Couldn't complex nuclear chain reactions be composed of multiple radioactive isotopes?

The potential range of synthetic nuclear radioactive isotopes is very large. So, isn't the range of complex nuclear chain reactions involving multiple radioactive isotopes, much larger? Have such complex chain reactions been investigated, at all? Complex chain reactions could redefine the concepts of both fissile, and fissionable materials, I would think. I guess I'm suggesting something a little unusual here. I'm talking about several, perhaps a large number of different radioactive isotopes, being involved in a single complex interaction resulting in the release of energy.