A March 12 explosion at the earthquake-damaged Fukushima Daiichi nuclear power plant in Okuma, Japan, appears to have caused a reactor meltdown.

The key piece of technology in a nuclear reactor is the control rods. Nuclear fuel generates neutrons; controlling the flow and production rate of these neutrons is what generates heat, and from the heat, electricity. Control rods absorb neutrons — the rods slide in and out of the fuel mass to regulate neutron emission, and with it, heat and electricity generation.