In particular, they don't have the passive safety systems that might have helped prevent the Fukushima accident in Japan.

WSJ: China's Nuclear Fears Could Be U.S. Companies' Gain

The model Southern is building, the AP1000, is totally new, with safety systems powered by gravity instead of electricity, a so-called passive design.

FORBES: Magazine Article

The passive feature means they rely less on electrically driven pumps and valves, for safety, and more on systems designed to shut down plants safely in emergencies and to prevent operator error.

WSJ: Nuclear Industry Likely to Reassess Safety Systems