[godelski]

Because the more fusion plants you build the easier it becomes to steal the tech. So your options are

1) Get geopolitical dominance by showing you have it first (while still trying to prevent theft of IP)

2) Use it in quiet and in low usage to decrease vulnerability to state actors from stealing the tech.

One more important thing. Hiding it only hides it from other governments' populations, not the foreign governments. Because of this, most countries go for option #1.

[Kliment]

Option 3: Offer to license it to anyone who wants it, have orders in other countries finance your own buildout, while positioning yourself as the primary source of expertise on the technology. Establish lots of joint ventures and send lots of staff to work on the plants in other countries, further establishing interdependencies. Use this to apply soft power to the rest of the world while giving your population very cheap (subsidized by other countries) energy, and watch your economy grow. This is a strategy that is much more sensible for China than trying to keep it exclusive or hidden, assuming they have a working technology.

EDIT: If it needs further clarification, this is the French model of fission plant buildout.

[jonplackett]

This is the first answer that seems very plausible. Makes perfect sense as the best of both worlds. Political capital + actual capital.