The federal government first relinquished its monopoly on atomic energy in 1954 by permitting the private development of nuclear power production for peaceful purposes. After an initial surge in the development of commercial nuclear power, the nuclear industry suffered a long period of dormancy due, at least in part, to political barriers, an unfavorable economic climate, prohibitive construction costs, and reactor accidents accompanied by a corresponding decline in the public's perception of nuclear energy's overall safety. However, after a 30-year lull in development following the Three Mile Island and Chernobyl accidents, the last half decade has generated what many have considered to be a "nuclear renaissance." This resurgence in enthusiasm for commercial nuclear power has been triggered by a number of factors, including a streamlined regulatory environment, the availability of economic incentives for construction and research development, and the absence of a major nuclear accident in the United States. In addition, increasing energy demand and national concerns about climate change and energy security have prompted considerable presidential and congressional support for the expansion of nuclear power, including the establishment of significant loan guarantee authority for the construction of new nuclear power plants. Moreover, as evidence of the "renaissance," license applications for more than two dozen new commercial reactors have been submitted to the Nuclear Regulatory Commission (NRC) since 2007—the first U.S. reactor applications since the 1970s. Recent events, however, have the potential to slow the current growth period. Most importantly, the earthquake and tsunami that caused significant damage to the Fukushima Dai-ichi nuclear power plant in Japan have heightened nuclear safety concerns in the United States. In addition, congressional and media focus on the federal government's failure to develop a disposal solution for the nation's growing stockpile of nuclear waste; reports of radioactive tritium leaks from nuclear reactors in various states; and a threat to a federal nuclear facility in New Mexico due to wildfires have all reinforced the health and safety concerns associated with nuclear power. Also, significant controversy has surrounded the NRC, the independent regulatory commission charged with ensuring the safety of nuclear power in the United States, relating to the Commission's role in determining whether to license the proposed Yucca Mountain nuclear waste facility. These various forces have culminated in increased concern over the safety of nuclear power generally—all during a period in which operating licenses for 18 reactors will expire by 2020 if not renewed. Given these recent events, a number of states have sought to take action to assure that power plants within their borders are operating safely. Most visibly, the State of Vermont has suggested that it will not approve the continued operation of the Vermont Yankee nuclear power plant, despite the NRC's approval of an extension to the plant's operating license. The dispute may have profound effects on establishing the scope of state control over nuclear power—including whether states have the authority to shut down a federally licensed and long-operating nuclear power plant. However, while safety concerns may prompt states to assert influence over nuclear power plants, federal law severely limits the extent to which states can regulate nuclear power. Indeed, the Supreme Court has expressly held that, while states retain authority over "questions of need, reliability, cost, and other related State concerns," federal preemption under the Atomic Energy Act (AEA) prevents states from regulating nuclear power for the purposes of radiological safety. However, the exact scope of the AEA's preemptive effects, and therefore the extent to which states can regulate nuclear facilities, has long been litigated and remains disputed. This report will look at general constitutional principles of preemption, analyze the Supreme Court's interpretation of the scope of federal preemption under the AEA, and apply established preemption principles to the Vermont Yankee licensing dispute. The legal doctrine of preemption is grounded in the established constitutional principle that federal law takes precedence over inconsistent state law. Under Article VI, cl. 2: "[t]he Constitution, and the Laws of the United States which shall be made in Pursuance thereof; and all Treaties made, or which shall be made, under the Authority of the United States, shall be the supreme Law of the Land." The Supremacy Clause, therefore, "elevates" the U.S. Constitution, federal statutes, federal regulations, and ratified treaties above the laws of the states. Thus, where a state law is in conflict with a federal law, the federal law must prevail. A state law, however, need not be utterly incompatible with federal law in order to be preempted. Where Congress has expressed an intent to displace state authority within a given subject matter by establishing exclusive federal authority, state action in the field will be deemed preempted and therefore invalid. Often, the mere decision by Congress to legislate (or by an agency to regulate) comprehensively in an area is enough to supplant state authority in a particular field. Additionally, in evaluating whether a state law has been preempted by federal law, a court often seeks to prevent "conflicting regulation of conduct by various official bodies which might have some authority over the subject matter." The doctrine of preemption, therefore, serves two purposes: first, to enforce federal supremacy over state law; and second, to reduce the burden of compliance with multiple, at times inconsistent, regulatory regimes. Although there is "no one crystal clear distinctly marked formula" for determining whether a state law is preempted by federal law, the Supreme Court has established three general classes of preemption: express preemption, conflict preemption, and field preemption. In each instance, however, "the question of preemption is one of determining congressional intent." Express preemption exists where the language of a federal statute explicitly states the degree to which related state laws are superseded by the federal statute. In including such language, Congress has expressed its clear intent that the federal statute preempt state attempts to legislate on the subject matter. For example, the Employment Retirement Income Security Act of 1974 contained an unusually broad express preemption provision, stating that the act "supersede[d] any and all State laws insofar as they may now or hereafter relate to any employee benefit plan." Congress, however, does not always articulate its view as to a statute's intended impact on state laws. Nonetheless, a court may imply preemption if there is evidence that Congress intended to supplant state authority. Even absent specific preemptive language, preemption is generally implied in two situations. First, under conflict preemption, a state law is preempted "where compliance with both federal law and state regulations is a physical impossibility ... or where state law stands as an obstacle to the accomplishment and execution of the full purposes and objectives of Congress." Thus, where one cannot simultaneously comply with both state and federal law, or where the state law directly frustrates the purpose of a federal law, the state law is preempted. Second, under field preemption, a state law is preempted where a "scheme of federal regulation is so pervasive as to make reasonable the inference that Congress left no room for the States to supplement it...." Where Congress has established a substantial regulatory framework, any state law falling within the occupied field—even if consistent with federal law—may be preempted. Congress can sufficiently occupy the field so as to displace state law either through statute or pursuant to a delegation to an agency to regulate extensively in the field. Much of the debate surrounding federal preemption of state regulation of nuclear power has centered on field preemption. Of the various forms of preemption, field preemption can be the most difficult to apply. Although the notion that Congress has exclusively "occupied" a field may be simple in theory, identifying the boundaries of the field that has been occupied by federal law, and whether a given state statute or regulation falls into that field, can be incredibly complex in application. In considering whether Congress intended to exclusively occupy a given field, courts will typically consider additional factors, such as whether Congress is regulating in an area of traditional federal responsibility; whether Congress intended to eliminate dual federal and state regulations; whether allowing state regulation in the area would interfere with the goals of the federal regulatory scheme; and, whether the state can assert an important and traditional state interest. Prior to 1954, the federal government maintained a complete monopoly on the use, control, and ownership of nuclear technology. However, the Atomic Energy Act of 1954 (AEA) marked a clear shift away from public ownership towards the private development of nuclear energy for peaceful purposes. In effectuating this transfer, the AEA encouraged private development of nuclear power pursuant to a strict federal licensing and regulatory regime. Accordingly, while private entities were granted the authority to own, construct, and operate commercial nuclear power reactors, they would do so under the extensive supervision of the Atomic Energy Commission (AEC or Commission). With a focus on ensuring national security and maintaining the public health and safety, the AEA provided the Commission with exclusive jurisdiction over the license, transfer, delivery, receipt, acquisition, possession, and use of all nuclear materials. Although states retained their traditional and established role over the "generation, sale, or transmission of electric power," given the Commission's exclusive and comprehensive regulatory authority over nuclear materials, "no significant role was contemplated for the states." In 1959, however, Congress amended the AEA to provide the states with greater authority in regulating nuclear materials and nuclear power. The amendments, which contained three key preemption-related provisions, were passed for the express purpose of "clarify[ing] the respective responsibilities ... of the States and the [Federal Government] with respect to ... nuclear materials." First, the amendments authorized the AEC to enter into agreements with states for the "discontinuance" of AEC authority over byproduct materials, source materials, and special nuclear materials in quantities not sufficient to form a critical mass (enough material to create a nuclear chain reaction). The provision provided the states with an explicit avenue for asserting increased regulatory authority, but only in limited circumstances and only with the consent of the AEC.