Fuel for nuclear power plants consists of fingernail-sized pellets of uranium dioxide, a radioactive compound. The pellets are fitted into hollow metal rods, typically constructed of zirconium alloy, and the rods are then gas pressurized. The rods are generally 12 to 14 feet in length and are bundled together into assemblies. A portion of the assemblies must be replaced every 1 to 2 years as the fuel in the reactor expends energy, becoming less efficient at producing heat. As part of the process of expending energy during a nuclear reaction, the fuel becomes highly radioactive and thermally hot. Spent fuel emits radiation as a consequence of radioactive decay. Barriers such as thick walls, sealed containers, and water are used to shield individuals from exposure to this radiation. NRC regulates not only the construction and operation of commercial nuclear power plants but also the storage, transportation (together with the Department of Transportation), and disposal of spent fuel. NRC requires each operating nuclear power plant to have safety and security programs. For example, NRC requires protective shielding and security systems, including armed guards, at nuclear power plants. When spent fuel assemblies are removed from a reactor, they are stored in large pools of cooling water. These pools are constructed according to NRC’s requirements, typically with 4- to 6-foot thick steel-lined concrete walls and floors. Pools are typically 30 to 60 feet long, 20 to 40 feet wide, and 40 feet deep. The location of these pools is dependent on the type of reactor. Essentially, all commercial power reactors in the United States are one of two types, either a boiling water reactor or a pressurized water reactor. For most boiling water reactors, the pools are located close to the reactors, several stories above ground. For pressurized water reactors, the pools are located in structures outside the reactor building, on the ground or partially embedded in the ground. Regardless of reactor type, these pools are required by NRC to be constructed to protect public health against radiation exposure, even after a natural disaster, such as an earthquake. The water in the pool is constantly cooled and circulated, and the fuel assemblies are generally 20 feet below the surface of the water. In 1982, through the Nuclear Waste Policy Act, the Congress directed DOE to construct an underground repository for disposal of spent fuel and other high-level radioactive waste. The Congress amended the act in 1987 and required DOE to only consider Yucca Mountain, Nevada, as a potential site for a repository. In 2002, the President recommended to the Congress, and the Congress approved, Yucca Mountain as a suitable site for the development of a permanent high-level waste repository. As we reported in 2001, for a variety of reasons, DOE is unlikely to open the repository as planned in 2010. Lacking a long-term disposal option now, some nuclear utilities must move a portion of their spent fuel into dry storage or face shutting down their plants because their wet pools are reaching capacity. Currently, 25 of the 72 storage sites use dry storage, and 11 other sites have plans to move some of their inventory of spent fuel into dry storage. Dry storage facilities for spent fuel typically consist of steel containers that are placed inside concrete vaults or bunkers where the fuel is cooled by air rather than water. These storage systems are required by NRC to be capable of protecting against radiation exposure and of surviving natural disasters. Because the move to dry storage is time-consuming and expensive, utilities are, wherever possible, modifying wet pool storage capacity so they can store larger quantities of spent fuel in these pools. To expose a large number of people to the harmful effects of radiation from spent fuel, the fuel would have to be released from its protective containers and dispersed over a wide or densely populated area. However, unlike many other hazardous materials, spent fuel is a hard, heavy ceramic material that is neither explosive nor volatile. To achieve a wide dispersal, some portion of the spent fuel assemblies would have to be pulverized into small particles by an external force—such as a high-speed impact or a violent explosion—or some portion of the spent fuel assemblies would have to burn in a sustained, high-temperature fire. According to NRC, the redundancy and robustness of the designs of the fuel containers make wide dispersal highly unlikely. In the event of a dispersal, the most significant health effects would involve persons who inhaled very small (respirable) particles—10 microns or less in diameter. Such particles would be absorbed into the body and possibly remain there for many years. In addition, these particles could be deposited on buildings and the ground where, in the absence of a costly cleanup effort, they could expose people to elevated levels of radiation. The transportation of spent fuel to Yucca Mountain—most likely by both truck and rail, but with a preference for using mostly rail—will be a major undertaking, spanning 20 to 30 years. According to DOE, more than 50,000 tons of the spent fuel have accumulated at 72 sites in 33 states, many located near urban areas in the Midwest and the East. DOE has estimated that the accumulated inventory will have grown to 69,000 tons by 2010 and that moving this volume could require approximately 175 shipments per year over 24 years, relying on a combination of truck and rail shipments. For the transportation of spent fuel, NRC has certification and inspection requirements for shipping containers to ensure that the containers protect against radioactive releases under accident scenarios. NRC has certified a number of shipping container designs for use on trucks and rail. The Nuclear Waste Policy Act of 1982, as amended, requires DOE to ship spent nuclear fuel and high-level radioactive waste to Yucca Mountain in containers that have been certified by NRC. The act also requires DOE to notify NRC in advance of spent fuel and high-level radioactive waste shipments. In addition to NRC, the Department of Transportation plays a role in regulating the transportation of spent fuel and other high-level waste. The department’s Research and Special Programs Administration sets certain safety standards for the transportation of hazardous materials, including spent fuel. These standards include, among other things, documentation and labeling of containers, including placards identifying the shipment, and requirements for separating certain radioactive materials while in transit. The Federal Motor Carrier Safety Administration oversees the safety of shipments by highway, and the Federal Railroad Administration oversees the safety of shipments by rail. The U.S. Coast Guard oversees the safety of shipments that may be made by barge. Studies conducted by NRC and DOE have consistently found that the likelihood of widespread harm to human health from a terrorist attack or a severe accident involving spent fuel is very low. None of the studies involving the transportation of spent fuel or dry storage of spent fuel identified a scenario resulting in widespread harm—largely because of the protective containers required by NRC. For example, these studies repeatedly found that transportation containers would be very difficult to penetrate, and in the worst-case scenarios where they may be penetrated, only a small fraction of the material would be released. Some studies involving spent fuel stored in pools of water found that widespread harm is possible under severe but unlikely accident conditions. Such conditions may include a catastrophic earthquake or a severe but unlikely accident that could uncover the fuel for several hours, possibly allowing it to spontaneously ignite and scatter radioactive material over a wide area. To respond to increased security concerns stemming from the September 11, 2001, terrorist attacks, NRC is further studying the safety and security of spent fuel in transit and in wet or dry storage, including the potential effects of more extreme attack scenarios such as deliberate aircraft crashes. Since the late 1970s, federal studies have examined the effects of both terrorist acts of sabotage and severe accidents involving shipping containers for spent fuel. Sabotage studies have sought to determine whether radioactive material could be released from shipping containers in specific sabotage scenarios, while accident studies have assessed whether radioactive material could be released in a variety of accidents, and the overall probability of their occurrence. Some of these studies were commissioned by NRC, and others by DOE, and many of them were conducted through DOE’s Sandia National Laboratory and other DOE laboratories. These studies collectively indicate that the construction of the shipping containers helps to limit releases. Although NRC is confident in these results, it is sponsoring assessments to further validate computer models and address heightened security concerns. The most recent sabotage study—conducted by DOE’s Sandia National Laboratory for DOE in 1999—estimated the amounts and characteristics of releases of radioactive materials from truck and rail spent fuel containers subjected to two different types of weapons. The results of this study confirmed the findings of earlier studies that armor-piercing weapons could penetrate shipping containers and release small quantities of radioactive material. The study found that, under a worst-case scenario, the weapon could penetrate a shipping container and release a small amount of material—equal to about 0.016 of 1 percent of the spent fuel in the container—as small, respirable particles. These small, respirable particles could become airborne and spread beyond the immediate vicinity of the attack. A subsequent DOE-sponsored report used the results of the 1999 Sandia National Laboratory study to estimate the human health impact of the most severe release. Using a computer-based analytic model and conservative assumptions, DOE’s contractor found that the predicted release from a truck container would cause about 48 cancer deaths over the long term and that a predicted release from a rail container would cause about 9 cancer deaths over the long term. DOE’s contractor’s analysis explained that these cancer deaths should be considered against a backdrop of an expected 1.1 million cancer deaths among the same population expected from other causes. This analysis assumed that the release would occur in an urban area with a population projected to the year 2035 under stable weather conditions. The analysis also assumed that the spent fuel release would contain twice the radioactive content of a typical spent fuel shipment and that there would be no evacuation or cleanup of the affected area for 1 year after the incident.