> Use nuclear magic to make the hot side, cool with ambient temperature.
If you use ambient temperature for cooling, you are severely limited in your total power output. Like, we're talking about less than a megawatt output (depending on how big the ambient heat dispensers are) compared to the ~1GW of a regular old nuclear plant.
You might say: that's fine, let's just build many small ones. But you still need to track your radioactive material, make sure it's not stolen etc., which is a lot of overhead per installation.
I don't entirely follow. A lot of existing nuclear plants use ambient temperature for cooling, via cooling towers, no? They use pumped coolant to get the heat out of the reactor, sure, but the cold end is just air.
Also, I guess you could have the hot end very hot too..? This improving efficiency. Especially if, by virtue of cooling being safer, you could run it at a higher temperature (less safety margin needed).
I'm familiar with some civil nuclear power plants, my father worked for decades in the industry, and I did some internships too. (No contact with nuclear power on submarines / carriers)
All the designs I know of have a pumped (active) cooling loop for the reactor, then a secondary loop where the coolant (typically water) evaporates and drives a turbine, and that secondary loop is then coupled to either river water cooling or evaporation towers. (There might even be another intermediary cooling loop, not entirely sure).
(You don't want potentially radioactive water to interact with your turbine directly, makes it a nightmare to maintain).
> Also, I guess you could have the hot end very hot too..?
There are some limiting factors:
* melting point of your fuel (you really want that to remain solid, so you can control where it is)
* The reactor core is usually contained in a pressure vessel, which is made out of steel. Steel becomes weaker with higher temperatures. Switching to other materials is super expensive (harder to machine, fewer people are good at machining it etc.)
* You really want to be able to reliably move fuel rods and control rods in and out of the reactor; thermal expansion must be taken into account. At the same time, you want as little leakage as possible out of the reactor core.
> All the designs I know of have a pumped (active) cooling loop for the reactor, then a secondary loop where the coolant (typically water) evaporates and drives a turbine, [...] You don't want potentially radioactive water to interact with your turbine directly, makes it a nightmare to maintain
A "Boiling Water Reactor" (BWR) has the reactor and the turbine on the same cooling loop. The radioactivity in the water going through the turbine is not a "nightmare", it is a manageable trade-off.
Some major currently-operating BWRs are Leibstadt (Switzerland, 1.2 GWe), Oskarshamn (Sweden, 1.4 GW) and several dozen in the USA. Germany also had some, they were shut down a few years ago (e.g. Grundremmingen).
https://www.gevernova.com/nuclear/carbon-free-power/large-re...
Cooling towers are active not passive cooling. They don’t work without pumps.
They aren't passive but only dump heat into ambient temperature. Which I thought is the bit you objected to.
Actually they use evaporation not just ambient temperature.
Explanation starts at ~minute 4. https://www.youtube.com/watch?v=tmbZVmXyOXM