In 1948 a report was commissioned at MIT for studying the feasibility of developing a nuclear-powered airplane. The final document, called the “Lexington Report,” contained some good news and some bad news. The good news was that building a nuclear-powered vehicle that could lift off the ground and fly on its own looked possible. The bad news was that it would take a billion dollars and 15 years to work out the details, and if the thing crashed somewhere, the debris field would be uninhabitable for thousands of years. The Air Force pounced on the good news. Together with the Joint Committee on Atomic Energy and a cadre of aircraft manufacturers, they overruled the nay-saying nuclear scientists, President Eisenhower, the Bureau of Budget, and the Secretary of Defense. The ANP got a green light to proceed in 1952.[98]
The project spread out all over the country, from Pratt & Whitney in Massachusetts to Lockheed in Georgia, from Convair in Texas to General Electric in Ohio. In July the largest chunk of the work went to the NRTS in Idaho, where the engines would be hot-tested out in the desert. There was jubilant celebration in every quarter.
A jet engine is basically a large metal tube, mounted with one open end pointing toward the front of the aircraft and the other end at the back. With the plane moving forward, air blows into the front of the tube. An axial compressor spinning at high speed at the front acts as a one-way door, encouraging air to come into the tube while preventing anything from escaping out. In the center of the tube is a continuous explosion of jet fuel mixed with the compressed incoming air. The mixture, burned and heated to the point of violence in the explosion, instead of blowing the airplane to pieces finds a clear path out through the back of the tube. The escaping explosion products create a reactive force, just as would be made by a rocket engine, pushing the engine and the vehicle to which it is attached forward. On its way out, the expanding gases spin a turbine, like a windmill, and it is connected forward to the spinning compressor wheel. The nuclear aircraft engine was to operate in this way, except that the continuously exploding jet fuel would be replaced by a nuclear reactor running perilously close to fiery destruction. General Electric got the contract for the engines, to be tested at the NRTS.[99]
A piece of desert about 30 miles north of the center of the NRTS was picked out and named Test Area North, or TAN. It was the farthest point from anyone else’s reactor experiment. A large assembly building was erected, the control room was buried for safety reasons, and the test stand was built a mile and a half away, with a four-track railway connecting back to the main site. The engine was put together in the assembly building, and then it was rolled out to the test stand using a lead-shielded locomotive. The engine weighed a hefty eight tons.
The first test engine was called “HTRE-1,” High Temperature Reactor Experiment One, or “Heater-One.” The two jets were modified GE J-47s, and the reactor having enough power to superheat the intake air turned out to be too large to fit in the space normally occupied by the fuel burners. The reactor used enriched uranium clad in nickel chromium, with water as the moderator. The airstream was taken from the jet engine tube immediately after the compressor stage at the intake opening. Using a large conduit, this compressed air was fed through a honeycomb of passages in the reactor, where it was heated and expanded as it would have been in the fuel burner in a normal engine. The air was then piped back into the engine in front of the turbine and out the exhaust nozzle. On November 4, 1955, the reactor was tested at criticality by itself, and on December 30, it was ready for a hot test in the fully assembled engine. The reactor was unrealistically large, meant to test the concept and not to be mounted in an airframe, and it heated the air for both tandem-mounted jet engines.
The assembly was rolled out to the test stand, bolted down to the concrete apron so it wouldn’t fly away, and hooked up to a long, horizontal pipe used to direct the exhaust into a filter bank. This would prevent disintegrating fuel rods from being blown all over NRTS. The pipe ended in a 150-foot vertical smokestack staring right up into the big Idaho sky. The operation crew, hunkered down in the control room, spun up the two compressors using electric starter motors, lit the flames in the burners, and powered up the reactor. When both engines reached operating temperature, the jet fuel automatically shut off, and the jets spooled up to screaming speed on pure atomic power. It performed as predicted, but the gamma radiation was far greater than had been anticipated. Operational plans for the bomber would have to be modified, and perhaps more crew shielding would be needed.
Testing of Heater One continued, and work began on the world’s first fully shielded bomber hangar. A special tracked vehicle, heavy with lead shielding, was built with robotic arms and a thick, lead-glass viewing port for the driver. It would be used by the mechanic to work on a radiologically dirty airplane, blazing with fission product contamination and neutron-activated metal parts. A 23,000-foot-long runway was surveyed, and test missions were scripted. An electric incinerator toilet was invented for use by the flight crew, and pre-packaged meals were planned. Money flowed.
There were problems with the extremely high temperature necessary in the reactor. Fuel and reactor internal components evolved into exotic ceramics. HTRE-1 was modified and renamed HTRE-2, changed into a high-temperature-materials test reactor by cutting a hexagonal, 11-inch hole in the middle of the reactor. Newly designed fuel elements were mounted in the hole and run up to 2,800°F. Progress was encouraging, and it was time for HTRE-3.
HTRE-3 was a complete redesign. One smaller, horizontally mounted reactor ran two tandem J-47 jet engines, mounted as they would be in the proposed airplane, with the reactor located at the center of balance of the airframe.[100] The reactor was sized realistically, such as would fit in the finished airplane, but it still dwarfed the big General Electric jets. The fuel pins and control rods took up a lot of space, but there still had to be enough air passageway to spin the turbines in two J-47s. The core diameter was 51 inches, and the length 43.5 inches. The moderator was a solid ceramic, zirconium hydride, and that also took up room in the reactor core. The whole thing was encased in a solid beryllium neutron reflector. The reactor would still be considered highly advanced 54 years later.
By November of 1958 Heater-Three was on the test stand and ready to show what it could do.[101] On the morning of November 18 the crew started the engine compressors and made the reactor supercritical by manual control. Power was increased slowly to 60 kilowatts and leveled off, just to “check for leaks.” Everything seemed fine. The crew shut it down and went to lunch.[102] Feeling fed and frisky, the crew decided to proceed with the experiment program and run it up to 120 kilowatts. The engines started smoothly, with power increasing by a factor of 2.7 every 20 seconds. When the power reached 12 kilowatts, they switched to automatic, released the control handles, and sat back to watch it happen.
The automatic control used an ion chamber to detect gamma rays originating in fission. The number of gamma rays detected per second was perfectly proportional to the power level of the reactor, and it was read out as kilowatts on a meter at the control panel. The same signal was fed to a pen-chart recorder, giving a permanent record of power history of the engines. The current from this same detector was also fed to an amplifier, and this enhanced signal controlled a set of electric motors connected to the reactor control rods, running them in or out of the reactor core to satisfy a pre-set level of gamma-ray production rate. The high-voltage line feeding electricity to the ion chamber had been modified as an improvement to the circuit. A filter had been installed to prevent clicks and hums originating in the electric motors from contaminating the gamma ray signal.
98
Not to be outdone by the Air Force, the U.S. Navy in 1954 commissioned a study by E.W. Locke Jr. to find the feasibility of an atomic-powered dirigible. That’s right, a rigid airship filled with two million cubic feet of helium with a feather-light nuclear reactor driving two T56 gas turbine engines. The design combined two dubious technologies: an enormous, lumbering military air vehicle blown around by the wind, and an unshielded nuclear power plant weighing less than 40,000 pounds. The Navy decided instead to build a nuclear-powered float plane (the Princess Project), but in 1959 Goodyear Tire and Rubber invested time in preliminary designs of a nuclear blimp. Francis Morse at the University of Boston proposed a 980-foot-long nuclear dirigible for the New York World’s Fair in 1964. It would be a “flying hotel” carrying 400 passengers. He argued that the spread of radioactive debris in the event of a crash would be manageable, because dirigibles crash softly. Fortunately for the public impression of nuclear technology, none of these plans were implemented.
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There were two nuclear jet engine designs in the ANP program: the direct cycle at GE of Ohio, and an indirect cycle at Pratt & Whitney of Massachusetts. For the indirect cycle, an intermediate heat exchanger would transfer heat from a centrally located reactor to multiple jet engines, while it was assumed that in the direct cycle a small reactor would take the place of the fuel burners in the middle of the jet engine. The P&W design was complicated, and its development was at least a year behind the GE engine. The ideal circulating coolant for the indirect cycle engine turned out to be lead, which seemed a cruel material to be used on a high-performance jet.
100
I first saw the HTRE-3 and HTRE-2 in 1980. They were near the security checkpoint for TAN. They were still considered to be radiologically unapproachable, and to examine them closely you had to use binoculars. A fellow who had worked on the project damned HTRE-3 with faint praise, saying “It was so powerful, it could practically lift its own weight off the ground.” Today, the two engines are tourist traps. You can go up and take a picture of your kids pointing into the exhaust nozzles. They are in the parking lot of the EBR-I, which is a National Historic Landmark, opened for touring between Memorial Day and Labor Day.
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There is a bit of confusion here. The NRTS records show that the HTRE-3 operated between September 1959 and December 1960, but this account is taken from
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I’m not sure there was anywhere to eat near the test stand, so they probably brought lunch with them or had it trucked in. I once had lunch at what was possibly the only restaurant within 40 miles of the HTRE test stand on Highway 33, called the “Broken Wheel.” As I stared out the window at the featureless, dun-colored desert, suddenly the ground-cover moved and a ripple went through it. An earthquake? No, as it turned out I had been looking at a vast herd of sheep, covered with dust and huddled close together against the extreme cold.