Scientists have achieved a major breakthrough in nuclear physics after making the first direct measurement of antineutrinos released by spent nuclear fuel following a reactor shutdown. The signal closely matched detailed simulations of the remaining nuclear fuel and the decay of long-lived fission products. It provided the first direct experimental confirmation of theoretical predictions for antineutrino emissions from shutdown reactors and spent nuclear fuel. Nuclear reactor monitoring The findings suggest antineutrino detectors could become useful not only while reactors are generating power, but also during refueling outages, maintenance work, and long-term storage of spent nuclear fuel. Results from the JUNO-TAO experiment, presented at the Neutrino 2026 conference, have also explored the detection of antineutrinos produced by spent nuclear fuel during reactor shutdowns.