AB.SG-0001 — Steam Generator Tube Leak
Purpose
Provides operator actions for responding to a confirmed or suspected steam generator tube leak, including classification of leak severity by action level and required shutdown actions based on leak rate and rate of change.
Entry Conditions
- Confirmed or suspected primary-to-secondary tube leak on any SG
- Entered based on chemistry sample results, radiation monitor trends, or condenser air ejector monitor alarms
Key Actions
Action Levels (Attachment 1 — Continuous Action Summary)
Action levels are based on SG leak rate (gpd) and rate of change (gpd/hr):
| Action Level | Criteria | Required Action |
|---|---|---|
| 1 | Leak rate thresholds met | Be in MODE 3 within 24 hours |
| 2 | Intermediate leak rate criteria | Intermediate shutdown actions |
| 3 (rate of change) | Leak rate >= 75 gpd AND rate of change >= 30 gpd/hr | Reduce power to <= 50% within 1 hour AND be in MODE 3 in following 2 hours |
| 3 (high rate) | Leak rate >= 150 gpd | Be in MODE 3 within 6 hours |
| Emergency | SI criteria met | Trip the reactor and actuate Safety Injection |
Exam — 2023 Q81
SG tube leak action levels are based on both leak rate AND rate of change. At Action Level 3 with leak rate >= 75 gpd and rate of change >= 30 gpd/hr, the required action is to reduce power to <= 50% in 1 hour and be in MODE 3 in the following 2 hours. Trap: a leak rate of 125 gpd with a 30 gpd/hr trend meets Action Level 3 (rate of change criterion), NOT the 150 gpd threshold for the 6-hour shutdown.
Scenario — 2022 #4
23 SG tube leak (25-30 gpm). Entry cue: RMS alarms 2R15, 2R19C (23 SG B/D Rad Monitor), 2R53C (MS Line Rad Monitor) with PZR level lowering. Key actions: transfer to centrifugal charging pump IAW step 3.5 to stabilize PZR level. CRS evaluates TS 3.4.7.2.c action a — be in Hot Standby within 6 hours. Continuous Action Summary: if leak exceeds makeup capability → trip reactor and actuate SI. In this scenario, the leak worsens to a 650 gpm tube rupture, triggering the CAS trip criteria.
Scenario — 2020 #4
21 SG tube rupture during EOP-TRIP-2. Diagnostic indications: RCS pressure and PZR level lowering, OHA A-6 alarm, 2R15 condenser off-gas rad monitor in alarm, 21 SG NR levels rising. CRS enters AB.SG-0001, implements CAS — leak exceeds makeup capability → manually initiate SI, return to EOP-TRIP-1. Eventually transition to EOP-SGTR-1 when 21 SG NR level identified as rising in an uncontrolled manner.
Exam — 2019 Q69
Step 3.37.B subcooling calculation with subcooling monitor NOT functional: convert psig to PSIA (add 15), then use steam tables to find TSAT. Subcooling = TSAT - Hottest CET (not TAVG). Example: 1200 psig → 1215 PSIA → TSAT ≈ 569 °F. Hottest CET = 540 °F. Subcooling = 569 - 540 = 29 °F. Two common errors: (1) subtracting 15 instead of adding (entering steam tables at 1185 PSIA → TSAT ≈ 565 °F), and (2) using TAVG instead of Hottest CET for the subcooling calculation.
JPM — 2019 SRO-A5
SGTR event with stuck-open MSIV: crew responds to valid SG tube leak on 23 SG, implements CAS to trip reactor and initiate SI, enters 2-EOP-SGTR-1. 23 MS167 fails to close from control room. After isolating the other three MSIVs, loud roaring noise heard — 23 SG pressure 850 psig and lowering rapidly, steam flows 12% and rising. This creates an uncontrolled release path (RCS through ruptured tube through open MSIV to atmosphere) = Site Area Emergency classification.
Exam — 2018 Q15
Step 3.31: set the affected MS10 (MS PWR RELIEF Vlv) setpoint to 1045 psig by depressing button A on the controller. Trap: button B raises the manual output to open the valve more — it does NOT change the controller setpoint. 1070 psig is the MS15 (MSSV) lift setpoint, not the AB.SG-0001 MS10 adjusted setpoint.
Exam — 2018 Q68
Step 3.7 — PZR level control during SG tube leak: reduce letdown to minimum by ONLY placing 2CV3 (45 gpm ORIFICE) in service — do NOT isolate letdown entirely. Step 3.11 — if PZR level cannot be maintained and the reactor has been tripped: initiate a Safety Injection PRIOR to transitioning to 2-EOP-TRIP-1. Trap: isolating letdown would provide more margin for PZR level but is NOT what the procedure directs — it directs reducing to minimum (45 gpm orifice only). Also, SI is initiated before going to TRIP-1, not deferred until TRIP-1 Step 5.
Connections
- Related systems: Steam Generator & Blowdown, RCS, Main Steam
- Related exam questions: 2018 Q15, 2018 Q68, 2019 Q69, 2023 Q81
- Related JPMs: 2019 JPM SRO-A5
- Related scenarios: 2022 Scenario 4, 2020 Scenario 4 — SGTR / PORV Failure
- Related exam: 2018 NRC Written Exam, 2019 NRC Written Exam, 2019 NRC Operating Exam, 2020 NRC Operating Exam, 2022 NRC Operating Exam, 2023 NRC Written Exam