SALEM
SALEM STUDY SYSTEM
Systems > Steam Dumps

Steam Dumps

⚠️ DRAFT

Steam Dumps

Function

The steam dump system dumps steam directly to the main condenser to prevent a reactor trip following a turbine trip or rapid load reduction. During cooldown, steam dumps operate in pressure control mode to achieve a controlled cooldown rate. (UFSAR 7.7.2.7)

Condenser Steam Dump Valves

  • Dumps steam to the condenser to prevent reactor trip on turbine trip or rapid load reduction
  • Controlled by: Tavg error signal (difference between Tavg and Tref)
  • Steam dump to condenser blocked by C-9 (high condenser pressure or loss of circulating water)
  • Steam dump blocked below P-12 (low Tavg)
  • Cooldown mode: controlled by steam pressure for controlled cooldown rate (UFSAR 7.7.2.7)

Steam Dump Controllers

Exam — 2018 Q35
Steam dump controller selection depends on which Reactor Trip Breaker opens: Plant Trip Controller activates when Reactor Trip Train B Breaker opens. Load Rejection Controller activates when ONLY Reactor Trip Train A Breaker opens (or neither breaker opens). The Load Rejection Controller has a 4°F dead band — it will stabilize RCS TAVG at 551°F (547°F no-load TAVG + 4°F dead band). The Plant Trip Controller has NO dead band and will restore TAVG to 547°F (no-load TAVG). Trap: confusing which controller has the dead band (Load Rejection, not Plant Trip) and which trip breaker activates each controller (Train B = Plant Trip, Train A only = Load Rejection).

Power Supplies and Failure Modes

Exam — 2019 Q34
Steam Dump I/P converters are powered by C/D 115 VAC Instrument Bus. Loss of power to the I/P converters causes the Steam Dumps to fail CLOSED. Steam Dump blocking solenoids are powered from 125 VDC (different power source than I/P converters). Trap: confusing I/P converter power (115 VAC) with blocking solenoid power (125 VDC). Also, steam dumps fail closed on loss of I/P power — not as-is.
Exam — 2019 Q40
Each TB40 Turbine Bypass Valve is rated for 5.33% steam flow. If 23TB40 fails fully open at 60% power, reactor power rises to approximately 65.33% (power follows steam flow — turbine control valves do NOT automatically compensate). Steam Dump Train A and Train B Arming/Blocking solenoids are in SERIES. Depressing BEZEL "OFF & RESET BYPASS TAVG" Pushbutton A OR B removes air pressure to 23TB40, causing it to close. Trap: if solenoids were in parallel, BOTH A AND B would need to be depressed. Since they are in series, either one is sufficient.
Exam — 2023 Q18
MSLI signals for high steam flow with Lo-Lo Tavg CANNOT be blocked — not even by manually actuating and resetting SI. If steam dump rate is too high during EOP-directed depressurization, high steam flow + P-12 (Lo-Lo Tavg) will actuate MSLI, closing all MSIVs and making steam dumps unavailable. Continue depressurization via MS10 atmospheric dump valves. High steamline differential pressure causes SI, not MSLI — different signals.
JPM — 2023 Sim-e
EOP-FRHS-1 condensate pump feed: isolate all MS lines EXCEPT the selected SG (22 or 24 preferred). Place steam dumps in Manual, adjust valve demand to 0%, then place in MS Pressure Control. Depressurize selected SG below 575 psig. Bypass Tavg Low-Low when reached. When condensate flow established and WR level rising, place steam dumps in auto.
Exam — 2020 Q61
2PT-507 (Steam Header Pressure Transmitter) fails HIGH with steam dumps in MS PRESS mode: controller sees high pressure → steam dump valves fully OPEN. Following a Rx Trip, all steam dumps open → high steam flows → rapidly lowering RCS temperatures. When Tavg < 543°F, MSLI and SI actuate (high steam flow coincident with Lo-Lo Tavg). Simultaneously, P-12 (Lo-Lo Tavg) blocks all steam dumps closed. Steam dumps will NOT re-open to cycle and maintain temperature — P-12 block holds them closed. Group 1 cooldown valves will not re-open until the operator manually selects BYPASS TAVG on both trains on 2CC3.
Exam — 2022 Q43
2PT-507 (Steam Header Pressure Transmitter) fails LOW: in MS PRESS mode, controller sees low pressure → steam dump valves CLOSE (modulate closed thinking pressure is already low). With steam dumps closed, SG pressure rises due to reduced heat removal from the RCS. MS10 atmospheric dump valves will open to maintain SG pressure. In TAVG mode, PT-507 failure has no effect on steam dump operation — TAVG mode uses Tavg error signal, not steam pressure.
Exam — 2018 Q70
BYPASS TAVG pushbuttons for post-LOCA cooldown: Train A and Train B BYPASS TAVG blocking solenoids are in SERIES — BOTH A AND B must be depressed to allow condenser steam dumps to function when TAVG < 543 °F. Per EOP-LOCA-2 Step 11, cooldown rate limit is 100 °F/HR (vs 50 °F/HR for normal IOPs). Trap: the arming/disarming solenoids for individual TB40 valves are also in series (A OR B can disarm a single valve per Q19 Q40), but the BYPASS TAVG function requires BOTH trains — both bezel pushbuttons must be depressed.

Connections