At 6:14 a.m. on 15 March, the pressure-suppression pool beneath the containment vessel of unit 2 was rocked by a blast.

3月15日6点14分，2号反应堆的安全壳下的抑压池发生爆炸。

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The telltale sign of trouble at reactor No. 2, Tokyo Electric Power Co. officials said, was that pressure had dropped in the "suppression pool" the part of the reactor that converts steam to water at the bottom of the container.

WSJ: Japan's Nuclear Crisis Escalates