Chapt Containing Underground Nuclear Explosi _ Underground nuclear tests are designed and reviewed for containment, with redundancyar conservatism in each step. atmospheric testing was conducted in the Chri: Island and Johnston Island area of the Pacific. 1961 through 1963, many of the underground vented radioactive material. The amounts small, however, in comparison to releases aboveground testing also occurring at that tim INTRODUCTION The United States’ first underground nuclear test, codenamed ‘*Pascal-A,"’ was detonated at the bottom of a 499-foot open drill-hole on July 26, 1957.) Although Pascal-A marked the beginning of underground testing, above ground testing continued for another 6 years. With testing simultaneously ,occurring aboveground,the release of radioactive material from underground explosions was atfirst not a major concern. Consequently, Pascal-A, like many of the early underground tests that were to follow, was conducted ‘‘roman candle’’ style in an open shaft With the success of the Rainier test, efforts made to understand the basic phenomenolo: contained underground explosions. Field e included tunneling into the radioactive zone, !2 tory measurements, and theoretical work to r the containment process. Through additional experience was gained in tunnel-stemming esses and the effects of changing yields. The attempts to explain the physical reason why u ground nuclear explosions do not always fr rock to the surface did little more than postula hypothetical existence of a **mystical magical | brane.”’ In fact, it took more than a deca underground testing before theories for the ph: basis for containment were developed. that allowed venting.” Aspublic sensitivity to fallout increased, guidelines for testing in Nevada became morestringent. In 1956, the weapons laboratories pursued efforts to reduce fallout by using the lowest possible test yields, by applying reduced fission yield or clean technology, and by containing explosions underground. Of these approaches. only underground testing offered hope for eliminating fallout. The objective was to contain the radioactive material,yet sul! collect all required information. The first experiment designed to contain an explosion completely underground was the ‘‘Rainier’’ test, which was detonated on September [9, 1957. A nuclear device with a known yield of 1.7 kilotons was selected for the test. The test was designed with two objectives: 1) to prevent the release of radioactivity to the atmosphere, and 2) to determine whether diagnostic information could be obtained from an underground test. The test was successful in both objectives. Five more tests were conducted the following year to confirm the adequacy of such testing for nuclear weapons development. In 1963, U.S. atmospheric testing ended wh: United States signed the Limited Test Ban 1 prohibiting nuclear test explosions in any en ment other than underground. The treaty prohibits any explosion that: ... causes radioactive debris to be present out the territorial limits of the State under wt jurisdiction or control such explosion is conduc With the venting of radioactive debris underground explosions restricted by treaty tainmenttechniques improved. Although man tests continued to produce accidental relea radioactive material, most releases were only « able within the boundaries of the Nevada Tes In 1970, however, a test codenamed **Banel resulted in a prompt, massive venting. Radic material from Baneberry was tracked as far Canadian border and focused concern aboutbi environmental safety and the treaty complia In November 1958, public concern over radioactive fallout brought about a nuclear testing moratorium that lasted nearly 3 years. After the United States resumed testing in September, 1961, almost all testing in Nevada was done underground, while 'The first underground test was the United States’ 100th nuclear explosion. 2It 1s interesting to note that even with an open shaft, 90% of the fission products created by Pascal-A were contained underground 3Article 1,1(b). 1963 Limned Test Ban Treaty —31-