The elephant's foot is a solidified pool of molten radioactive material which resulted from the April 26, 1986 Chernobyl meltdown. When the reactor ran out of control, the nuclear fuel got so hot it literally melted right through the floor of the core, down through several more floors, and collected in various glassy, black ponds underneath the reactor.
The elephant's foot was the first of these solidified pools to be discovered, so named because of its odd shape and wrinkled appearance. It is so radioactive that even with full radiation suits, researchers absorb up to 30 rads per quick visit. Even through the radiation danger, it is vitally important that the study of the Chernobyl facility continue, however. The structure is no longer stable and must be reinforced. Further collapse could spread radioactive dust for miles. Cleanup must continue.
Studying the elephant's foot itself is no easy task. It is very hot (due to the continuing radioactive decay) and incredibly hard. It is also so radioactive that a visit of more than a few seconds would be insane. Still, a sample had to be taken for study to determine the nuclear fuel content. Is it a danger of creating a second catastrophe?
A drilling machine could not penetrate the surface. Blows from an axe glanced off it without a scratch. Ultimately a Kalashnikov rifle was needed to chip a shard off the elephant's foot for collection. Analysis provided the first good news since the meltdown occurred: The "Chernobyl lava", as it was called, consisted mainly of uranium and zirconium from the fuel rods, and silicon from the sand packed around the reactor. It also contained some plutonium, cesium, and other radioactive elements resulting from radioactive decay. But the uranium was too dilute to allow a new nuclear chain reaction.
The elephant's foot itself contained only a small fraction of the reactor's 180 tons of nuclear fuel. The rest of it collected in similar pools discovered elsewhere under the reactor or had been blown out in the explosion. Research, unfortunately, has been cut back in recent years because of safety concerns. Chernobyl is just too radioactive to work around for very long, and the death rate is too high.
Repairs, cleanup, and reinforcement of the structure must continue, however, because the structure is on the verge of collapse. Some beams have been left supporting five times their rated load and can't keep that up forever. Radioactive dust must be sprayed down with glue to keep it from spreading. A new containment wall must be poured because the old one, hastily built, is cracked and chipped. Robots may be the future workers and researches of Chernobyl, if even they can survive the deadly conditions.
Sources:
http://www.antenna.nl/wise/430/4240.html
http://grok.ecn.uiowa.edu/Main/PR/Chernobyl/3_23_98BW.html
http://www.usnews.com/usnews/doubleissue/heroes/borovoi.htm