  We propose that the outer portions of cooling flows (CFs) in clusters of
galaxies are frequently disrupted by radio jets, and that their effective ages
are much shorter than the cluster ages. The inner regions, where the gas
density is higher, are more difficult to disrupt, and may continue to harbor
CFs even after disruption events. The main assumption of the proposed scenario
is that, on a time scale of about 2-4 times 10^9 years the cD galaxies in CF
clusters undergo powerful bursts of AGN activity that produce strong radio
jets. The jets excite shock waves moving at several thousands km/sec and heat
the CF region, hence terminating it in the outer regions. The total accreted
mass due to the CF is an order of magnitude lower than the mass accreted
according to the "standard" CF model (which assumes an undisturbed CF for a
time equal to the age of the cluster). The scenario, therefore, brings to
agreement the observations that a large fraction of clusters harbor CFs, that
strong optical and radio activity are present only in the very inner regions of
CFs, and the lack of a satisfactory reservoir of the expected (in the standard
CF model) large mass that has been cooling over the life of the cluster.
