Nuclear Power Plant Systems and Components
Heat transport path
In a PWR, reactor coolant pumps push subcooled water up through the core, out the hot legs, through steam generator U-tubes, and back down the cold legs. The pressurizer is the only place the coolant boils: heaters raise RCS pressure, spray from a cold leg lowers it, and safety/relief valves protect the boundary. A BWR is a direct cycle: recirculation pumps (driving jet pumps) set core flow, steam separators and dryers produce dry steam that goes straight to the turbine, and the vessel itself is the pressure boundary.
Components a candidate must know
ECCS: high-pressure injection, low-pressure injection, PWR accumulators (passive, nitrogen-driven), the RWST, and sump recirculation. Support systems: auxiliary feedwater, emergency diesel generators, service water, HVAC, DC and inverters. Steam side: main steam isolation valves, turbine stop/control valves, bypass, condenser.
Traps
- PWR/BWR feature swaps: PWRs have no jet pumps; BWRs have no pressurizer, no steam generators (so no SGTR), and no accumulators.
- SRVs versus code safety valves: SRVs can be opened remotely or by automatic depressurization logic; code safeties are strictly overpressure devices and cannot be manually cycled.
- BWR RCIC/HPCI initially take suction from the condensate storage tank and shift to the suppression pool on high torus level.
Rule of thumb
Subcooling margin = T_sat(P_RCS) − T_hot leg. Design programs keep roughly 15–20 °F of margin at full power so no bulk boiling reaches the core exit; a PWR core ΔT of about 60–75 °F at rated power is typical.