Speaker
Description
We present measurements of the integral and spectral characteristics of the reactor electron antineutrino ($\bar{\nu}_e$) flux obtained with the iDREAM detector at Unit 3 of the Kalinin Nuclear Power Plant, which operates a VVER-1000 reactor. The measured positron spectrum from $\bar{\nu}_e$ interactions with protons in the iDREAM liquid scintillator is compared with a prediction based on the isotope-dependent $\bar{\nu}_e$ spectra of the KI model, a spatial model of the VVER-1000 reactor core, and a Monte Carlo simulation of the detector response. In the energy range of approximately $4$--$6~\mathrm{MeV}$, a local excess of the measured spectrum over the prediction is observed, confirming the presence of the reactor $\bar{\nu}_e$ spectral anomaly. The iDREAM data also confirm a decrease in the inverse beta-decay interaction rate normalized to the reactor thermal power as $^{235}\mathrm{U}$ is depleted and $^{239}\mathrm{Pu}$ accumulates in the reactor core during fuel burnup. Using the measured $\bar{\nu}_e$ interaction rate, the evolution of the $^{235}\mathrm{U}$ and $^{239}\mathrm{Pu}$ fission fractions is reconstructed while the contributions from $^{238}\mathrm{U}$ and $^{241}\mathrm{Pu}$ are kept fixed. These results are further used to obtain a model-dependent estimate of the relative change in the $^{239}\mathrm{Pu}$ mass in the reactor core over the course of the fuel cycle.
