Double Chooz Collaboration Measures Antineutrino Emissions from Shutdown Nuclear Reactor

Scientists from the Double Chooz collaboration have made a significant breakthrough by measuring antineutrino emissions from a nuclear reactor even after it has been shut down. This groundbreaking research, led by Anthony Onillon and Thierry Lasserre at the Max-Planck-Institut für Kernphysik (MPIK) in Heidelberg, Germany, was published in Physical Review Letters. The findings indicate that antineutrino detectors can provide valuable information about nuclear reactors during shutdowns, enhancing monitoring, safety, and safeguards.

Detecting Antineutrinos From a Shutdown Reactor

The measurements were conducted at the Chooz nuclear power plant in northern France, utilizing the Double Chooz detector located 400 meters underground from the plant’s two reactor cores. The detector comprises over 30 cubic meters of liquid scintillator, which emits flashes of light when antineutrinos interact with it.

“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,” noted Thierry Lasserre from the independent research group OMINA at MPIK. This unique signal enables scientists to identify antineutrinos emitted from the reactors.

During the study, researchers analyzed 17.2 days of data collected while both reactor units were offline, identifying around 100 antineutrino candidate events linked to residual radioactivity in the reactor cores and nearby spent-fuel cooling pools.

Measurements Match Nuclear Fuel Predictions

The detected antineutrino signal closely aligned with simulations that incorporated the remaining nuclear fuel and the decay of long-lived fission products, providing the first experimental confirmation of predictions about antineutrino emissions from shut-down reactors and spent fuel.

“Until now, reactor antineutrino experiments have mainly focused on operating reactors, where the antineutrino flux is much larger. Detecting the tiny residual signal after shutdown required exceptionally low backgrounds and careful analysis techniques developed by the Double Chooz collaboration over many years,” Dr. Onillon explained.

Initial results from other experiments, like JUNO-TAO presented at Neutrino 2026, indicate that researchers are also examining reactor-off data to study faint antineutrino signals from spent nuclear fuel. The Double Chooz findings now provide a benchmark for exploring residual signals from shut-down reactors and spent-fuel pools.

A New Tool for Nuclear Reactor Monitoring

The implications of these findings suggest that antineutrino detectors could serve as important tools not only during reactor operation but also during maintenance and post-shutdown phases. Such measurements may assist in independently verifying reactor status and tracking spent-fuel inventories.

Initially built to explore neutrino oscillations, Double Chooz was instrumental in measuring the neutrino mixing angle θ13, vital for understanding neutrino behavior. The recent detection of the residual antineutrino emissions expands its scientific contributions in the field.