Chapter 3—Containing Underground Nuclear Explosions « 49 of the experimental equipment. Mighty Oak and Camphor are the only tests where radioactivity escaped out of vessel IJ. In no test. other than Camphor, has radioactive material escaped out of vessel HII. Camphor resulted in an uncontrolled release of radioactive material that was detected only onsite. There have been several instances when smail amounts of radioactivity were released intentionally to the atmosphere through controlled purging. In these cases, the decision was madeto ventthe tunnel and release the radioactivity so the experimental results and equipment could be recovered. The events that required such a controlled release are the 10 tests where radioactive material escaped out of vessel I and into vessel IT, namely: Hybla Fair, October 28, 1974. Hybla Gold, November 1, 1977. 3'of the table showsthatthe release of radioactive material from underground nuclear testing since Baneberry (54,000 Ci) is extremely small in compar- ison to the amount of material released by preBaneberry underground tests (25,300,000 Ci), the early atmospheric tests at the Nevada Test Site. or even the amount that would be released by a 1-kiloton explosion conducted above ground (10,000,000 Ci). From the Perspective of Human Health Risk If a single person had been standing at the boundary of the Nevada Test Site in the area of maximum concentration of radioactivity for every test since Baneberry (1970), that person’s total exposure would be equivaient to 32 extra minutes of normal background exposure (or the equivalent of 1/1000 of a single chest x-ray). A FEW EXAMPLES: Miners Iron, October 31, 1980. Huron Landing, September 23, 1982. Mini Jade, May 26, 1983. Mill Yard, October 9, 1985. Diamond Beech, October9, 1985. Misty Rain, April 6, 1985. Mighty Oak, April 10, 1986. Mission Ghost, June 20, 198778 In most cases, the release was dueto thefailure of somepart of the experimentprotection system. Table 3-1 includes every instance (for both announced and unannouncedtests) where radioactive material has reached the atmosphere under any circumstances whatsoever from 1971 through 1988. The lowerpart of table 3-1 summarizes underground tests prior to 1971 and provides a comparison with other releases of radioactive material. Since 1970, 126 tests have resulted in radioactive material reaching the atmospherewith total release of about 54,000 Curies(Ci). Of this amount, 11,500 Ci were due to containment failure and late-time seeps. The remaining 42,500 Ci were operational releases and controlled tunnel ventilations—with Mighty Oak (36,000 Ci) as the main source. Section 28The Mission Ghost retease was due to a post-shot drill hole. 29Op.cit., footnote 20. Although over 90 percent of all test explosions occur as predicted, occasionally something goes wrong. In somecases,the failure results in the loss of experimental equipmentorrequires the controlled ventilation of a tunnel system. In even more rare cases (less than 3 percent), the failure results in the unintentional release of radioactive material to the atmosphere. A look at examples shows situations where an unexpected sequence of events contnbute to create an unpredicted situation (as occurred in Baneberry (see box 3-1)), and also situations where the full reason for containmentfailure sull remains a mystery. 1. Camphor (June 29, 1971, horizontal tunnel test. less than 20 kilotons, radioactivity detected only on-site. ) The ground shock produced by the Camphor explosion failed to close the HLOSpipe fully. After about 10 seconds, gases leaked through and eroded the stemming piug. As gases flowed through the stemming plug, pressure increased on the closure door behind the experiment. Gases leaked around the cable passage ways and eroded open a hole. Pressure was then placed on the final door. which held but leaked slightly. Prior to the test, the containment plan for Camphor received six ‘'I'’s from the CEP.”