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Corral That Bomb Testing (C.T.B.T.) Part 4 – Cheaters
Travis | Mar 17, 2009 |
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Atomic bomb explosion in the Marshall Islands (National Archives photo)
Part 4 of 4
Also see:
Corral That Bomb Testing Part 1 – Politics
Corral That Bomb Testing Part 2 – Messaging
Corral That Bomb Testing Part 3 – Verification
Any discussion of Comprehensive Test Ban Treaty (CTBT) ratification must devote a few words to cheating and evasion. A 2002 report from the National Academy of Sciences concluded that mine masking and cavity decoupling are “the only evasion [aka cheating] scenarios that need to be taken seriously at this time.”
Mine masking involves triggering a large chemical explosion in a nearby mine to cloak a nuclear test. First of all, it does not have a high probability of being successful when employed on its own without cavity decoupling (the use of large underground cavities to hide nuclear tests). Second of all, chemical explosions in mines usually are fired in rapid succession (“ripple-fired”) and therefore are incapable of creating seismic signals big enough to mask a nuclear weapon detonated in a single, massive burst. Even if a chemical explosion were triggered that was large enough to cover up a nuclear explosion, the peculiarity of such a chemical explosion would be difficult to explain away. This means mine masking would be an extremely risky method for CTBT cheaters to disguise their nuclear tests.
Cavity decoupling involves constructing a cavity underground that is large enough to reduce nuclear blast pressure on the cavity walls, which stifles the explosion’s seismic waves and makes detection more challenging. In 1999, CTBT opponents cited the Central Intelligence Agency’s concerns about decoupling as a reason to reject the treaty.
However, as Lynn Sykes, a seismologist at the Lamont-Doherty Earth Observatory of Columbia University, said at the time, “Testing in a cavity is portrayed as easy, when in fact it is exceedingly difficult.” To date, no country is known to have fully decoupled a nuclear explosion in an underground cavity.
The requirements for a country to cheat on the CTBT via decoupling are daunting: construct an elaborate cavity, which includes keeping digging equipment and displaced dirt hidden from satellites; execute a nuclear test that performs at the intended yield and doesn’t unintentionally go over (known as a “yield excursion”); and prevent any radioactive gases from venting into the atmosphere. Clearly these objectives would be virtually impossible to achieve for a country with limited nuclear testing experience (although a notable exception would be an aspiring nuclear power simply testing a design based on blueprints it obtained from a state already possessing nuclear weapons).
As a result of the technical demands inherent in evading detection, the National Academy of Sciences judged that under a fully functional International Monitoring System (IMS), “an underground nuclear explosion cannot be confidently hidden if its yield is larger than 1 or 2 [kilotons].” Dr. Ray Kidder, a physicist at the Lawrence Livermore National Laboratory in California and a former bomb designer, said in 1999 about an aspiring nuclear power such as Iran, “The chance of a beginner doing anything under a kiloton is zilch.”
Countries like China and Russia are more likely to possess the technical sophistication needed to successfully cheat on the CTBT but, as the JASON government advisory panel concluded in 1995, low yield nuclear tests by countries with extensive prior test experience would provide only minimal gains in new weapon design. These gains would likely be militarily insignificant and fail to alter the strategic balance vis-à-vis the United States. Of course, designing a new weapon typically cannot be accomplished with a single test and every additional test substantially increases the odds of detection (Israel’s nuclear program might be an exception. We just know so little about it).
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