Comparing to coal...
It takes a given amount of energy to produce coal (from wooden logs "cooked" in oxygen-free clay ovens, for example), and it takes some energy to release the stored energy in the said coal (matches, anyone? zippo? two sticks?). I'm talking activation energy here...
If it takes gobs of energy to store it, I bet it also takes gobs of energy to release it. A nuclear zippo, perhaps? The energy itself perhaps can be stored in compact units, but the energy release mechanism cannot.
On the other hand, what kind of usable energy density are we talking about? Comparing to Uranium, also?