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EOPs > EOP-FRTS-1 — Response to Imminent Pressurized Thermal Shock

EOP-FRTS-1 — Response to Imminent Pressurized Thermal Shock

⚠️ DRAFT

EOP-FRTS-1 — Response to Imminent Pressurized Thermal Shock

Purpose

Entered when the Thermal Shock Critical Safety Function Status Tree indicates an imminent Pressurized Thermal Shock (PTS) condition. Directs mitigating actions to reduce the likelihood of brittle fracture of the reactor vessel.

Entry Conditions

RED path on the Thermal Shock CFST: RCS T-Cold cooldown rate exceeds 100 degrees F in the last 60 minutes AND RCS pressure/temperature points are not to the right of Limit A in Figure 4A.

PURPLE path on the Thermal Shock CFST: RCS Cooldown > 100 degrees F/hr AND RCS T-Colds > 230 degrees F but < 280 degrees F.

Key Mitigating Actions

Exam — 2020 Q32
FRTS-1 bases: ECCS flow may have contributed to the RCS cooldown or may prevent a subsequent reduction in RCS pressure — therefore SI termination is directed. An RCP restart is attempted to mix the cold incoming ECCS water and the warm reactor coolant water, thereby decreasing the likelihood of a PTS condition. SI termination is NOT because a soak requires it — some SBLOCA conditions prevent SI termination. RCP restart is NOT for normal spray use or boron equalization — it is specifically for thermal mixing.
Exam — 2022 Q85
RED Path in Thermal Shock Status Tree: all RCS T-Cold cooldown rates not less than 100 degrees F in the last 60 minutes AND RCS pressure/temperature points not to the right of Limit A in Figure 4A (e.g., T-Colds < 230 degrees F at 1100 psig). This RED path takes priority over YELLOW path (Heat Sink) and PURPLE path (Shutdown Margin).
Exam — 2020 Q85
FRTS-1 step 1 (RCS Pressure Status): if RCS pressure < 300 psig AND RHR flow ≥ 300 gpm, then return to procedure in effect — no further FRTS-1 actions are implemented. Entry is still required on PURPLE path (cooldown > 100°F/hr, T-Colds 230-280°F), but the low-pressure/adequate-RHR-flow condition means PTS is not a concern. Trap: entry into FRTS-1 IS required even with low RCS pressure — the CFST drives entry regardless. The one-hour soak is not performed when step 1 directs return. AB.LOCA-0001 (Shutdown LOCA) is only applicable in MODE 4 or MODE 3 with accumulators isolated — not for MODE 3 at normal operating pressure.

RCS Soak (Step 29)

Exam — 2019 Q74
FRTS-1 Step 29 RCS soak requirements: during the soak, the crew must maintain RCS temperature stable AND NOT raise RCS pressure. The RCS soak is designed to reduce temperature stresses present in the Reactor Vessel (not the RCS piping or pressurizer). Trap: the soak controls BOTH temperature and pressure — not temperature only. Also, the target component is the reactor vessel specifically, not the RCS piping system in general.
Scenario — 2018 #2
RED path for Thermal Shock entered during EOP-LOCA-1 (LBLOCA). Entry/exit criteria: RCS pressure NOT > 300 psig (420 psig adverse) AND RHR flow at least 300 gpm on 21 or 22 SJ49 cold leg injection meters. Crew returns to EOP-LOCA-1 immediately (enter/exit — no prolonged actions in FRTS-1).

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