  Sensitive searches for antineutrino oscillations in 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 ~1000 m and ~100 m from the
reactor(s). We show that antineutrinos emitted from the stored irradiated fuel
can differently distort the soft part of positron spectra measured in the far
and near detector and thus mimic (or hide) the oscillation signal
