Within constitutional limits Congress may pre-empt state authority by so stating in express terms. Absent explicit language, Congress' intent to supersede state law altogether may be found from a scheme of federal regulation so pervasive as to make reasonable the inference that Congress left no room for the states to supplement it, because the Act of Congress may touch a field in which the federal interest is so dominant that the federal system will be assumed to preclude enforcement of state laws on the same subject, or because the object sought to be obtained by the federal law and the character of obligations imposed by it may reveal the same purpose. Where Congress has not entirely displaced state regulation in a specific area, state law is pre-empted to the extent that it actually conflicts with federal law, which arises when compliance with both federal 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.
A California statute provides that, before additional nuclear power plants may be built, the state energy commission must determine on a case-by-case basis that there will be adequate capacity for storage of a plant's spent fuel rods at the time such nuclear facility requires such storage. Another section of the statute imposes a moratorium on the certification of new nuclear plants until the energy commission finds that there has been developed and that the United States through its authorized agency has approved and there exists a demonstrated technology or means for the disposal of high level nuclear waste. Two electric utility companies brought an action, requesting that the two sections of the California statute be declared invalid under the supremacy clause of the United States Constitution(Art VI, cl 2) because they are pre-empted by the Atomic Energy Act of 1954 (42 USCS 2011 et seq.). The United States District Court for the Eastern District of California held that the utility companies had standing to challenge the two sections, that the issues were ripe for adjudication, and that the two provisions were void because they were pre-empted by and in conflict with the Atomic Energy Act (489 F Supp 699). The United States Court of Appeals for the Ninth Circuit affirmed the District Court's ruling that the utility companies had standing and also agreed on the ripeness for review of the challenge to the provision imposing a moratorium on certification until the energy commission finds that there exists a demonstrated technology or means for the disposal of high level nuclear waste. The Court of Appeals concluded, however, that the challenge to the provision requiring the energy commission to determine on a case-by-case basis that there will be adequate capacity for storage of a plant's spent fuel rods was not ripe for review. The Court of Appeals held on the merits that the nuclear moratorium provisions that were ripe for adjudication were not pre-empted (659 F2d 903).
Can a federal law preempt a state law even if they are not mutually exclusive?
The Court held that Cal. Pub. Res. Code § 25524.2 was not preempted by the ACE because § 25524.2 was concerned with the costs of long-term storage, while the ACE pervasively regulated the radiological safety aspects of the construction and operation of nuclear plants. Therefore, § 25524.2 did not interfere with the objectives of the ACE. In sum, Congress has not required States to "go nuclear," in whole or in part. The Atomic Energy Act's twin goals were to promote the development of a technology and to ensure the safety of that technology. Although that Act reserves to the NRC decisions about how to build and operate nuclear plants, the Court reads too much into the Act in suggesting that it also limits the States' traditional power to decide what types of electric power to utilize. Congress simply has made the nuclear option available, and a State may decline that option for any reason. Rather than rest on the elusive test of legislative motive, therefore, it was concluded that the decision whether to build nuclear plants remains with the States. A ban on construction of nuclear powerplants would be valid even if its authors were motivated by fear of a core meltdown or other nuclear catastrophe.