They did not understand what had happened immediately because the radioactive gas had no odour or colour.

BBC: Eyewitness: Tragedy of Soviet nuclear submarine K-27

The power plant has been shut down since this winter, when a small amount of radioactive gas escaped from a steam generator during a water leak.

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No new plants have been ordered there since the accident at Three Mile Island in Pennsylvania in 1979 (when radioactive gas escaped from a nuclear power plant), though some that were being built were completed.

ECONOMIST: Boom

Xenon-133 is a radioactive noble gas produced during nuclear fission that poses no concern at the detected level.

FORBES: EPA Sounds an 'All-Clear' (so far) for Western U.S.

Neutrinos react with chlorine in the fluid and change it to radioactive argon, a gas.

ECONOMIST: Particle physics

Cooling problems have resulted in damage to radioactive fuel rods, hydrogen gas explosions, fires and radiation releases.

WSJ: GE Steps Up Aid in Reactor Crisis

But the indictment makes no mention of a plot to detonate a radioactive "dirty bomb" or blow up apartment buildings with natural gas -- allegations made previously in public statements and court arguments by Justice Department officials.

CNN: Specter launches probe of handling of case