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Molten FLiBe

FLiBe is a mixture of lithium fluoride (LiF) and beryllium fluoride (BeF2). As a molten salt it is proposed as a nuclear reactor coolant, and was actually used in the Molten-Salt Reactor Experiment.

The 2:1 mixture with proportions Li2BeF4 has a melting point of 459°C, a boiling point of 1430°C, and a density of 1.94 g/cm3. Its heat capacity is 4540 kJ/m3, which is similar to that of water, more than four times that of sodium, and more than 200 times that of helium (at typical reactor conditions). [1] The eutectic mixture is slightly greater than 50% BeF2 and has a melting point of 360°C. [2]

Contents

Coolant

As a molten salt it can serve as a coolant which can be used at high temperatures without reaching a high vapor pressure. Unlike sodium or potassium which can also be used as high-temperature coolants, it is not flammable and does not react with air or water.

Nuclear properties

The low atomic weight of lithium, beryllium and to a lesser extent fluorine make FLiBe an effective neutron moderator. If only lithium-7 is used, FLiBe also has a low cross section for neutron absorption. Natural lithium also contains lithium-6 which absorbs neutrons producing tritium and alpha particles.

Beryllium will occasionally disintegrate into two alpha particles and a neutron when hit by a fast neutron. This provides a small degree of neutron multiplication.

Applications

In the Molten-Salt Reactor Experiment it served as solvent for the fissile and fertile material fluoride salts, as well as moderator and coolant.

Some other designs (sometimes called molten-salt cooled reactors) use it as coolant, but have conventional solid nuclear fuel instead of dissolving it in the molten salt.

See also

References

  1. ^ http://www.ornl.gov/~webworks/cppr/y2001/pres/122842.pdf CORE PHYSICS CHARACTERISTICS AND ISSUES FOR THE ADVANCED HIGH-TEMPERATURE REACTOR (AHTR), Ingersoll, Parma, Forsberg, and Renier, ORNL and Sandia National Laboratory
  2. ^ http://www.fusion.ucla.edu/apex/meeting4/5sze0798.pdf FLIBE: WHAT DO WE KNOW?, Sze and Wang, 1998, Argonne National Laboratory
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