From: "Paul F. Dietz" <dietz@interaccess.com>
Newsgroups: sci.space.policy,sci.astro,sci.misc
Subject: Re: (Liquefying the sand into slag) Re: Yours, Mine or 
	Ours:WhoOwns,the    Moon?
Date: Sun, 20 Feb 2000 12:51:44 -0600

Matthew Montchalin wrote:

> Can't other liquids be used as coolants?  For instance, any of
> the inert gases, or even the metal mercury?

Mercury can, and has, been used as a coolant in reactors.
Other coolants that have been used include gases (carbon
dioxide, helium, air), sodium, sodium/potassium eutectic,
lead, lead/bismuth eutectic, and molten fluoride salts
(the latter with the fuel salts dissolved into the coolant.)

Liquid metals are often used in fast reactors, since
they have no hydrogen and do not moderate the neutrons
nearly as much as water does.  Reactors on the lunar
surface will probably be fast reactors, with highly
enriched fuel.  The lack of air on the moon will ease
some of the oxidation problems these coolants face
on Earth.

The reactor should operate at high temperature (radiator
area scales as the inverse fourth power of radiator
temperature), so there's nothing much wrong with using
as a coolant a molten metal with a melting point somewhat
above "room temperature", especially if its boiling point
is also high.

	Paul

From: "Paul F. Dietz" <dietz@interaccess.com>
Newsgroups: sci.space.tech
Subject: Re: Nuke on the Moon?
Date: Sat, 01 Apr 2000 16:28:29 -0600

Michael J Wise wrote:

> So what you need is a metal that is still liquid before it's white-hot.
> Has anyone tried cooling a reactor with Mercury? Hmmm. Bad choice.
> How about liquid sulfur? Melts at 115c, boils at 444c. Better choice?

Element		MP (C)		BP at 1 bar (C)

Ga		 29.8		2403
Sn		232.0		2270
In		156.6		2080
Pb		327.5		1740
Bi		271.3		1560
Li		180.5		1342

(Gallium and indium are quite expensive and rare,
 however, it may be possible to get more gallium
 from asteroids.  6Li is incompatible with
 a thermal reactor, due to the high neutron
 absorption cross section, but is relatively
 easy to separate from 7Li.)

Melting points of eutectics:

Bi(52.5)/Pb(32.0)/Sn(15.5)	 95 C
Bi(55.5)/Pb(44.5)		124 C
Sn(63)/Pb(37)			183 C

The Russians have operated reactors using Bi/Pb
coolant.

	Paul

From: henry@spsystems.net (Henry Spencer)
Newsgroups: sci.space.tech
Subject: Re: Nuke on the Moon?
Date: Sun, 2 Apr 2000 16:50:58 GMT

In article <Pine.MAC.4.10.10003301135260.15778-100000@kapu.net>,
Michael J Wise  <mjwise@kapu.net> wrote:
>> ...and radiator heat output per unit area is
>> proportional to the *fourth power* of temperature, so operating radiators
>> at LOX-condensing temperatures is a big step backward.  You want them to
>> run hot, the hotter the better, to keep radiator size and mass down.
>
>So what you need is a metal that is still liquid before it's white-hot.

Correct, probably.  The orthodox preference in the past has been to use
liquid potassium, possibly with some sodium mixed in because an Na-K alloy
melts at a lower temperature than potassium alone.  Lithium was mentioned
as a possible coolant for more advanced systems.

(I say "probably" and "orthodox" because there were a few voices in the
wilderness saying that water is not as bad a choice as it first appears,
and could be competitive when various secondary issues are considered
carefully -- e.g., the reliability problems of equipment operating at
liquid-metal temperatures.)

>Has anyone tried cooling a reactor with Mercury? Hmmm. Bad choice.

Quite bad, because it's a neutron poison.  Reactor coolants need good
nuclear properties in addition to being good coolants.  Mercury was often
chosen for the secondary coolant loop, boiled in a heat exchanger by the
hot NaK from the primary loop.

>How about liquid sulfur? Melts at 115c, boils at 444c. Better choice?

Never seen it suggested, which makes me suspect there's something wrong
with it (e.g., bad nuclear properties), but I don't know for sure.

>So, any work on liquid sulfur reactors, and would they be a good choice
>for a moonbase? The lower preasure requirements would be a good idea if
>the pipes are going to be flowing past a vacuum, yes?

There's little practical difference between 1atm and vacuum outside from
the viewpoint of powerplant plumbing -- it generally runs at considerably
higher pressures anyway.
--
"Be careful not to step                 |  Henry Spencer   henry@spsystems.net
in the Microsoft."  -- John Denker      |      (aka henry@zoo.toronto.edu)