Fuel-Composition Dependent Reactor Antineutrino Yield at RENO.

Area of Science:

• Nuclear Physics
• Particle Physics
• Reactor Physics

Background:

• Reactor electron antineutrinos are crucial for understanding nuclear processes.
• Discrepancies between predicted and observed antineutrino fluxes, known as the reactor antineutrino anomaly (RAA), persist.
• The influence of specific fuel isotopes on antineutrino yield requires precise measurement.

Purpose of the Study:

• To investigate the fuel-dependent yield of reactor electron antineutrinos.
• To determine the contribution of different isotopes, specifically Uranium-235 and Plutonium-239, to the antineutrino yield.
• To assess the impact of these findings on resolving the reactor antineutrino anomaly.

Main Methods:

• Analysis of 850,066 electron antineutrino candidate events from inverse beta decay interactions.
• Utilized data from six 2.8 GWth reactors at the Hanbit nuclear power plant over 1807.9 live days.
• Employed statistical analysis to correlate antineutrino yields with fuel isotopic composition, particularly Uranium-235 fraction.

Main Results:

• A statistically significant (6.6σ) fuel-dependent variation in the measured antineutrino yield was observed.
• The measured average inverse beta decay (IBD) yield is (5.84±0.13)×10⁻⁴³ cm²/fission.
• Specific yields were determined for Uranium-235 ((6.15±0.19)×10⁻⁴³ cm²/fission) and Plutonium-239 ((4.18±0.26)×10⁻⁴³ cm²/fission).
• A deficit in the Uranium-235 IBD yield relative to predictions was noted, potentially resolving the RAA.

Conclusions:

• The study confirms a significant fuel-dependent antineutrino yield, primarily driven by Uranium-235.
• Reevaluation of the Uranium-235 IBD yield offers a primary solution to the reactor antineutrino anomaly.
• Plutonium-239's role in the anomaly requires further investigation, though it's not entirely ruled out.