North Korea Underground Nuclear Test - The Mechanism of Underground Nuclear Tests

"North Korea carried out its second nuclear test on Monday. The North Korean government said it was part of the country's programme to improve its defence capability."

"Monday's blast was 20 times more powerful than the first nuclear test in 2006, underscoring advances in North Korea's nuclear programme."

"Three hours after the blast, North Korea test fired two short-range missiles.
US President Barack Obama said Pyongyang's action was a reckless challenge warranting action from the international community."

Countries uses Underground Nuclear testing to test whether their nuclear bom succes or not. Also use to measure the explosion yield.



Mechanism of Underground Nuclear Explosion



Basically dig a hole very deep ground , no water bed , and must be ontop of rocks layer underground..Once underground hole is dug , a lif tunnel is used to access the hole , and later nuclear device will be sent down using this lif.

Usually hole in more than 1 km before ground.

The detonation of an underground nuclear explosion generates quasi-instantaneously an amount of energy, e, which is then converted into other forms of energy through a series of processes.

First few microseconds during undergrd nuclear explosion , nuclear device and surrounding rock . water and whatever will vaporise.

Next few seconds , cavity of the underground expand , because of the formed gas of very high temperature , producing also shock wave going vertically , causing chimney to be produced and top soil collapse downward especially after another few seconds , when gas starts to cool down.

The cavity of the molten rocks start to cool down and seal the cavity helping to contain the radioactivity of the device. The initial hot gas is so hot , a chamber of glass can be formed or crystals.




Top soil explosion , from underground explosion..Few seconds later , crater will be form.





NEVADA TEST SITE pix above.
Underground Nuclear Test

The HURON KING underground nuclear test was a DOD sponsored event on 24 June 1980. The test involved a device with a yield of less than 20 kilotons, and tested the effects of system generated electromagnetic pulse [SGEMP] on a full-scale operating DSCS-3 military communications satellite. The spacecraft was contained in a large above-ground tank

""** Detailed Explanation Below **""
The Mechanics and Effects of Underground Nuclear Explosions

The detonation of an underground nuclear explosion generates quasi-instantaneously an amount of energy, e, which is then converted into other forms of energy through a series of processes.

Firstly, a few microseconds after the explosion, the device and some surrounding rock and water are vaporised. A fraction of the initial energy released by the explosion is expended in this process. Secondly, a few tens of microseconds after the explosion, the cavity expands to a final radius of rc under the influence of the internal energy of the gas in the cavity which is at extremely high temperature and pressure. The gas expands doing work on the surrounding rock generating a shock wave. Part of the energy of the gas is also dissipated in melting some of the rock surrounding the cavity. The volume of the final cavity is proportional to the energy yield, e, so that the final cavity radius may be expressed as

rc = r'c e1/3 (1)

For the test conditions at the CEP, r'c ~ 10 -12 m/kt1/3 so that a 1 kt explosion produces a cavity of radius 10-12 m, depending on the depth of burial. A deep 150 kt explosion would produce a cavity with a radius of approximately 55 m.

With increasing distance from point zero, the shock wave becomes weaker and transforms initially into a plastic wave producing crushing and shear damage of the rock, and then into an elastic wave at a distance from point zero of

rd = r'de1/3 (2)

Thus, at least 90% of the energy liberated by the explosion is dissipated within an approximately spherical volume of rock of radius rd. Depending on the magnitude of the in situ stress field (the IGC has concluded that the horizontal in situ stresses at Mururoa and Fangataufa are quite low), some discrete tensile cracking may develop beyond radius rd. Figure 3 illustrates the damage zones produced by a 1 kt explosion. The elastic or seismic wave produced by the explosion may propagate over huge distances and be detected by seismic monitoring systems in other parts of the world. It can also produce shock loadings on structures and slopes within a few km of the source.

As the gas inside the cavity cools with time and there is some seepage of the gas into the surrounding rock, the pressure inside the cavity falls to well below the original lithostatic pressure. At the same time, the molten rock around the cavity periphery begins to solidify and accumulate at the bottom of the cavity. Under these conditions, and especially when the horizontal in situ stresses are low, the crushed and sheared rock above the cavity will collapse progressively. Over a period of a few minutes to a few hours after the explosion, the caved zone or chimney will propagate upwards until it stabilises naturally. As the blocky rubble accumulates in the cavity and then in the chimney void, it will bulk and occupy a greater volume (say 20-30% more) than it did in situ. This factor will cause the eventual arrest of the upward propagation of the chimney. Post-test drilling carried out by DIRCEN/CEA (Bouchez and Lecomte 1996) and the IGC's calculations indicate that the chimney height can be in the range 4 -10 rc , with values near the lower end of this range (5 - 6 rc ) being most likely.

The IGC has estimated that in test area 4 of Mururoa where the total yield was 750 kt (see Figure 1), the total cavity volume created was about 5,000,000 m3, the total chimney volume about 40,000,000 m3, the total damaged volume about 0.68 km3, and the inelastically strained volume about 2.3 km3. The total volume of the layer in which the testing in this area took place is approximately 5 km3. "" source wikipedia

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