  A dynamical pair breaking effect is evidenced at very low excitation
energies. For this purpose, a new set of time-dependent coupled channel
equations for pair-breaking in superfluid systems are deduced from the
variational principle. These equations give the probability to destroy or to
create a Cooper pair under the action of some perturbations or when the mean
field varies in time.
  The odd-even effect in fission is investigated within the model as an
example. For this purpose, the time-dependent probability to find the system in
a seniority-one or in a seniority-two state is restricted in the sense that the
perturbations are considered only in the avoided crossing regions.
