Chapter 1—£xecutive Summary « 5 person’s total exposure would be equivalent to 32 extra minutes of normal background exposure (or the equivalent of 1/1000 of a single chest x-ray). A worst-case scenario for a catastrophic accident at the test site would be the prompt, massive venting of a 150-kilotontest (the largest allowed under the 1974 Threshold Test Ban Treaty). The release would be in the range of 1 to 10 percent of the total radiation generated by the explosion (compared to 6 percent released by the Baneberry test or an estimated 10 percent that would be released by a test conducted in a hole open to the surface). Such an accident would be comparable to a 15-kiloton abovegroundtest, and would release approximately 150,000,000 Ci. Although such an accident would be considered a major catastrophe today, during the early years at the Nevada Test Site 25 abovegroundtests had individual yields equal to or greater than 15 kilotons. SPECIFIC CONCERNS Recently, several specific concerns aboutthe safety of the nuclear testing program have arisen, namely:3 1. Does thefracturing ofrock at Rainier Mesa pose a danger? The unexpected formation of a surface collapse crater during the 1984 Midas Myth test focused concern about the safety of testing in Rainier Mesa. The concern was heightened by the observation of ground cracksat the top of the Mesa and by seismic measurements indicating a loss of rock strength out to distances greater than the depth of burial of the nuclear device. The specific issue is whetherthe repeatedtesting in Rainier Mesa had fractured large volumes of rock creating a ‘‘tired mountain’’ that no longer had the strength to successfully contain future undergroundtests. The inference thattesting in Rainier Mesa posesa high level of risk implies that conditions for conducting a test on Rainier are more dangerousthan conditions for conduct- ing a test on Yucca Flat.* But, in fact, tests in Rainier Mesa are buried deeper and spaced further apart than comparable tests on Yucca Flat.> Furthermore, drill samples show noevidence of any permanent decrease in rock strength at distances greater than two cavity tadii from the perimeterof the cavity formed by the explosion. The large distance of decreased rock strength seen in the seismic measurements is almost certainly due to the momentary opening of pre-existing cracks during passage of the shock wave. Mostfractures on the top of the mesa are due to surface spall and do not extend downto the region ofthe test. Furthermore, only minimal rock strength is required for containment. Therefore, none of the conditions of testing in Rainier Mesa—burial depth, separation distance, or material strength—imply that leakage to the surface is more likely for a tunnel test on Rainier Mesa than for a vertical drill hole test on Yucca Flat. 2. Could an accidental release of rudtoactive material go undetected? A comprehensive system for detecting radioactive material is formed by the combinationof: e the monitoring system deployed for each test; e the onsite monitoring system run bythe Departmentof Energy (DOE) and: e the offsite monitoring system, run by Environmental Protection Agency (EPA), including the community monitoring sta- tions. There is essentially no possibility that a significant release of radioactive material 3Detailed analysis of these concerns is included in chs. 3 and 4. 4Approximately 90 percentof all nuclear test explosions are vertical drill hole tests conducted on Yucca Flat. See ch. 2 for an exptanation of the various types of tests. 5The greater depth of burial is due to convenience.It is easier to mine tunnels lower in the Mesa.