N. Korea calls nuclear test a success

AP via Yahoo! ^ | October 11, 2006 | HANS GREIMEL

[GOP_1900AD]

What is the Worst Case for Cavity Decoupling?
AU: * Leith, W
EM: wleith@usgs.gov
AF: U.S. Geological Survey, 951 National Center, Reston, VA 20192 United States
AB: A central issue for nuclear monitoring is the possibility that a nuclear test could be conducted while evading identification by international and national monitoring systems. Of several proposed evasion scenarios, decoupling an explosion in a large, deep, underground cavity has received considerable attention. While improvements in monitoring networks and technologies have decreased the event detection threshold in many regions, achievements in underground construction have also increased the feasibility of constructing large caverns that could conceivably be used for nuclear explosion decoupling. The yield range of greatest uncertainty lies between 1 and 10 kt, where underground explosions could be decoupled in salt and perhaps in hard rock. Assuming that full decoupling can be achieved in elongated cavities of moderate aspect ratio (up to 10:1), I have reviewed the literature on large-cavern construction in hard rock and salt (including cost), and the containment of nuclear explosions in these media, with the goal of defining the worst case for cavity decoupling. In thick salt deposits and domes, it is feasible to construct stable cavities of sufficient volume for full decoupling of nuclear tests larger than 10 kt. Salt probably provides an ideal environment for both cavity construction and containment, and it is possible that the cavity would not leak radioactivity for years. However, at 10 kt, the resulting seismic event would be detected and probably identified by regional monitoring networks. Suitable salt deposits are relatively rare and are not present in many countries of nuclear proliferation concern. Salt regions can usually be identified in the literature and by remote sensing, and could conceivably be monitored. In hard rock, construction of cavities of sufficient volume for full decoupling is limited to at most about 10 kt, mainly because of the difficulty in constructing a cavern of sufficient size at depths required for containment, and the possibility of detection. Avoiding identification of a decoupled test in the 1-10 kt range would require: careful site selection; plausible denial (e.g., a mining activity), adequate depth, high-quality rock with low gas content; concealment of the mining operation from public knowledge and remote monitoring systems; attention to containment issues (geologic faults and engineered openings to the cavity); and favorable weather conditions, given the likelihood that radioactivity from the test would eventually seep. As the decoupled yield approaches 10 kt, more elongate cavities (up to 10:1) are required in hard rock. Because suitable thick salt deposits are present in many naturally-seismic regions of proliferation concern, these areas will require special attention to ensure adequate monitoring. For yields less than ~1 kt, construction of the required cavity is not limited by the available mining technology, based on many examples of construction at depth, worldwide. With attention to selection of geologic environment, adequate depth, and stemming of the tunnel complex, the evader could be confident that the test would not promptly vent, limiting detectability by the radionuclide monitoring network. The decoupled test would not be seismically identified for broad areas of most countries. Important technical issues for decoupling in hard rock could be addressed by field experiments using conventional explosives. It is significant that evading identification of a cavity-decoupled nuclear test is not limited so much by geology and engineering technology as it is by the capabilities of regional seismic and other monitoring systems. These findings are inconsistent with the recent joint SSA/AGU statement on the verification of the CTBT.
UR: http://geology.er.usgs.gov/eespteam/EESPT_PUB.html
DE: 1734 Seismology
DE: 7219 Nuclear explosion seismology
SC: S
MN: 2001 Spring Meeting

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