Is chain reaction possible in stable isotopes? Is nuclear chain reaction possible in isotope that is considered stable? Are there examples?
 A: A chain reaction happens when an isotope, hit by a neutron, undergoes fission with more than one neutron being produced in the process - and where the neutrons produced have a sufficiently high probability of themselves creating further fission.
Now there is nothing in the above that requires the isotope to be unstable to begin with - as long as you hit it with the initial neutron that starts the reaction. In other words - you do need "kindling" for a chain reaction, but it might be sustained by fuel that is itself stable.
However, there is the little problem of the atoms that nature has actually made available. According to this list, only Uranium (233, 235), Plutonium (239, 241), Curium (243, 245, 247) and Californium (251) are fissile - that is, they undergo fission when bombarded with thermal neutrons. That's a pretty short list - and none of them are "stable".
U-233  159 k years
U-235  704 M years
Pu-239  24.1 k years
Pu-241  14   years
Cu-243  29.1 years
Cu-245   8.5 k years
Cu-247  15.6 M years
Cf-251 900   years

I guess that means the answer to your question is "no".
