Virginia Tech is said to researching accelerator-driven reactor designs with its GEM*STAR collaboration project. The idea of a sub-critical reactor is to have a sub-critical reaction running that is kept going by supplementing it with an external source of neutrons.  A particle accelerator supplies the necessary neutrons.

Thus what exists is a sub-critical atomic fission driven from an external source.  No runaway ‘China Syndrome’ meltdown is possible.  Switch off the particle accelerator and the reaction can’t proceed.  Public perception problem No. 1 is then answered.

The Gem*Star reactor design as developed by ADNA Corp uses a particle accelerator instead of the fuel itself as a neutron source. Neutrons are a product from the split atoms in fission.  As each atom fissions neutrons come out and blast other atoms causing the chain reaction needed to go ‘critical’ or self-sustaining.  This means it can burn un enriched uranium or any other fissionable material that isn’t blended to the point where it can sustain criticality.  This opens the door to vast array of fuels from spent uranium fuel that is no longer able to maintain the ‘critical’ state to lighter thorium.

GemStar Molten Salt Sub Critical Reactor Block Diagram. Click image for the largest view.

ADNA is now working on a molten-salt based accelerator-driven sub-critical reactor. They claim to be ready to build a grid-connected 100MW demo plant in Los Alamos County. The project would use a 180m ‘linac’ (Linear Accelerator) to produce spallation neutrons. The linac is projected to be 25% of the plant’s cost. Electricity could be sold at $0.07/kWh, vs. $0.09/kWh the current Los Alamos County average. ADNA even has a site in mind.

Nuclear Fission Animated

Backing up the theory and research is Duke University and Triangle Universities’ Nuclear Laboratory who have already collaborated with ADNA.  “In this design, a full fuel load does not provide sufficient numbers of neutrons to sustain the fission chain reaction.  Instead, an accelerator provides additional neutrons.  Also, plutonium and can be completely transmuted to materials that are not weapons useful.  In this concept we propose to locate a transmutation reactor at each (existing nuclear) power-plant site, thus eliminating the issues associated with transporting radioactive materials over public highways and railways.  This design also can be the basis of new reactors that burn mainly thorium, which does not produce weapons useful materials.”

There goes public issue No. 2 the matter of making plutonium useful for weapons is not only not a waste product but the plutonium in the spent fuel used would be transmuted into lighter useless heavy elements.

Last year Virginia Tech physics professor Bruce Vogelaar said, “The components exist. What needs to happen is the integration of the systems and the demonstration that things work as anticipated. It’s not a question of whether the technology, in principle, will work. The question is, ‘Does it work as well as we anticipate?’ ”

ADNA founder Charles Bowman that integrated accelerator technology into nuclear reactors in the 1990s.  A 1956 graduate of Virginia Tech who got his Ph.D. from Duke University in 1961, he splits his time between Los Alamos and Franklin County, Virginia, where his family farm and some ADNA facilities are located.

There are several sites in Virginia, New Mexico, Tennessee and Nevada that qualify as candidates for the location of a pilot plant.  Bowman said the design phase of the demonstration facility could take about two years and the entire project about seven years, “So what we have to do is bring engineering to bear on the design of the demonstration facility. The science at this point is more in the area of refinement.”

One of the most expensive aspects of conventional fission nuclear technology is the need to create fuels that when critical, emit enough energetic neutrons to sustain a reaction. In order to accomplish this, uranium has to be enriched. Naturally occurring uranium contains several different isotopes of the element, the most common being uranium-238. Over 99% of the mineral, in its natural state, is U-238.  But U-238 alone isn’t fissionable in critical reactors. It doesn’t emit enough neutrons with sufficient energy to create a self-sustaining chain reaction. This chain reaction is needed to generate a useful, energy-producing reaction. To correct for this, the uranium is usually submitted to an enrichment process that increases the percentage of a different isotope, uranium-235.

Even slow-moving neutrons can split U-235 easily and release energy. This, in turn, not only releases energy – parts of the split atom go on to split more atoms. The reaction can be controlled by the use of a neutron moderator, a medium used to slow down the neutrons. Most reactors use some form of water as a moderator.

Enriching uranium is an expensive process, and the equipment used to do it can also be used to create highly enriched uranium suitable for use in nuclear weapons.  That’s the major concern as Iran scales its effort to enrich uranium fuel.

Added up, no meltdown, no weapons grade waste, no enrichment, use alternative fuels, using up and reducing already used nuclear fuel, a technical postponement for Yucca Mountain’s waste repository, and the fuel preparation savings, sub critical designs have powerful incentives.

But revolutionary new reactor designs like this are going to be up against the enormous regulatory hurdles. On the other hand, the political climate of late has changed significantly in favor of nuclear power generation.

The flip side is the fuels would not be exploited to their fullest potential.  Other much more challenging technologies exist that might extract more energy.  Yet the sub-critical path is enticing.   Who’s to say though that the minimized reaction wastes down to 10% wouldn’t be useful as technology improves – the remaining heavy elements would still have great potential.

For a NextBigFuture look at sub-critical news click here.


10 Comments so far

  1. Matt Musson on July 14, 2010 12:46 PM

    Destroy nuclear waste and create power at the same time? Seems like a slam dunk to me.

    If only we had a Nuclear Regulator Commission that actually knew what it was doing.

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  5. Shannon Janosek on May 23, 2011 6:03 PM

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  7. Arnulfo Mondelli on September 18, 2011 6:20 PM

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  8. Sam C on November 28, 2011 11:43 AM

    Interesting and it seems to be getting a lot of academic attention, at least. I wonder what would be involved in processing the used fuel rods, in order to adapt it for use, for “locate a transmutation reactor at each (existing nuclear) power-plant site”? How is the used fuel “re-packaged”?

  9. Christine J. Hruska on April 29, 2014 7:31 AM

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  10. Matt Wade on October 21, 2018 7:02 AM

    Just because no has built a U233 bomb does not mean it can not be done so the non proliferation is a bit iffy. also nuclear waste that is only
    Dangerous for half the time of existing nuclear waste sounds good but nuclear waste that is still dangerous for 100s of years is still scary nasty stuff…..Sorry to rain on the parade but
    Real issues here.

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