3-11 Becomes Japan's 9-11

Japan Earthquake: Third Reactor at Fukushima Nuclear Plant Explodes

A new explosion at a Fukushima Daiichi nuclear plant reactor in Japan early Tuesday may have left the reactor leaking water, according to the company that runs the plant.

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Watch: Second Nuclear Explosion in Japan

A senior U.S. official said the blast -- the third in three days at the plant since a powerful earthquake struck Japan on Friday -- may be more dangerous than the others.
While the two previous explosions -- at Fukushima Daiichi reactors No. 1 and 3 -- were hydrogen blasts caused by a buildup of steam in the reactor units, the new blast at reactor No. 2 has officials unsure of the cause.