E-1 — Loss of Reactor or Secondary Coolant

Entered from E-0 when LOCA symptoms are diagnosed (decreasing RCS
pressure with rising containment pressure, sump level, or activity).
Maintains adequate core cooling via continued SI, manages RCS pressure
to optimize SI flow, and prepares the plant for cooldown and transfer
to long-term recirculation cooling.

Step 1 verify-loca-symptoms

Check: RCS pressure «PT-455» decreasing AND containment pressure «CTMT-PR» rising OR containment sump level «CTMT-SUMP-LVL» rising OR containment radiation «CTMT-RAD» rising
- LOCA confirmed → #verify-si-active
- Symptoms ambiguous → ES-0.0
Because: rediagnosis required when LOCA indicators are not consistent

Step 2 verify-si-active

Check: SI signal «SI-SIG» active AND high-head SI pumps «SI-PUMP-A» / «SI-PUMP-B» running
Action: if SI not active and required, manually actuate SI
- SI active, pumps running → #check-rcp-status
- SI cannot be actuated → FR-C.1
Because: ECCS unavailability with LOCA in progress is inadequate core cooling

Step 3 check-rcp-status

Check: RCS pressure «PT-455» AND subcooling margin «SUB-MARGIN» AND RCP status («RCP-1», «RCP-2», «RCP-3», «RCP-4»)
Caution: tripping RCPs after voiding has begun may stop natural circulation; do not restart RCPs once voiding is established
Within: 30 seconds of identifying subcooling loss — RCP seal damage accumulates rapidly once voiding begins
Action: if subcooling margin «SUB-MARGIN» < 30 °F AND RCPs running, trip all RCPs
- RCPs tripped per criterion or already tripped → #verify-msiv-status
Because: preserves RCP integrity and avoids interrupting natural circulation later
- Subcooling margin ≥ 30 °F → #verify-msiv-status
Because: positive subcooling means no voiding at RCP suction

Step 4 verify-msiv-status

Check: MSIVs status — closed if MSLI signal was generated
Action: if MSIV open with MSLI signal active, manually close
- MSIVs closed (or MSLI not generated) → #monitor-sg-levels

Step 5 monitor-sg-levels

Check: SG narrow-range levels («SG-A-LVL-NR», «SG-B-LVL-NR», «SG-C-LVL-NR», «SG-D-LVL-NR») and AFW flow to each SG
Action: maintain SG levels at no-load setpoint with AFW
- Levels controllable on all SGs → #verify-ecc-alignment
- One SG level dropping uncontrollably with steam line break indications → E-2
- AFW flow lost to all SGs → FR-H.1

Step 6 verify-ecc-alignment

Check: ECCS aligned in injection mode (high-head pumps suction from RWST, low-head pumps available, accumulators armed)
Action: if misaligned, correct alignment and verify flow
- Alignment correct or corrected → #check-rcs-pressure-trend

Step 7 check-rcs-pressure-trend

Check: RCS pressure «PT-455» trend after SI delivery
Decision: classify break severity and recovery path from the RCS pressure response to full SI
1. RCS pressure stable or recovering above the subcooling threshold — small break, normal SI termination criteria apply
2. RCS pressure continuing to drop despite full SI flow — break exceeds ECCS injection capacity (large break or recirculation-failure mode)
3. RCS pressure dropping AND containment pressure NOT rising — leak path bypasses containment (LOCA outside containment)
Note: pressure trend is the primary classifier of break size and disposition
- RCS pressure stable or recovering above subcooling threshold → #check-si-termination-criteria
- Pressure continuing to drop despite full SI → ECA-1.1
Because: large break or ECCS recirculation failure mode
- Pressure decreasing AND containment pressure NOT rising → ECA-1.2
Because: LOCA outside containment — leak path bypasses containment

Step 8 check-si-termination-criteria

Check: all four SI termination criteria
Note: criteria are (1) subcooling ≥ minimum, (2) secondary heat sink available, (3) RCS pressure stable or rising, (4) pressurizer level on-scale or recovering
- All four criteria met → ES-1.1
Because: SI termination procedure restores normal RCS makeup
- Criteria not met → #manage-rcs-pressure

Step 9 manage-rcs-pressure

Action: maintain SI; control RCS pressure via charging and PORV operation as appropriate
Caution: do not interrupt SI flow before all four termination criteria are satisfied
- Pressure stabilizing, criteria approaching → #monitor-rwst-level
- Cooldown needed before recirc transfer → ES-1.2

Step 10 monitor-rwst-level

Check: RWST level «RWST-LVL» trend
Within: anticipate transfer to recirculation when RWST reaches low-low setpoint
- RWST level adequate → #check-natural-circulation
- RWST level approaching low-low → ES-1.3
Because: transfer to cold-leg recirculation before RWST depletion

Step 11 check-natural-circulation

Check: hot-leg / cold-leg ΔT and Tcold trends in each loop using «TE-411-HOT» / «TE-411-COLD» (loop 1) and analogous loop-2/3/4 instruments (only relevant if RCPs tripped)
- Natural circulation indicated or RCPs running → #check-cold-leg-recirc-needed
- Natural circulation not established → FR-C.2
Because: degraded core cooling if no flow path established

Step 12 check-cold-leg-recirc-needed

Check: time since LOCA; cold-leg recirc transfer status
- Recirc transfer not yet needed (RWST adequate) → #check-si-termination-criteria
- Recirc transfer in progress → ES-1.3
- Hot-leg recirc transfer time approaching (8-24h post-LOCA) → ES-1.4
Because: prevent boric acid precipitation in core

Tags

• id: PT-455
  description: pressurizer pressure (wide range)
  sim-path: rcs.pressurizer.pressure_wr
  units: psig
  equipment: pressurizer
  source: Vogtle UFSAR §5.4
  range: [0, 3000]

• id: CTMT-PR
  description: containment building pressure
  sim-path: containment.pressure
  units: psig
  equipment: containment
  source: Vogtle UFSAR §6.2

• id: CTMT-SUMP-LVL
  description: containment recirculation sump level
  sim-path: containment.sump.level
  units: percent
  equipment: containment
  source: Vogtle UFSAR §6.2

• id: CTMT-RAD
  description: containment area radiation monitor
  sim-path: rad.containment.high_range
  units: rem_per_hr
  equipment: containment
  source: Vogtle UFSAR §6.2

• id: SI-SIG
  description: safety injection actuation signal (latched)
  sim-path: ess.si.actuation_signal
  units: bool
  equipment: si-system
  source: Vogtle UFSAR §6.3

• id: SI-PUMP-A
  description: high-head SI pump A status
  sim-path: ess.si_pump.a.status
  units: enum[STOPPED,RUNNING,FAULT]
  equipment: si-system
  source: Vogtle UFSAR §6.3

• id: SI-PUMP-B
  description: high-head SI pump B status
  sim-path: ess.si_pump.b.status
  units: enum[STOPPED,RUNNING,FAULT]
  equipment: si-system
  source: Vogtle UFSAR §6.3

• id: RCP-1
  description: reactor coolant pump 1 status
  sim-path: rcs.rcp.1.status
  units: enum[STOPPED,RUNNING,FAULT]
  equipment: rcp-1
  source: Vogtle UFSAR §5.4.1

• id: RCP-2
  description: reactor coolant pump 2 status
  sim-path: rcs.rcp.2.status
  units: enum[STOPPED,RUNNING,FAULT]
  equipment: rcp-2
  source: Vogtle UFSAR §5.4.1

• id: RCP-3
  description: reactor coolant pump 3 status
  sim-path: rcs.rcp.3.status
  units: enum[STOPPED,RUNNING,FAULT]
  equipment: rcp-3
  source: Vogtle UFSAR §5.4.1

• id: RCP-4
  description: reactor coolant pump 4 status
  sim-path: rcs.rcp.4.status
  units: enum[STOPPED,RUNNING,FAULT]
  equipment: rcp-4
  source: Vogtle UFSAR §5.4.1

• id: SG-A-LVL-NR
  description: SG-A narrow-range level
  sim-path: secondary.sg.a.level_nr
  units: percent
  equipment: sg-a
  source: Vogtle UFSAR §10.3

• id: SG-B-LVL-NR
  description: SG-B narrow-range level
  sim-path: secondary.sg.b.level_nr
  units: percent
  equipment: sg-b
  source: Vogtle UFSAR §10.3

• id: SG-C-LVL-NR
  description: SG-C narrow-range level
  sim-path: secondary.sg.c.level_nr
  units: percent
  equipment: sg-c
  source: Vogtle UFSAR §10.3

• id: SG-D-LVL-NR
  description: SG-D narrow-range level
  sim-path: secondary.sg.d.level_nr
  units: percent
  equipment: sg-d
  source: Vogtle UFSAR §10.3

• id: TE-411-HOT
  description: RCS loop 1 hot-leg temperature
  sim-path: rcs.loop1.t_hot
  units: degF
  equipment: rcs-loop-1
  source: Vogtle UFSAR §5.1.1

• id: TE-411-COLD
  description: RCS loop 1 cold-leg temperature
  sim-path: rcs.loop1.t_cold
  units: degF
  equipment: rcs-loop-1
  source: Vogtle UFSAR §5.1.1

• id: RWST-LVL
  description: refueling water storage tank level
  sim-path: rwst.level
  units: percent
  equipment: rwst
  source: Vogtle UFSAR §6.3.2

• id: SUB-MARGIN
  description: RCS subcooling margin (T_sat at PT-455 minus hot-leg temperature)
  sim-path: rcs.subcooling_margin
  units: degF
  equipment: rcs
  source: Vogtle UFSAR §15.6 (RCP-trip subcooling threshold; nominal 30 °F)

Leave feedback on this section

Correction Suggestion Missing info Unclear

Submit feedback