Antineutrino background from spent-fuel storage in sensitive searches for θ13 at reactors

Sensitive searches for antineutrino oscillations in the atmospheric mass-parameter region much discussed in recent years are based on accurate comparison of the inverse-beta-decay positron spectra measured in two (or more) detectors, far and near, stationed, e.g., at about 1000 and about 100 m from the reactor(s). We show that antineutrinos emitted from the stored irradiated fuel can distort in a different way the soft part of positron spectra measured in the far and near detectors and thus mimic (or hide) the oscillation signal