SOMA, Japan — A third explosion in four days rocked the earthquake-damaged Fukushima Dai-ichi nuclear plant(工厂) in northeast Japan early Tuesday, the country's nuclear safety agency(部门) said.
Two sources told NBC News' Robert Bazell that the latest blast(爆炸) breached(破坏) the containment structure and that radiation(辐射) has leaked out.
Chief government spokesman Yukio Edano told news agencies that the suppression(抑制) pool appeared to be damaged. He said, however, that measuring devices in the area did not indicate(表明) an increase in radiation as a result of the damage.
The suppression pool is used to turn steam(蒸汽) back into water to cool the reactor(反应堆) and also plays a role in removing radioactive particles(放射性微粒) from the steam.
If confirmed, it would be the first direct damage to a reactor at the Fukushima Dai-ichi complex since the massive earthquake and tsunami(海啸) on Friday.
The blast at Dai-ichi Unit 2 followed two hydrogen(氢气) explosions at the plant — the latest on Monday — as authorities struggled to prevent the catastrophic(惨重的，灾难性的) release of radiation in the area devastated by a tsunami.
The troubles at the Dai-ichi complex began when Friday's massive quake and tsunami in Japan's northeast knocked out power, crippling(削弱，使瘫痪) cooling systems needed to keep nuclear fuel from melting down(熔化).
The latest explosion was heard at 6:10 a.m. local time on Tuesday, a spokesman for the Nuclear Safety Agency said at a news conference. The plant's owner, Tokyo Electric Power Co., said the explosion occurred near the suppression pool in the reactor's containment vessel. The pool was later found to have a defect.
Radiation levels in the air surrounding the plant have risen four-fold(四倍的) after a fresh explosion at the site on Tuesday, the plant operator said.
The radiation reading at 08:31am local time (2331 GMT) climbed to 8,217 microsieverts an hour from 1,941 about 40 minutes earlier, Tokyo Electric Power Co said.
The company said some employees of the power plant were temporarily evacuated(撤离的) following Tuesday morning's blast.