Nuclear plant with three parts: a central steam generator, a water/steam exchanger, and extra steam turbines. All of these parts are rail-fed, with a 3-7-0 liquids train assumed to run between the parts. Here is the train schedule:
Central Plant Water Pickup
5 seconds of inactivity or Fluid: Water=175000
Central Plant Water Feeder
Fluid: Steam > 0 and 10 seconds passed and Fluid: Water = 0
Central Plant Steam Stop (controlled by circuits to turn on or off based on the amount of stored steam) You will need two of the "just turbines" blueprints hooked up for a full 2GW.
5 seconds passed or Empty cargo inventory