Saturday, February 24

Convair NB-36H, the huge strategic bomber that flew with a nuclear reactor

During the Cold War some of the most ambitious and extreme military and technological inventions in history emerged. At the time, the United States—and the Soviet Union for its part—believed that having atomic-powered strategic bombers was a good idea. Thus, in order to give life to this project, the Convair NB-36Ha plane that crossed the skies with a nuclear reactor inside.

The development of an aircraft with these characteristics may seem strange today, but in the 1940s and 1950s, in the latter especially, there was a certain obsession with atomic energy. Reactors appeared in power plants, submarines, and cars like the Ford Nucleon. The United States Air Force was no stranger to this reality, which is why in 1947 it launched the Aircraft Nuclear Propulsion (ANP) program.

The challenging project of the first nuclear plane

The engineers in charge of the project had a series of enormous challenges on their hands. These ranged from how to prevent radiation from affecting the health of the aircraft crew, to evaluating the performance of the materials used, the development of avionics, and the transfer system. One of the team’s biggest concerns was precisely how to run traditional nuclear-powered aircraft engines safely and efficiently.

The first concrete step was to choose a boost configuration. To this end, different alternatives were tested and evaluated, including dual reactors, combined with jet fuel propulsion and single systems. Finally it was decided that a single reactor would be enough to provide the reliability needed for flight. Later, three types of reactors, known as HTRE-1, HTRE-2 and HTRE-3, were experimented with, and the latter was chosen due to its lower construction complexity.

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Nb 36h Plane With Nuclear Reactor 3

HTRE-3 consisted of a direct cycle configuration. The air entered the engine through the turbojet compressor and passed to a system that directed it towards the reactor core. The air, which acted as a coolant, continued its way through the engine’s turbine and finally to an exhaust pipe. With this method, the plane would start with traditional fuel plane and then, when the core reached the ideal temperature, he would start using the nuclear reactor.

Having overcome the aforementioned challenges, the team focused on developing the protection system for the crew and the avionics. An initial proposal considered covering the reactor with an important layer of cadmium, paraffin wax, beryllium oxide and steel. But this approach proved ineffective and they adopted a novel method of distributing the armor between the cockpit and the rector, which was not only very effective but also significantly reduced weight.

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Later it was the turn to find an aircraft to test the jet configuration that had been developed. In the midst of this task, Carswell Air Force Base, Texas, was hit by a tornado that severely damaged several of its aircraft. Among them was a B-36 Peacemaker bomber. Convair convinced the authorities that this damaged model should be recovered and become the first prototype of the nuclear aircraft.

The company was successful in its order and the aircraft was released for testing. Although it was a 1947 design, the Peacemaker’s features are impressive to this day. It had a wingspan of 70 m, a length of 50 m, a height of 14.2 m and a wing area of ​​443 m². In addition, it could support a maximum takeoff weight of 185,973 kg, an advantage that made it ideal for easily housing a heavy nuclear reactor with its corresponding shielding.

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The transformation process

In the conversion phase, the aircraft’s original cabin was replaced with a fully armored 11-ton structure. The entire bomb delivery and transport system was also removed (if the project was successful it would have to be relocated) and replaced by a one megawatt air-cooled nuclear reactor, whose weight was 16,000 kg. The original boost system, Pratt & Whitney R4360-53 + General Electric J47-19, was replaced with a General Electric J47 + four turbojets.

Nb 36h Plane With Nuclear Reactor 2

Following the aforementioned modifications, the B-36 Peacemaker was officially renamed the Convair NB-36H, also known as “The Crusader”. Between the summer of 1955 and 1957, the aircraft made 47 test flights, many of them with the R-1 reactor on, but not with the aim of feeding the engines, but as a way to test and collect data on the viability of the project. The reports showed that the shielding was safe, but, in the event of an accident, there was a risk of radioactive contamination.

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Although most tests were positive, shortly after its last test flight, the NB-36H was decommissioned and its nuclear reactor removed. At that time, with the Cold War underway, the US government decided to suspend the project and focus on bombers with conventional jet engines. In March 1961, John F. Kennedy buried the program. That same year, the USSR began its experimental nuclear aircraft program with the Tupolev Tu-95LAL.

However, as a document from the United States Congress points out, the technological advances obtained in the nuclear plane project were not in vain. These became the foundation for the research and development of nuclear reactors used by NASA.

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Pictures | Wikimedia Commons | USAF

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