EOP-TRIP-6 — Natural Circulation Cooldown Without RVLIS
⚠️ DRAFT — Reconstructed from exam materials
Purpose
Provides guidance for natural circulation cooldown with steam voids in the vessel when RVLIS is NOT available. Entered from EOP-TRIP-4 when both trains of RVLIS are unavailable and rapid cooldown/depressurization is required.
Key Actions / Information
Exam — 2022 Q84
Maximum allowable RCS cooldown rate depends on RCS T-Hot temperature: with T-Hots > 500°F, maximum cooldown is 50°F/hr; with T-Hots < 450°F, maximum cooldown is 100°F/hr. 2PT-405 (Wide Range RCS Pressure) is an input to Train B RVLIS. If Train A RVLIS is OOS and 2PT-405 fails, both trains of RVLIS are unavailable — enter EOP-TRIP-6, not EOP-TRIP-5.
Exam — 2020 Q84
Rapid natural circulation cooldown rates: without RVLIS, initial cooldown to 500°F is limited to < 50°F/hr, then < 100°F/hr afterwards. With RVLIS, maximum rate is 100°F/hr for the entire cooldown. Note: The 2020 exam labels TRIP-5 as "without RVLIS" and TRIP-6 as "with RVLIS" — this is reversed from the 2022 exam labeling. The cooldown rate values are consistent across both exams. The procedure numbering may reflect a revision change.
JPM — 2018 Sim-c
Step 12 — SI Accumulator Isolation during natural circulation cooldown with RCS pressure <1000 psig: remove lockout from 21-24 SJ54 at 2RP4. Close all four SJ54 Accumulator Outlet Valves. 24SJ54 fails at intermediate position (alternate path). Vent 24 Accumulator: verify RCS pressure > accumulator N2 pressure, open 2NT35 (N2 HDR VALVE) and 24SJ93 (N2 SUPPLY VALVE) to vent to atmospheric pressure, then close both vent valves when pressure reaches zero.
Exam — 2018 Q8
Per 1-EOP-TRIP-6 Step 1: before restarting an RCP, saturated conditions must first be established in the PZR. The reason is to limit the PZR pressure DECREASE upon RCP restart. Saturation determination requires converting psig to psia: at 2005 psig (2020 psia), T-sat = 637°F. If PZR liquid temperature is 635°F, the PZR is subcooled (not saturated). Trap: steam tables use psia, not psig — must add ~15 psi to convert. Also: the concern is pressure DECREASE, not increase. A water-solid pressurizer concern (pressure rise) applies during different plant conditions.
Connections
- Related systems: RVLIS, RCS, ECCS
- Related EOPs: EOP-TRIP-4 — Natural Circulation, EOP-TRIP-5 — Natural Circulation Cooldown With RVLIS
- Related procedures: S2.OP-SO.SJ-0002 — Accumulator Operations
- Related exam questions: 2018 Q8, 2022 Q84, 2020 Q84
- Related JPMs: 2018 JPM Sim-c
- Related exam: 2018 NRC Written Exam, 2018 NRC Operating Exam, 2022 NRC Written Exam, 2020 NRC Written Exam