  Third-generation dark matter detectors will be fully sensitive to the boron-8
solar neutrino flux. Because of this, the characterization of such a background
has been the subject of extensive analyses over the last few years. In
contrast, little is known about the impact of reactor neutrinos. In this letter
we report on the implications of such a flux for dark matter direct detection
searches. We consider five potential detector deployment sites envisioned by
the recently established XLZD consortium: SURF, SNOLAB, Kamioka, LNGS and
Boulby. By using public reactor data we construct five reactor clusters --
involving about 100 currently operating commercial nuclear reactors each -- and
determine the net neutrino flux at each detector site. Assuming a xenon-based
detector and a 50 tonne-year exposure, we show that in all cases the neutrino
event rate may be sizable, depending on energy recoil thresholds. Of all
possible detector sites, SURF and LNGS are those with the smallest reactor
neutrino background. On the contrary, SNOLAB and Boulby are subject to the
strongest reactor neutrino fluxes, with Kamioka being subject to a more
moderate background. Our findings demonstrate that reactor neutrino fluxes
should be taken into account in the next round of dark matter searches. We
argue that this background may be particularly relevant for directional
detectors, provided they meet the requirements we have employed in this
analysis.
