From BBC News:
GMT1320: Noriyuki Shikata, from Japanese PM's office tweets: "TEPCO's [Tokyo Electric Power Company] efforts to depressurize the container was successful. Additional measures are now taken tonight using sea water and boric acid. "
Officials say reactor 3 lost its emergency cooling system. A similar problem led to a blast at reactor 1 at the plant on Saturday.
And government spokesman Yukio Edano acknowledged it was possible that a meltdown had occurred at reactor 3.