Question: The "Green Run" was a secret U.S. Government release of radioactive fission products during which date span, at the Hanford Site plutonium production facility?
Context: Reprocessed uranium (RepU) is the uranium recovered from nuclear reprocessing, as done commercially in France, the UK and Japan and by nuclear weapons states' military plutonium production programs.  This uranium actually makes up the bulk of the material separated during reprocessing.  Commercial LWR spent nuclear fuel contains on average (excluding cladding) only four percent plutonium, minor actinides and fission products by weight.  Reuse of reprocessed uranium has not been common because of low prices in the uranium market of recent decades, and because it contains undesirable isotopes of uranium. Caesium-137 ( Cs , Cs-137), cesium-137, or radiocaesium, is a radioactive isotope of caesium which is formed as one of the more common fission products by the nuclear fission of uranium-235 and other fissionable isotopes in nuclear reactors and nuclear weapons.  It is among the most problematic of the short-to-medium-lifetime fission products because it easily moves and spreads in nature due to the high water solubility of caesium's most common chemical compounds, which are salts. The Kamioka Liquid Scintillator Antineutrino Detector (KamLAND) is an electron antineutrino detector at the Kamioka Observatory, an underground neutrino detection facility near Toyama, Japan.  The device is situated in a drift mine shaft in the old KamiokaNDE cavity in the Japanese Alps.  The site is surrounded by 53 Japanese commercial nuclear reactors. Nuclear reactors produce electron antineutrinos (formula_1) during the decay of radioactive fission products in the nuclear fuel.  Like the intensity of light from a light bulb or a distant star, the isotropically-emitted formula_1 flux decreases at 1/R per increasing distance R from the reactor.  The device is sensitive up to an estimated 25% of antineutrinos from nuclear reactors that exceed the threshold energy of 1.8 megaelectronvolts (MeV) and thus produces a signal in the detector. Nuclear fission splits a heavy nucleus such as uranium or plutonium into two lighter nuclei, which are called fission products.  Yield refers to the fraction of a fission product produced per fission. Hanford was a small agricultural community in Benton County, Washington, United States.  It was depopulated in 1943 along with the town of White Bluffs in order to make room for the nuclear production facility known as the Hanford Site.  The town was located in what is now the "100F" sector of the site. Major General Kenneth David "Nick" Nichols (13 November 1907 – 21 February 2000) was a United States Army officer and an engineer.  He worked on the Manhattan Project, which developed the Atomic Bomb during World War II, as Deputy District Engineer to James C. Marshall, and from 13 August 1943 as the District Engineer of the Manhattan Engineer District.  He was responsible for both the uranium production facility at the Clinton Engineer Works at Oak Ridge, Tennessee and the plutonium production facility at Hanford Engineer Works in Washington state. Nuclear fission products are the atomic fragments left after a large atomic nucleus undergoes nuclear fission.  Typically, a large nucleus like that of uranium fissions by splitting into two smaller nuclei, along with a few neutrons, the release of heat energy (kinetic energy of the nuclei), and gamma rays.  The two smaller nuclei are the "fission products".  (See also Fission products (by element)). Iodine-131 (I) is an important radioisotope of iodine discovered by Glenn Seaborg and John Livingood in 1938 at the University of California, Berkeley.  It has a radioactive decay half-life of about eight days.  It is associated with nuclear energy, medical diagnostic and treatment procedures, and natural gas production.  It also plays a major role as a radioactive isotope present in nuclear fission products, and was a significant contributor to the health hazards from open-air atomic bomb testing in the 1950s, and from the Chernobyl disaster, as well as being a large fraction of the contamination hazard in the first weeks in the Fukushima nuclear crisis.  This is because I-131 is a major fission product of uranium and plutonium, comprising nearly 3% of the total products of fission (by weight).  See fission product yield for a comparison with other radioactive fission products.  I-131 is also a major fission product of uranium-233, produced from thorium. The Hanford Site is a mostly decommissioned nuclear production complex operated by the United States federal government on the Columbia River in the U.S. state of Washington.  The site has been known by many names, including: Hanford Project, Hanford Works, Hanford Engineer Works and Hanford Nuclear Reservation.  Established in 1943 as part of the Manhattan Project in Hanford, south-central Washington, the site was home to the B Reactor, the first full-scale plutonium production reactor in the world.  Plutonium manufactured at the site was used in the first nuclear bomb, tested at the Trinity site, and in Fat Man, the bomb detonated over Nagasaki, Japan. The "Green Run" was a secret U.S. Government release of radioactive fission products on December 2–3, 1949, at the Hanford Site plutonium production facility, located in Eastern Washington.  Radioisotopes released at that time were supposed to be detected by U.S. Air Force reconnaissance.  Freedom of Information Act (FOIA) requests to the U.S. Government have revealed some of the details of the experiment.  Sources cite 5500 to of iodine-131 released, and an even greater amount of xenon-133.  The radiation was distributed over populated areas, and caused the cessation of intentional radioactive releases at Hanford until 1962 when more experiments commenced.
Answer: December 2–3, 1949