‘Worst Case’ Nuclear Disaster Hangs on Unlikely Events

For Tokyo Electric Power Co.’s stricken nuclear reactors to release catastrophic amounts of radioactive material into the atmosphere, a rare chain of events needs to happen.

Averting a full-scale meltdown depends on cooling the fuel rods at Fukushima Dai-Ichi’s Reactor No. 2, said S.K. Malhotra, a scientist at India’s Department of Atomic Energy in Mumbai. A worst-case outcome, which scientists say isn’t likely, may occur if overheating in the reactor culminates in the rupture of the steel lining protecting radioactive material.