Fuel for commercial nuclear power reactors is typically made from low enriched uranium fashioned into thumbnail-size ceramic pellets of uranium dioxide. These pellets are fitted into 12- to 15-foot hollow rods, referred to as cladding, made of a zirconium alloy. The rods are then bound together into a larger assembly. A typical reactor holds about 100 metric tons of fuel when operating—generally from 200 to 800 fuel assemblies. The uranium in the assemblies undergoes fission—a process of splitting atoms into fragments and neutrons that then bombard other atoms—resulting in additional fission reactions and a sustainable chain reaction that creates an enormous amount of heat and radioactivity in the form of radioisotopes, or radioactive substances. The heat is used to generate steam to turn a turbine, which generates electricity. The radioisotopes produced in a reactor can remain hazardous from a few days to many thousands of years; these radioisotopes remain in the fuel assemblies and as components of the resulting spent nuclear fuel. Figure 1 shows what a fuel pellet for a commercial nuclear reactor and a fuel rod in an assembly look like. Each fuel assembly is typically used in the reactor from 4 to 6 years, after which most of the uranium dioxide is no longer cost-efficient at producing energy. Reactor operators typically discharge about one-third of the fuel assemblies from a reactor every 18 months to 2 years and place the spent nuclear fuel in a pool to cool. Most commercial spent nuclear fuel is stored immersed in pools of water designed to cool and isolate it from the environment. Water circulates in the pool to remove the heat generated from the radioactive decay of some of the radioisotopes. In recent years, reactor operators have used fuel that is burned longer in the reactor under the same operating conditions, resulting in higher “burn-up” and higher decay heat in comparison to the lower burn-up fuel that had been in use. The pools of water for cooling spent nuclear fuel are typically about 40 feet deep, with at least 20 feet of water covering the spent fuel. Figure 2 shows a typical spent nuclear fuel pool. Industry practice has been to store the spent nuclear fuel in the pools for at least 5 years, with an industry expectation that, at some point, DOE would begin to accept it. Spent nuclear fuel typically must remain in a pool for at least 5 years to decay enough to remain within the heat limits currently allowed for dry cask storage systems. Spent nuclear fuel can be sufficiently cool to load into dry storage systems earlier than 5 years, but doing so is generally not practical. Some dry storage systems, depending on the rated heat load, may not accommodate a full load of spent nuclear fuel. High burn-up fuel may have to remain in a pool longer than low burn- up fuel to cool sufficiently. The pools at commercial nuclear power reactors have largely reached their maximum capacities, however. When spent nuclear fuel is discharged from a reactor at a plant where the spent nuclear fuel pool is at maximum capacity, spent nuclear fuel equal to the amount of spent nuclear fuel discharged from the reactor must be transferred to dry storage. The dry storage systems typically consist of either a thick-walled, bolted steel vertical cask, or a welded steel canister inside a vertical or horizontal steel-reinforced concrete cask. Dry storage systems are designed with thick steel and concrete walls to provide radiation shielding and passive pathways for removal of spent nuclear fuel decay heat, such as air vents in the casks. In one typical process of transferring spent fuel to dry storage, reactor operators place a steel canister inside a larger steel transfer cask and lower both into a pool. Spent nuclear fuel is loaded into the canister, a lid is placed on the canister, and then both the canister and transfer cask are removed from the pool. The transfer cask shields nearby workers from the radiation produced by the spent nuclear fuel in the canister. The water is drained and a lid is welded onto the canister. Then the canister and transfer cask are aligned with a storage cask and the canister is maneuvered into the storage cask. The transfer cask can be re-used. The storage casks, in either vertical or horizontal designs (see fig. 3), are usually situated on a large concrete pad with safety and security measures, such as radiation detection devices and intrusion detection systems. NRC requires that spent fuel in dry storage be stored in approved systems that offer protection from significant amounts of radiation. NRC requires storage systems to demonstrate compliance with its regulations, including through physical tests of the systems, scaled physical tests, and computer modeling. Once a dry storage system is approved, NRC issues a certificate of compliance for a cask design or a specific license. Figure 4 shows spent nuclear fuel on a concrete pad in dry storage. Most U.S. reactors were built during the 1960s and 1970s and, after a 40- year licensing period have received a 20-year license extension, and some may apply for subsequent extensions. Nevertheless, these reactors may begin permanently shutting down in large numbers by about 2030 and emptying their pools by about 2040 absent additional license renewals. In the absence of a repository, the reactors’ accumulated spent nuclear fuel will be “stranded” in a variety of different dry storage systems, with no easy way of repackaging the spent fuel should repackaging be required to meet future storage or disposal requirements. NRC regulations require radioactive contamination to be reduced at a reactor to a level that allows NRC to terminate the reactor’s license and release the property for other use after a reactor shuts down permanently. This cleanup process is known as decommissioning. Spent nuclear fuel is expected to accumulate at an average rate of about 2,200 metric tons per year in the United States, mostly in wet storage, but this rate and the amount in wet storage are expected to decrease as more reactors, as projected, begin to shut down in the 2030s. More specifically, according to data provided by the Nuclear Energy Institute, the rate of accumulation will be about 2,100 metric tons in 2031, decreasing to about 1,200 metric tons in 2040, about 200 metric tons in 2050, and less than 100 metric tons per year from 2051 through 2055, when the last one of the currently operating nuclear power reactors is expected to shut down. These rates assume that except for the few reactors that have announced early permanent shutdown dates, the nation’s current reactors continue to operate through a 20-year extended license period without any further license extensions and continue to produce spent nuclear fuel at the same rate, and that no new reactors are brought online. Shutdown of Nuclear Reactors in the United States Of the 118 nuclear reactors in the United States, 18 reactors have permanently shut down. Three of these reactors are located on a site that also has an operating reactor. The remaining 15 reactors are located on 12 sites where the reactors have been or will be dismantled and decontaminated. After this decommissioning, the site can be used for other purposes and the only relic remaining at the site will be the spent nuclear fuel storage facility and the associated safety and security infrastructure. By the end of fiscal year 2013, DOE reported that it had signed contracts with owners and generators of spent nuclear fuel involving 118 reactors. The spent nuclear fuel from these 118 reactors is stored at 75 sites in both wet and dry storage systems. Several reactors share the same site. For example, the Palo Verde site in Arizona has 3 operating reactors. In 2013, about 70 percent of accumulated spent nuclear fuel—about 50,000 metric tons—was stored in pools, with the remaining 30 percent— about 22,000 metric tons—in dry storage. Figure 5 shows the 75 spent nuclear fuel wet and dry storage sites, including shut-down sites, in the United States. In the future, more spent nuclear fuel is expected to be put into dry storage for two reasons. First, since most spent nuclear fuel pools have reached their maximum capacities, reactor operators must transfer fuel from the pools to dry storage to make room for newer spent nuclear fuel, a time-consuming and costly process. Second, the amount of spent nuclear fuel transferred to dry storage is expected to increase as reactors shut down and their pools are closed. According to data from the Nuclear Energy Institute, by 2024, the proportion of spent fuel in wet storage and dry storage from currently existing reactors should be roughly equal— about 48,000 metric tons each. By 2040, about 70 percent of the spent fuel is expected to be in dry storage, or about 89,000 metric tons, compared to about 39,000 metric tons in wet storage. By 2067—after the last of the currently operating reactors have shut down—nearly all the 139,000 metric tons of spent fuel expected to be generated by currently operating reactors is expected to be in dry storage. Figure 6 shows the estimated amounts of spent nuclear fuel accumulation and transfer from wet storage to dry storage through 2067. Federal liability for managing spent nuclear fuel has been based on costs that owners and generators of this fuel have paid because DOE has not met its contractual obligations to begin disposing of this fuel, and DOE’s estimate of future liability—$21.4 billion through 2071—is based on how long the federal government is expected to pay these costs. This estimate is based on DOE’s strategy to begin accepting spent nuclear fuel in 2021 and assumes no delays in their schedule. Generally, the U.S. Court of Federal Claims has held that the federal government’s liability covers the cost of managing the spent nuclear fuel that DOE was obligated to begin disposing of in 1998. The Department of Justice has also agreed to pay such costs as a result of settlement agreements. (See app. IV for additional information on the settlement agreements.) Under the standard contract, DOE was obligated to take title to and dispose of a certain quantity of spent nuclear fuel beginning in 1998.