Inside Nuclear Reactors

High-Energy Museum Piece
It was in 1942 that physics legend Enrico Fermi switched on the first functioning nuclear reactor, using an 8-ft.-long (2.4 m) cubic block made of 30 tons of graphite and 2.5 tons of uranium. In 1956, when this photo was taken, that same mass was installed in a subcritical reactor assembly at Argonne National Laboratory. Here, a courageous — or heedless — engineer measures the relatively low levels of radiation the block emits.

• Robots Survey Fukushima's Damaged Reactor Buildings