Reply To: would nuclear energy really be accessible to all?

[jamesr]

vansig wrote:

The anode would have helium gas pumped through, in order to keep its surface below 800K or so. The outside of the vacuum chamber and other parts (eg. the capacitors) can be conventionally water cooled.

for 5MW of cooling to an exit temperature of 800K, I’m getting that ~2 kg/s of helium gas would need to be pumped.

delta-T = 527° (800K – 373K, if the secondary coolant is water);
Helium heat capacity = 20.786 J·mol−1·K−1
5MW / 20.786 J·mol−1·K−1 / 527° = 456 mol/s
= 1.8 kg/s

If the anode is constructed to enable co-axial flow, of cool helium up through the centre (~1cm diameter “artery”), and to exit back down along the adjacent layer, closer to the surface (“veins”), what is the max flow rate?

I love this kind of quick & dirty calculation. It lets you get a grasp on what are fairly intangible concepts and bring them into reality.

The outer surface or the anode would get that hot, but there would be a steep thermal gradient down to the cooling “veins” running through it. So their inner wall temperature, even if they are only 1mm below the surface would be quite a bit less. Hence the volume of coolant, I reckon, would probably be a bit more than your estimate.