50 ¢ The Containment of Underground Nuclear Explosions 2. Diagonal Line (November 24, 1971, vertical shaft test. less than 20 kilotons, radioactivity detected off-site.) In a sense, the Diagonal Line seep waspredicted by the CEP.Priorto the test, Diagonal Line received all ‘‘A’’ categorizations, except from one member who gaveit a *°B.’°39It was a conclusionofthe panel that due to the high CO, content, a late-time (hours or days after detonation) seepage was a high probability. They did not believe, however, that the level of radiation would be high enough to be detectable off-site. Permission to detonate was requested and granted because the test objectives were judged to outweighthe risk. Diagonal Line was conducted in the northern part of Frenchman Fiat. It is speculated that carbonate material released CO, gas that forced radioactive material to leak to the surface. Diagonal Line wasthe last test detonated on Frenchman Flat. 3. Riola (September 25, 1980, vertical shaft test, less than 20 kilotons, radioactivity detected off-site.) Ironically, Riola was originally proposed for a different location. The Containment Evaluation Panel, however, did not approve the first location and so the test was moved.Atits new location, Riola was characterized by the CEP priorto the test with 8 *‘A’’s. Rioia exploded with only a small fraction of the expected yield. A surface collapse occurred and the failure of a containmentplug resulted in the release of radioactive material. 4. Agrini (March 31, 1984, vertical shaft test, less than 20 kilotons, radioactivity detected only onsite.) The Agrini explosion formed a deep subsidence crater 60 feet west of the emplacernent hole. A small amountof radioactive material was pushed through the chimmney by noncondensible gas pressure and was detected onsite. The containment plan for Agrini received seven **A’’s and two ‘*B’’s from the CEPpriorto the test. The *'B’’s were due to the use of a new stemming plan. 5. Midas Myth (February 15, 1984, horizontal tunnel test, less than 20 kilotons, no release of radioactive material.) All of the radioactive material produced by the Midas Myth test was contained within vessel [, with no release of radioactivity to either the atmosphere or the tunnel system.It is therefore not considered a containment failure. Three hours after the test, however, the cavity collapsed and the chimney reached the surface forming an unanticipated subsidence crater. Equipmenttrailers were damaged and personnel were injured (one person later died as a result of complications from his injuries) when the collapse crater formed.?! Analysis conducted after the test indicated that the formation of the collapse crater should have been expected. Shots conducted on Yucca Flat with the same yield and at the same depth of burial did, at times, produce surface collapse craters. In the case of Midas Myth, collapse was not predicted because there had never been a collapse crater for a tunnel event and so the analysis was not madepriorto the accident. After analyzing the test, the conclusion of the Surface Subsidence Review Committee was: That the crater is not an indicanon of some unusual, anomalous occurrence specific to the U12T.04 emplacement site. Given the normal variation in explosion phenomena, along with yield, depth of burial, and geologic setting, experience indicates an appreciable chance for the formation of a surface subsidence crater for Midas Myth. Prior to the test, the Containment Evaluation Panel characterized Midas Myth with nine ‘*A’'s. 6. Misty Rain ( April 6, 1985, horizontal tunnel test, less than 20 kilotons, no unintentional release of radioactive material.) Misty Rain is unusual in that it is the only tunnel test since 1970 that did not have three containment vessels. In the Misty Rain test, the decision was madethat because the tunnel system was so large. a vessel II was not needed.3* Despite the lack of a vessel II, the CEP categorized the containmentof Misty Rain with eight ‘*A’’s, and one ‘B."'3> Dunng the test, an early flow of energy down the HLOSpipe prevented the complete closure of the MAC doors. The MAC doors overlapped, but stopped a couple inches short of full closure. The TAPS door closed only 20 percent before the deformation from ground shock prevented it from closing. A small amount of Ibid. 31 The injuries were due to the physical circumstancesof the collapse. There was no radiation exposure. 32The drifts in the runnel system created over 4 million cubic feet of open volume. 330Qne CEP memberdid not mutually categorizethetest, after receiving additional information concerningthe test, he categorized the test with an “A.”