Nuclear Heat On Tap
Fully Automated Reactors
I have long argued in favor of nuclear energy as the only way to go,
eventually, for supplying the needs of an advanced, industrialized
civilization. Energy density
is the key not only to doing familiar things better, but also to being
able to do new things altogether. The densities available from
transitions of the atomic nucleus are thousands of times greater than
those involved in rearranging the outer shells of atoms, which forms
the basis of all chemical processes, and hence offer efficiencies in
generating electricity and process heat that can't be attained from
conventional forms of combustion or from solar. Nuclear technology has
the potential of opening up revolutionary approaches to such things as
materials extraction and processing, transmutation of elements, space
transportation, desalination of seawater, and the total recycling of
all forms of waste. Although such issues as radiation fears, accidents, and waste disposal
have been shown to be vastly exaggerated, media sensationalism and
ideological opposition have conspired to keep public fears at a level
not justified by the realities.
Baseless fears can still be real, however. One approach that
has been proposed to addressing the various concerns that continue to
do the rounds is to design the reactor as a self-contained unit that
would reside underground, operating fully automatically for its entire
lifetimeThe concept is described in a study entitled "Completely
Automated Nuclear Reactors For Long-Term Operation" by Edward Teller,
Muriel Ishikawa, Lowell Wood, Roderick Hyde, and John Nuckolls, posted
some years ago by the Lawrence Livermore National Laboratory at www-phys.llnl.gov/adv_energy_src/ICENES96.html.
A 2 gigawatt heat source -- suitable for producing 1 gigawatt, or 1,000
megawatts of electrical power, i.e. the output of a large power plant
-- is situated 100 meters below ground and requires no human access,
precluding the possibilities of hazard due to error or abuse. The heat
engine and electrical generators are above ground, the only connection
being via coolant conduits carrying high-temperature helium gas up to
the turbines. The heat-source takes the form of a cylinder 10 meters
long and 3 meters in diameter containing thorium or uranium fuel
functioning as a breeder reactor, with a centrally positioned ignitor
module. Ignition creates an expanding "burn wave" front behind which
moderately enriched fuel is produced and the reaction is concentrated.
The burn wave diverges radially outward and then propagates gradually
toward the two ends. The process continues for a design life of 30
years until reactivity ends with fission product accumulation and
depletion of fertile material.
Multiple automatic thermostats control local flows of lithium to
regulate the neutron flux, maintaining the helium coolant temperature
at 1,000 degrees K. In addition, triple independent, passive (i.e.
self-activating through gravity on power loss) energy dumping systems
remove heat from core in the event of loss-of coolant for any reason
and at the end of operational life. On shut down, the site is flooded
with a neutron-absorber to nullify beta-decay. No maintenance or
replacement of fuel elements is called for, and the site becomes its
own waste repository, obviating the need to transport spent fuel.
Economic performance is indicated as a result of achieving high
safety without the overhead of expensive safety mechanisms, personnel,
and regulations, and low operating and maintenance combined with high
conversion efficiency. The projections for 21st-century
fuel needs dictate that a breeder approach will be required eventually.
Thorium is widespread and cheap, while the use of unenriched fuel
minimize requirements for isotope separation. Once people take to the
idea (and why not? There's probably enough gasoline alone in most
cities to kill the inhabitants several times over) an urban location
would reduce power transmission costs and make the waste heat available
for industry and space heating.