Prospects for improved understanding of isotopic reactor antineutrino fluxes

Abstract

Predictions of antineutrino fluxes produced by fission isotopes in a nuclear reactor have recently received increased scrutiny due to observed differences in predicted and measured inverse beta decay (IBD) yields, referred to as the "reactor antineutrino flux anomaly." In this paper, global fits are applied to existing IBD yield measurements to produce constraints on antineutrino production by individual plutonium and uranium fission isotopes. We find that fits including measurements from highly U235-enriched cores and fits including Daya Bay's new fuel evolution result produce discrepant best-fit IBD yields for U235 and Pu239. This discrepancy can be alleviated in a global analysis of all data sets through simultaneous fitting of Pu239, U235, and U238 yields. The measured IBD yield of U238 in this analysis is (7.02±1.65)×10-43 cm2/fission, nearly two standard deviations below existing predictions. Future hypothetical IBD yield measurements by short-baseline reactor experiments are examined to determine their possible impact on the global understanding of isotopic IBD yields. It is found that future improved short-baseline IBD yield measurements at both high-enriched and low-enriched cores can significantly improve constraints for U235, U238, and Pu239, providing comparable or superior precision to existing conversion- and summation-based antineutrino flux predictions. Systematic and experimental requirements for these future measurements are also investigated.