Nuclear energy for the third millennium Page: 5 of 14
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CONVERSION OF HEAT INTO ELECTRICITY
As stated above, production of nuclear heat in this new type of reactor system
occurs at an underground depth of approximately 200 meters. In most present reactor
designs, the heat is transferred to units generating electricity by the means of steam.
We plan to replace water cooling by helium cooling, thereby permitting reactor core
operation at higher temperature and higher thermodynamic efficiency. At the same
time, helium is chemically inert at all temperatures while water becomes chemically
quite active at high temperatures.
The generation of electricity is to occur above the surface or perhaps slightly
underground. The generating unit and the coolant lines are indicated in Figure 1. The
hot helium is to be used in a manner similar to the functioning of modern combined
cycle generating units burning natural gas. The rate of power generation is regulated
by the rate of pumping hot helium out of the reactor's thermostated core. This point
will be discussed below.
For long-term addressing of energy supply, it is essential to burn-up a major
fraction of the readily available actinides, e.g., thorium. This means that we must
utilize the methods discussed under the designation of "fast breeders" (which refers to
fast neutrons carrying the nuclear chain reaction). Indeed, slow (thermal) neutrons
are strongly absorbed by fission products, so that any candidate slow breeder could
utilize only a small fraction of thorium (or uranium) before the accumulation of the
fission products would prevent further thermal neutron chaining.
The functioning of a fast breeder is practically independent of temperature and,
therefore, means must be arranged to function as "control rods" in order to quench
neutron multiplication at excessive temperatures. One means by which this can be
accomplished is by constructing thermal-neutronic units containing the readily
available light isotope of lithium, Li6, which is a strong neutron absorber. Many small
reservoirs of Lithium-6 are located outside the core of the reactor, where the residual
neutrons contribute nothing to the power-producing chain reaction. Small modules of
Li7 are positioned throughout the reactor's fuel charge. Thermal expansion of the
liquid Li7 when the nuclear fuel reaches maximum design temperature pushes Li6
from out of the reservoirs through capillary tubes into compartments within the fuel
where the neutron absorption by Li6 will quench the chain reaction. Lithium is a3
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Teller, E. Nuclear energy for the third millennium, article, October 1, 1997; California. (https://digital.library.unt.edu/ark:/67531/metadc679862/m1/5/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.