XYLENE POWER LTD.

TRITIUM BREEDING

By Charles Rhodes, P. Eng., Ph.D.

LITHIUM ISSUES:
In the PIF process the principal energy producing nuclear reaction is:
H-2 + H-3 = He-4 + n
However, there are constraints because the originally contemplated means of producing the H-3 fuel component involved alloying lithium (Li) with the liquid lead. However, that concept is unworkable because the alloyed Li prevents adiabatic plasma compression by the liquid lead and prevents the plasma spheromaks having sufficient lifetime due to allow formation of the liquid lead shell. Further problems with the alloy concept are:
a) the relatively high vapor pressure of metallic Li at the contemplated range of liquid lead operating temperatures;
b) the low work function of metallic Li and hence high thermal electron emission by Li at the contemplated liquid lead operating temperature;
c) Tendency of alloyed Li to evaporate or sputter off the interior surface of the liquid lead shell wall at the contemplated liquid lead operating temperature.

The presence of alloyed Li in the liquid lead detracts from the ion energy gain during the adiabatic compression by the liquid lead by reducing the average atomic weight of the compressing liquid metal and by adding unwanted Li ions to the plasma being compressed.

A furthur problem with alloyed Li is that on contact with water vapor in the air it spontaneously forms LiOH which melts at 462 degrees C. This LiOH acts as a flux and leads to liquid metal depositing on the surfaces of electrical insulators, which is a major problem in the spheromak generators.

Attempts to mitigate the Li alloy problems trigger expensive lead isotope separations.
 

During the adiabatic compression the He-4 nuclei bounce off the lead atoms and add their kinetic energy to heating of the plasma. The plasma electrons emit x-rays that are in absorbed near the inner surface of the liquid lead creating a high pressure mix of lead and lithium vapor. To minimize the lithium vapor problems it is contemplated that the lithium will be chemically bound to fluorine. At high liquid lead pressures the lower density LiF will tend to migrate away from the inner lead radius Ri due to its buoyancy. This buoyancy will effectively keep LiF away from the inner surface of the liquid lead shell and hence will minimize the Li vapor problem.
 

At this lead thickness there may be significant fast neutron wear on the reaction chamber pressure vessel and the liquid lead guns.

There must be enough liquid lead present in the pressure vessel to absorb fast neutrons and to carry away the heat released. Hence, in addition to the gun accelerated liquid lead the system needs additional liquid lead circulating over the inner surface of the spherical pressure vessel for heat removal and to attenuate impacts from fast neutrons and high radial velocity liquid lead droplets.

This web page last updated December 11, 2014