Hydrogen leakage, which is frequent and with high-risk, severely threatens the operation of hydrogen cooling generator.

漏氢是氢冷发电机运行中发生频率较高且危害性很大的事件，严重影响了机组的安全运行。

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That was to prevent a repeat of the hydrogen explosions that blew radiation out of the plant soon after cooling systems failed in the wake of the tsunami.

海啸发生之后冷却系统失效导致了氢气爆炸，这把放射物吹出了核电站，注入氮气的行为就是为了防止这一悲剧再次发生。

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Hydrogen collected in the secondary containment buildings, where it exploded, blowing the tops off units 1 and 3, and damaging the cooling system of unit 2.

氢气在第二层安全壳内聚集，最终爆炸，将1号和3号的顶盖炸飞，损毁了2号的冷却系统。

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Hydrogen is building up because, due to low levels of cooling water, fuel rods are partially exposed, causing them to overheat.

BBC: Japan quake: Nitrogen pumped into nuclear reactor

That was to prevent a repeat of the hydrogen explosions that blew radiation out of the plant soon after cooling systems failed in the wake of the tsunami.

ECONOMIST: A spreading cloud of economic and human costs

Cooling problems have resulted in damage to radioactive fuel rods, hydrogen gas explosions, fires and radiation releases.

WSJ: GE Steps Up Aid in Reactor Crisis