一号、二号和三号反应堆中的核燃料棒因冷却系统失灵而熔毁，导致其围护结构遭受破坏。

The nuclear fuel rods in reactors one, two and three melted down due to a failure of the cooling systems, causing damage to their containment structures.

youdao

海啸过后，四号反应堆曾发生过爆炸，但目前认为其危险程度还没到一号、二号和三号反应堆那种程度，那三个反应堆曾发生核反应堆堆芯熔毁事件。

There was an explosion at reactor number four after the tsunami, but it is not considered as dangerous as reactors one, two and three which experienced a nuclear meltdown

youdao

海啸过后，四号反应堆曾发生过爆炸，但目前认为其危险程度还没到一号、二号和三号反应堆那种程度，那三个反应堆曾发生核反应堆堆芯熔毁事件。

There was an explosion at reactor number four after the tsunami, but it is not considered as dangerous as reactors one, two and three which experienced a nuclear meltdown.

youdao