The probability is hard to calculate primarily because of the possibility of what are called common-cause accidents, where the loss of off-site power and of on-site power are caused by the same thing.

这个几率很难去计算的原因主要是因为发生所谓共发生事故的可能性，也就是说造成站外及站内电源掉线的是同一个原因。

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The probability is hard to calculate primarily because of the possibility of what are called common-cause accidents, where the loss of off-site power and of on-site power are caused by the same thing.

发生此类事故的概率很难估计，因为发生由于同种因素导致核电站内外同时断电的概率难以计算。

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Tepco said the reactors shut due to the loss of offsite power due to the malfunction of one of two off-site power systems.

电力公司说，由于外部电源厂系统故障，由于外部电源供应问题导致了反应堆停运。

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