The Green Run was a classified, intentional release of radioactive fission products conducted on December 2 and 3, 1949, at the Hanford Site plutonium production complex in Eastern Washington. The experiment was conducted by the United States Atomic Energy Commission and the United States Air Force, with General Electric as Hanford's operating contractor. For the test, irradiated uranium fuel from Hanford's F Reactor was processed after a 16-day decay period rather than the longer cooling period normally used, and off-gas scrubbers were not operated during the release from the T Plant chemical separation facility.
The test took place during heightened U.S. concern about Soviet nuclear capabilities after the first Soviet nuclear test. According to the GAO, a premise of the Green Run was that aerial monitoring and sampling of a radioactive cloud, even at long distances from its source, could provide evidence of nuclear materials. Reported release estimates vary: GAO reported about 7,800 curies of radioactive iodine and 20,000 curies of xenon, while Robkin's later reanalysis estimated about 11,000 curies of iodine-131 and 29,000 curies of xenon-133.
Weather conditions during the test limited the intended atmospheric diffusion, and radioactive iodine was later found on vegetation over large areas of southeast Washington and Oregon. The release exceeded Hanford's then-existing vegetation deposition tolerance in the Yakima, The Dalles, Spokane, and Blue Mountains areas. The Department of Energy later categorized the Green Run as one of the 14 most significant safety-related incidents in Hanford's history. The experiment remained undisclosed for decades, until declassified references and Freedom of Information Act requests brought it to public attention; the Advisory Committee on Human Radiation Experiments later concluded that the Green Run did not conform to Hanford's public-safety practices in effect in 1949.
Background The Green Run took place at the Hanford nuclear site in Washington, where plutonium production involved irradiating uranium fuel and chemically separating plutonium-239. The project took its name from the processing of uranium at the Hanford B Reactor, an open-loop, water-cooled nuclear reactor used to irradiate uranium-238 and produce fissile plutonium-239. Because other unwanted and highly radioactive decay products were also formed, normal batch processing took place 83 to 101 days after reactor extraction, allowing radioactive isotopes to decay before the plutonium-239 was extracted more safely.
For the Green Run test, the batch was fresh from the reactor and had only a scheduled 16-day decay period before it was processed and vented into the atmosphere. The irradiated fuel for the Green Run was supplied by the "F" reactor. As a result, the unfiltered exhaust from the production facility was much more radioactive than exhaust from a normal batch.
The Green Run test occurred shortly after the first Soviet nuclear test, during heightened U.S. concern about Soviet nuclear capabilities. The Green Run was reportedly designed to test United States Air Force nuclear weapons monitoring systems intended for use against the Soviet Union and their evolving nuclear weapons program. Before the experiment, Hanford staff, using radiation air samples from equipment on Rattlesnake Ridge with Air Force assistance, had detected evidence of the first Soviet nuclear detonation, reportedly the only successful sampling of it within the United States. The test results from the Soviet nuclear samples were entirely confiscated by the Air Force the same night they were confirmed. According to a test participant cited by the GAO, the Green Run was premised on the idea that aerial monitoring and sampling of a radioactive cloud, even at long distances, could reveal evidence of nuclear materials. The Green Run testing was also related to United States government fears of radiological warfare and dirty bombs; part of its purpose was to study how an unexpected release of radioactive gases over a populated area could be detected. ORNL-341, a secret Oak Ridge National Laboratory document that examined the proposed Green Run in April 1949, had recommended releasing even higher doses of radiation into Washington state.
Planning Unknown United States Atomic Energy Commission officials authorized the Green Run operation on October 25, 1949. Jack Healy, a chemical engineer at Hanford who worked on Green Run, was interviewed in 1995 by staff from the DOE, Battelle Memorial Institute, Los Alamos National Laboratory, and the Pacific Northwest National Laboratory. Healy and Lieutenant W.E. Harlan prepared the plans for Green Run locally at Hanford in 1949. Healy reported that he and other science staff at the time were unaware of the full risks of environmental radioactivity and the "milk-to-man pathway", and that he believed the staff would have objected to Green Run. He said the milk contamination theory was only proven ten years later due to the United Kingdom's Windscale nuclear accident.
The Air Force conducted multiple aerial surveys of the region in the weeks before Green Run began. A dedicated air sampling station was set up in Spokane before the test began. The Air Force managed its own radiation monitoring operations separately from the DOE during the Green Run. The General Electric Company was involved with the Green Run and had set several conditions that were to be met before the test could be initiated safely and successfully, including that the test could not be run while precipitation was underway in the area. General Electric's Health Instrument Division had laid out specific conditions required for the test to succeed. The U.S. Air Force was responsible for all meteorological data and determinations related to the Green Run experiment. The final test conditions required a cold layer of air near ground level, with an inversion that would deflect gases away from soil contamination; no precipitation or rainfall; wind speed at an altitude of 200 feet below 15 MPH; wind from the west or southwest; and all of those conditions remaining in place until the experiment ended.
By December 2, particularly bad weather in the local Palouse area had already caused the government's preferred Green Run testing schedule to fall increasingly behind. The next recommended release window was designated for December 3 at 1:00 a.m. because favorable weather was predicted then. However, the Green Run began releasing radioactive gas early, at 8:00 p.m. on December 2. The weather was reportedly fine at the initiation of the test, near 8 P.M., but by 2 A.M., the wind had fully calmed and then began blowing more southward along the Columbia River. Michele Gerber, the Hanford Site Historian, explained that the military had been waiting for the opportunity to begin the Green Run.
Release The radioactive release experiment was ordered to begin uncontrolled dispersal on a day with adverse wet and windy weather conditions, despite testing requirements, causing concentrated radioactive material to fall as rain and snow over Spokane and Walla Walla on December 2 and 3. At the time the test began, weather conditions were reported to be unpredictable, rapidly changing, and incompatible with the experiment's stated requirements. It also rained and snowed. For the Green Run, the filtering air scrubbers were intentionally deactivated to maximize the release of radioactive material. The resulting radioactive gases bypassed the filters and were released from the T Plant chemical separation facility. System filters designed to prevent the release of radioactive materials into the surrounding environment were intentionally bypassed as part of the Green Run.
Douglas C-47 Skytrain airplanes were involved in monitoring the active Green Run experiment. By sunrise on December 3, U.S. Air Force pilots observing the secret test conditions had begun reporting problems, as prior Air Force meteorological predictions were upended by sudden and unexpected increases and shifts in wind speed, along with the unplanned appearance of a temperature inversion. Testing equipment necessary for Green Run's experiment was known to be contaminated by radiation before the test, causing high background signals; the already bad weather conditions during the release worsened this by concentrating radioactive materials at the release stacks. Other portions of the test included a lost weather balloon and failing air pumps.
The complete discharge of iodine-131 and xenon-133 from the beginning of the Green Run operation took a total of 12 to 17 hours. Sources cite of iodine-131 released, along with an even greater amount of xenon-133. Robkin's 1992 reanalysis calculated 0.40 PBq ± 30% (11,000 Ci ± 30%) of iodine-131, somewhat larger than the earlier estimates of 0.15-0.30 PBq (4,000-7,780 Ci) from Singlevich (1950) and Jenne and Healy (1950). Robkin also estimated that approximately 29,000 Ci (1.07 PBq) of xenon-133 was released. Goliszek gave the Green Run release as almost 8,000 curies of iodine-131 and 20,000 curies of xenon-133 in 2003. For unknown reasons, double the initially expected amount of iodine-131 and nearly triple the expected amount of xenon-133 were released in an initial wind-swept plume that was long and wide. Approximately 8,000 curies of iodine-131 were released during the incident. The Green Run was the single largest one-day release of radioiodine from Hanford during its peak years of operation at the height of World War II.
Officials involved in the test said the release was not considered unsafe at the time, and GAO noted that no regulatory limits then existed for the amount of such emissions, despite the release being highly concentrated over a 12-hour period. GAO reported conflicting recollections among AEC contractor officials about who approved the weather conditions for the test, with one account placing the decision with AEC contractor officials and another stating that the AEC did not want to proceed but the Air Force ordered the test. The U.S. government in 1949 designated the Green Run as top secret for national security reasons, but declined to classify it as human experimentation because the test was "not undertaken with the intent of testing the effects of radiation in humans or designed to measure human exposure."
Spread The Green Run radioactive plume then "stagnated" in the local air and weather conditions for "several days" before a new storm sent it toward the north and northeast, further worsening the spread of radioactive materials. Green Run radioactive contamination spread from Richland north to Kettle Falls, Washington, and south to Klamath Falls, Oregon, as well as to Kennewick, to the southeast and against the wind at the time of the release. The 1949 Green Run nuclear contamination spread over towns and cities. After the Green Run, thyroid radiation levels eighty times the daily safe limits were detected in animal sampling on the Hanford site grounds, while radiation sampling along the full plume pathway detected levels four hundred times above safe limits. The release exceeded Hanford's then-existing vegetation deposition tolerance in the Yakima, The Dalles, Spokane, and Blue Mountains areas.
The radiation released from the Green Run exceeded the amount released in 1979 during the Three Mile Island accident by roughly seven hundred times. Three Mile Island was a widely disclosed 1979 event with voluntary evacuations; no evacuation or disclosure orders were issued for the Green Run. The Department of Energy later categorized the Green Run as one of the 14 most significant safety-related incidents in Hanford's history.
Later releases