Reactor Systems and Components
Domain 5 tests the major flow paths and how components interact: RCS, pressurizer, steam generators, turbine, condensate/feedwater, and safety systems.
Core rules
- The RCS transfers heat from fuel to steam generators. Charging and letdown control pressurizer level and RCS inventory; the pressurizer itself is a pressure-control volume, not a primary makeup source.
- The pressurizer uses heaters to raise pressure and spray to lower it. Level shrink and swell follow RCS temperature and pressure changes; do not chase level with makeup before understanding the cause.
- Steam generators are the secondary-side heat sink. Feedwater level control protects tube integrity; auxiliary feedwater provides backup on low level or loss of main feedwater.
- ECCS includes accumulators, high-pressure injection, and low-pressure injection/RHR. Accumulators inject on low RCS pressure; check valves and injection alignment determine where flow actually goes.
- The turbine and condenser are secondary-side components: a turbine trip removes load and can cause a reactor trip on high pressure or high Tavg.
Worked example
A main feedwater pump trips. Steam generator level falls; auxiliary feedwater should auto-start on low-low level. If AFW flow is confirmed but level continues to fall, suspect a stuck feedwater control valve, a sensing line blockage, or a closed isolation valve. The correct response is to verify the flow path and instrument indication, not to open another makeup path into the RCS.
Traps
Treating pressurizer level as a direct inventory gauge. Confusing charging with letdown. Assuming an ECCS pump start proves injection; valve lineup and check-valve direction matter. Overlooking that a turbine trip can create a secondary-side transient that trips the reactor.