EOP-LOCA-4 — Transfer to Hot Leg Recirculation
Purpose
Directs the realignment of ECCS flow from cold leg injection to hot leg injection to prevent boron precipitation in the reactor vessel during a prolonged LOCA. Hot leg recirculation alternates the injection point to flush boron from the core region.
Key Actions / Information
JPM — 2023 Sim-b
Hot leg recirculation alignment with one SI pump tripped and one RHR pump C/T: at Step 5.0, determine the 22 SI pump is NOT running (alternate path) and proceed to Step 8. To realign 21 SI pump: STOP 21 SI Pump → CLOSE 21SJ134 (cold leg discharge) → OPEN 21SJ40 (hot leg discharge, key-locked) → START 21 SI Pump. Also at Step 4.0: CLOSE 22CS36 (RHR supply to CS) and OPEN 22SJ49 (cold leg isolation valve).
JPM — 2019 Sim-b
Nearly identical scenario to 2023 Sim-b. Two alternate paths during hot leg recirc alignment: (1) at Step 4 cont'd, 21SJ45 is CLOSED for 21 RHR pump maintenance — RHR-to-SI pump cross-connect unavailable; (2) at Step 4.1, 22 SI pump NOT running (tripped during LOCA-3) — must use 21 SI pump via Step 6.1. Realignment sequence: STOP 21 SI Pump → CLOSE 21SJ134 → OPEN 21SJ40 (key-locked) → START 21 SI Pump. Starts in LOCA-1 at Step 27 (remove SJ40 lockouts, wait for 6.5 hour time requirement), then transitions to LOCA-4.
Exam — 2018 Q77
EOP-LOCA-1 timing requirements: start preparations for hot leg recirculation 12 hours after SI actuation; perform EOP-LOCA-4 (Transfer to Hot Leg Recirculation) 14 hours after SI actuation. Trap: 12 hours is when preparations START, 14 hours is when the actual transfer is PERFORMED. With SI at 07:00, LOCA-4 performance time is 21:00, NOT 19:00.
Connections
- Related systems: ECCS, RHR
- Related EOPs: EOP-LOCA-1 — Loss of Reactor or Secondary Coolant, EOP-LOCA-5 — Loss of Emergency Coolant Recirculation
- Related exam questions: 2018 Q77, 2019 Q77
- Related JPMs: 2019 JPM Sim-b, 2023 JPM Sim-b
- Related exam: 2018 NRC Written Exam, 2019 NRC Written Exam, 2019 NRC Operating Exam, 2023 NRC Operating Exam