Atomic Science Fission Reactor is Disabled..?

[gidonyou]

As you are seeing on screen shot, it is not disabled, and it is default setting..

 

However, When I check creative or NEI, Fission Reactor is GONE, Not there.. Any solution to problem?

[jakalth]

fission reactor is now called "reactor cell".  Simple as that.  The reactor cell can be stacked to make a more powerful multiblock reactor.  Controlling the reactor though is still touch and go.