Sedan test on 6 July 1962 - Massive crater, massive contamination

6 July 1962: 'Sedan' - Massive Crater, Massive Contamination

The blast displaced 12 million tons of earth.

On 6 July 1962 the United States conducted the ‘Sedan’ nuclear test at the Nevada Test Site. The device had an explosive power of 104 kilotons, the equivalent of around eight Hiroshima bombs. The blast displaced more than 12 million tons of soil and created a crater 100 metres deep and 390 metres in diameter – the largest man-made crater in the United States.

Nuclear testing reached an all-time high in 1962 (click to enlarge).

The test was a so-called “peaceful nuclear explosion” (PNE), carried out to determine the feasibility of using nuclear detonations to excavate large amounts of earth both quickly and economically. A PNE is qualitatively no different from a weapons test in terms of fallout and has the technical characteristics of an explosive device, see nuclear testing chapter. Over 150 of all 2,050 nuclear explosions were classified as PNEs. When the total number of nuclear explosions (both weapon tests and PNEs) conducted worldwide in 1962 reached 178, it marked an all-time high, fuelling political tensions on the eve of the Cuban Missile Crisis.

Research from the United States National Cancer Institute (PDF) shows that the Sedan test released about 880,000 curies of Iodine-131, see effects of nuclear testing chapter. The fallout reached parts of Iowa, Nebraska, South Dakota and Illinois. According to a 1999 National Cancer Institute report, the Sedan test was the second most fallout-intensive nuclear test of all U.S. continental tests after the 'Harry' test of 19 May 1953.

The fallout had multiplied normal radiation readings a hundredfold…We found radioactive iodine in all of the children, milk and vegetation that we measured in the whole northern section of the state.Radiologist Dr. Robert C. Pendleton after the Sedan test
Thyroid doses of I-131 received by Americans from Nevada atmospheric nuclear bomb tests. Source: National Cancer Institute (1997)

Excerpt from Killing Our Own (PDF), Harvey Wassermann and Norman Solomon, (1982):

Probably little would have been learned about this planned disaster had not some University of Utah graduate students and their outspoken professor been visiting a canyon about twenty miles southeast of Salt Lake City. On July 7, 1962, radiologist Dr. Robert C. Pendleton was with students on a field trip in Big Cottonwood Canyon. "We were measuring levels of radioactivity in different environmental situations," Dr. Pendleton remembered. "A cloud of radioactive material came over and all the measurements began to go nuts. I recognized that we were getting fallout and took the students off the hill and back down in the valley.

The United States conducted its last nuclear test on 23 September 1992 and shortly afterwards announced a moratorium on nuclear testing. The 1996 Comprehensive Nuclear-Test-Ban Treaty (CTBT) bans all nuclear explosions. The United States was the first country to sign the CTBT but has yet to ratify it. U.S. ratification is a precondition for the CTBT’s entry into force, together with those of China, the Democratic People’s Republic of Korea, Egypt, India, Iran, Israel and Pakistan.


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