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| Fig. 1: The Sedan Crater at the Nevada Test Site, created by a 104-kiloton nuclear detonation on July 6, 1962 as part of Project Plowshare. (Source: Wikimedia Commons) |
Between 1961 and 1973, the United States Atomic Energy Commission (AEC) conducted 27 nuclear detonations comprising 35 individual explosive devices under Project Plowshare, spending approximately $770 million in the process. [1] The program, established in June 1957, sought to develop peaceful applications of nuclear explosives in two categories: large-scale excavation and underground engineering. [2] The program had a number of proposed applications. The first was for canal and harbor excavation, with a proposal being made for a new sea-level Panama Canal. The second was for natural gas stimulation which can allow natural gas deposits that are trapped in tight and dense rock to be stimulated, and for the gas to be extracted. Lastly, it was also proposed to use nuclear blasts to break up mineral ores to allow for easier mining. [2]
The program's first shot, Project Gnome (3.1 kt), was fired on December 10, 1961, in a salt bed near Carlsbad, New Mexico. [3] The last was Rio Blanco on May 17, 1973, in western Colorado. [3] The detonations were divided into two categories: excavation tests conducted at shallow depth, and underground engineering tests at hundreds to thousands of meters depth designed to fracture rock. The largest shot was Sedan (104 kt), which alone accounts for roughly 27% of the program's total yield. [3] The total combined yield of all 27 Plowshare detonations was approximately 385 kt. For comparison, the total yield of all 1,032 U.S. nuclear explosions was on the order of 200 megatons. [4] As such, Plowshare was less than 385/200,000 = 0.2% of that total.
The energy released by the 104-kt Sedan detonation was:
| E | = | 104 kt × 4.184 × 1012 J/kt |
| = | 4.35 × 1014 J |
This single device displaced approximately 1.2 × 107 short tons = 1.09 × 1010 kg and created the crater pictured in Fig. 1, measuring 390 m in diameter and 100 m deep. [3] For context, a single Sedan-class device released more energy than roughly 100,000 metric tons of conventional explosive. The AEC envisioned scaling this up: the proposed nuclear excavation of a sea-level Panama Canal would have required approximately 250 devices with a combined yield of 120 megatons. [5] In 1964, preliminary estimates put the nuclear canal cost at $747 million, roughly one-third the then-estimated cost of conventional construction. By 1970, after six years of on-site study, the nuclear estimate had risen to $3.1 billion, exceeding the $2.88 billion estimate for conventional construction on a different Panama route. [5]
The Sedan shot, buried at only 194 m, lofted a radioactive cloud to 3,600 m and released approximately 880 kCi (33 PBq) of I-131. [6] The fallout was measured by the AEC's Health and Safety Laboratory (HASL) using a nationwide network of gummed-film collectors, which captured gross beta activity at approximately 100 sites. [6] The NCI subsequently used these measurements, combined with meteorological dispersion models and precipitation data, to estimate I-131 deposition density on a county-by-county basis for all 3,094 counties in the contiguous United States. [6] A later study by Beck at DOE's Environmental Measurements Laboratory calculated county-level deposition densities for Cs-137 and other radionuclides from the NCI I-131 data using the Hicks (1981) radionuclide ratios, and found that the three most heavily affected counties from Sedan received committed effective doses of 0.25 to 0.35 mSv. [7] These counties were concentrated in northern Iowa, consistent with the northeastward trajectory of the fallout cloud. [7]
It is worth checking whether this 880 kCi (33 PBq) figure is physically reasonable. If one assumes that the entire 104-kt yield came from fission, and that every fission produces one atom of a long-lived isotope such as Cs-137 or Sr-90 (half-life ≈ 30 years), the maximum possible activity of these isotopes would be:
|
4.35 × 1014 J × ln(2)
200 × 106 eV fission-1 × 1.602 × 10-19 J eV-1 × 30 y × 365 d/y × 24 h/d × 3600 s/h |
|
| = | 9.95 × 1015 Bq ≈ 10 PBq |
Since only about 10% of fissions produce these particular long-lived isotopes, the realistic figure is closer to ~1 PBq of Cs-137 and Sr-90. The 33 PBq total reported byh the National Cancer Institute is therefore not dominated by these long-lived species. [6] Instead, it is dominated by short-lived isotopes, principally I-131 itself, which has a half-life of only 8.02 days and is therefore far more radioactive per atom than Cs-137. Furthermore, the Plowshare devices were designed to derive most of their yield from fusion rather than fission, using a small fission "spark plug" to ignite a larger DT fusion reaction.
Separate from the excavation program, Plowshare also pursued underground nuclear gas stimulation: detonating devices deep in shale formations to release trapped natural gas. When a device detonates underground, it vaporizes rock and creates a cavity whose roof then collapses into a column of fractured rubble called a "chimney." Gas from the surrounding formation flows into this chimney and up to the surface. However, the fusion and fission reactions also produce tritium and Kr-85 as byproducts, which mix directly into the recovered gas. Tritium is especially problematic because it chemically bonds with the methane molecules to form tritiated methane, meaning you can't just filter it out and that it becomes the gas, chemically speaking. [8] The gas recovered from the Gasbuggy stimulation test was heavily contaminated with tritium, measuring at 800 pCi/cm3. [8] For gas to be safely burned in household stoves and heaters, a 1974 Oak Ridge study used a reference concentration of 1 pCi/cm3 for dose calculations. [9] Gasbuggy's gas was 800 times over that threshold. After three years of pumping out and burning off contaminated gas, it was still 40 times too high. [8]
The Threshold Test Ban Treaty of 1974 capped underground yields at 150 kt. The gas contamination data showed tritium levels three orders of magnitude above commercial thresholds. Public opposition mounted: Project Wagon Wheel, proposed for Wyoming, was blocked by protests before execution, and eventually Congress completely defunded Plowshare in 1977. [1]
work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.[1] C. M. Beck, S. R. Edwards, and M. L. King, "The Off-Site Plowshare and Vela Uniform Programs," Vol. 3 of 3, U.S. Department of Energy, DOE/NV/26383-22, September 2011.
[2] E. Teller, "Plowshare," Lawrence Radiation Laboratory, UCRL-7222, February 1963.
[3] "United States Nuclear Tests, July 1945 through September 1992," U.S. Department of Energy, DOE/NV-209-REV 16, September 2015.
[4] N.-O Bergkvist and R. Ferm, "Nuclear Explosions 1945 - 1998," Förvarets Forskningsanstalt, Stockholm, FOA-R-00-01572-8E, July 2000.
[5] "Interoceanic Canal Studies 1970," Atlantic-Pacific Interoceanic Canal Study Commission, December 1970.
[6] "Estimated Exposures and Thyroid Doses Received by the American People from Iodine-131 in Fallout Following Nevada Atmospheric Nuclear Bomb Tests," U.S. National Cancer Institute, October 1997.
[7] "Report on the Feasibility of a Study of the Health Consequences to the American Population From Nuclear Weapons Tests Conducted by the United States and Other Nations," U.S. Department of Health and Human Services, May 2005, Appendix E.
[8] C. F. Smith Jr., "Project Gasbuggy: Gas Quality Analysis and Evaluation Program - Tabulation of Radiochemical and Chemical Analytical Results," Lawrence Radiation Laboratory, UCRL-50635, November 1969.
[9] C. J. Barton and S. A. Reynolds, "Estimated Radiation Doses from Ingestion of Tritium-Containing Consumer Products Made with Hydrocarbons from Nuclearly Stimulated Natural Gas Wells," Oak Ridge National Laboratory, ORNL-TM-4730, December 1974.
