Aircraft Nuclear Propulsion

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HTRE-2, left, and HTRE-3, right, on display at the Idaho National Laboratory near Arco, Idaho Aircraft Reactors Arco ID 2009.jpg
HTRE-2, left, and HTRE-3, right, on display at the Idaho National Laboratory near Arco, Idaho

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 Forces initiated Project NEPA on May 28, 1946. [1] After funding of $10 million in 1947, [2] NEPA operated until May 1951, when the project was transferred to the joint Atomic Energy Commission (AEC)/USAF ANP. [3] 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. [4]

Nuclear-powered aircraft aircraft powered by nuclear energy

A nuclear-powered aircraft is a concept for an aircraft intended to be powered by nuclear energy. The intention was to produce a jet engine that would heat compressed air with heat from fission, instead of heat from burning fuel. During the Cold War, the United States and Soviet Union researched nuclear-powered bomber aircraft, the greater endurance of which could enhance nuclear deterrence, but neither country created any such operational aircraft.

United States Army Air Forces Aerial warfare branch of the United States army from 1941 to 1947

The United States Army Air Forces, informally known as the Air Force,or United States Army Air Force, was the aerial warfare service of the United States during and immediately after World War II (1939/41–1945), successor to the previous United States Army Air Corps and the direct predecessor of the United States Air Force of today, one of the five uniformed military services. The AAF was a component of the United States Army, which in 1942 was divided functionally by executive order into three autonomous forces: the Army Ground Forces, the Services of Supply, and the Army Air Forces. Each of these forces had a commanding general who reported directly to the Army Chief of Staff.

United States Atomic Energy Commission former agency of the United States federal government

The United States Atomic Energy Commission, commonly known as the AEC, was an agency of the United States government established after World War II by U.S. Congress to foster and control the peacetime development of atomic science and technology. President Harry S. Truman signed the McMahon/Atomic Energy Act on August 1, 1946, transferring the control of atomic energy from military to civilian hands, effective on January 1, 1947. This shift gave the members of the AEC complete control of the plants, laboratories, equipment, and personnel assembled during the war to produce the atomic bomb.


Direct Air Cycle

Aircraft Reactor Experiment building at ORNL ARE Building.JPG
Aircraft Reactor Experiment building at ORNL

Direct cycle nuclear engines would resemble a conventional jet engine, except that there would be no combustion chambers. The air gained from the compressor section would be sent to a plenum that directs the air into the nuclear reactor core. An exchange takes place where the reactor is cooled, but it then heats up the same air and sends it to another plenum. The second plenum directs the air into a turbine, which sends it out the exhaust. The end result is that instead of using jet fuel, an aircraft could rely on the heat from nuclear reactions for power.

Combustion chamber turbine engine

A combustion chamber is that part of an internal combustion engine (ICE) or a reaction engine in which the fuel/air mix is burned.

A plenum chamber is a pressurised housing containing a gas or fluid at positive pressure. One function of the plenum is to equalise pressure for more even distribution, because of irregular supply or demand. A plenum chamber can also work as an acoustic silencer device.

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 to be heated by it before being exhausted through the turbine.

Evendale, Ohio Village in Ohio, United States

Evendale is a village in Hamilton County, Ohio, United States. The population was 2,767 at the 2010 census.

Jet engine reaction engine which generates thrust by jet propulsion

A jet engine is a type of reaction engine discharging a fast-moving jet that generates thrust by jet propulsion. This broad definition includes airbreathing jet engines. In general, jet engines are combustion engines.

Turbine rotary mechanical device that extracts energy from a fluid flow

A turbine is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work. The work produced by a turbine can be used for generating electrical power when combined with a generator. A turbine is a turbomachine with at least one moving part called a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades so that they move and impart rotational energy to the rotor. Early turbine examples are windmills and waterwheels.

Aircraft Reactor Experiment

The United States 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, was moderated by beryllium oxide (BeO), used liquid sodium as a secondary coolant and had a peak temperature of 860 °C. It operated for a 1000-hour cycle in 1954. It was the first molten salt reactor. Work on this project in the United States stopped after intercontinental ballistic missiles made it obsolete. The designs for its engines can currently be viewed at the Experimental Breeder Reactor I memorial building at the Idaho National Laboratory.

A thermal-neutron reactor is a nuclear reactor that uses slow or thermal neutrons.

Nuclear reactor device to initiate and control a sustained nuclear chain reaction

A nuclear reactor, formerly known as an atomic pile, is a device used to initiate and control a self-sustained nuclear chain reaction. Nuclear reactors are used at nuclear power plants for electricity generation and in propulsion of ships. Heat from nuclear fission is passed to a working fluid, which in turn runs through steam turbines. These either drive a ship's propellers or turn electrical generators' shafts. Nuclear generated steam in principle can be used for industrial process heat or for district heating. Some reactors are used to produce isotopes for medical and industrial use, or for production of weapons-grade plutonium. Some are run only for research. As of early 2019, the IAEA reports there are 454 nuclear power reactors and 226 nuclear research reactors in operation around the world.

Power density is the amount of power per unit volume.

Heat Transfer Reactor Experiments

HTRE-3. HTRE-3.jpg

In 1955, 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). [5] The first full power test of the HTRE-1 system on nuclear power only took place in January 1956. A total of 5004 megawatt-hours of operation was completed during the test program. [6] 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.

General Electric J47 A Turbojet Engine Produced by GE in 1947

The General Electric J47 turbojet was developed by General Electric from its earlier J35. It first flew in May 1948. The J47 was the first axial-flow turbojet approved for commercial use in the United States. It was used in many types of aircraft, and more than 30,000 were manufactured before production ceased in 1956. It saw continued service in the US military until 1978. Packard built 3,025 of the engines under license.

Pratt and Whitney Aircraft Reactor-1

On February 5, 1957, another reactor was made critical at the Critical Experiments Facility of the Oak Ridge National Laboratory (ORNL) as part of the circulating-fuel reactor program of the Pratt and Whitney Aircraft Company (PWAC). This was called the PWAR-1, the Pratt and Whitney Aircraft Reactor-1. The purpose of the experiment was to experimentally verify the theoretically predicted nuclear properties of a PWAC reactor. The experiment was only run shortly; by the end of February 1957 all data had been taken and disassembly had begun. The experiment was run at essentially zero nuclear power. The operating temperature was held constant at approximately 675 °C (1,247 °F), which corresponds closely to the design operating temperature of the PWAR-l moderator; this temperature was maintained by external heaters. Like the 2.5 MWt ARE, the PWAR-1 used NaF-ZrF4-UF4 as the primary fuel and coolant. [7]

Indirect Air Cycle

Indirect cycling involves thermal exchange outside of the core with compressor air being sent to a heat exchanger. The nuclear reactor core would heat up pressurized water or liquid metal and send it to the heat exchanger as well. That hot liquid would be cooled by the air; the air would be heated by the liquid and sent to the turbine. The turbine would send the air out the exhaust, providing thrust.

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 turbopumps and radiators. The Indirect Cycle program never came anywhere near producing flight-ready hardware. [8]

MX-1589 project

The NB-36H in a test flight, shadowed by a Boeing B-50 Superfortress NB-36H with B-50, 1955 - DF-SC-83-09332.jpeg
The NB-36H in a test flight, shadowed by a Boeing B-50 Superfortress

On September 5, 1951, the USAF awarded Convair a contract to fly a nuclear reactor on board a modified Convair B-36 Peacemaker [9] 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 aircraft, 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.


After numerous problems the project was shut down in March 1953 only to be re-opened a year later. Technological competition with the Soviet Union (as represented by the launch of Sputnik 1), and continued strong support from the Air Force allowed the program to continue, despite divided leadership between the DOD and the AEC. The election of John F. Kennedy as President changed the course. Kennedy wrote "15 years and about $1 billion have been devoted to the attempted development of a nuclear-powered aircraft; but the possibility of achieving a militarily useful aircraft in the foreseeable future is still very remote" in his statement officially ending the ANP on March 26, 1961. [3]

See also

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The WS-125 was an American super long-range strategic bomber project during the Cold War to develop a nuclear-powered aircraft, which was scheduled to be designated the B-72.

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Project Rover was an American project to develop a nuclear thermal rocket. The program ran at the Los Alamos Scientific Laboratory from 1955 through 1972 and involved the Atomic Energy Commission, and NASA. The project was managed by the Space Nuclear Propulsion Office.

Convair NB-36H

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