>> Several years ago it occurred to me that exceptionally high grade
>> plutonium 239 could be made by briefly exposing U 238 in solution to
>> neutrons, removing the plutonium with from the solution with ion
>> exchange and pumping the solution back though the reactor to convert
>> more U 238 to plutonium 239.  (U 238, depleted uranium, is scattered
>> all over Iraq.)

>[. . .]

>> In spite of all the problems, including this one, vast numbers of
>> nuclear reactors are one of the few central power plant approaches
>> to replacing coal and doing something about global warming.

>> The only other approach I know about is solar power satellites,
>> lifted to GEO either with rockets or a space elevator.  If nanotube
>> cable can be made at low cost and strong enough, then a mechanically
>> powered elevator is possible.  (Per the presentation I created
>> for the recent ESA conference.)

>There are fission reactors which cannot be used the way
>you describe, because they have no cooling water.

>http://en.wikipedia.org/wiki/Pebble_bed_reactor