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United States I: Pressure for Nuclear Testing Likely on ‘Bunker Buster,’ Expert Says By David Ruppe Princeton University physicist Robert Nelson told Global Security Newswire the testing would be sought to certify the nuclear warhead would produce a precisely sized explosion after undergoing the significant force needed to send it deep underground. Precision of yield is necessary to accurately anticipate potential radioactive fallout and civilian casualties, he said. To reliably produce a low-yield blast equivalent to 100 tons of TNT — or less than 1 percent of the bomb used on Hiroshima during World War II — “the critical mass that’s being produced in the explosion has to be finely tuned to be just a tiny bit over critical,” Nelson said. “And in your design, just the shape of the material, how the neutrons propagate through it during the explosion, if you’re off just a little bit, you could end up generating a five-ton explosion or a 500-ton explosion,” he said. U.S. military doctrine requires that commanders weigh potential collateral damage, which involves taking into account the known capability of a nuclear weapon, before recommending use of such a weapon to the president. Current Restrictions Although former President Bill Clinton signed the Comprehensive Test Ban Treaty in 1996, the U.S. Senate later rejected the treaty. President George W. Bush has indicated he will not ratify the treaty, but has also said he has no plans for breaking the 10-year moratorium initiated by his father on U.S. nuclear weapons testing. Bush will not rule testing out, however, and his fiscal 2003 budget requests Energy Department funding to shorten the preparation time to conduct a test and for continuing study on various options for earth-penetrating warheads (see GSN, March 22). Furthermore, if the United States did wish to develop a low-yield weapon, it would need Congress to overturn a 1994 law prohibiting research and development on them that said, “low-yield nuclear weapons blur the distinction between nuclear and conventional war.” Energy Secretary Spencer Abraham told a March 14 hearing that no testing is required “at this time.” “We have not examined nor is it even in the current discussion stages as to the issue of any kind of need for testing,” he said. Surviving Impact A key challenge for U.S. earth penetrator designers is in developing a casing for the warhead that can withstand the force necessary to plow it deep enough to better contain a small nuclear explosion — without significantly damaging the warhead, Nelson said. “If you impact the ground too fast, the missile will just crumble,” said Nelson. Another possibly more urgent challenge, he said, is to protect the weapon’s electronics from the rapid deceleration of the warhead as it burrows down. Current earth-penetrating technology can burrow a warhead as deep as 50 feet into the earth, he said. The depth needed to contain a one-kiloton explosion is 300 feet, he said. Testing Without the Blast? Two U.S. national laboratories are studying two designs, the B61 and the B83, for modification to provide an enhanced earth-penetrating capability that could be used for striking enemy bunkers or cave hideouts deep underground. The studies are expected to run through the next three years (see GSN, March 19). An earth penetrator, the B61-11, was developed in the mid-1990s, incorporating the B61 into a hard, protective casing for penetration. Nuclear blast testing was not done on the modified weapon. Rather, the weapon, minus the nuclear material, was tested, according to Jay Coghlan, director of the arms control organization Nuclear Watch of New Mexico. There is a lot of testing that can be done on the system without actually conducting a nuclear test, Nelson said. “My belief is that there will be a lot of pressure to test it because they won’t be able to guarantee a particular sized yield, because it is very sensitive at these low values,” he said. Low-Yield Under Consideration? Cornell University physicist Kurt Gottfried raised questions about Nelsons comments about the precision of low-yield penetrator warheads. “It’s my understanding that [destroying a deeply buried, hardened bunker] can’t be done with a low-yield weapon, period,” he said, citing a recent Los Angeles Times opinion piece by a former high-level Sandia scientist and a 2000 paper by Stephen Younger, associate Los Alamos director in charge of nuclear weapons research. The Times article said for a warhead penetrated at 50 feet, yields greater than 1 kiloton would be required to damage hardened targets deeper than about 200 feet. “Much larger yields — in the range of 100 kilotons or more — are needed to create enough ground shock to destroy a hardened structure at a 1,000-foot depth,” it said. Just how low a yield is being considered by the laboratories is not public. Neither the B61 nor B83 is a low-yield weapon, Abraham told the committee. Both have yields substantially higher than five kilotons he said. According to information published by the Federation of American Scientists, though, the B61-11 has a yield range of 300 tons to 340 kilotons. Nelson says there are people within the Energy Department pressing for development of low-yield nuclear weapons. Younger in his article, in fact, argued low-yield nuclear weapons could be used to destroy hardened targets, though not very deeply buried targets, causing fewer civilian casualties than might larger yield. Minimizing Casualties Nelson in much-reported analysis in a Federation of American Scientists newsletter last year, wrote that even a buried low-yield explosion would create a large radioactive crater and spread deadly radioactive fallout widely. Significant civilian casualties are almost inevitable using even a low-yield weapon, particularly in an urban area, because of limitations on the technology for delivering it deep enough to be contained, he said in the interview. “What I can say with confidence is no matter what you do, you’re never going to be able to penetrate deeply enough into the ground to contain the explosion and to contain the fallout to protect anybody on the surface,” said Nelson.
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