The Nuclear Industry Association (NIA) said the UK does not currently have the capacity to build parts such as reactor pressure vessels.

BBC: Sizewell C proposal

The next heaviest element in the periodic table, the inert gas helium, is used for detecting cracks in pressure vessels and the like.

ECONOMIST: Tech.view: Hydrogen tries again | The

Another is to use high-tech pressure vessels made of carbon-fibre.

ECONOMIST: Tech.view

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