Simple Mekanism Fission Reactor + Industrial Turbine
The designs in this tutorial are taken straight from the Wiki as a "minimally viable stable" Reactor+Turbine setup. You can, of course, make something bigger than this but the core mechanics will be the same. Scroll to the bottom of the album if you're interested in a sample Fissile Fuel generation setup.
Start with the Fission Reactor. The smallest Fission Reactor you can make is 3x4x3. Start with a 3x3 base layer of Fission Reactor Casing.
On the next layer, continue building up the outer walls with Fission Reactor Casing. Optionally, use Reactor Glass on these walls for decoration. Note: The outside edges of your Fission Reactor can *only* be Casings. The edges cannot be glass.
In the center, place a Fission Fuel Assembly in the middle.
On the next layer, continue building up the outer wall.
In the center, place a Control Rod Assembly in the middle.
On the final layer, place Fission Reactor Casings on the outer edges. The center block can either be a Casing or Glass - it doesn't matter.
That's it, for now. The Fission Reactor multiblock should form. You will see redstone particles if the multiblock formed correctly. Right clicking anywhere on the multiblock will open the GUI.
We will return to this to place our ports for getting resources in and out of the reactor.
For the Industrial Turbine, we will build a small one that can match the output of our small Fission Reactor.
Start with a 5x5 base of Turbine Casings.
Begin building up the outer wall. The edges must be Turbine Casings, but the faces may be Casings or Structural Glass.
In the center, place a Turbine Rotor. Right click the Turbine Rotor twice while holding Turbine Blades to place two blades on this section of Turbine Rotor.
Continue building up the outer wall and the Turbine Rotor and Blades. This step is exactly the same as the previous step.
Continue building up the outer wall and the Turbine Rotor and Blades. This step is exactly the same as the previous step, again, again, and again. This is the final height of your Turbine Rotor. You should have a 5-block tall Turbine Rotor with 10 Turbine Blades on it in total.
Place a Rotational Complex on top of the Rotor.
Continue building up the exterior wall. Place a ring of Pressure Dispersers around the Rotation Complex. This layer must always be filled completely with Pressure Dispersers surrounding the Rotation Complex, no matter how big your Turbine is.