I think I placed some thoughts in another comment. In terms of someone building a lot reactors, this would be a GOOD thing. The availability of reliable, affordable energy is really the difference between modern economies and impoverished societies.
It is important to not evaluate an energy backed currency as a direct substitute for a physical commodity backed currency. If you are only interested in a 'currency' that can be kept under your mattress, the potential for using energy as a currency backer is going to have limited appeal.