Today's piece of forty-year-old engineering lunacy

[fivemack]

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19690014329_1969014329.pdf

is a design for a heat exchanger, from the primary sodium-potassium-eutectic coolant loop of a space-based nuclear reactor to the secondary mercury coolant loop. Not quite the chemical fun of a liquid-sodium/water heat exchanger, but I think sodium and potassium both dissolve enthusiastically in mercury to produce amalgams combining the toxicity and gets-everywhere of mercury with the violent reactivity with everything of the alkali metals.

See http://www.dself.dsl.pipex.com/MUSEUM/POWER/mercury/mercury.htm for more examples of the lure of boiling mercury to power-station designers; it seems to be a very appealing improvement on normal superheated steam, at least if you're not too concerned about expense, weight or neurotoxicity.

In a similar vein, http://www.dself.dsl.pipex.com/MUSEUM/POWER/steamwheel/steamwheel.htm talks at length about a variety of designs for steam engines with liquid-metal pistons, dating all the way back to James Watt. You have the choice between mercury, which is not good for kittens and other living things, or bismuth/tin-based alloys, which solidify when the steam-engine is turned off, and sometimes expand enough to burst the engine.

Comments

[nojay.livejournal.com]

As I said before in Another Place, if the secondary loop working fluid of a nuclear reactor escapes into the wild you usually have worse things to worry about other than its toxicity or reactive chemistry, given that such material will almost certainly be in some form of containment system designed to do the job of keeping it tamed.

If it's primary loop leakage, multiply that worry by ten even if it's just "plain" water/steam.

What was more fun in design terms were the early "back-of-a-napkin" designs for reactors which had only one thermal stage, feeding reactor-generated steam directly into the turbines with no heat exchanger to get in the way. Very efficient for obvious reasons, but not really maintainable in the long term.