Going Nuclear: startup, operation and shutdown
Handbook · Steam loop · Next: Reactor physics
These steps explain a first BWR in REALISTIC mode, with a separate SIMPLE-mode section below. The RBMK has additional rules. There is no universal starting rod percentage: geometry, fuel and operating history change the position needed for criticality.
Control Desk and Controller
The Reactor Control Desk operates the nearest reactor; the bundled interface specifies a reactor within 32 blocks. With several plants, check which one the desk has selected. The Physics Desk provides measurements and calculations.
| Control | Purpose |
|---|---|
| START | Enable operation; does not replace a calculated rod setting |
| STOP / SCRAM | Stop operation / trigger emergency shutdown |
| Rods | Set desired insertion |
| PUMP | Control the reactor's internal pump function |
| VALVE | Hold the pressure-relief valve open |
| Two Link slots | Set a Redstone Link item-pair frequency for remote SCRAM |
100% insertion means fully inserted. Lower percentages withdraw rods and increase reactivity. Rods move at a finite speed, so demand and actual position may differ temporarily.
The Create value box on the Controller also sets 0–100%. Scroll it or hold right-click to open its input. A normal right-click requests a structural scan; it no longer applies an automatic 25-percentage-point rod change.
Before first startup
- Scan and resolve every structure error.
- Fully insert rods. Check for an unintended remote SCRAM signal.
- Start water supply and verify actual filling of the vessel.
- Check the internal pump and external Create pumps separately.
- Verify the correct fuel reaches the Fuel nozzle.
- Keep the waste line clear to a water-filled Spent Fuel Pool.
- Check steam pipes, turbines, condensate outlets and available stress capacity.
- Prepare the Relief nozzle, shielding, an exit route and remote SCRAM.
- Calculate rod demand and cooling requirements at the Physics Desk.
An assembled structure or a full fuel tank is only one part of this checklist.
Start slowly in REALISTIC mode
Open Physics Desk → Calculate → Rods in at and test a planned position. Watch for PROMPT CRITICAL or expected-trip warnings. Under Power at, calculate the steam and water requirements. These results describe the current core, not a universal starting number.
Enable START and withdraw rods in small steps. After each step, wait for actual rod travel and the resulting power trend. Monitor power, period or SUR, temperature, pressure, water inventory and steam intake together. Stabilise at low power before increasing demand.
ROD STOP means protection is holding withdrawal because power is rising too fast. Do not keep lowering the target insertion. Let the plant settle, reduce the demand and recalculate. A short period can trigger automatic SCRAM when that protection is enabled.
If your pack uses SIMPLE
Use the same structure, water, steam and waste checks. Enable START with rods
inserted, then reduce insertion slightly. Power follows the rod setting with a
delay; allow it to settle while watching water, pressure and temperature.
The default simpleResponseSeconds = 8 is a response time constant, not a
promise that startup finishes after eight seconds.
Critical rod calculations and short-period trips concern REALISTIC mode. Cooling, radiation, waste and possible meltdowns remain relevant in SIMPLE. Increase power only when the current output can be removed continuously.
Normal operation
Watch trends as well as individual readings. Falling water inventory, accumulating steam and rising temperature matter before a trip limit is reached. Monitor fuel production, acid supply, waste capacity and the rotational network.
MAIN, PLANT, core, power-chain and trend views distribute the information. Some labels predate the current model. An electrical-model readout does not establish that the block exports FE to another mod's power network.
Local BuildUp snapshot: Automatic SCRAM, protection, period trip and rod withdrawal block are enabled. Configured automatic-SCRAM temperature is 1,000 °C and meltdown temperature 1,800 °C. These are emergency limits, not operating targets. Other servers can use different settings.
Planned shutdown
Insert rods to reduce power and end operation at the desk. Confirm that rods actually move in and fission power falls. Keep water and heat removal running: decay heat remains, and the spent-fuel pool also needs cooling.
Disconnect pipes or dismantle core components only after sufficient cooling, controlled pressure and an organised destination for fuel and waste. Pressing STOP does not establish that the reactor is safe to dismantle.
SCRAM and restart
For rapid power rise, cooling loss or critical alarms, trigger SCRAM, preserve cooling and follow the emergency procedure. SCRAM stops the chain reaction but does not instantly remove decay heat.
Fix the cause before resetting. Use Physics Desk → Hours after trip to check xenon dead time and remaining decay heat. Do not compensate by withdrawing all rods. The physics chapter explains the risk when xenon later decays or burns away.