are not as far away as fusion, but they are in no way to be considered mature. They are, at best, at the prototype stage, where they have been for the last 60 years. Reason being that the technology (especially materials wise) is really hard. The concepts being looked upon today are more or less the same ones worked on in the 50's. The other reasons is that the real impetus for generation IV reactors never came from dealing with waste (which can be dealt with in other ways, i.e. deep repository) or cost (ordinary light water reactors fill this niche very well), but from a fear of uranium scarcity, When it was understood that uranium reserves (and especially resources) were vast and the anticipated mass expansion of nuclear didn't materialize, the entire impetus for breeders (gen IV) disappeared.

The Bush II administation breathed life back into nuclear research which had recieved savage cuts under Clinton (dash for gas), probably because doing that involved much less costs and efforts than actually builing new conventional reactors.

The bottom line is that nuclear today and within any kind of foreseeable future means generation III+ reactors, which are improved LWR's. The same kind of reactors that we already have, except better. Examples of these are Areva's EPR, Mitsubishi's APWR, GE-Hitachi's ESBWR and Toshiba-Westinghouse's AP1000.

Peak oil is not an energy crisis. It is a liquid fuel crisis.