nuclear-news

First measurement of antineutrinos from spent nuclear fuel confirms emissions persist after reactor shutdown

Phys Org, by Max Planck Societ, edited by Sadie Harley, reviewed by Robert Egan, August 4, 2026

Even when the lights go out and nuclear reactors are turned off, the story inside the reactor core still has a great deal to tell. Radioactive, long-lived fission products continue to decay for months or even years, producing a faint flux of a specific type of particle known as antineutrinos. (Anti)neutrinos are the lightest and most elusive known particles in the universe, allowing them to escape unhindered from both the reactor and the surrounding shielding.

Researchers in the Double Chooz collaboration have now measured this residual antineutrino emission for the first time. The study, which was published in Physical Review Letters, was led by Anthony Onillon and Thierry Lasserre from the Max-Planck-Institut für Kernphysik (MPIK) in Heidelberg, Germany.

The results demonstrate that antineutrino detectors can probe nuclear reactors even during shutdown periods, opening new perspectives for reactor monitoring, nuclear safety and safeguards.

How Double Chooz sees the signal

The measurement was performed at the Chooz nuclear power plant in northern France.   The Double Chooz detector is located underground at a distance of about 400 meters (1,300 feet) from the two reactor cores. The detector contains more than 30 cubic meters of liquid scintillator, a material that emits tiny flashes of light when an antineutrino interacts inside the detector.

“Antineutrinos interact only extremely rarely with matter. However, when one interacts within the Double Chooz detector, a characteristic double-light signal is produced that can be distinguished from background events,” explains Lasserre from the independent research group OMINA, also located at MPIK. This allows researchers to identify the reactor antineutrinos.

The collaboration analyzed 17.2 days of data recorded while both reactor units were completely shut down. During this period, the detector observed around 100 antineutrino candidate events originating from residual radioactivity in the reactor cores and nearby spent-fuel cooling pools.

The measured signal agrees remarkably well with detailed simulations of the remaining nuclear fuel inventory and the decay of long-lived fission products. This constitutes the first direct experimental validation of predictions for antineutrino emission from shutdown reactors and spent fuel…………………………………………………………………………………………………………………………………………………………………………………………………………………………..https://phys.org/news/2026-08-antineutrinos-spent-nuclear-fuel-emissions.html

August 8, 2026 - Posted by Christina Macpherson | France, wastes