LANL could impact space exploration with their new and novel idea for creating power for space travel. They tested a mockup of the concept at the Nevada test site calling the test “Demonstration using Flattop Fissions (DUFF).

(Modified: 10 AM MST; 11/27/12)

A new and novel idea for creating power for space travel was designed by researchers at Los Alamos National Laboratory (LANL). They tested a mockup of the concept at the Nevada test site calling the test “Demonstration using Flattop Fissions (DUFF). The design uses heat pipes to transfer the heat from the reactor to a Stirling engine which then creates electricity that can power a spacecraft. Stirling engines have been under development at NASA for space missions for many years and provide high efficiency.

I began my career in space nuclear power and find this near direction for space power very exciting. In the past we focused on creating nuclear power systems in the kilowatt range. On the SP-100 program we were trying for a 100 kWe with the possibility of increasing to several hundred kW’s for the Star War’s program. I always worked as a systems engineer ensuring that the subsystems would work well together and that we would meet the launch, safety and mission requirements. This design is optimized for 10’s to 500 watts of power which is the amount of power needed by most spacecraft.

This is an important advancement in power technology for NASA deep space missions as a replacement for Radioisotope Thermoelectric Generators (RTG) which uses Pu-238 as the heat source. Almost all of NASA’s deep space missions have depended upon RTG’s and they have provided long-term and highly reliable power for many spectacular missions. The issue is the US does not produce Pu-238 which is made in nuclear reactors through the irradiation of Np-237. The Np-237 is a side product that can be separated from spent nuclear fuel from commercial nuclear power plants but the US does not reprocess spent fuel. Therefore there is little, if any, of the base material.

In the 1990’s the US purchased Pu-238 from the Russians from the Mayak facility in Chelyabinsk but the Russia’s are saying that they no longer have the capability to produce the material either now that they have shut down their weapons production reactors. The Russians do have an excess quantity of Np-237 separated from their Mayak RT-1 reprocessing plant which reprocesses VVER-440 spent nuclear fuel.

A small nuclear reactor such as the one being designed by the team at LANL – my former group when I did reactor design at the lab – also reduces the risk of radioactive material contamination at the launch. The reactor is fueled with enriched uranium but as little radioactivity prior to going critical and operating. In comparison, the Pu-238 capsules are highly radioactive but are designed to ensure they can remain intact under launch accidents.

The other key point is that the enriched uranium is plentiful and will be able to power space missions for years and years to come. This is an important design for the future of space exploration.

According to World Nuclear News:

  • A full-scale reactor would consists of just six sections: a 23 kg enriched uranium core, a core reflector, a single control rod fully capable of turning the reactor on and off, radiation shielding and eight heat pipes connected to eight Stirling engines that would generate electricity. The entire unit would be compact and passively safe – relying on principles of nuclear physics to adjust reactivity and power output rather than any additional equipment.

According to the lab press release by James Rickman:

  • “A small, simple, lightweight fission power system could lead to a new and enhanced capability for space science and exploration”, said Los Alamos project lead Patrick McClure. “We hope that this proof of concept will soon move us from the old-frontier of Nevada to the new-frontier of outer space”.
  • Researchers configured DUFF on an existing experiment, known as Flattop, to allow for a water-based heat pipe to extract heat from uranium. Heat from the fission reaction was transferred to a pair of free-piston Stirling engines manufactured by Sunpower Inc., based in Athens Ohio. Engineers from NASA Glenn designed and built the heat pipe and Stirling assembly and operated the engines during the experiment. Los Alamos nuclear engineers operated the Flattop assembly under authorization from the National Nuclear Security Administration (NNSA).
  • Los Alamos research on the project was made possible through Los Alamos’s Laboratory-Directed Research and Development Program (LDRD), which is funded by a small percentage of the Laboratory’s overall budget to invest in new or cutting-edge research. NASA Glenn and NSTec also used internal support to fund their contributions to the experiment.
  • “Perhaps one of the more important aspects of this experiment is that it was taken from concept to completion in 6 months for less than a million dollars,” said Los Alamos engineer David Dixon. “We wanted to show that with a tightly-knit and focused team, it is possible to successfully perform practical reactor testing.”

Three cheers for the team at Los Alamos for their innovation and ability to get something going! Wishing them continued success – and looking forward to the first mission.

Cheers Susan Voss

To learn more about the early space nuclear reactor program go to:  GNNA LLC and download the SNAP Reactor Overview report

An animation of the new reactor concept can be seen on Los Alamos National Laboratory’s YouTube channel.

Image: LANL – John Bounds of Los Alamos National Laboratory’s Advanced Nuclear Technology Division makes final adjustments on the DUFF experiment, a demonstration of a simple, robust fission reactor prototype that could be used as a power system for space travel. DUFF is the first demonstration of a space nuclear reactor system to produce electricity in the United States since 1965.


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