron design made possible lower-cost, higher-volume cask production. The idea was to license the CASTOR for both storage and transport, facilitating shipment of spent fuel to the proposed reprocessing site at Gorleben.

The 5.8-by-2.4-meter CASTOR V, still in use today, has iron walls more than 38-centimeters thick and weighs about 105 tons without fuel. Its heavy construction makes it strong enough to resist aircraft impacts and missile attacks. Furthermore, no water cooling is required. The cask is filled with helium to facilitate leak detection, and radioactive decay heat is transferred via radiation and convection of the helium from the spent fuel within the cask to the massive walls and then transferred passively via natural convection to the air outside. Because the thick walls also provide radiation protection, the CASTOR can be used for both transport and storage without additional shielding. 3 For several years, the CASTOR was the world's only spent-fuel transport and storage cask. A typical dry-storage cask holds 10 tons of spent fuel and costs about $1 million-$2 million each. (The CASTOR is at the upper end of that range.) This translates to a cost of less than one-twentieth of a penny per kilowatt-hour–about 1 percent of the cost of generating nuclear power. 4

Unlike reactors and spent-fuel pools, casks are not subject to loss-of-coolant accidents because they are cooled via natural convection by the air around them. If the helium leaks out and air enters the cask, passive cooling would continue to be adequate. After spending 5-7 years in a cooling pool, the spent fuel in a cask generates about 20 kilowatts of heat, which is, per square meter of the cask's surface, equivalent to about one-half of the solar energy that is absorbed by a dark roof on a clear summer day. The thick walls of the cask shield the contents from all but armor-piercing munitions. The CASTORs at the Surry Nuclear Power Plant have had their licenses extended to 40 years and, if necessary, the licenses probably could be extended for one or more additional 20-year periods.

Preliminary testing in 1978 to determine the strength of the CASTOR included 30-foot drops–which were successful even without the additional shock absorbers normally fitted to the ends of the cylinder and even when the cask was frozen to negative 40-degrees Celsius. Simulations of aircraft impacts were carried out by propelling a 1970s-era NATO fighter-bomber turbine shaft at 312 meters per second into the cask's side and then also into the lid. The side impact resulted only in some bent cask cooling fins, and the vertical lid impact resulted in a minor leak of helium. The casks were tested against kerosene fires and modern antitank weapons as well. The lessons learned made it possible to design better storage buildings to protect the casks.

The CASTOR test results convinced DWK in 1979 to build a dry-cask central storage facility instead of cooling pools. Dry casks were less costly and offered superior protection combined with “zero releases” of fission-product gases, improving public acceptance of central spent-fuel storage considerably and making it possible for the government to proceed with construction of dry-cask storage facilities at Gorleben and Ahaus.

At that time, GNS didn't have domestic customers for the CASTOR because all German spent fuel was transported for reprocessing in France and Britain, which had crafted specifications that excluded the use of German-origin casks. Therefore, GNS only could sell the CASTOR for the transport of spent fuel to the small experimental German reprocessing facility in Karlsruhe and for storage of some difficult-to-reprocess, first-generation spent mixed-oxide (MOX) fuel (a combination of uranium and plutonium oxides).

Dry casks were less costly and offered superior protection combined with “zero releases” of fission-product gases, improving public acceptance of central spent-fuel storage considerably and making it possible for the government to proceed with construction of dry-cask storage facilities at Gorleben and Ahaus.

So, GNS looked abroad and found customers in Switzerland in 1983; in the United States, at the Energy Department's Idaho National Engineering Laboratory in 1984; and at the Virginia Electric Power Company's Surry reactor site in 1985. Russia's Voronesh Nuclear Power Plant, southwest of Moscow, became a customer in the mid-1980s. Finally, in the early 1990s, there was a large German order for 420 small casks to hold spent fuel from the country's experimental high-temperature pebble bed reactors for which no reprocessing options were available.

By 1980, however, reprocessing was no longer seen as a viable long-term solution to the nuclear waste problem. The United States had abandoned its reprocessing plans a few years earlier, and the cost of French and British reprocessing services had skyrocketed. Most economic comparisons–except unsurprisingly those made by the French and British reprocessing companies–showed a clear cost advantage for direct disposal of spent fuel in repositories. Direct disposal was now being taken seriously in Germany as well. By 1985, DWK had produced the Pollux cask, intended for the underground disposal of spent fuel. 5 Smaller and lighter than the CASTOR, the Pollux weighs less than 75 tons and is designed to be lowered into a repository by cable. It also is welded shut since it is never intended to be opened again. And finally, unlike the CASTOR, which is designed to hold intact fuel assemblies, fuel is placed in Pollux casks as naked fuel rods, with the rest of the fuel-assembly hardware that holds the rods in place in a reactor stripped off.

By 1984, DWK began construction of a $2.4-billion (in 2007 dollars) reprocessing facility in Wackersdorf, Bavaria, after the proposal to site the facility at Gorleben was abandoned due to political considerations. (It did, however, continue to be used as a storage site.) By 1989, the price had soared to roughly $9 billion and the plant was still far from finished. This was in the wake of the 1986 Chernobyl accident, and proposals for new nuclear projects in Germany were encountering major public opposition. Also, the Socialist Party, which had been a driving force for nuclear power and reprocessing up to this point, had, after the 1979 Three Mile Island accident and Chernobyl, increasingly turned against nuclear energy. The German utilities, therefore, decided to abandon their domestic reprocessing facility project, but due to long-term contracts with France and Britain, continued to send their spent fuel to be reprocessed there until 2005. After that year, a ban on shipment of German spent fuel to foreign reprocessing plants came into force.

At the same time that reprocessing was being abandoned, the commercialization of fast reactors was failing in a number of countries. The U.S. Congress cancelled the 350-megawatt demonstration Clinch River Breeder Reactor in 1983. Germany completed its $5-billion demonstration 300-megawatt breeder reactor in 1986 but did not start it up and eventually abandoned it in 1991. The site was sold to a Dutch entrepreneur who turned it into a children's water park, dubbed “Nuclear Water Wonderland.” France's 1,200-megawatt Superphénix went into operation in 1985 but suffered one problem after another until it was finally closed in 1998 by Socialist Prime Minister Lionel Jospin, who came into office with the support of France's anti-nuclear Green Party. The French plant operator, Électricité de France (EDF), didn't fight the closure as both the capital and fuel-cycle costs of Superphénix were so high relative to conventional LWRs that there was little hope that it–or, in fact, any large-scale, commercial fast reactor–could be competitive for decades to come. Determined to keep reprocessing alive, EDF turned to recycling plutonium from LWR fuel and making MOX fuel for use in LWRs. Yet the uranium savings were relatively low, around 20 percent, and the cost was much higher than simply using newly mined and enriched uranium fuel.

It wasn't until 1994 that the German government allowed direct disposal of spent fuel as an alternative to reprocessing. GNS, which had inherited many of DWK's facilities and responsibilities when the reprocessing project was finally abandoned, built a plant for dismantling spent-fuel assemblies and packing the fuel rods as well as other types of spent fuel into its newly acquired Pollux casks. All of this took place at Gorleben, which, after domestic reprocessing was abandoned, was turning into the national site for storing, conditioning, and disposing of German spent fuel.

Nuclear power opponents throughout Germany tried to stop the developments at Gorleben. Tens of thousands of demonstrators blocked and even tore up the rails to prevent train transports of spent fuel and high-level vitrified reprocessing waste to the interim storage facility, and a comparable number of police were deployed to ensure the trains got through. Stopping the activities at Gorleben was seen, by anti-nuclear activists, as stopping German nuclear power in general. In 1994, the atmosphere became so heated that anti-nuclear protesters threatened to murder Janberg's family and disfigure his eldest daughter. His daughter was threatened yet again in 1997 when a train carrying a British-manufactured cask derailed in France, on its way from Germany to Britain. The threat came from someone who apparently assumed that the British cask was a German CASTOR.

Dry-cask storage at nuclear power plant sites is a safe interim strategy that gives countries roughly 50 years to properly site future geologic repositories. Dry-cask storage also is much safer and much cheaper than reprocessing, which is being promoted in the United States by France's nuclear conglomerate Areva.

Concerns about possible attacks on the casks increased when the Russian Army left East Germany in 1994. It was rumored that Russian soldiers had sold a good share of their weaponry on the black market before they left, and a concern was that extremists might use Russian antitank missiles against the transport casks. To deal with this possibility, GNS developed a simple method to plug a hole in a damaged CASTOR by hand with a lead spike. Janberg travelled with the first trainload of spent fuel to Gorleben in 1995 with a suitcase of such spikes in case of this type of attack. (Incidentally, the release of radioactivity in such a scenario would be quite minimal.)

Germany's long nuclear phaseout.

In 1998, a Socialist-Green coalition came to power. Phasing out German nuclear power was part of the coalition-forming agreement, but it would be gradual. Nuclear power supplied 30 percent of the country's electricity and shutting down the plants immediately would both have led to blackouts and required huge government compensation payments to the utilities.

In 2001, the agreement banning German utilities from sending their spent fuel to foreign reprocessing plants after 2004 was signed. The utilities also reluctantly agreed to shut down each of their nuclear reactors after the equivalent of 32 years of full power production. This would give them time to convert the plutonium separated at the foreign reprocessing plants into MOX fuel and use it in German reactors before they were shut down. In the 2002 revision to Germany's Atomic Energy Act, it was agreed that each nuclear power plant would store its spent fuel in CASTORs or other qualified casks at on-site storage facilities. Vitrified high-level reprocessing waste coming back from France and Britain would be transported to the central dry-cask storage facility that had been completed in Gorleben.

Starting in 1998, work on the underground high-level waste and spent-fuel repository at Gorleben was slowed and in 2001, suspended. (Dry-cask storage facilities at Germany's nuclear power plant sites came into operation in 2006 and 2007.) This was despite the fact that several miles of galleries had been dug into the salt dome at a depth of about 900 meters without finding any evidence that would disqualify the site as an adequate geologic repository. Socialist Environment Minister Jürgen Trittin and his successor Sigmar Gabriel said they wanted other sites to be explored in order to find the “most suitable one.” At the same time, a former iron mine near Salzgitter in Lower Saxony was licensed as a repository for low- and medium-level radioactive waste and successfully survived several legal challenges. No more spent fuel has been shipped to the central above-surface, dry-cask storage sites at Gorleben or Ahaus, except for several casks of fuel from a decommissioned research reactor at the Rossendorf Research Center in Dresden. More than $1 billion was spent at Gorleben to build a permanent repository there, before the government abandoned the effort. The Socialist-Green government that was in power at that time did not want to approve any activity at Gorleben that could be interpreted as accepting it as a final-disposal site. (In November 2008, however, Gorleben was again the site of a huge protest against a 12-cask shipment of solidified high-level waste from France's reprocessing plant.)

All of the above is highly applicable to the United States today. Regardless of the country, it is politically difficult to site permanent repositories for radioactive waste. Such failures in the United States and other countries prove that repositories can't be forced on unwilling communities. In contrast, positive experiences in Finland and Sweden, where repository projects are moving forward, have shown that it is possible to find a site if communities are meaningfully consulted throughout the process. In the meantime, dry-cask storage at nuclear power plant sites is a safe interim strategy that gives countries roughly 50 years to work out these issues and properly site future repositories. Dry-cask storage also is much safer and much cheaper than reprocessing, which is being promoted in the United States by France's nuclear conglomerate Areva. Reprocessing generates huge quantities of liquid high-level waste that could be dispersed as a result of a terrorist attack. At least as importantly, reprocessing produces separated plutonium that could be used for bombs. Given that fast reactors won't be competitive with LWRs anytime soon, there is simply no justification for reprocessing at this time. Reprocessing persists in France only because the law requires it, and Japan reprocesses only because its local governments won't allow dry-cask interim storage at reactor sites and no prefecture is willing to host a centralized interim storage site.

Looking at the risks and costs of the alternatives, the United States–like Germany–should be grateful for the humble dry cask.