Supreme Court Leaves Price-Anderson Act Split in Place

On Monday, the Supreme Court rejected a plea to decide a critical question regarding the Price-Anderson Act (the PAA), the federal statute that governs suits stemming from public radiation exposure from nuclear facilities. Last year, in Mazzocchio v. Cotter Corp. the Eighth Circuit held that plaintiffs in nuclear public liability suits may rely on state-law tort standards of care rather than upon the federal nuclear-safety regulations that five other courts of appeal have held provide the exclusive standard of care in such cases.¹ Rather than resolving this split in authority, the Supreme Court denied the defendant’s petition for certiorari, leaving the Eighth Circuit’s precedent, and the circuit split, in place for now.² As a practical matter, the lingering uncertainty over the governing Price-Anderson standard may incentivize plaintiffs to test the waters in other circuits, and consequently, may risk a chilling of the Trump administration’s efforts to jumpstart investment in the nuclear industry.³

As discussed in Arnold & Porter’s analysis of the Eighth Circuit case,⁴ Mazzocchio arose from claims by Missouri residents that radioactive materials associated with legacy U.S. nuclear activities contaminated local areas and resulted in cancers.⁵ The defendants in the case moved to dismiss on the grounds that the complaint did not adequately allege violations of federal nuclear radiation-dose standards, which all prior circuits to consider the issue had held to be a necessary element of a public liability claim against nuclear operators.⁶ Specifically, because the Atomic Energy Act gives the federal government exclusive authority over nuclear safety, several courts of appeals had previously held that federal regulations define the exclusive standard of care applicable in these types of suits.⁷ These courts have also worried that a jury should not, in applying open-ended state-law standards governing negligence, decide “permissible levels of radiation exposure” or “the adequacy of safety procedures at nuclear plants” where the federal government has already brought ample scientific expertise to bear through notice-and-comment rulemaking.⁸ The Mazzocchio district court disagreed, however, concluding that plaintiffs could also look to state law in defining the applicable standard of care. Recognizing the split of opinion on the subject, the district court certified the question for interlocutory appeal.⁹

The Eighth Circuit affirmed the district court’s judgment.¹⁰ Looking to the Price-Anderson Act’s instruction that state law supplies the substantive rules for decision unless inconsistent with the PAA, the court concluded that state-law tort standards were not displaced merely because they concerned nuclear safety.¹¹ The decision squarely conflicts with decisions from other circuits holding that federal law supplies the exclusive standard of care.¹²

That split made Mazzocchio an obvious candidate for Supreme Court review. Rule 10 of the Supreme Court’s rules consider the existence of a split of authority amongst circuit courts on an important question of federal law a key criterion for certiorari. One of the defendants filed a petition for review, and, as it often does on questions of the interpretation of federal statutes, the Supreme Court asked for the views of the Solicitor General.

In April 2026, the United States filed a response recommending that the Supreme Court deny certiorari. The government’s recommendation was surprising, however, because the brief largely agreed with the petitioners. The government agreed, for example, that the Eighth Circuit decision is wrong and that federal law preempts the application of state law standards of care in PAA suits.¹³ The government also agreed with the petitioners that the Eighth Circuit’s decision created a split amongst the courts of appeals. Ultimately, however, the government thought the Supreme Court could wait and review the question at a later time, when it is clearer whether the applicable state-law standards actually differ from the relevant federal standards and whether any such difference would make a practical difference to the outcome in the Mazzocchio case.¹⁴

The Supreme Court agreed with the United States’ recommendation and denied certiorari and provided no reasoning. Though the denial does not necessarily signal agreement with the Eighth Circuit, it nonetheless carries real consequences for nuclear litigation and the nuclear industry as a whole. The Solicitor General’s tack also suggests the administration is grappling with significant tension and complexity in pursuing its nuclear agenda. Plaintiffs now have additional leeway to test whether Mazzocchio can be extended beyond its facts to additional theories of state-law liability, to apply Mazzocchio in circuits that have not yet opined on the question, and/or to test whether the composition of circuits that ruled on the question years ago (in some cases decades ago) might drive a divergence from prior precedent today. That dynamic is likely to persist until the Supreme Court takes up the question in a later case, perhaps after final judgment in Mazzocchio or after another court of appeals weighs in.

For nuclear industry operators, the Supreme Court’s denial exacerbates legal and business risk. While the relevant Price-Anderson Act claims refer specifically to “nuclear incidents,” the statutory definition of such claims is expansive and has been interpreted as extending to any claims alleging property damage or personal injury as a result of exposure to nuclear material. Without the shield of federal permit compliance as a complete defense in tort, even nuclear facilities with minimal permitted radiation emissions could be susceptible to burdensome suits. And it is possible that exposure claims with little evidence could be leveraged into suits designed to test these issues. Defendants in Price-Anderson Act cases should continue to preserve the federal-standard-of-care argument early and clearly, even in jurisdictions where the issue appears settled. Defendants should also develop the record on why allowing state-law radiation-safety duties would conflict with the federal nuclear regulatory scheme, particularly where plaintiffs seek to impose obligations different from those established by federal regulators.

Arnold & Porter has successfully defended Price-Anderson Act suits and helped clients navigate the political complexity associated with operating nuclear facilities. As always, we will continue to monitor developments in litigation affecting the nuclear industry.

© Arnold & Porter Kaye Scholer LLP 2026 All Rights Reserved. This Advisory is intended to be a general summary of the law and does not constitute legal advice. You should consult with counsel to determine applicable legal requirements in a specific fact situation.