SALEM
SALEM STUDY SYSTEM
Systems > SECs

SECs

⚠️ DRAFT

SECs

Function

Safeguards Equipment Controllers (SECs) automatically initiate and sequence safeguards loads onto vital buses following a Safety Injection signal or loss of offsite power. SECs ensure diesel generators are not overloaded during accident response by sequencing loads on in a prescribed order with time delays. (UFSAR 7.3, 8.3)

Safeguards Sequence

On SI signal with loss of offsite power:

  1. Diesel generators auto-start
  2. Vital bus loads shed
  3. Diesel generators connect to vital buses
  4. Safeguards loads sequenced on in prescribed order and time delays
  5. Ensures diesel generators not overloaded during accident response (UFSAR 7.3, 8.3)

SEC Operating Modes

Exam — 2023 Q37
After SI and SEC reset, a subsequent LOOP causes EDGs to auto-start on blackout signal. SECs operate in Mode 2 (blackout only) — only charging pumps are auto-started. SI pumps, RHR pumps, and CFCUs must be manually started since SI/SECs were reset prior to the LOOP. EDG auto-start on loss of voltage is independent of SI status.
Exam — 2020 Q47
SEC operating modes after SI/SEC reset: with SI and SECs reset, a subsequent degraded voltage condition causes the SEC to actuate in Mode II* (Single Bus Degraded UV) — NOT Mode III or IV (which require an active SI signal). The SEC strips the affected bus from offsite power and loads it onto its EDG. Key distinction: Mode I = Blackout (complete loss of voltage, all buses), Mode II* = Single Bus Degraded UV (degraded voltage on one bus, SI reset), Mode III = SI Only, Mode IV = SI + Degraded UV. After SI reset, only Modes I and II* are available.
Exam — 2020 Q35
SEC Mode III (Blackout + SI) CCW pump behavior: CCW pumps are stripped and NOT reloaded onto EDGs. Additionally, any CCW pump selected for AUTO is transferred to Manual. This AUTO-to-Manual transfer occurs in SEC Modes II, III, and VI. Trap: Mode II (Blackout only) restarts CCW pumps and also forces AUTO to Manual. Mode I (SI only) does NOT force AUTO to Manual — only Modes II, III, and VI do. Mode III does NOT restart CCW pumps but DOES force AUTO to Manual.
Exam — 2019 Q5
Following a Reactor Trip and Safety Injection coincident with a LOOP, SECs operate in Mode III (SI + Blackout). After SEC Mode III loading completes, CCW Pumps will be STOPPED — CCW pumps are NOT automatically started as part of SEC Mode III loading. SEC Mode II is Blackout only (no SI signal). Mode II DOES restart CCW pumps. The presence of the SI signal is what makes this Mode III, not Mode II.
Exam — 2019 Q16
SEC Mode 1 (SI only, no LOOP) AFW pump behavior: the SEC sends automatic start signals to ONLY the motor-driven AFW pumps (21 and 22). The turbine-driven AFW pump (23) does NOT receive an SEC start signal. SEC start signals override LOCAL MANUAL controller alignment — even with all AFW pump controllers in LOCAL MANUAL, 21 and 22 AFW pumps will auto-start on SEC Mode 1 actuation.
Exam — 2019 Q19
SEC Mode 2 (blackout only) includes MDAFW pump start: when 2B 4KV Vital Bus de-energizes and 2B SEC actuates in Mode 2, the SEC load sequencer restores power and starts 22 AFW Pump (powered from 2B bus). SEC Mode 2 starts AFW pumps on the associated bus. The SG Lo-Lo level MDAFW start (2/3 on 1/4 SGs <14%) was NOT met in this scenario — the SEC Mode 2 start was the sole reason 22 AFW started.

1RP4 Panel Relationship

Exam — 2019 Q23
1RP4 is the main control room panel that gives visual status of all safety related equipment including the SECs. Since 1RP4 is NOT safety related, the interface between the SECs and 1RP4 is isolated. Loss of ALL AC and DC power to 1RP4 does NOT affect SEC operation. When a Reactor Trip and Safety Injection occurs, the SECs will automatically actuate in Mode 1 regardless of 1RP4 status. Trap: loss of power to a control bezel (e.g., AFW Control Bezel) prevents automatic and manual operation of components via that bezel. This logic does NOT apply to 1RP4 because it is an indication-only panel — SECs operate independently.
Exam — 2019 Q52
After SEC and SI reset during EOP-LOCA-3, a subsequent blackout on a 4KV vital bus: SEC performs blackout loading ONLY — ECCS pumps and safeguards equipment are NOT automatically started. Must be manually operated because blackout loading starts different equipment than safeguards loading. Also: after resetting all SECs, the 230V control centers must be MANUALLY reset by the crew (20-minute auto-removal notwithstanding). Trap: LBLOCA is in progress but SI is reset — the SEC has no SI signal, so it performs blackout loading (Mode 2), not SI + blackout loading (Mode III).
Exam — 2018 Q60
LOOP in MODE 4 with 2C EDG paralleled to the grid for surveillance: 2A and 2B 4KV Vital Buses sense Instantaneous UV → ALL three SECs (2A, 2B, 2C) enter Mode II (Blackout Only) because 2/3 Vital Buses sense Instantaneous UV. SEC Mode II causes the 2C EDG Output Breaker to OPEN then reclose (even though 2C EDG was already running and loaded). RHR pumps are NOT automatically loaded in SEC Mode II — they are only sequenced in Mode I (SI only) and Mode III (SI + Blackout). 21 RHR Pump (on 2A bus) will be stopped after SEC 2A completes Mode II sequencing. Trap: candidates may assume the running EDG output breaker remains closed, or that RHR pumps restart after SEC sequencing completes.
Scenario — 2018 #2
2B SEC fails to actuate on SI signal after LBLOCA. RO reports available equipment on 2B bus failed to start. Recovery: Block 2B SEC, reset 2B SEC, manually start safeguards loads for 2B bus using EOP-TRIP-1 Table A. Also: 2SW26 NOT in required position — PO manually closes. After SI/Phase A/Phase B reset, 2A and 2C SECs reset normally; 2B SEC is de-energized.

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