Why Depleted Uranium APFSDS Rounds Explode Inside a Tank

Depleted uranium (DU) armor-piercing fin-stabilized discarding sabot (APFSDS) rounds are designed to penetrate armored targets such as tanks. One of the characteristic behaviors of DU rounds is that they can create a fireball when they enter a tank. This raises the question: why do they only explode inside the tank and not outside it?

Why It Explodes Inside the Tank

Kinetic Energy and Penetration

- DU rounds are typically fired at extremely high velocities, often exceeding 1500 meters per second. Upon penetrating armor, the round generates a significant amount of kinetic energy. This kinetic energy can ignite explosive materials or ammunition stored within the tank, leading to an explosive fireball.

Chemical Reaction

- Depleted uranium is pyrophoric, meaning it can ignite spontaneously when it is finely divided or heated. Upon impact and penetration, the DU generates enough heat and friction to ignite, contributing to the fireball.

Ignition of Internal Materials

- Tanks are often equipped with various combustible materials, including fuel, ammunition, and other flammable substances. When the DU penetrator breaches the tank's armor, the combination of the penetrator's heat and the presence of these materials can lead to a catastrophic explosion.

Why It Doesn’t Explode Outside the Tank

Lack of Contained Environment

- Outside the tank, the DU round does not encounter the same conditions as it would after penetrating the armor. There are no flammable materials or confined space to create a significant explosion or fireball.

Armor Design

- Tank armor is specifically designed to absorb and dissipate the energy from incoming projectiles, reducing the likelihood of an external explosion. The armor's thickness and material properties help to mitigate the effects of the round upon impact.

Impact Mechanics

- The impact with the tank's armor can cause the DU round to deform or fragment. However, without the necessary conditions, such as confined space and combustible materials, it does not produce a fireball or explosion in the same way it might after penetrating the armor.

Summary

Summarizing, the combination of high kinetic energy, the pyrophoric nature of depleted uranium, and the presence of combustible materials inside the tank lead to the explosive effects observed after penetration. On the other hand, the external environment does not provide the conditions necessary to produce such an explosion or fireball.