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EOPs > EOP-LOCA-2 — Post LOCA Cooldown and Depressurization

EOP-LOCA-2 — Post LOCA Cooldown and Depressurization

⚠️ DRAFT

EOP-LOCA-2 — Post LOCA Cooldown and Depressurization

Purpose

Guides operators through cooldown and depressurization following a loss of coolant accident, including evaluation of natural circulation conditions.

Key Actions / Information

Exam — 2023 Q2
Step 19.1 evaluates natural circulation conditions: subcooling >0 degrees F, SG pressures stable, T-Hots dropping, CETs lowering, T-Colds at SG saturation temperature.
Exam — 2023 Q76
PZR vapor space SBLOCA procedure path: EOP-LOCA-1 SI termination criteria met (subcooling, PZR level rising, RCS pressure stable) → transition to EOP-TRIP-3 (SI Termination) → reduce ECCS flow → RCS pressure lowers with unisolable leak → EOP-TRIP-3 transitions to EOP-LOCA-2. The path is LOCA-1 → TRIP-3 → LOCA-2, not directly from LOCA-1 to LOCA-2.
JPM — 2023 Sim-c
Step 20 RCS depressurization: with no RCPs running, normal spray is unavailable. Attempt PORV (2PR2) — if it fails to open, RCS pressure NOT dropping → use Auxiliary Spray: OPEN 2CV75, CLOSE 2CV77 and 2CV79. Stop depressurization when PZR level >77% (74% adverse) or RCS subcooling <10F. Restore aux spray to normal: close 2CV75, reopen 2CV77 or 2CV79.
Exam — 2020 Q3
EOP-LOCA-2 Step 21 "Charging Pump Reduction": subcooling requirements from Table C depend on number of SI pumps running, RCP status, and containment conditions (normal vs adverse). With only 1 SI pump running (2A 4KV bus faulted), all RCPs stopped, and containment pressure at 4.3 psig (adverse conditions), the required subcooling is 141°F. To use steam tables: convert 1035 psig to 1049.7 psia, look up T-Sat = 550.56°F, then max CET = 550.56 - 141 = 409°F. Common error: using psig directly in steam tables instead of converting to psia (add 14.7). Using 1035 psia gives T-Sat of 548.83°F and an incorrect answer of 407°F.
Exam — 2022 Q27
During ECCS pump reduction for vital bus redundancy: 22 SI Pump stopped because it shares 2C 4KV bus with the 22 Charging Pump (must maintain charging for RCS makeup/boration). 21 SI Pump stays running (separate 2A bus).
Exam — 2020 Q27
Step 14 NOTE — voiding identification during depressurization: without RCPs running, the upper head remains relatively hot compared with the active regions of the RCS. Steam formation during depressurization in the upper head displaces water into the Pressurizer, causing rapidly increasing Pressurizer level. Rising PZR level (not lowering SI flow, rising RCS pressure, or lowering subcooling) is the procedural indication for voiding per EOP-LOCA-2.

Step 11 — RCS Cooldown to Cold Shutdown

Exam — 2018 Q70
Step 11 — T-COLD Cooldown Rate limit: maintain less than 100 °F/HR maximum. To use condenser steam dumps when TAVG is less than 543 °F (P-12 Lo TAVG block), BOTH "BYPASS TAVG" BEZEL Pushbuttons (A AND B) must be depressed. Trap: 50 °F/HR is the normal cooldown limit per S2.OP-IO.ZZ-0006 (Hot Standby to Cold Shutdown) — EOP-LOCA-2 allows 100 °F/HR. Also, the BYPASS TAVG blocking solenoids are in SERIES — BOTH A AND B must be depressed (not A OR B). If they were in parallel, either one alone would suffice.

Step 29 — Natural Circulation Monitoring

Exam — 2018 Q50
EOP-LOCA-2 Step 29 natural circulation evaluation requires ALL of the following:
• RCS Subcooling based on CETs > 0°F
• SG Pressure stable or lowering
• RCS THOT stable or lowering
• CETs stable or lowering
• SG pressure at saturation pressure for RCS TCOLD
Example: CETs 600°F, RCS 1645 psig (TSAT = 609°F → subcooling = 9°F), TCOLD 509°F (PSAT = 725 psig matches SG pressure) → natural circulation IS established. If NOT established, raise steam dumping rate (increases SG heat removal → promotes natural circulation flow). Trap: lowering steam dumping rate raises SG pressure, which REDUCES the temperature differential and works AGAINST natural circulation.

CAS — ECCS Pump Restart Criteria

Exam — 2019 Q73
EOP-LOCA-2 CAS ECCS restart criteria (after SI/Charging Pump reductions): the crew must restart ECCS Pumps when EITHER RCS Subcooling reaches 0°F OR PZR Level cannot be maintained greater than 11%. These are OR conditions — either condition alone triggers ECCS pump restart, not BOTH required simultaneously.

Step 22 — Charging Pump Reduction Decision Logic

Exam — 2019 Q76
EOP-LOCA-2 POST Step 22 Charging Pump Reduction with 2 SI Pumps running, 1 RCP running, and NORMAL containment conditions (pressure < 4.0 psig): required subcooling from Table C is 38°F. If subcooling requirement met AND PZR level > 25% (33% adverse), the next action is to stop a Charging Pump. Step 22.2 checks if at least two T-Hots are less than 365°F — this step is only reached if subcooling is NOT met. Trap: four different paths through Step 22 depending on subcooling status, T-Hot status, and PZR level status. Must evaluate in order: 22.1 → 22.4 (if subcooling met), or 22.1 → 22.2 → 22.3/22.4 (if subcooling not met).

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