Fuel-Composition Dependent Reactor Antineutrino Yield at RENO.

Gyeonghwan Bak ,J Yoo,W Kim,E Kwon,K Ju,C Rott,I Yu,H Seo,Chang Dong Shin ,S Y Kim ,S B Kim ,D H Moon ,Jiwon Choi ,J G Kim ,Dongmin Jung ,D H Lee ,S Jeon ,I T Lim ,J W Seo ,M Y Pac ,H I Jang ,Jie Yang ,J S Jang ,S H Seo ,J Y Kim ,H G Lee ,J H Kim ,Y C Lee ,Y S Park ,K K Joo

doi:10.1103/physrevlett.122.232501

Abstract

We report a fuel-dependent reactor electron antineutrino (ν[over ¯]_{e}) yield using six 2.8 GW_{th} reactors in the Hanbit nuclear power plant complex, Yonggwang, Korea. The analysis uses 850 666 ν[over ¯]_{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 5MeV excess and the reactor fuel isotope fraction of ^{235}U.

Highlights

We report a fuel-dependent reactor electron antineutrino yield using six 2.8 GWth reactors in the Hanbit nuclear power plant complex, Yonggwang, Korea
We report a 2.9 σ correlation between the fractional change of the 5 MeV excess and the reactor fuel isotope fraction of 235U
As reactor νe experiments suffer from large reactor related uncertainties of the expected νe flux and energy spectrum [3,4,5,6,7], an identical detector configuration is essential to cancel out the systematic uncertainties

Summary

Introduction

We report a fuel-dependent reactor electron antineutrino (νe) yield using six 2.8 GWth reactors in the Hanbit nuclear power plant complex, Yonggwang, Korea. The observed IBD yield variation over 235U 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 ð6.15 Æ 0.19Þ × 10−43 and ð4.18 Æ 0.26Þ × 10−43 cm2=fission for two dominant fuel isotopes 235U and 239Pu, respectively.

Results

Conclusion