Here is a concept I thought up.

 

I would think that you could make smaller, say maybe melon size or grapefruit sized mini reactors. These can be used from a material point of view in construction to aid nuclear reactions of some type, I would hopefully think fission. Now that reason I hope you could use the nanotech is again to aid the reaction from any possible point on a material scale, but to aid in controlling it to possibly higher levels of detail. You could link of many of these say units of reaction to create or sustain a certain level of reaction by controlling the extent of the reaction. The containers could also be designed to integrate desires to handle nuclear waste and or minimize such. I would think that such an application could be used small scale along with say solar power to help generate a hydrogen economy. Its not only this but I would like to think that we could control the resulting products enough as to say generate particular elements maybe even for use as by products of the reaction. I don’t know if such is possible right now but is it possible?

 

I have more to the idea but I think this is good enough for now.

So... grapefruit sized nuclear reactors... possible yes/no? Is that the gist?

you can have reactors even Smaller than this too, think Betavoltaics in Pacemakers.

the only problem is that they don`t give of much more power than a battery a fraction of the size, they just last longer

It is a function of efficiency. The Cassini space probe currently orbiting Saturn is about the size of a small cottage, and is powered by a small fission reactor, showing that it is possible. However, those who designed this probe did not care if the reactor wasted energy - as long as it produced enough for the probe's needs.

 

If you were to make small reactors, there would be enormous energy lost, and thus enormous cost. The nuclear waste would be in proportion to the energy output - even if most of that output was wasted. Thus, for your needs, you would have a device that cost megabucks, and produced far more waste per unit useful energy than nuclear power stations.

Melon sized!!! Only the "shield" would take much more room!

 

In public the word nuclear reactor means something really really dangerous and fearsome! And if they heard that a nuclear reactor was made at the size of a melon they'd feel like it is not properly controlled and the energy released from the reaction could (with no problem) break the roper and create havoc!

It would probably be a bad idea. And if you wanted it to have critical mass and shielding high efficiency and be accepted by the public, it would be impossible. However, for certain applications, getting energy from non-critical nuclear reactions (eg nuclear battery) would be reasonable.