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

Because this was a reactor that operated on water that was already at its boiling point, this also meant that the pressure inside the reactor was rising as well.

FORBES: Explainer: What Caused The Incident At Fukushima-Daiichi

Many outside analysts believe North Korea sees its nuclear threat as a negotiating tool to force the U.S. and other countries to provide it with money and security guarantees, and restarting its 1980s-era reactor would add further pressure to the North's foes.

WSJ: North Korea to Restart Yongbyon Nuclear Plant

In February 2009, pressure levels spiked inside Reactor 1, forcing the release of steam through an emergency valve.

WSJ: Japan Plant Had Troubled History

The telltale sign of trouble at reactor No. 2, Tokyo Electric Power Co. officials said, was that pressure had dropped in the "suppression pool" the part of the reactor that converts steam to water at the bottom of the container.

WSJ: Japan's Nuclear Crisis Escalates

In addition, the modular design could make it more difficult to inspect and maintain key components, many of which would be located within the pressure vessel at the heart of the reactor, he said.

CNN: U.S. backs project for small nuclear reactors

Eight of the more than 9, 700 tubes in one of the unit 3 generators failed a pressure test, while six tubes in unit 2's reactor needed to be plugged, the NRC has found.

CNN: SHARE THIS

The drywell is a large steel pressure vessel that looks like a giant upside-down pear and holds the reactor and primary pumps, and the wetwell is a large toroidal vessel that looks like a donut.

FORBES: Explainer: What Caused The Incident At Fukushima-Daiichi