Reliable Nuclear Reactor Tested for Spaceflights

A new concept for a reliable nuclear reactor that could be used on spaceflights has been demonstrated by researchers including engineers from Los Alamos National Laboratory.

They demonstrated how to cool a small nuclear reactor with a heat pipe. They also showed how to power a Stirling engine 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.

This experiment was conducted by a team of engineers from Los Alamos, the NASA Glenn Research Center and National Security Technologies LLC (NSTec) .

It was in 1963 that heat pipe technology was invented at Los Alamos. A heat pipe is a sealed tube with an internal fluid that can efficiently transfer heat produced by a reactor with no moving parts.  A closed loop engine, the Stirling  converts heat energy into electrical power using  pressurized gas to move a piston. The two devices are used in tandem for the creation of a simple, reliable electric power supply that can be adapted for space applications.

For the current experiment the researchers configured the DUFF known as Flattop, to allow for a water-based heat pipe to extract heat from uranium.

DUFF is the first demonstration of a space nuclear reactor system to produce electricity in the U.S. since 1965, and the experiment confirms basic nuclear reactor physics and heat transfer for a simple, reliable space power system.

Heat from the fission reaction was transferred to a pair of free-piston Stirling engines. 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).

"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."

"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 of NASA Glenn. "A flight system might use several modules to produce approximately one kilowatt of electricity."

The availability of more power could potentially boost the speed with which mission data is transmitted back to Earth, or increase the number of instruments that could be operated at the same time aboard a spacecraft.

"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."

"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."