The Elephant's Foot

Lore & Background

The mass is a black, many-layered material that looked like tree bark and glass when it was first found. It is a ceramic made mainly of silicon dioxide, with smaller amounts of oxides of uranium, calcium, iron, zirconium and other elements.

After the explosion corium pooled in the room directly under the reactor. Part of it melted through 2 m of reinforced concrete, ran along corridor floors like lava and dropped through cable openings to the floor below, where it settled into several separate masses. The foot is the largest of the 3 masses in that room, and it is only a small part of the corium in the building.

In late June 1986 two dosimetrists climbing a staircase towards the corridor saw their instrument, which could read up to 3,000 roentgens per hour, go off the scale and break. They had found the first intensely radioactive gamma source inside Unit 4 without knowing what it was.

Reader's Guide

The formation has a popular reputation as the most radioactive object in history, which is false. Several masses of corium at the site are more radioactive, and a spent nuclear fuel rod can emit as much as 10 times its radiation. Decay has also greatly reduced the radiation it gives off.

Sampling proved difficult. The material was dense and resisted a drill mounted on a remote-controlled trolley, and armor-piercing rounds fired from a rifle were needed to break off usable pieces. The mass has been changing ever since: by June 1998 its outer layers were turning to dust and it had begun to crack, and in 2021 its consistency was described as similar to sand.

Did You Know?

• Zircon crystals have slowly started to form inside it as it cools.
• A widely seen photograph of it was taken in 1996.