On September 13, the research team demonstrated the first use of a heat pipe to cool a small nuclear reactor and the first use of a Stirling engine to convert the reactor heat into electricity. The test was conducted at the Nevada National Security Site’s Device Assembly Facility near Las Vegas. The Demonstration Using Flattop Fissions (DUFF) experiment produced 24 watts of electricity.A heat pipe is a sealed tube with an internal fluid that can efficiently transfer heat produced by a reactor with no moving parts. Heat pipe technology was invented at Los Alamos in 1963 and is used widely by NASA for aerospace applications. A Stirling engine is a relatively simple closed-loop engine that converts heat energy into electrical power using a pressurized gas to move a piston within a magnetic field. Using the two devices in tandem allowed for creation of a simple, reliable electric power supply that could be adopted for space applications.
Researchers configured DUFF on an existing experiment, known as Flattop, to allow for the water-filled 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., in Athens Ohio. Engineers from 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.
DUFF is the first demonstration of a space nuclear reactor system to produce electricity in the United States since 1965. It confirms the basic nuclear reactor physics and heat transfer for a simple, reliable space power system.
“The heat pipe and Stirling engine used in this test are meant to represent one module that could be used in a space system,” said Marc Gibson, Glenn’s lead engineer for the test. “A flight system might use several modules to produce approximately one kilowatt of electricity.”
“The nuclear characteristics and thermal power level of the experiment are remarkably similar to our space reactor flight concept,” said Los Alamos engineer David Poston. “The biggest difference between DUFF and a possible flight system is that the Stirling input temperature would need to be hotter to attain the required efficiency and power output needed for space missions.”
A power system based on the concept demonstrated by DUFF could be attractive for future space exploration missions that may require significantly higher power levels than current systems can easily provide.
“Perhaps one of the more important aspects of this experiment is that it was taken from concept to completion in six months,” 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.”
Glenn’s contributions were made possible through resources provided by the NASA Radioisotope Power Systems Program Office within the Science Mission Directorate and the Nuclear Systems project under the NASA Office of Chief Technologist, Game Changing Development Program.
The Los Alamos participation in this experiment was made possible through Los Alamos’s Laboratory-Directed Research and Development Program and program office support.
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