The Aircraft Nuclear Propulsion (ANP) program and the preceding Nuclear Energy for the Propulsion of Aircraft (NEPA) project worked to develop a nuclear propulsion system for aircraft. The United States Army Air Force initiated Project NEPA on May 28, 1946,[1]. After funding of $10 million in 1947,^[1] NEPA operated until May 1951, when the project was transferred to the joint Atomic Energy Commission (AEC)/USAF ANP.^[2] The USAF pursued two different systems for nuclear powered jet engines, the Direct Air Cycle concept which was developed by General Electric, and Indirect Air Cycle which was assigned to Pratt & Whitney. The program was intended to develop and test the Convair X-6, but was cancelled in 1961 before that aircraft was built.^[3]

[edit] Direct Air Cycle program

The General Electric program, which was based at Evendale, Ohio, was pursued because of its advantages in simplicity, reliability, suitability and quick start ability. Conventional jet engine compressor and turbine sections were used, with the compressed air run through the reactor itself to heat it before being exhausted through the turbine.

Aircraft Reactor Experiment building at ORNL

The US Aircraft Reactor Experiment (ARE) was a 2.5 MW thermal nuclear reactor experiment designed to attain a high power density for use as an engine in a nuclear powered bomber. It used the molten fluoride salt NaF-ZrF₄-UF₄ (53-41-6 mol%) as fuel and was moderated by beryllium oxide (BeO), liquid sodium as a secondary coolant, and it had a peak temperature of 860 °C, it operated for a 1000 hr cycle in 1954. It was the first molten salt reactor. Work on this project in the US stopped after ICBMs made it obsolete. The designs for its engines can currently be viewed at the EBR-I memorial building at the Idaho National Laboratory.

In 1955,[2] this program produced the successful X-39 engine, two modified General Electric J47s with heat supplied by the Heat Transfer Reactor Experiment-1 (HTRE-1). The HTRE-1 was replaced by the HTRE-2 and eventually the HTRE-3 unit powering the two J47s. The HTRE-3 used "a flight-type shield system" and would probably have gone on to power the X-6 had that program been pursued.

HTRE 1, left, and HTRE 3, right, on display at the Idaho National Laboratory near Arco, Idaho

[edit] Indirect Air Cycle program

The Indirect Air Cycle program was assigned to Pratt & Whitney, at a facility near Middletown, Connecticut. This concept would have produced far less radioactive pollution. One or two loops of liquid metal would carry the heat from the reactor to the engine. This program involved a great deal of research and development of many light-weight systems suitable for use in aircraft, such as heat exchangers, liquid-metal turbo pumps and radiators. The Indirect Cycle program never came anywhere near producing flight-ready hardware.

[edit] MX-1589 project

On September 5, 1951, the USAF awarded Consolidated-Vultee a contract to fly a nuclear reactor onboard a modified Convair B-36[3] under the MX-1589 project of the ANP program. The NB-36H Nuclear Test Aircraft (NTA) was to study shielding requirements for an airborne reactor, to determine whether a nuclear aircraft was feasible. This was the only known airborne reactor experiment by the U.S. with an operational nuclear reactor on board. The NTA flew a total of 47 times testing the reactor over West Texas and Southern New Mexico. The reactor, named the Aircraft Shield Test Reactor (ASTR), was operational but did not power the plane, rather the primary purpose of the flight program was shield testing.

Based on the results of the NTA, the X-6 and the entire nuclear aircraft program was abandoned in 1961.

[edit] See also

• Nuclear aircraft
• Convair X-6
• Project Pluto
• WS-110A
• Georgia Nuclear Aircraft Laboratory
• Project Pluto
• Molten salt reactor

[edit] References

[edit] External links

• Dreams of Nuclear Flight - The NEPA and ANP programs
• The Bureau of Atomic Tourism
• Nuclear HTRE propulsion