---
type: procedure
procedure-md: 0.7
procedure-id: E-3
title: Steam Generator Tube Rupture
profile: nuclear-erg
applies-to: Westinghouse-style 4-loop PWR
reference-plant: vogtle
category: diagnostic-eop
csfs-monitored: [containment, rcs-inventory, heat-sink]
entry-triggers: [steam-generator-tube-rupture]
---

# E-3 — Steam Generator Tube Rupture

Entered from [[E-0]] when an SG shows symptoms of primary-to-secondary
leakage through ruptured tubes — typically uncontrolled rising level on
the affected SG and rising secondary-side radiation. Identifies the
ruptured SG, isolates it to terminate offsite radiological release path,
controls RCS pressure to match ruptured-SG pressure, and cools down via
intact SGs to terminate the leak.

The four overall objectives (in priority order):

1. Identify and isolate the ruptured SG
2. Cool down RCS using intact SGs to establish subcooling margin
3. Depressurize RCS below ruptured-SG pressure to terminate leakage
4. Terminate SI when criteria are met

## Step 1 [id: identify-ruptured-sg]
Decision: identify the ruptured SG using the following detection paths in priority order
1. N-16 monitor reading on a single SG main steam line («SG-A-N16», «SG-B-N16», «SG-C-N16», «SG-D-N16») elevated above other lines — fastest, most specific (primary-to-secondary leakage carries N-16 directly into the steam line)
2. SG narrow-range level rising uncontrollably on a single SG («SG-A-LVL-NR», «SG-B-LVL-NR», «SG-C-LVL-NR», «SG-D-LVL-NR») despite normal AFW alignment — slower but unambiguous when steady
3. Steam-line activity grab sample showing elevated nuclide concentration on a single line — confirmatory, requires sample-station turnaround time
4. Blowdown radiation monitor or condenser air-ejector activity «AEJ-RAD» — supports identification when primary monitors disagree
Caution: positive identification is critical — isolating the wrong SG removes a working heat sink and worsens the radiological release
Within: 10 minutes of SGTR diagnosis from E-0 — leak duration drives release magnitude
- Ruptured SG identified positively via path 1 (N-16) → #verify-intact-sg-available
  Because: N-16 specificity allows immediate isolation
- Ruptured SG identified via paths 2-4 with corroborating evidence → #verify-intact-sg-available
  Because: multi-path agreement is operationally equivalent to direct N-16
- Identification ambiguous after exhausting all four paths → [[ES-0.0]]
  Because: rediagnosis with expanded symptom check before any SG isolation
## Step 2 [id: verify-intact-sg-available]
Check: at least one intact SG with normal level, pressure, and AFW capability
- Intact SG available → #isolate-ruptured-sg
- No intact SG (multiple SGTRs or concurrent faults) → [[FR-H.1]]
## Step 3 [id: isolate-ruptured-sg]
Action: close MSIV on ruptured SG («MSIV-A» / «MSIV-B» / «MSIV-C» / «MSIV-D» as identified); close blowdown isolation («BLOWDOWN-A» etc.); close sample line isolation; isolate AFW to ruptured SG («AFW-A-CV» etc.)
Caution: isolating AFW removes one heat sink; verify intact SG AFW flow first
- Isolation complete → #verify-mfw-and-blowdown
- MSIV cannot close, steam release cannot be terminated → [[ECA-3.3]]
## Step 4 [id: verify-mfw-and-blowdown]
Check: main feedwater («MFW-A-CV» etc.) and blowdown («BLOWDOWN-A» etc.) isolated on ruptured SG
Action: if not isolated, manually isolate
- Verified isolated → #control-rcs-pressure
## Step 5 [id: control-rcs-pressure]
Check: pressurizer pressure «PT-455» controllable via PORV («PORV-456A» / «PORV-456B»), normal spray, or auxiliary spray
- Pressure controllable → #initiate-cooldown
- Pressure cannot be controlled (failed PORV, lost spray) → [[ECA-3.3]]
  Because: SGTR without pressure control requires alternative pressure-management procedure

## Step 6 [id: initiate-cooldown]
Action: cool down RCS using intact SG steam dump (preferred to condenser, atmospheric if necessary)
Note: minimize time to leak termination — every minute of continued primary-to-secondary flow adds to integrated radiological release
- Cooldown progressing AND subcooling maintained → #depressurize-rcs
- Cooldown lagging but subcooling intact → #depressurize-rcs
## Step 7 [id: depressurize-rcs]
Action: depressurize RCS using pressurizer PORV or auxiliary spray to a target below ruptured-SG pressure (compare «PT-455» to ruptured-SG «SG-A-PR» / «SG-B-PR» / «SG-C-PR» / «SG-D-PR»)
Caution: maintain at least minimum subcooling margin during depressurization (monitor «TE-411-HOT» vs. «PT-455» saturation)
- Subcooled, RCS pressure ≤ ruptured SG pressure → #verify-leak-terminated
- Saturated conditions developing → [[ECA-3.2]]
  Because: saturated SGTR recovery has different cooldown trajectory
- Significant inventory loss with subcooling intact → [[ECA-3.1]]
## Step 8 [id: verify-leak-terminated]
Check: ruptured SG level stable; no continued primary-to-secondary flow indications
- Leak terminated → #check-si-termination
- Leak continuing → #depressurize-rcs
  Because: lower RCS pressure further to terminate leak

## Step 9 [id: check-si-termination]
Check: SI termination criteria (subcooling, heat sink, pressure stable, pressurizer level recoverable)
- All criteria met → #terminate-si
- Criteria not met → #check-si-termination
  Because: continue SI; reassess after further cooldown

## Step 10 [id: terminate-si]
Action: stop SI pumps; isolate SI; restore normal charging and letdown
Caution: if any SI termination criterion is lost after termination, immediately re-establish SI
- SI terminated, conditions stable → #monitor-during-recovery
- Conditions degrading after termination → #check-si-termination
## Step 11 [id: monitor-during-recovery]
Check: ruptured-SG level (overfill risk), secondary-side radiation release, intact SG conditions
Note: monitoring throughout the post-termination phase before path selection
- Stable progression → #select-cooldown-method
- Secondary overfill imminent → [[ES-3.2]]
  Because: blowdown procedure provides level control during recovery
- Radiation release approaching limits → [[FR-Z.3]]
## Step 12 [id: select-cooldown-method]
Check: which post-SGTR cooldown path applies — depends on ruptured-SG control method available
- Backfill (condensate or AFW into ruptured SG) available → [[ES-3.1]]
- Blowdown of ruptured SG required → [[ES-3.2]]
- Steam dump only (no condensate, atmospheric release) → [[ES-3.3]]

## Tags

- 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: SG-A-N16
  description: SG-A main steam line N-16 radiation monitor
  sim-path: rad.msl.a.n16
  units: cps
  equipment: sg-a-msl
  source: Vogtle UFSAR §11.5

- id: SG-B-N16
  description: SG-B main steam line N-16 radiation monitor
  sim-path: rad.msl.b.n16
  units: cps
  equipment: sg-b-msl
  source: Vogtle UFSAR §11.5

- id: SG-C-N16
  description: SG-C main steam line N-16 radiation monitor
  sim-path: rad.msl.c.n16
  units: cps
  equipment: sg-c-msl
  source: Vogtle UFSAR §11.5

- id: SG-D-N16
  description: SG-D main steam line N-16 radiation monitor
  sim-path: rad.msl.d.n16
  units: cps
  equipment: sg-d-msl
  source: Vogtle UFSAR §11.5

- id: AEJ-RAD
  description: condenser air-ejector radiation monitor
  sim-path: rad.condenser.air_ejector
  units: cps
  equipment: condenser
  source: Vogtle UFSAR §(equipment-not-mapped)

- 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: MSIV-A
  description: SG-A main steam isolation valve position
  sim-path: secondary.msiv.a.position
  units: enum[OPEN,CLOSED,INTERMEDIATE]
  equipment: sg-a-msl
  source: Vogtle UFSAR §11.5

- id: MSIV-B
  description: SG-B main steam isolation valve position
  sim-path: secondary.msiv.b.position
  units: enum[OPEN,CLOSED,INTERMEDIATE]
  equipment: sg-b-msl
  source: Vogtle UFSAR §11.5

- id: MSIV-C
  description: SG-C main steam isolation valve position
  sim-path: secondary.msiv.c.position
  units: enum[OPEN,CLOSED,INTERMEDIATE]
  equipment: sg-c-msl
  source: Vogtle UFSAR §11.5

- id: MSIV-D
  description: SG-D main steam isolation valve position
  sim-path: secondary.msiv.d.position
  units: enum[OPEN,CLOSED,INTERMEDIATE]
  equipment: sg-d-msl
  source: Vogtle UFSAR §11.5

- id: BLOWDOWN-A
  description: SG-A blowdown isolation valve position
  sim-path: secondary.blowdown.a.position
  units: enum[OPEN,CLOSED]
  equipment: sg-a
  source: Vogtle UFSAR §10.3

- 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: MFW-A-CV
  description: SG-A main feedwater control valve position
  sim-path: secondary.mfw.a.cv_position
  units: percent
  equipment: mfw-system
  source: Vogtle UFSAR §10.4.7

- 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: PORV-456A
  description: pressurizer PORV 456A position
  sim-path: rcs.pressurizer.porv.456a.position
  units: enum[OPEN,CLOSED,INTERMEDIATE]
  equipment: pressurizer
  source: Vogtle UFSAR §5.4

- id: PORV-456B
  description: pressurizer PORV 456B position
  sim-path: rcs.pressurizer.porv.456b.position
  units: enum[OPEN,CLOSED,INTERMEDIATE]
  equipment: pressurizer
  source: Vogtle UFSAR §5.4

- 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