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RE: [cdn-nucl-l] re super-critical water fission reactors
WR-1 had some terrific capabilities, including continuous operation with 380C outlet temp (it reached a max of 425), only 2 MPa primary pressure, and very low fields in the primary circuit. Visit http://www.cns-snc.ca/history/wr-1/wr-1_1.html for details
Some of the fluorides have a lower melting point than WR-1's outlet temperature.
For example, fluoristan - or Stannous fluoride - SnF2 :
Physical and Chemical Properties (from http://www.sciencelab.com/xMSDS-Stannous_fluoride-9925082 )
Physical state and appearance: Solid. (Crystalline solid.)
Molecular Weight: 156.69 g/mole
Boiling Point: 850°C (1562°F)
Melting Point: 215°C (419°F)
Specific Gravity: 2.79 (Water = 1)
See also http://www.energyfromthorium.com/forum/viewtopic.php?t=434
The transition to "fast" reactors requires the substitution of the water coolant with something else: molten salt, liquid metals, or even "gases". With these coolants the process conditions seem to be less onerous than those associated with scw.
Organically cooled thermal fission reactors present a middle-ground option -- lower efficiency for steam to electricity than scw, but better than pressurized water.
Please note that molten salt reactors don't need to be fast reactors as implied above.
And with the possibility of increasing operating temp. well above Organically cooled thermal fission reactors, you can go from "middle ground" to "high ground" in energy conversion efficiency - especially when using Brayton rather than Rankine cycles :O)
Seeing that WR-1 was operated decades ago, with a flammable PHT coolant at 2MPa, instead of a nice safe fluoride salt at zero (or vacuum) pressure, one could probably claim that a switch to salt coolant would be more "evolutionary" than "revolutionary."
Besides eliminating high pressure in the fuel channels, dissolving fuel in the salt would also eliminate those pesky fueling machines, and all the problems associated with ceramic UO2 fuel damage following long irradiation periods.
The one new thing since WR-1 is development of various composite materials able to handle the relatively corrosive nature of fluoride compounds....
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