ECA-1.2 — LOCA Outside Containment¶
Entered from E-1 when LOCA symptoms (decreasing RCS pressure,
pressurizer level loss) exist but containment pressure and containment
sump are not rising — meaning the leak path
bypasses containment. Likely causes: interfacing-system LOCA (ISLOCA)
through a check-valve failure that connects RCS to a lower-pressure
auxiliary system, instrument-line break outside containment, letdown
heat-exchanger tube rupture, or RHR-system leak when RHR is in service.
The radiological signature is in the auxiliary building rather than
containment; ECA-1.2 entry is typically corroborated by «MAB-RAD»
elevated. Vogtle UFSAR §15.6.3 covers analyzed ISLOCA cases.
CSF: containment
CSF: rcs-inventory
CSF: rcs-integrity
Step 1 identify-leak-location¶
Decision: identify the leak location based on auxiliary-building radiation, system-pressure mismatches, and inventory tracking
1. RHR system leak when RHR was aligned (V-sequence ISLOCA) — RHR-system pressure rising; «MAB-RAD» elevated; containment pressure «CTMT-PR» and sump «CTMT-SUMP-LVL» both NOT rising (the diagnostic distinction)
2. Letdown heat-exchanger tube rupture — letdown CCW outlet activity «CCW-RAD» elevated
3. Instrument-line break outside containment — small leak, sample-flow indicators show flow with no return
4. SI / CVCS suction valve failure — RCS pressure mismatch with downstream system
Caution: leak-location identification under ISLOCA can be slow because the leak path is by definition non-obvious; defensive isolation is preferred to forensic certainty
- Leak located → #isolate-leak
Because: isolation is the immediate response
- Cannot locate after exhausting symptom evidence → ES-0.0
Because: rediagnosis required
Step 2 isolate-leak¶
Within: 5 minutes of leak-location identification — every minute of continued ISLOCA contributes to off-containment release
Action: isolate the leak path at the closest accessible boundary — RHR motor-operated valves «RHR-ISOL», letdown-line isolation «LET-ISOL», or other system-specific path
Action: verify isolation by observing the downstream pressure / level / flow indication
Caution: isolation may sometimes worsen conditions briefly — for instance, isolating RHR may strand RCS coolant in the affected loop; balance against the radiological-release reduction
- Leak isolated successfully → E-1
Because: return to LOCA management with the leak now bounded
- Isolation impossible or partial → #limit-leak-impact
Because: defensive action — minimize SI flow into the leak path while preserving core cooling
Step 3 limit-leak-impact¶
Action: minimize SI flow «SI-PUMP-A» / «SI-PUMP-B» into the leak path while maintaining the subcooling margin «SUB-MARGIN» ≥ 30 °F at the core exit
Action: increase letdown to balance charging if letdown path is unaffected — maintains RCS inventory in the leak-bypass
Caution: this step trades core-cooling margin against radiological release; require shift-supervisor authorization for any SI reduction below normal demand
- Stabilized (core cooling adequate, release rate bounded) → #monitor
Because: holding pattern; continue restoration attempts
- Cannot stabilize → FR-C.1
Because: inadequate-core-cooling response engages when SI is insufficient
Step 4 monitor¶
Check: leak rate (via «MAB-RAD» trend, downstream system pressure if measurable); core cooling status
Within: re-evaluate every 15 minutes during continued ISLOCA management
- Leak isolated or rate decreasing → E-1
Because: return to normal LOCA management
- Continuing → #monitor
Because: holding pattern
Tags¶
-
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: MAB-RAD
description: main auxiliary building area radiation monitor
sim-path: rad.mab.area
units: rem_per_hr
equipment: rad-monitoring
source: Vogtle UFSAR §11.5 -
id: CCW-RAD
description: component cooling water outlet radiation monitor (letdown HX outlet)
sim-path: rad.ccw.let_hx_outlet
units: rem_per_hr
equipment: rad-monitoring
source: Vogtle UFSAR §11.5 -
id: RHR-ISOL
description: RHR system isolation valve (representative)
sim-path: ess.rhr.isolation_valve
units: enum[OPEN,CLOSED]
equipment: rhr-system
source: Vogtle UFSAR §5.4.7 -
id: LET-ISOL
description: CVCS letdown isolation valve
sim-path: cvcs.letdown.isolation
units: enum[OPEN,CLOSED]
equipment: charging-system
source: Vogtle UFSAR §9.3.4 -
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: 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