ASTR Tower Experiment Film

The Reactor that Flew (1958)

By Dr. Nick Touran, Ph.D., P.E., 2024-11-08, Reading time: 25 minutes

In January, 1946, the U.S. Air Force started working to build a long-range nuclear-powered bomber. The program evolved and became multi-pronged and truly massive. At one point they actually loaded a nuclear reactor onto an airplane, took off, and turned the reactor on in flight (it didn’t propel the plane though). We recently learned of a historic film from 1958 discussing this flying reactor and follow-up experiments where they lifted it up into the air on a huge tower in Oak Ridge. We found it, got it scanned, and have posted it online here:

Show transcript

00:30	During the first half of 1958, Convair Fort Worth conducted a series of studies at the
00:40	Oak Ridge National Laboratories to gain additional radiation shielding information.
00:45	This was the final phase of the airborne shielding program performed with the aircraft shield
00:50	test reactor as a radiation source.
00:56	The program began in September 1955 when Convair's nuclear test aircraft first carried the aircraft
01:03	shield test reactor along.
01:06	The nuclear test aircraft was a conventionally powered B-36, modified to carry a shielded
01:11	crew compartment for the five-man crew, a half-scale crew compartment, and the aircraft
01:18	shield test reactor and its nuclear instrumentation.
01:24	The crew compartment utilized lead and rubber as shielding materials.
01:30	The cylindrical half-scale crew compartment was carried to simplify dose-rate analysis.
01:37	Sleeves of different wall thickness were slipped into the half-scale crew compartment to obtain
01:41	dose rates as a function of wall thickness.
01:46	The radiation source, the ASTR, was a water-cooled, water-moderated reactor designed to operate
01:53	horizontally. Shield tanks which surrounded the reactor core could be
01:59	filled or drained in flight to change the source pattern. An external lead
02:06	shield augmented the gamma shielding. The ASTR was rated at 1 megawatt maximum
02:14	thermal power. Thus assembled, the NTA was used to study the effects of air
02:23	structure, and ground scattering of gamma and neutron radiation. A three-phase
02:30	program was carried out to separate the individual scattering components and
02:34	determine their contribution to the total dose rate. The first studies
02:40	involved the ASTR and the half-scale crew compartment to learn the air and
02:45	ground scattering effects. The second included the NTA to determine the air,
02:51	ground and structure effects. The flight program was intended to determine the
02:58	air and structure effects. At first it was thought that by a simple process of
03:04	subtraction, the three individual components of scattering could be
03:08	separated into air, structure and ground effects.
03:17	But it was soon learned that the structure was changing the air and ground scattering
03:24	to such an extent that it was impossible to separate the three effects directly.
03:32	Additional information on air effects alone was necessary.
03:36	Convair then planned to take the ASTR and the crew compartments to the tower shielding
03:41	facility at Oak Ridge, Tennessee.
03:45	With the ground and structure effects removed, the air scattering component could be determined.
03:53	Auxiliary equipment to support the ASTR tower experiment was designed and fabricated.
03:59	It consisted of a truss to carry the two crew compartments aloft, a reactor support system
04:06	designed to rotate the ASTR through 360 degrees.
04:13	And a heat exchanger for reactor cooling.
04:18	As fabrication and testing of equipment neared completion, the crew compartment was removed
04:23	from the NTA and made ready for the move to Oak Ridge.
04:30	The ASTR normally was housed in a loading pit, from which it was remotely installed
04:35	in the NTA. Following a final checkout of the modified control system the 35,000
04:43	pound reactor was removed from the loading pit and ready for its
04:47	cross-country trip. A truck convoy was assembled to carry all the equipment
04:54	from Fort Worth to the Oak Ridge site.
05:05	The convoy arrived at the tower shielding facility 44 hours after leaving Convair.
05:23	Preparations for the first phase of the experiment began immediately.
05:31	This phase consisted of source term mapping near the ground to compare with results obtained
05:36	at Fort Worth.
05:41	Radiation detection instruments were placed in constant temperature control cans and mounted
05:45	at various positions to determine the fast neutron and gamma dose rates and thermal neutron
05:51	flux.
05:54	Prior to reactor startup, the heat exchanger and moderator water systems were thoroughly
05:59	checked. Shield tanks were filled to obtain the correct configuration.
06:29	When the system reached the desired altitude of 186 feet, the mapping phase of the experiment was ready to begin.
06:42	An intercom system warned personnel to leave the outside area and go to the shielded control room.
06:51	Standard procedure at the tower shielding facility calls for close surveillance of local weather conditions with radar.
06:59	When the radar observer was satisfied that the local weather was clear, the reactor engineer
07:04	started up the reactor.
07:07	Shem and dynamic rods were adjusted until desired power level was reached.
07:16	The reactor was rotated to various positions to obtain a map of the radiation patterns
07:21	for different reactor configurations.
07:25	These values were used as source terms in the analysis of the experiment and for correlations
07:31	with the data from the NTA program.
07:35	Cables carried the radiation signals more than 575 feet to the recording instruments.
07:43	These instruments, located in the control room, recorded the data from the fast neutron,
07:48	gamma, and thermal neutron detectors.
07:52	Personnel remained in the control room until the reactor was shut down and lowered to the ground.
08:00	Phase two of the tower experiment involved the three major components of the NTA.
08:07	The ASTR, the crew compartment, and the half-scale crew compartment in their same relative position as in the aircraft.
08:16	Radiation detectors were located in the same positions as in the NTA program.
08:24	The tower studies simulated the flight portion of the NTA program with only the airplane structure missing.
08:33	Under these simulated conditions, it was possible to isolate the air-scattered radiation component.
08:41	Comparing information obtained at the tower with the ground and flight experiments,
08:45	it was possible to determine the structure and ground effects and their interrelationships.
08:52	The information obtained during the airborne shielding program has been useful in two important ways.
08:59	It has been directly applied to shield design problems and has verified design methods.
09:07	This program has contributed greatly toward developing efficient shield systems
09:12	and constitutes a major step forward in development of nuclear-powered aircraft.

Catalog description: Coverage of the transfer of the Convair Airborne Shielded Test Reactor and NB-36 crew compartments from Ft. Worth, Texas, to Oak Ridge, Tennessee National Laboratories for further airborne and ground radiation reflection tests using a tower rig. 1) Animation and live photography depicting early airborne tests of the ASTR using the NB-36 aircraft. 2) Crew compartment of the NB-36 being removed. 3) Reactor is removed from the Convair storage pool and placed on a flat bed trailer. 4) Truck convoy carrying the reactor, crew compartments, and associated test equipment leaving the Convair test site at Ft. Worth and arriving at the National Laboratories, Oak Ridge, Tennessee. 5) Preparations for, and mapping of, ground radiation reflection from the reactor at the tower site. 6) Radiation reflection testing of the crew compartment, and a 1/2 scale crew compartment suspended from the towers, in the same relationship to the reactor as they were in the NB-36 aircraft. Good (Basic: Orig color, A&B Rolls)

This is film 67389 in our catalog.

Thanks to Gil Brueckner for making this happen!

More info about the ASTR

The Air Force Programs (NEPA and ANP) built reactors hooked to jet engines and also built the first molten salt reactor: the Aircraft Reactor Experiment. Besides reactor and heat transfer technology, radiation shielding questions needed answers. Could pilots and crew in a nuclear-propelled aircraft be appropriately shielded from the radiation? What kind of radiation scattering would occur off the air under and around the reactor?

To answer these questions, the NB-36 program was created to operate a nuclear reactor onboard a flying aircraft. The reactor would be at power, but would not itself be propelling the aircraft. On September 5, 1955 the first nuclear reactor to operate in the air went critical in a modified Convair B-36 called the Nuclear Test Aircraft (NTA). The reactor put onboard was the Aircraft Shield Test Reactor (ASTR).

The NTA flew 47 flights over two years with the reactor on it. It took off from Carswell Airforce Base in Texas with the reactor shut down, flew to the New Mexico desert, then powered up the reactor for testing, then powered it back down and flew back to base. (ref: NX-2) Remotely coupled hydraulic, mechanical, and electrical connections were tested many times before the reactor was operated at high enough power to become overly radioactive.

As a shield test reactor, the reactor necessarily emitted lots of radiation, to the point that personnel access to unload, maintain, and reload the reactor into and out of the aircraft was prohibited. It was all done remotely, with sophisticated reactor handling equipment.

For maintenance, the reactor was removed from the aircraft, placed into a large pool of water, and then maintained with long tools. The reactor was placed into a cradle that allowed it to be flipped over: forward side up for fuel loading/unloading, and aft side up for instrumentation and control adjustments.

Great photos of the equipment trucks/etc. (Gantz, 1960, p. 187)

The ASTR had the following characteristics (Nance & Perry, 1958):

Thermal power: 1000 kw
Thermal flux: 6.3e12 avg, 1.2e13 peak
Fuel: plat type U-Al with Al clad (MTR type)
Isotope: 150 gm U-235 per element, 4800 gram U-235 total
Shape: Right cylinder on side
Control: 3 cadmium-lined steel rods inserted horizontally from aft
Coolant: light water, 500 gpm
Heat sink: Water (ground operations), Air (flight operations)

In 1959, the ASTR was redesignated as the Aerospace Systems Test Reactor and upgraded from 1 to 3 MWt. In 1963 it was further modified and updated to 10 MW. It was also once known as the Aerospace Shield Test Reactor. It was used to support other astronuclear-related work (Warinner, 1983).

The reactor was permanently installed at the Nuclear Aerospace Research Facility (NARF) at General Dynamics/Fort Worth, Texas, for shielding, cryogenic-heating, and radiation-effects experiments.

The Tower Shielding Facility was a facility in Oak Ridge, TN where they hooked operating nuclear reactors up to cables and lifted them high into the air to measure various characteristics of elevated radiation sources and shielding (Muckenthaler, 1997). It was built as part of the ANP.

As of 2024 the towers are still standing.

ASTR Tower Experiment Film

More info about the ASTR

Read more about the Aircraft Shield Test Reactor

Help find these non-digitized references

See Also