"The fundamental issue is that reprocessing spent fuel involves extracting plutonium from fuel pellets. (Although the terms “reprocessing” and “recycling” are often used interchangeably, the former refers to separating out the usable material; the latter refers to deploying this material again in a reactor.) And nuclear nonproliferation experts are deeply concerned about any process that makes plutonium more accessible.

The U.S. has had no plan for permanent disposal of high-level radioactive waste since plans for a deep geological repository at Yucca Mountain in Nevada broke down in 2010.

“The most difficult part of making a nuclear weapon is obtaining the material,” said Ross Matzkin-Bridger, senior director of nuclear materials security at the Nuclear Threat Initiative, a nonprofit global security organization. The requisite ingredients — highly enriched uranium, or plutonium in more than trace amounts — are not naturally occurring. “It takes a lot of effort, human-made effort, to actually create these materials,” he said. “So that’s a great thing. But once you have the material, it’s not all that hard [to create a weapon], and that’s a really bad thing.”

Beyond proliferation concerns, there’s a host of other challenges, experts say. New waste streams are created along the way — everything that is touched during reprocessing, such as equipment, gets contaminated. And even after reprocessing, waste remains — the highly radioactive “fission products,” including cesium and strontium. Matzkin-Bridger acknowledged that the concept of recycling has appeal, but he insisted that it was illusory. “Yes, you could go through a very expensive, messy, and unsecure, dangerous process to extract and reuse this material,” he said. “But why would you do it, if it’s messy, it’s dangerous, and you can accomplish the same goals that you’re after by just using more uranium?”