The issue is so thorny that the Supreme Court has now weighed in. A June 18 decision allows work to move forward on a privately operated facility, to be located in Texas, that would store nuclear waste on an interim basis. The state of Texas fought the facility on the grounds that the Nuclear Regulatory Commission, which licensed the facility, did not have the authority to issue such a license. Rather than explicitly confirming the NRC’s ability to license the facility, the court found that Texas and landowners included in the complaint did not have the legal authority to challenge the license.

Spent fuel is initially kept in a pool of water that cools it. (The ongoing radioactive decay produces enough heat that, without cooling, the spent fuel could cause a fire.) After a few years, the radioactivity drops enough that the fuel can be moved to cylindrical containers called dry casks. “They have the spent nuclear fuel in the center of this cask and then a layer of air that can flow and circulate and cool, just through natural convection, and then you’ve got a big layer of concrete around the outside,” says nuclear engineer Riley Fisher of the University of Michigan in Ann Arbor. “[It’s] very effective in the way that it works.”

A further complication: Some of the power plants that produced the waste are no longer operating, such as the San Onofre Nuclear Generating Station in California. But, with nowhere else to go, the waste from these decommissioned plants often remains onsite, meaning the facility must still be secured and monitored by the plant’s owner. “We’ve got a whole bunch of waste at reactor sites that are … in a limbo state right now,” Fisher says.