think you only have to know one in depth (which basicly i think everyone does thermal)
just refer to your book or notes for a better expansion of the answer.
just remember what:
control rods do and what material they could be made out of
what are fuel rods (possibly how much uranium - plutonium - is needed)
moderator (water, D20, air)
coolant (air, water)
How does it produce power (heats up the water and the water turns into steam and turns the turbines)
what kind of shilding is needed (sufficient enough to reflect heat - thermal shielding, to stop gamma rays and beta particles... not really that important to stop any alphas)