The layer of molten steel at the top of the oxide may create a zone of increased heat transfer to the reactor wall; this condition, known as "heat knife", increases the probability of formation of a localized weakening of the side of the reactor vessel and subsequent corium leak.In the case of high pressure inside the reactor vessel, breaching of its bottom may result in high-pressure blowout of the corium mass. It was both physically hot and nuclear-hot, radioactive to the point that approaching it for more than a few seconds constituted a death sentence. Flooding of the corium mass with water, or the drop of molten corium mass into a water pool, may result in a temperature spike and production of large amounts of hydrogen, which can result in a pressure spike in the containment vessel. The layer of solidified corium ranged in thickness from 5 to 45 cm. The most dangerous radioactive waste in the world is likely the "Elephant's Foot," the name given to the solid flow from the nuclear meltdown at the At the 10-year point, radiation from the corium was down to 1/10th its initial value, but the mass remained physically hot enough and emitted enough In the first phase, only the melt itself is ejected; later a depression may form in the center of the hole and gas is discharged together with the melt with a rapid decrease of pressure inside the reactor vessel; the high temperature of the melt also causes rapid erosion and enlargement of the vessel breach. If the hole is in the center of the bottom, nearly all corium can be ejected. Eight days after the meltdown the melt penetrated the lower Three different lavas are present in the basement of the reactor building: black, brown and a The coriums consist of a highly heterogeneous silicate glass matrix with inclusions. The elemental constitution was about 70 wt.% Some samples contained a small amount of metallic melt (less than 0.5%), composed of silver and The bulk density of the samples varied between 7.45 and 9.4 g/cmThe largest known amounts of corium were formed during the The Chernobyl corium is composed of the reactor uranium dioxide fuel, its zircaloy cladding, molten concrete, and decomposed and molten The molten corium settled in the bottom of the reactor shaft, forming a layer of graphite debris on its top. Free and chemically bound water is released from the concrete as steam. There are differences between During a meltdown, the temperature of the fuel rods increases and they can deform, in the case of zircaloy cladding, above 700–900 °C (1,292–1,652 °F). A second explosion threw part of the radioactive core into the air, showering the area with radiation and starting fires. The samples were generally dull grey, with some yellow areas. What researchers discovered was that the Elephant's Foot was not, as some had expected, the remnants of the nuclear fuel. Five types of material can be identified in Chernobyl corium:The molten reactor core accumulated in room 305/2, until it reached the edges of the steam relief valves; then it migrated downward to the Steam Distribution Corridor. These may be gas phase, such as molecular The composition of corium depends on the design type of the reactor, and specifically on the materials used in the control rods, coolant and reactor vessel structural materials. The core temperature of the reactor rose, causing an even greater power surge, and the control rods that might otherwise have managed the reaction were inserted too late to help. Should it manage to find water, another explosion could result. If you were to look at the corium, you'd see black and brown ceramic, slag, pumice, and metal. The Brief re-criticality (resumption of neutron-induced fission) in parts of the corium is a theoretical but remote possibility with commercial reactor fuel, due to low enrichment and the loss of moderator. The corium melt then accumulate at the bottom of the If the vessel is sufficiently cooled, a crust between the corium melt and the reactor wall can form. The corium of the Elephant's Foot was considerably lower 10 years after the accident but still insanely dangerous. Scientists put a camera on a wheel and pushed it out to photograph and study the mass. As molten sludge oozed through the remaining pipes and melted concrete, it eventually hardened into a mass resembling the foot of an elephant or, to some viewers, Medusa, the monstrous Gorgon from Greek mythology. Scientists analyzed the composition of corium to determine how it formed and the true danger it represents. High-pressure conditions push the cladding onto the fuel pellets, promoting formation of The temperature of corium can be as high as 2,400 °C (4,350 °F) in the first hours after the meltdown, potentially reaching over 2,800 °C (5,070 °F). A large amount of heat can be released by reaction of metals (particularly zirconium) in corium with water. Instead, it was a mass of melted concrete, core shielding, and sand, all mixed together. The fast erosion phase of the concrete basemat lasts for about an hour and progresses to about one meter in depth, then slows to several centimeters per hour, and stops completely when the melt cools below the decomposition temperature of concrete (about 1,100 °C [2,010 °F]). 4 of the Chernobyl Nuclear Power Plant, under reactor room 217. About 41,900 pounds (19,000 kg) of material melted and relocated in about 2 minutes, approximately 224 minutes after the reactor scram.

The mass was found to be homogeneous, primarily composed of molten fuel and cladding. A hole in the side of the vessel may lead to only partial ejection of corium, with a retained portion left inside the reactor vessel.After breaching the reactor vessel, the conditions in the reactor cavity below the core govern the subsequent production of gases. With no means to cool the reaction, the temperature ran out of control. A pool of corium formed at the bottom of the reactor vessel, but the reactor vessel was not breached. Even if no explosion occurred, the reaction would contaminate the water. Two masses of corium were found, one within the fuel assembly, one on the lower head of the reactor vessel.