I made multiple reactors and cant get them to work, in creative and survival.
Both reactors had: 1 controller, 2 access ports, and a power tap. And the multi-block structures are completed. It takes the fuel, and fills up the Core Fuel Status to 100%, and when I turn on the reactor, nothing happens.
My reactor in survival.

This is the controller image:

It is passively cooled by Blazing Pyrotheum.

Its the newest version of FTB Infinity, so it is also the newest version of Big Reactors.

Ive also tried relogging.

Please show a screenshot of the top of your reactor.

Inserting the control rods at 100% basically switches the reactor off (it is on but doesn't use yellorium and doesn't produce energy). You have to use a value lower than 100% (the lower the insertion the higher the output).

Here you go, XFactHD:

Each of the fuel rods are at 100% inserted.

And the Blazing Pyrotheum has a bad habit of setting blocks on fire. So in creative I tried a 3x3x3 reactor without a coolant, in case that was the issue. and it still didnt fix it.

Blazing pyrotheum is a valid coolant?

Yea, and Blood, from Tinkers' is better according to the Wiki. I know, weird. Lol

Wow. Thanks. That worked. (What % insertion do you find is a decent medium for fuel used/RF produced)

This depends on the reactor size. There is a BR Reactor Simulator which, IIRC, can simulate this.