April 02, 2010

Molten-salt based accelerator-driven subcritical reactor

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User clumma on the EnergyfromThorium discussion forum provides highlights of the Second Thorium Energy Alliance Conference

Andrew Hutton - Jefferson Lab (Nat'l Accel. Facility)
ADNA (Accelerator-Driven Neutron Applications) Corporation - GEM*STAR

These two were in the ADS (Accelerator-driven Systems) breakout session. I think it's safe to say that everyone in the room was blown away. Cost of neutrons in kg/Joule has gone down by SEVEN orders of magnitude since 1965. Thousands of accelerators using superconducting RF technology deployed worldwide.

ADNA is a company working on a molten-salt based accelerator-driven subcritical reactor. They claim to be ready to build a grid-connected 100MW demo plant in Los Alamos county. It will use a 180m linac (Linear Accelerator) to produce spallation neutrons. The accelerator is 25% of the plant cost. Electricity for $0.07/kWh, vs. $0.09/kWh Los Alamos county average. They have a site in mind.

The way they put it was extremely compelling: the perceived problems with fission have always stemmed from a shortage of neutrons. Well, if we can make neutrons effectively, these go away. No enrichment OR reprocessing. Burn fluorinated spent fuel, depleted uranium, Thorium, the works. Leave fission products in the reactor, just crank up the beam. They claim a net energy gain of 20-60 depending on the fuel mix.

They also showed VERY interesting work on graphite, which should interest anyone concerned about the LFTR "plumbing problem

Transmutation of Radioactive Materials using Thermal Neutrons

GEM*STAR is owned by Accelerator‐Driven Neutron Applications, ADNA Corp
– Goal is to build a pilot plant through private venture capital

A 44 page presentation at Oak Ridge by ADNA Pierson

ADNA estimates criticality at 8 tons with new graphite for a natural uranium graphite reactor

Gem*Star reactor Benefits

• Can use natural uranium as fuel
• Produces twice as much energy from mined uranium as LWRs
• Can use spent fuel from LWRs and get just as much energy out
• Recycling the molten salt fuel several times with supplemental neutrons reduces long‐lived waste by factor of 10
• Defers need for a geologic deposit for a century
• Divorces nuclear energy from nuclear weapons

Fission Energy With Waste Burn-up and Without Enrichment or Reprocessing

Adna asks - What would an optimized accelerator-driven nuclear-energy program look like?
If more neutrons were emitted in fission, there would be no need for enrichment or reprocessing, and much more of the mined uranium could be burned without proliferation-prone and expensive technologies. The purpose of enrichment and reprocessing is to make up for the limited neutrons from fission. The ADNA Corporation in collaboration with the physics staff of Duke University and Virginia Tech have embarked on an alternative approach to nuclear energy to reduce the non-beneficial loss of neutrons and to add external neutrons to sub-critical reactors from accelerators and ultimately fusion neutron sources. These external sources in combination with molten salt fuel enable the fuel to be recycled many times without separations that generate a waste stream. Because waste is not removed, waste is concurrently burned so that the ultimate waste storage requirements are reduced by about a factor of ten and delayed for generations. This approach, which works best with graphite-based reactors, will be cheaper than the combination of enrichment, reprocessing, and fast reactors and would not be burdened with proliferation concerns. Graphite systems were the original path for nuclear energy and we believe graphite systems should be brought back owing to many advantages that were not realized in early development. Our first step towards this concept was to study neutron diffusion in bulk quantities (an 8’x8’x8’cube) of modern graphite. Neutron losses in moving through certain modern graphites were found to be 40 % less than in older graphite. Neutron scattering studies on small samples of graphite at the Los Alamos National Laboratory revealed the physics basis. The consequences of reduced neutron loss are enhanced performance of graphite-based critical reactors and better performance with external neutron sources than previously thought.

GEM*STAR: The Alternative Reactor Technology Integrating Graphite, Molten Salt, and Accelerators

GEM*STAR, 8 page powerpoint presentation from Oct 2009

• sub-critical graphite moderated reactor driven by supplementary neutrons
– intrinsic safety: no critical mass ever present
– thermal neutrons: better tolerance to fission products
• molten-salt fuel in equilibrium throughout reactor life
– exceptional neutron economy: allows deeper burning
• high-temperature & low pressure operation
– higher thermal to electric conversion efficiency
– no high-pressure containment vessel

Virginia Tech budget for research which includes Gem*star is about $2 million/year

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