Convair X - 6 The Convair X - 6 was a proposed experimental aircraft project to develop and evaluate a nuclear - powered jet aircraft . The project was to use a Convair B - 36 bomber as a testbed aircraft , and though one NB - 36H was modified during the early stages of the project , the program was cancelled before the actual X - 6 and its nuclear reactor engines were completed . The X - 6 was part of a larger series of programs , costing US $ 7 billion in all , that ran from 1946 through 1961 . Because such an aircraft ' s range would not have been limited by liquid jet fuel , it was theorized that nuclear - powered strategic bombers would be able to stay airborne for weeks at a time . History . In May , 1946 , the Nuclear Energy for the Propulsion of Aircraft ( NEPA ) project was started by the Air Force . Studies under this program were done until May , 1951 when NEPA was replaced by the Aircraft Nuclear Propulsion ( ANP ) program . The ANP program contained plans for two B - 36s to be modified by Convair under the MX - 1589 project . One of the B - 36s was to be used to study shielding requirements for an airborne reactor while the other was to be 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 3 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 . To shield the flight crew , the nose section of the aircraft was modified to include a 12 - ton lead and rubber shield . The standard windshield was replaced with one made of acrylic glass . The amount of lead and water shielding was variable . Measurements of the resulting radiation levels were then compared with calculated levels to enhance the ability to design optimal shielding with minimum weight for nuclear - powered bombers . 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 . After the ASTR was removed from the NB - 36H , it was moved to the National Aircraft Research Facility . Based on the results of the NTA , the X - 6 and the entire nuclear aircraft program was abandoned in 1961 . Development plans . 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 - 39 engines ( J47 engines modified to use nuclear energy as fuel ) , utilizing a P - 1 reactor . In a nuclear jet engine , the reactor core was 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 , Idaho to house the X - 6 project , but the project was cancelled before the planned runway was built , necessitated by the expected weight of the nuclear - powered aircraft . Soviet program . In the 1960s , the Soviet Union ' s Tupolev design bureau conducted a similar experiment using a Tupolev Tu - 119 , which was a Tu - 95 bomber modified to carry an operational reactor .