The
PACER project, carried out at Los Alamos
National Laboratory
in the mid-1970s, explored the possibility of a
fusion power system that would involve
exploding small hydrogen bomb (fusion
bombs)—or, as stated in a later proposal, fission bombs—inside an underground
cavity.
The proposed system would absorb the energy of the explosion in a
molten salt, which would then be used in a
heat exchanger to heat water for use in a
steam turbine. In the original
fusion-bomb proposal, a huge cavity would be emptied in a
salt dome, but further developments used
engineered cavities instead.
A typical design called for a 4 m thick
steel alloy blast-chamber, 30 m (100 ft) in diameter and
100 m (300 ft) tall, to be embedded in a cavity dug into
bedrock in Nevada
.
Hundreds of 15 m (45 ft) long bolts were to be driven into the
surrounding rock to support the cavity. The space between the
blast-chamber and the rock cavity walls was to be filled with
concrete; then the bolts were to be put under enormous tension to
pre-stress the rock, concrete, and blast-chamber. The blast-chamber
was then to be partially filled with molten fluoride salts to a
depth of 30 m (100 ft), a "waterfall" would be initiated by
pumping the salt to the top of the chamber and letting it fall to
the bottom, and while being surrounded by this falling coolant, a
1-kiloton fission bomb would be detonated; this would be repeated
every 45 minutes. The fluid would also absorb
neutrons to avoid damage to the walls of the
cavity.
Another example: a 2-kiloton bomb; this produces an energy of
8 TJ (8 × 10
12 joules), which
would be absorbed by 2,000
metric tons of
FLiBe (a mixture of
lithium and
beryllium
fluorides), i.e. 4 MJ/kg; the energy
the coolant absorbs per mass for heating and evaporation is the
same as the energy value of
TNT,
hence the amount of coolant has to be the same as the TNT-value of
the bomb.
As an energy source, the system is the only one that could be
demonstrated to work using existing technology. However it would
also require a large, continuous supply of nuclear bombs, making
the economics of such a system rather questionable. The production
of thermonuclear, or even just nuclear, bombs requires high
immediate capital expenses, and also has long-term environmental
costs. Additionally, the political effects of beginning a
large-scale production of nuclear bombs could potentially be large,
and with increasing bomb numbers, increased security measures would
be necessary. The entire system—fissile material production, bomb
fabrication, and power generation—could be carried out in a single
well-guarded site, but only for great development costs that would
likely never be recovered by generating energy.
See also
References
- Garwin, Richard L.; Charpak,
Georges (2001). Megawatts and Megatons: A Turning Point in the
Nuclear Age? Knopf. ISBN 0-375-40394-9.
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