Elephant's Foot (Chernobyl)

Artur Korneyev's photo of the Elephant's Foot, 1996

The Elephant's Foot is the nickname given to the large mass of corium, composed of materials formed from molten concrete, sand, steel, uranium, and zirconium. The mass formed beneath Reactor 4 of the Chernobyl Nuclear Power Plant, near Pripyat, Ukraine, during the Chernobyl disaster of 26 April 1986, and is noted for its extreme radioactivity. It is named for its wrinkled appearance and large size, evocative of the foot of an elephant.

Discovered in December 1986, the “foot” is located in a maintenance corridor below the remains of Reactor No. 4, though the often-photographed formation is only a small portion of several larger corium masses. It has a popular reputation as one of the most radioactive objects in history, though the danger has decreased over time due to the decay of its radioactive components.^[1]^[2]

Origin

The Elephant's Foot is a mass of black corium with many layers, resembling tree bark and glass. It was formed during the Chernobyl disaster of April 1986 from a lava-like mixture of molten core material that had escaped the reactor enclosure, materials from the reactor itself, and structural components of the plant such as concrete and metal.^[3] The Foot was discovered in December 1986 in Room 217/2, 15 meters to the southeast of the ruined reactor and 6 meters above ground level.^[4]^[5] The material making up the Elephant's Foot had burned through at least 2m of reinforced concrete, then flowed through pipes and fissures and down a hallway to reach its current location.^[5]

Composition

The Elephant's Foot is a black ceramic composed primarily of silicon dioxide, with smaller amounts of other oxides, primarily uranium, calcium, iron, zirconium, aluminum, magnesium, and potassium.^[1]^[2]^[6]^[7] Over time, zircon crystals have started to form slowly within the mass as it cools, and crystalline uranium dioxide dendrites are growing quickly and breaking down repeatedly.^[3] Despite the distribution of uranium-bearing particles not being uniform, the radioactivity of the mass is evenly distributed.^[3] The mass was quite dense and unyielding to efforts to collect samples for analysis via a drill mounted on a remote-controlled trolley, and armor-piercing rounds fired from an AK-47 assault rifle were necessary to break off usable chunks.^[5]^[1]^[2] By June 1998, the outer layers had started turning to dust and the mass had started to crack, as the radioactive components were starting to disintegrate to a point where the structural integrity of the glass was failing.^[3] In 2021, the mass was described as having a consistency similar to sand.^[8]

Radioactivity

At the time of its discovery, about eight months after formation, radioactivity near the Elephant's Foot was approximately 8,000 to 10,000^[9] roentgens, or 80 to 100 grays per hour,^[2] delivering a 50/50 lethal dose of radiation (4.5 grays)^[10] within 3 minutes.^[2]^[11] Since that time, the radiation intensity has declined significantly, and in 1996, the Elephant's Foot was briefly visited by the deputy director of the New Safe Confinement Project, Artur Korneyev,^[a] who took photographs using an automatic camera and a flashlight to illuminate the otherwise dark room.^[13]

The Elephant's Foot is roughly 10% uranium by mass, which is an alpha emitter.^[3] While alpha radiation is ordinarily unable to penetrate the skin, it is the most damaging form of radiation when radioactive particles are inhaled or ingested, which has renewed concerns as samples of material from the meltdown (including the Elephant's Foot) turn to dust.^[8] Nevertheless, the corium still poses an external gamma radiation hazard due to the presence of fission products, mainly caesium-137.

Notes

^ Korneyev was interviewed by The New York Times reporter Henry Fountain in 2014 in Slavutich, Ukraine, before his retirement.^[12]

References

^ ^a ^b ^c Higginbotham, Adam (2019). Midnight in Chernobyl: The Untold Story of the World's Greatest Nuclear Disaster. Random House. p. 340. ISBN 9781473540828. The substance proved too hard for a drill mounted on a motorized trolley, ... Finally, a police marksman arrived and shot a fragment of the surface away with a rifle. The sample revealed that the Elephant's Foot was a solidified mass of silicon dioxide, titanium, zirconium, magnesium, and uranium ...
^ ^a ^b ^c ^d ^e United States Foreign Broadcast Information Service, ed. (1989). Daily Report: Soviet Union. The Service. p. 133. The radiation level near it was approximately 8,000 roentgens per hour in 1986. Even five minutes spent near the 'foot' would have killed a man ... the substance failed to yield to a drill mounted on a special remote-controlled truck ... A skilled marksman ... fired armor-piercing bullets into it ... Analysis of the fragments obtained in this way showed that they consisted of 70–90% silicon dioxide (fused sand), 2–10% fuel particles, and, in addition, contained graphite (hence the black color), metal alloys, and so on ...
^ ^a ^b ^c ^d ^e Vlasova, Irina; Shiryaev, Andrey; Ogorodnikov, Boris; Burakov, Boris; Dolgopolova, Ekaterina; Senin, Roman; Averin, Alexey; Zubavichus, Yan; Kalmykov, Stepan (2015). "Radioactivity distribution in fuel-containing materials (Chernobyl "lava") and aerosols from the Chernobyl "Shelter"". Radiation Measurements. 83: 20–25. Bibcode:2015RadM...83...20V. doi:10.1016/j.radmeas.2015.06.005. ISSN 1350-4487.
^ Hill, Kyle (4 December 2013). "Chernobyl's Hot Mess, 'the Elephant's Foot', Is Still Lethal". Nautilus. ISSN 2372-1766.
^ ^a ^b ^c R. F. Mould (2000). Chernobyl Record: The Definitive History of the Chernobyl Catastrophe. CRC Press. p. 130. ISBN 9781420034622.
^ Jaromir Kolejka, ed. (2002). Role of GIS in Lifting the Cloud Off Chernobyl. NATO Science: Earth and environmental sciences. Vol. 10 (illustrated ed.). Springer Science & Business Media. p. 72. ISBN 9781402007682.
^ Ann Larabee (2000). Decade of Disaster (illustrated ed.). University of Illinois Press. p. 50. ISBN 9780252068201.
^ ^a ^b Stone, Richard (5 May 2021). "'It's like the embers in a barbecue pit.' Nuclear reactions are smoldering again at Chernobyl". Science. Archived from the original on 2021-05-12. Retrieved 12 May 2021.
^ "The Elephant's Foot of the Chernobyl disaster, 1986 - Rare Historical Photos". Rare Historical Photos. 2014-07-02. Retrieved 2022-04-29.
^ "Lethal Dose (LD)". US Nuclear Regulatory Commission. 21 March 2019. Retrieved 21 March 2019.
^ Hill, Kyle (2013-12-04). "Chernobyl's Hot Mess, "the Elephant's Foot," Is Still Lethal". Nautilus. Retrieved 2024-05-11.
^ Fountain, Henry (27 April 2014). "Chernobyl: Capping a Catastrophe". The New York Times. Retrieved 12 January 2024.
^ Goldenberg, Daniel (24 January 2016). "The Famous Photo of Chernobyl's Most Dangerous Radioactive Material Was a Selfie". Atlas Obscura. Retrieved 21 March 2019.