This is actually about nanoparticles for better batteries: http://www.technologyreview.com/Energy/20524/?a=f But my point is that nanoparticle fabrication is becoming a known, industrially mass-produceable manufacturing technique. So why can't nuclear fuel elements be made nano-sized? What is the lower limit on the size of nuclear fuel elements? TRISO fuel elements used in various advanced reactors are supposed to be mere hundreds of microns in diameter. What prevents similar fuel elements from being made hundreds of nanometers in diameter? The advantage? Well, you'd need less fuel to achieve a given power output, and you'd achieve a higher burnup fraction, with less unused fuel sitting in the waste. There'd be less need for reprocessing, and more efficient consumption of that fuel. As a result, you could then use such nuclear fuel to power spacecraft, mars rovers, etc, or even perhaps to power certain vehicles here on Earth, to reduce consumption of greenhouse fuels. So what then is the lower limit on the size of nuclear fuel elements, for practical purposes?