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Reactor neutrino experiments have seen major improvements in precision in recent years. With the experimental uncertainties starting to surpass those from theory, it is important to carefully consider all sources of e in making theoretical predictions. One source of e that is often neglected arises from the irradiation of the non-fuel materials in reactors. The e rates and energies from these sources vary widely based on the reactor type, configuration, and sampling stage during the reactor cycle and have to be carefully considered for each experiment independently. In this article, we present a formalism for selecting the possible e sources arising from the neutron captures on reactor and target materials. We apply this formalism to the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory (ORNL), the e source for the the PROSPECT experiment. Overall, we observe that the non-fuel e contributions from HFIR to the PROSPECT amount to 1% above the Inverse Beta Decay (IBD) threshold with a maximum contribution of 9% in the 1.8 - 2.0 MeV range. Non-fuel contributions can be particularly high for research reactors like HFIR due to the choice of structural and reflector material in addition to the intentional irradiation of target material for isotope production. We show that typical commercial pressurized water reactors (PWR) fueled with low-enriched uranium (LEU) will have significantly smaller non-fuel e contribution.
Physical Review C (Nuclear Physics)