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  • Fuel-Composition Dependent ...
    Bak, G; Choi, J H; Jang, H I; Jang, J S; Jeon, S H; Joo, K K; Ju, K; Jung, D E; Kim, J G; Kim, J H; Kim, J Y; Kim, S B; Kim, S Y; Kim, W; Kwon, E; Lee, D H; Lee, H G; Lee, Y C; Lim, I T; Moon, D H; Pac, M Y; Park, Y S; Rott, C; Seo, H; Seo, J W; Seo, S H; Shin, C D; Yang, J Y; Yoo, J; Yu, I

    Physical review letters, 2019-Jun-14, Volume: 122, Issue: 23
    Journal Article

    We report a fuel-dependent reactor electron antineutrino (νover ¯_{e}) yield using six 2.8 GW_{th} reactors in the Hanbit nuclear power plant complex, Yonggwang, Korea. The analysis uses 850 666 νover ¯_{e} candidate events with a background fraction of 2.0% acquired through inverse beta decay (IBD) interactions in the near detector for 1807.9 live days from August 2011 to February 2018. Based on multiple fuel cycles, we observe a fuel ^{235}U dependent variation of measured IBD yields with a slope of (1.51±0.23)×10^{-43}  cm^{2}/fission and measure a total average IBD yield of (5.84±0.13)×10^{-43}  cm^{2}/fission. The hypothesis of no fuel-dependent IBD yield is ruled out at 6.6σ. The observed IBD yield variation over ^{235}U isotope fraction does not show significant deviation from the Huber-Mueller (HM) prediction at 1.3 σ. The measured fuel-dependent variation determines IBD yields of (6.15±0.19)×10^{-43} and (4.18±0.26)×10^{-43}  cm^{2}/fission for two dominant fuel isotopes ^{235}U and ^{239}Pu, respectively. The measured IBD yield per ^{235}U fission shows the largest deficit relative to the HM prediction. Reevaluation of the ^{235}U IBD yield per fission may mostly solve the reactor antineutrino anomaly (RAA) while ^{239}Pu is not completely ruled out as a possible contributor to the anomaly. We also report a 2.9 σ correlation between the fractional change of the 5 MeV excess and the reactor fuel isotope fraction of ^{235}U.