Underground nuclear shelters

03-11-2022 | Posted by Joaquín Martí

The world is scared at the prospect of Russia using nuclear weapons to try to reverse its current military fortunes in Ukraine and at the possible escalation thereafter. Whether this eventually occurs or not, let us hope it does not, it may be a good opportunity to talk about some of the effects of nuclear weapons and the attempts to shelter from them underground.

In a nuclear explosion, an enormous amount of energy is released in a very short time and in a very small space. As a result, there is a huge increase in temperatures and pressures, with the materials present becoming hot gases and expanding rapidly, which starts a shock wave in the surrounding medium, whether air, water, or the ground.

The magnitude of the effects depends, first of all, on the yield of the weapon, from a fraction to several tens of kilotons in the case of tactical weapons, to the much larger yields of the strategic weapons, typically in the hundreds of kilotons or the megaton range. For comparison, the bombs detonated at Hiroshima and Nagasaki in WWII had yields of about 15-20 kt.

A second consideration is the height of burst. Atmospheric explosions may take place at various heights, including the optimum one to maximise surface destruction, a function of the yield. Such explosions couple relatively little of their energy to the ground, only affected through the airblast.

But the explosion may also occur at the ground surface, or even at a small depth if delivered with an earth-penetrating weapon, as when intended against hardened underground facilities. Note that a weapon that detonates only a few metres inside the ground may cause the same ground shock as one with 20 times greater yield that detonates upon contact with the ground surface.

Ground shock considerations would of course be pointless if one happened to be in the crater zone. For a surface blast of 1 Mt, the resulting crater may be more than 30 m deep and extend some 150 m. Other things being equal, effects of this type tend to scale with the cube root of the yield.

Generally, a sufficient thickness of earth constitutes an excellent initial protection against the direct effects of a nuclear explosion, such as airblast, ground shock, light, heat, and radiation. But one cannot remain indefinitely isolated underground, and other aspects like access, power, supplies, communications, etc. also need to be provided over a longer term.

Principia has gathered considerable experience in evaluating the effects of terrorist and other explosions, including nuclear blasts, as well as in designing structures able to withstand them.

In today’s world this is a field that unfortunately cannot be disregarded, as there are scarce grounds to suspect that mankind is turning more peaceful. Nevertheless, we trust that the conclusions of our studies, however proud and satisfied we are with our work, will remain purely theoretical in the sense that their accuracy will not be verified experimentally.