  We examine the evolution of inhomogeneities (fragments) of supernova ejecta
in compact supernova remnants by means of hydrodynamical modeling and
simplified analytical calculations. Under the influence of intense post-shock
cooling the fragments become strongly compressed as they traverse the hot
shocked region between the reverse and outer shocks of the remnant. We find
that the most likely outcome of the interaction of fragments with the reverse
shock and the hot shocked region is their disruption resulting in generation of
secondary fragments. Secondary fragments arriving at the thin and dense outer
shell of the remnant give rise to brief X-ray flashes. Under suitable
conditions the primary fragments may traverse the hot shocked region without
being completely destroyed, to eventually reach the outer shell as dense,
elongated structures. Collisions of such fragments with the shell are likely to
give rise to powerful X-ray flares.
