page_title: Aircraft Reactor Experiment
section_title: Operation and Experiments
hierarchical_section_title: Aircraft Reactor Experiment / Operation and Experiments
caption_attribution_description: English: Aircraft Reactor Experiment control room at initial criticality
context_page_description: The Aircraft Reactor Experiment was an experimental nuclear reactor designed to test the feasibility of fluid-fuel, high-temperature, high-power-density reactors for the propulsion of supersonic aircraft. It operated between November 8-12, 1954 at the Oak Ridge National Laboratory with a maximum sustained power of 2.5 megawatts, and generated a total of 96 MW-hours of energy.
  The ARE was the first reactor to use circulating molten salt fuel. The hundreds of engineers and scientists working on ARE provided technical data, facilities, equipment, and experience that enabled the broader development of molten salt reactors as well as liquid metal cooled reactors.
context_section_description: The ARE was operated successfully. It became critical with a mass of 32.8 lbs (14.9kg) Uranium-235. It was very stable as a result of its strong negative fuel temperature coefficient (measured at -9.8e-5 dk/k/°F). 
  The assembly was first sufficiently assembled on August 1, 1954, at which point a three-shift operation commenced for tests. Hot sodium metal was flowed through the system beginning on September 26 to test the process equipment and instrumentation. Problems with the sodium vent and sodium purification systems required lengthy repairs. After several sodium dumps and recharges, carrier salt was introduced to the system on October 25th. Fuel was first added to the reactor on October 30, 1954. Initial criticality was reached at 3:45 P.M. on November 3, after a painstaking and careful process of adding the enriched fuel. Much of the 4 days was spent removing plugs and repairing leaks in the enrichment line. 
  A series of fuel samples were taken periodically. Most notably, they showed an increase in Chromium content at a rate of 50 ppm/day, indicating rapid corrosion of the fuel pipes. 
  A series of experiments were performed in the ARE supporting its mission.
  Critical experiment
  Subcritical measurement of reactor temperature coefficient
  Power determination at 1 watt (nominal)
  Regulating rod calibration vs. fuel addition
  Fuel system characteristics
  Power determination at 10 watts
  Regulating rod calibration vs. reactor period
  Calibration of shim rod vs. regulating rod
  Effect of fuel flow on reactivity
  Low-power measurement of reactor temperature coefficient
  Adjustment of chamber position
  Approach to power: 10-kW run
  Test of off-gas system
  Approach to power: 100-kW to 1-MW runs
  High-power measurement of the fuel temperature coefficient
  High-power measurement of the reactor temperature coefficient
  Reactor startup on temperature coefficient
  Sodium temperature coefficient
  Effect of a dollar of reactivity
  High-power measurement of reactor temperature coefficient
  Moderator temperature coefficient
  Xenon run at full power
  Reactivity effects of sodium flow
  Xenon buildup at one-tenth full power
  Operation at maximum power
  At 4:19 P.M. on November 8, during the ascent to high power, the reactor was shut down due to high airborne radioactivity measurements in the basement. It appeared that the gas fittings to the main fuel pump were leaking fission-product gases and vapors into the pits, and the pits were leaking into the basement through defective seals in some electrical junction panels. A 2-in. pipeline was run from the pits 1000 ft. (305m) south into an uninhabited valley. Portable compressors and a jet were used to bring the pits to sub-atmospheric pressure for the rest of the experiment. The safety radiation detectors shut down the reactor a few times during restart and were withdrawn to be further away from the reactor. Eventually, the reactor started back up and reached high power. 
  On November 12, operation of the reactor was demonstrated to Air Force and ANP personnel who had gathered at ORNL for a quarterly information meeting. Load following was demonstrated by turning the blowers on and off. With all operational objectives attained, the decision to cease operation was made. Colonel Clyde D. Gasser was visiting the lab at this time and was invited to officiate the termination of the experiment. At 8:04 P.M., he scrammed the reactor for the last time. 
  Much information was published about the operation of the reactor, including detailed experimental logs, power traces, and a total of 33 lessons learned.
caption: Aircraft Reactor Experiment control room at initial criticality
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