Here we present semi-analytical solutions of the hydrodynamics of compact supernova remnants ( cSNRs ) and their chemical evolution .
Two models of 15 M _ { \odot } and 25 M _ { \odot } supernova explosions evolving in a high density medium ( n _ { 0 } \sim 10 ^ { 7 } cm ^ { -3 } ) are throughly discussed .
We demostrate , that after a few years of evolution , diffusion leads to an homogeneous distribution of the SN products inside the cold , thin shell formed after cooling of the swept-up matter sets in .
We find metallicity values within a range 5.5 \leq Z _ { O } / Z _ { \odot } \leq 6.0 for M _ { SN } = 25 M _ { \odot } 
and 1.0 \leq Z _ { O } / Z _ { \odot } \leq 1.5 for M _ { SN } = 15 M _ { \odot } , and speculate wheather these metallicities could be related to the observed QSOs super solar elemental abundances ( Ferland et al .
1996 , Hamann & Ferland 1999 ) .