In May 1946, the
Nuclear Energy for the Propulsion of Aircraft (NEPA) project was started by the
United States Army Air Forces. Studies under this program were done until May 1951 when NEPA was replaced by the Aircraft Nuclear Propulsion (ANP) program. The ANP program included plans for Convair to modify two B-36s under the
MX-1589 project. One of the B-36s was used to study shielding requirements for an airborne reactor, while the other became the X-6.
Nuclear Test Aircraft The first modified B-36 was called the Nuclear Test Aircraft (NTA), a B-36H-20-CF (Serial Number 51-5712) that had been damaged in a tornado at
Carswell AFB on September 1, 1952. This plane was redesignated the XB-36H, then the
NB-36H and was modified to carry a 1
megawatt, air-cooled
nuclear reactor in its bomb bay. The reactor, named the Aircraft Shield Test Reactor (ASTR), was operational but did not power the plane. Water, acting as both moderator and coolant, was pumped through the reactor core and then to water-to-air heat exchangers to dissipate the heat to the atmosphere. Its sole purpose was to investigate the effect of radiation on aircraft systems. The NTA completed 47 test flights and 215 hours of flight time (during 89 of which the reactor was operated) between September 17, 1955, and March 1957 over
New Mexico and
Texas. This was the only known airborne reactor experiment by the U.S. with an operational nuclear reactor on board. The NB-36H was scrapped at Fort Worth in 1958 when the Nuclear Aircraft Program was abandoned. Based on the results of the NTA, the X-6 and the entire nuclear aircraft program was abandoned in 1961.
Development plans in
Idaho, the first power reactor, now a museum. The reactor is in the building top right, the two structures lower left are reactors from the Aircraft Nuclear Propulsion Project Had the program progressed, follow-on aircraft would have been based on the successor to the B-36, Convair's swept-wing
B-60. The X-6 would have been powered by
General Electric X-40 engines (J53 engines modified to use nuclear energy as fuel), utilizing a P-1 reactor. In a nuclear jet engine, the reactor core would be used as a heat source for the turbine's air flow, instead of burning
jet fuel. One disadvantage of the design was that, since the airflow through the engine was used to cool the reactor, this airflow had to be maintained even after the aircraft had landed and parked. GE built two prototype engines, which can be seen outside the
Experimental Breeder Reactor I in
Arco, Idaho. A large, wide hangar was built at Test Area North, part of the National Reactor Testing Station (now part of the
Idaho National Laboratory;
Monteview) to house the X-6 project, but the project was canceled before the planned runway was built, necessitated by the expected weight of the nuclear-powered aircraft. ==Specifications==