# Investigation of antineutrino spectral anomaly with reactor simulation uncertainty

## TL;DR

This paper evaluates the uncertainties in reactor simulations affecting antineutrino spectral measurements, highlighting the importance of fission cross-section and manufacturing uncertainties for understanding spectral anomalies.

## Contribution

It introduces a Monte Carlo-based sampling method to quantify fission fraction uncertainties in reactor simulations relevant to antineutrino experiments.

## Key findings

- Fission cross-section uncertainties significantly impact $^{235}$U, $^{239}$Pu, and $^{241}$Pu.
- Fuel density is the main manufacturing uncertainty, but overall impact is small.
- Total fission fraction uncertainties are below 3%, smaller than previous estimates.

## Abstract

Recently, three successful antineutrino experiments (Daya Bay, Double Chooz, and RENO) measured the neutrino mixing angle theta_{13}; however, significant discrepancies were found, both in the absolute flux and spectral shape. Much effort has been expended investigating the possible reasons for the discrepancies. In this study, Monte Carlo-based sampling was used to evaluate the fission fraction uncertainties. We found that fission cross-section uncertainties are an important source of uncertainty for $^{235}$U, $^{239}$Pu, and $^{241}$Pu, but for $^{238}$U, elastic and inelastic cross-sections are more important. Among uncertainty related to manufacturing parameters, fuel density is the main uncertainty; however, the total manufacturing uncertainty was very small. The uncertainties induced by burnup were evaluated through the atomic density uncertainty of the four isotopes. The total fission fraction uncertainties from reactor simulation were 0.83%, 2.24%, 1.79%, and 2.59% for235U, 238U, 239Pu, and 241Pu, respectively, at the middle of the fuel cycle. The total fission fraction uncertainty was smaller than the previously derived value of 5\%. These results are helpful for studying the reactor antineutrino anomaly and precisely measuring the antineutrino spectrum in the Daya Bay antineutrino experiment.