This episode of Real Engineering is brought
to you by CuriosityStream, watch over 2,400 documentaries for free for 31 days at curiositystream.com/realengineering. Some crazy things happened during the Cold
War. Dogs were put into orbit, bears were fired out of supersonic jets, and humans landed
on the moon. Needless to say, humans were going through a rough break-up and were really
trying to find themselves. All of these events were centered around one technology that changed
the game for every human on this planet, nuclear energy. The bombing of Nagasaki and Hiroshima woke
the world to a nuclear future. Changing the political and cultural landscape of the world
forever. Infecting the imaginations of people all over the world. Spawning monster stories
like Godzilla, in Japan, and heroes like the Incredible Hulk and Spiderman in the United
States. People dreamed of a future where electricity was free, while simultaneously fearing the
ever-present threat of nuclear annihilation. These fears and dreams came together to form
perhaps one of the most interesting technologies conceived during the Cold War. Nuclear powered
planes. During World War 2 research and development
of nuclear energy had been focused on its weaponization, but with the wars conclusion,
the United States began to seek out ways of utilizing the power of the atom to fuel their
energy needs. The Atomic Energy Commission was created in 1946 with the express purpose
of commercialising this new technology, and just one year later the US Air Force invested
10 million dollars [1] into studying the feasibility of utilizing this energy to power their long-range
bombers. In an era before in-flight refueling and ICBMs had been perfected, the technology
was appealing. With just a small amount of fuel, a bomber could fly indefinitely. It
would be capable of reaching anywhere in enemy territory. An omnipotent threat to any advisory.
Despite the obvious dangers of combining these two technologies, the possibilities proved
too tantalizing. From 1948 to 1951 the brunt of the research
centered around a means to transfer the energy generated by nuclear fission to propulsion. Heat energy is gained through nuclear fission.
When uranium is bombarded with a neutron it absorbs that neutron into its nucleus, which
causes severe vibrations ripping the atom apart, producing heat, additional neutrons
and new lighter atoms. But the sum of products of that split are lighter than the original
atom.[2] Experimental proof of Einstein's ground breaking 1905 paper teaching the world
of the energy and mass relationship through the equation of E equals m c squared. The
energy released by a single uranium fission reaction like this is tiny, at 200 million
electron volts [3], but crucially uranium produces additional neutrons when it splits
allowing for a chain reaction to occur. So, for very little input energy we can get a
tremendous amount of kinetic energy as an output in the form of heat. When controlled
this reaction can give us energy to heat water and power our steam turbines when uncontrolled
this reaction gives us the atomic bomb. Experiments began here in the Idaho National
Engineering and Environment Laboratory. Dubbed the HTRE, standing for Heat Transfer Reactor
Experiment, these engines sought to find the most efficient solution for transforming this
thermal energy into thrust. [4] They eventually came to the HTRE-3. Consisting
of 2 modified general electric J47 engines, that would perform both propulsion and cooling
functions. Air would be ducted from the low-pressure compressor through the reactor core, where
it would gain heat and expand, this air would then pass through the high-pressure turbine
and exhaust to provide power and thrust. As the air was needed for cooling, the engine
had to be started using traditional fuel sources, allowing the air to pass through the cool
reactor. Once sufficient airflow was achieved the reactor could then be brought up to power.
The engine contained a temperature control thermocouple [5], which fed data to a control
module that would automatically close the chemical fuel valve as the heat of the nuclear
reactor began to be added until the valve was completely closed. The HTRE-3 was successfully run multiple times,
but there were still several problems to be solved. Perhaps chief among these was the
energy transfer method’s propensity for spewing radioactive air out of its exhaust. This was an open or direct cycle configuration,
meaning the air is directly used to cool the reactor core. [6] This was a simpler set-up,
requiring no additional pumps within the nuclear reactor, that the program managers at General
Electric preferred, but resulted in air passing through the highly radioactive core and thus
being contaminated, and subsequently exhausted to atmosphere. Obviously not an ideal situation, and this
program actually spurred the creation of the very first molten salt nuclear reactor through
the ARE, or Aircraft Reactor Experiment. This was instead a closed cycle system, where
a molten uranium tetrafluoride salt is used a fuel, while a secondary closed loop containing
molten salt with no uranium was used as a coolant. This coolant would then pass through
a liquid-to-air heat exchanger to power the turbine. This would result in radically reduced
radioactivity in the exhaust, but required more plumbing to circulate the liquids in
the two inner closed loops, and resulted in a lower efficiency as we are introducing an
additional heat transfer step that allows more heat to the be lost to the plumbing and
environment. This method was never tested with a jet engine,
but this is the earliest ancestor of the thorium reactors which are easily the most requested
topic on this channel, as a result of their potential to provide cheap and safe nuclear
energy, but research and funding for this technology was gradually dropped. Had the program developed further, these molten
salt reactors likely would have gone on to power any eventually bomber, had the power
to weight issues been overcome. These power to weight issues were one of the
primary roads blocks facing designers. While nuclear energy can provide extremely long
lasting energy, its power output, the energy provided per unit time, is not infinite. Nuclear
reactors like this have maximum power settings, limited by the heat the cooling system can
transport away before it can begin to melt and damage the reactor and it’s control
mechanisms. This made it difficult to design a reactor capable of providing enough energy
to power jet engines with enough thrust to get the gargantuan weight of the reactor off
the ground. The HTRE-3 is estimated to have weighed 45
metric tonnes and could produce up to 35 megawatts of thermal output. Far too large and heavy,
and short of the 50 megawatts of thermal output targeted for a flight worthy power source.
[2] The HTRE-3 did include removable radiation
shielding, consisting of a stainless steel shell with a lead core surrounded by water
[R1-4], but further testing was needed to design and assess shielding for an aircraft. To do this Convair modified a B-36, renaming
it the NB-36H Crusader. The B-36 was the only aircraft in the United State’s arsenal capable
of taking off with a massive nuclear reactor, and it’s associated shielding and coolant
systems. Fitting it with a small 1 megawatt reactor, dubbed the ASTR, or aircraft shield
test reactor, which was lifted from a shielded underground vault and mounted in the B-36s
bomb bay moments before take-off. [1][10] A plane could never carry the amount of lead
needed to shield every facet of a reactor, so this plane would test shadow shielding,
which would primarily shield the crew and instruments in the cockpit. Shielding for
the reactor was achieved with water tanks which could be filled or drained to vary the
shielding and allow the nuclear engineers on board to assess the minimum volume of water
needed to protect the planes crew and instruments, with a 5 tonne 13-centimetre lead shield mounted
between the reactor and the crew compartment. On top of this, the crew compartment was an
11 tonne lead and rubber shielded removable section. The leaded glass windows were a foot
thick, and a closed circuit tv system was used to monitor the reactor. The plane was further modified with air scoops
to funnel air to the coolant system that would trade heat with the internal closed loop water
coolant, and then exhaust the heat to atmosphere. The Crusader made its maiden flight on September
17th 1955. The reactor provided no power to the engines, but the plane would make a total
of 47 flights, which occured only over remote land far from human populations. The plane
was escorted at all times by a B-50, which contained sensors to measure any air scattered
radiation emitted from the reactor and air coolant system. It also contained a team of
marines ready to parachute and secure a crash location if the need arose. At this point, the United States was at the
forefront of aircraft nuclear propulsion technology and likely could have developed the technology
far enough to produce an nuclear-powered plane. But, for the best, it never came to fruition. On November 18th, 1958 the HTRE-3 engine suffered
a meltdown when temperature sensors malfunctioned, recording a lower temperature and withdrawing
control rods. [7] This may have been the impetus to shake sense
into the US Government, to remind them that a mobile nuclear meltdown was simply not something
they wanted to contend with. On top of all this, with the advancement of aerial refueling
and intercontinental ballistic missiles, the technology was made completely redundant. President Kennedy ultimately cancelled the
program in 1961, just 1 month into his presidency. Putting an end to the insane idea. This hysteria
and fear of aerial bombing has made humans do some astounding evil and stupid things.
If you would like to learn more about this gradual descent into madness that the advent
of aerial bombing fostered, I highly recommend watching this documentary titled the Bombing
War: From Guernica to Hiroshima. It takes you from the first small grenade dropped from
a plane in World War 1 all the way to the monstrous and unnecessary bombing campaigns
that took place in Europe and Asia in World War 2. It’s a fascinating insight into the
minds of the civilians that lived through those times and the madness that gripped the
military leaders that approved them. You can watch it now, for free, by signing
up to curiositystream using the code realengineering, or using the link the description. This will
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to all my Patreon supporters. If you would like to see more from me, the links to my
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