Inner tank dome overlaps outer tank sidewall to prevent rainwater, snow and debris from entering into the containment basin.

内部罐顶与外部罐壁重叠，起到防雨、雪和泥土进入的作用。

youdao

That is a very different situation than at Fukushima Daiichi, where the fuel in three reactors is thought to have burned holes in their immediately surrounding pressure vessels, and in one case to have fallen all the way through to the bottom of the outer containment vessel.

WSJ: Japan to Take 40 Years to Dismantle Fukushima Nuclear Plant