Extremely Efficient Nuclear Fuel
Could Take Man To Mars In Just Two Weeks
Source:Ben-Gurion University Of The Negev
December 28, 2000
Beer-Sheva - Scientists at Ben-Gurion University of the
Negev have shown that an unusual nuclear fuel could speed space
vehicles from Earth to Mars in as little as two weeks. Standard
chemical propulsion used in existing spacecraft currently takes from
between eight to ten months to make the same trip. Calculations
supporting this conclusion were reported in this month's issue of
Nuclear Instruments and Methods in Physics Research A (455: 442-451,
2000) by Prof. Yigal Ronen, of BGU's Department of Nuclear Engineering
and graduate student Eugene Shwagerous.
In the article, the researchers demonstrate that the
fairly rare nuclear material americium-242m (Am-242m) can maintain
sustained nuclear fission as an extremely thin metallic film, less
than a thousandth of a millimeter thick. In this form, the extremely
high-energy, high-temperature fission products can escape the fuel
elements and be used for propulsion in space. Obtaining
fission-fragments is not possible with the better-known uranium-235
and plutonium-239 nuclear fuels: they require large fuel rods, which
absorb fission products.
Ronen became interested in nuclear reactors for space
vehicles some 15 years ago at a conference dedicated to this subject.
Speaker-after-speaker stressed that whatever the approach, the mass
(weight) of the reactor had to be as light as possible for efficient
space travel. At a more recent meeting, Prof. Carlo Rubbia of CERN
(Nobel Laureate in Physics, 1984) brought up the novel concept of
utilizing the highly energetic fragments produced by nuclear fission
to heat a gas; the extremely high temperatures produced would enable
faster interplanetary travel.
To meet the challenge of a light nuclear reactor, Ronen
examined one element of reactor design, the nuclear fuel itself. He
found at the time that of the known fission fuels, Am-242m is the
front-runner, requiring only 1 percent of the mass (or weight) of
uranium or plutonium to reach its critical state. The recent study
examined various theoretical structures for positioning Am-242m metal
and control materials for space reactors. He determined that this fuel
could indeed sustain fission in the form of thin films that release
high-energy fission products. Moreover, he showed how these fission
products could be used themselves as a propellant, or to heat a gas
for propulsion, or to fuel a special generator that produces
electricity.
"There are still many hurtles to overcome before
americium-242m can be used in space," Ronen says. "There is the
problem of producing the fuel in large enough quantities from
plutonium-241 and americium-241, which requires several steps and is
expensive. But the material is already available in fairly small
amounts. In addition, actual reactor design, refueling, heat removal,
and safety provisions for manned vehicles have not yet been examined.
"However, I am sure that americium-242m will eventually
be implemented for space travel, as it is the only proven material
whose fission products can be made available for high speed
propulsion. Indeed, Carlo Rubbia has also recognized that this is the
most probable fuel that will be getting us to Mars and back. I think
that we are now far enough advanced to interest international space
programs in taking a closer look at americium-based space
vehicles."
http://www.bgu.ac.il/
http://www.sciencedaily.com/releases/2001/01/010103073253.htm