Nuclear crisis worsens,breach in reactor unit

The implications of overheating in the fuel rod pool at No. 4 seemed potentially dire.

Japans nuclear crisis intensified Wednesday after authorities announced that a second reactor unit at the stricken Fukushima Daiichi plant may have ruptured and appeared to be releasing radioactive steam.

The break,at the No. 3 reactor unit,worsened the already perilous conditions at the plant,a day after officials said the containment vessel in the No. 2 reactor had also cracked.

The possibility of high radiation levels above the plant prompted the Japanese military to put off a highly unusual plan to dump water from helicopters to lower temperatures in a pool containing spent fuel rods that was overheating dangerously at the No. 4 reactor.

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But in one of a series of rapid and confusing pronouncements,the authorities insisted that damage to the containment vessel at the No. 3 reactor the main focus of concern earlier on Wednesday was unlikely to be severe.

The revised official assessment notwithstanding,the implications of overheating in the fuel rod pool at No. 4 seemed potentially dire. In Washington,Energy Secretary Steven Chu told two House Committees Wednesday,We think there is a partial meltdown at the plant.HIROKO TABUCHI & KEITH BRADSHER