ECA-2.1 — Uncontrolled Depressurization of All Steam Generators¶
Entered from E-2 when faulted-SG isolation is impossible because
ALL SG pressures are decreasing simultaneously — main steam header
break upstream of the MSIVs, common-cause MSIV failure, or excessive
steam release across multiple ARVs. Cannot identify a single SG to
isolate. RCS cooldown is rapid and unbounded; PTS challenge develops
quickly. Vogtle UFSAR §15.1.5 (steam-system piping failure inside
or outside containment).
CSF: heat-sink
CSF: rcs-integrity
Step 1 confirm-all-sg-depress¶
Check: all SG pressures «SG-A-PR» / «SG-B-PR» / «SG-C-PR» / «SG-D-PR» decreasing simultaneously; main steam header pressure «MS-HEADER-PR» decreasing; no isolatable break point evident
- All SGs depressurizing AND no single isolation point → #limit-cooldown
Because: extreme-conditions response — single-SG isolation procedure (E-2) is not applicable
- Single SG faulted (others recovering or stable) → E-2
Because: standard faulted-SG procedure applies
Step 2 limit-cooldown¶
Within: 2 minutes — RCS cooldown rate under all-SG depressurization can exceed 200 °F/hr; PTS challenge develops within minutes
Action: trip RCPs «RCP-1» / «RCP-2» / «RCP-3» / «RCP-4» — eliminates forced cooldown component, reduces ongoing primary-to-secondary heat transfer rate
Action: close any isolatable steam path: dispatch operators to close upstream-of-break MSIVs, isolate atmospheric reliefs «ARV-A» / «ARV-B» / «ARV-C» / «ARV-D» if not the break source
Action: maintain AFW «AFW-A-CV» / «AFW-B-CV» / «AFW-C-CV» / «AFW-D-CV» to all SGs initially — partial isolation may reveal an intact SG
Caution: tripping RCPs accelerates loss of letdown / charging temperature-control; pressurizer pressure control may shift to auxiliary spray; monitor «PT-455»
Caution: excessive RCS cooldown drives PTS — if «TE-411-COLD» rate of decrease exceeds 100 °F/hr, branch to FR-P.1
- Cooldown rate limited (RCPs tripped, partial isolation succeeded) → #manage-rcs
Because: bounded cooldown; manage RCS conditions while diagnosis continues
- Excessive cooldown unbounded → FR-P.1
Because: PTS RED-path response
Step 3 manage-rcs¶
Action: maintain RCS inventory by maximizing charging «CHG-FLOW» and minimizing letdown «LET-FLOW»; verify SI «SI-PUMP-A» / «SI-PUMP-B» actuated if RCS pressure dropping below SI setpoint
Action: pressurizer heaters «PZR-HTR» energized as conditions allow to slow pressure decrease
Caution: do NOT allow RCS to depressurize to a point where SI overpressurization would occur on cold restart — coordinate with shift-supervisor for SI throttling decisions
- Stable (RCS inventory maintained, RCS pressure trending toward equilibrium with SG pressure) → #monitor-recovery
Because: bounded; proceed to recovery monitoring
- LOCA also developing (RCS pressure dropping faster than secondary, containment pressure rising) → E-1
Because: concurrent LOCA + SG-depressurization is the worst-case; LOCA management takes precedence
Step 4 monitor-recovery¶
Check: SG conditions (any recovering pressure, any intact SG identifiable); RCS conditions; PTS trajectory
Within: re-evaluate every 5 minutes during recovery phase
- One intact SG identified (pressure recovering, level controllable) → E-2
Because: faulted-SG isolation now possible with the recoverable SG as the heat sink
- Long-term cooling needed via natural-circ → ES-0.2
Because: natural-circulation cooldown procedure handles RCP-tripped path
Tags¶
-
id: SG-A-PR
description: SG-A steam pressure
sim-path: secondary.sg.a.steam_pressure
units: psig
equipment: sg-a
source: Vogtle UFSAR §10.3 -
id: SG-B-PR
description: SG-B steam pressure
sim-path: secondary.sg.b.steam_pressure
units: psig
equipment: sg-b
source: Vogtle UFSAR §10.3 -
id: SG-C-PR
description: SG-C steam pressure
sim-path: secondary.sg.c.steam_pressure
units: psig
equipment: sg-c
source: Vogtle UFSAR §10.3 -
id: SG-D-PR
description: SG-D steam pressure
sim-path: secondary.sg.d.steam_pressure
units: psig
equipment: sg-d
source: Vogtle UFSAR §10.3 -
id: MS-HEADER-PR
description: main steam header pressure
sim-path: secondary.ms_header.pressure
units: psig
equipment: secondary
source: Vogtle UFSAR §10.3 -
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: PT-455
description: pressurizer pressure (wide range)
sim-path: rcs.pressurizer.pressure_wr
units: psig
equipment: pressurizer
source: Vogtle UFSAR §5.4 -
id: PZR-HTR
description: pressurizer heater bank energization status
sim-path: rcs.pressurizer.heaters.status
units: enum[OFF,ON,FAULT]
equipment: pressurizer
source: Vogtle UFSAR §5.4 -
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: ARV-A
description: SG-A atmospheric relief valve position
sim-path: secondary.arv.a.position
units: enum[OPEN,CLOSED,INTERMEDIATE]
equipment: sg-a-msl
source: Vogtle UFSAR §10.3.2 -
id: ARV-B
description: SG-B atmospheric relief valve position
sim-path: secondary.arv.b.position
units: enum[OPEN,CLOSED,INTERMEDIATE]
equipment: sg-b-msl
source: Vogtle UFSAR §10.3.2 -
id: ARV-C
description: SG-C atmospheric relief valve position
sim-path: secondary.arv.c.position
units: enum[OPEN,CLOSED,INTERMEDIATE]
equipment: sg-c-msl
source: Vogtle UFSAR §10.3.2 -
id: ARV-D
description: SG-D atmospheric relief valve position
sim-path: secondary.arv.d.position
units: enum[OPEN,CLOSED,INTERMEDIATE]
equipment: sg-d-msl
source: Vogtle UFSAR §10.3.2 -
id: AFW-A-CV
description: SG-A AFW control valve position
sim-path: afw.a.cv_position
units: percent
equipment: afw-system
source: Vogtle UFSAR §10.4.9 -
id: AFW-B-CV
description: SG-B AFW control valve position
sim-path: afw.b.cv_position
units: percent
equipment: afw-system
source: Vogtle UFSAR §10.4.9 -
id: AFW-C-CV
description: SG-C AFW control valve position
sim-path: afw.c.cv_position
units: percent
equipment: afw-system
source: Vogtle UFSAR §10.4.9 -
id: AFW-D-CV
description: SG-D AFW control valve position
sim-path: afw.d.cv_position
units: percent
equipment: afw-system
source: Vogtle UFSAR §10.4.9 -
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: CHG-FLOW
description: charging flow rate
sim-path: cvcs.charging.flow
units: gpm
equipment: charging-system
source: Vogtle UFSAR §9.3.4 -
id: LET-FLOW
description: letdown flow rate
sim-path: cvcs.letdown.flow
units: gpm
equipment: charging-system
source: Vogtle UFSAR §9.3.4