FR-P.1 — Response to Imminent Pressurized Thermal Shock Condition¶
CSF RCS integrity — RED path. Entered when RCS pressure-temperature
trajectory crosses or is about to cross the reactor vessel PTS limit
curve — high RCS pressure combined with rapidly falling cold-leg
temperature. The combination loads the vessel beltline weld with a
through-wall stress gradient that can propagate brittle flaws.
Recovery is by terminating the cold-injection mechanism (stopping or
throttling SI) and re-warming the RCS with pressurizer heaters /
charging while pressure relief is held available. See Vogtle UFSAR
§5.3.3 (PTS analysis) and 10 CFR 50.61 (PTS Rule).
The PTS limit curve is plant- and cycle-specific; for Vogtle the
applicable curves are in Tech Spec 3.4.3 figures (heatup and cooldown
P-T limits, RTNDT-shifted for end-of-life vessel embrittlement).
CSF: rcs-integrity
Step 1 verify-pts-trajectory¶
Check: RCS pressure «PT-455» AND cold-leg temperatures (lowest of «TE-411-COLD» / «TE-421-COLD» / «TE-431-COLD» / «TE-441-COLD»); compare against the PTS limit curve (Tech Spec 3.4.3); trajectory must be evaluated as (T_cold, P_RCS) point AND its rate of motion toward the limit
Caution: PTS is a TRAJECTORY criterion not a point criterion — entry into FR-P.1 is justified by predicted crossing within minutes, not by exceeding curve at current instant
Note: the dominant PTS-driving event is a small-break LOCA at the end of cycle, where high-pressure SI continues injecting cold borated water into the cold legs while RCS pressure remains above the SI shutoff head
- PTS trajectory confirmed (current point + trajectory crossing PTS curve within minutes) → #limit-cooldown
Because: RED-path PTS response is non-discretionary
- Off-trajectory (point within curve, trajectory not crossing) → E-0
Because: false alarm or recovered; return to diagnostic flow
Step 2 limit-cooldown¶
Within: 5 minutes — PTS trajectory recovery requires several minutes for thermal masses to redistribute; act before further damage potential accumulates
Action: throttle high-head SI «SI-PUMP-A» / «SI-PUMP-B» flow to the minimum needed for subcooling — full SI flow with high RCS pressure is the primary PTS driver
Action: stop low-head SI / RHR injection if RCS pressure is well above accumulator setpoint (~600 psig) — accumulators won't deliver and low-head can't push against high RCS pressure anyway, but verify isolation
Action: energize pressurizer heaters «PZR-HTR» up to maximum allowed to add heat and slow cold-leg cooldown
Action: open pressurizer PORVs «PORV-456A» / «PORV-456B» if pressure must come down (PTS limit relaxes at lower pressure)
Caution: throttling SI reduces inventory makeup during an ongoing LOCA — balance PTS prevention against core-cooling need; if subcooling margin «SUB-MARGIN» drops, escalate to FR-C.2
- PTS trajectory recovering (T_cold rising OR pressure dropping into safe region) → #verify-recovery
Because: response succeeded; verify before declaring recovery
- Cannot interrupt PTS trajectory → FR-P.2
Because: anticipated-PTS response handles the slower-rate case; some PTS-mitigation actions may stabilize at ORANGE rather than RED
Step 3 verify-recovery¶
Check: (T_cold, P_RCS) point + trajectory back inside the PTS curve with positive margin; subcooling margin «SUB-MARGIN» maintained ≥ 30 °F
Within: hold this step for ≥ 5 minutes of stable, improving trends before exit — vessel-beltline thermal-stress relaxation takes longer than instrument-loop time constants
- Off PTS trajectory AND subcooling maintained → E-0
Because: RCS integrity CSF restored to GREEN; return to diagnostic flow
- Still challenged → FR-P.2
Because: ORANGE-path response continues until trajectory clearly clears
Tags¶
-
id: PT-455
description: pressurizer pressure (wide range)
sim-path: rcs.pressurizer.pressure_wr
units: psig
equipment: pressurizer
source: Vogtle UFSAR §5.4 -
id: TE-411-COLD
description: RCS loop 1 cold-leg temperature
sim-path: rcs.loop1.t_cold
units: degF
equipment: rcs-loop-1
source: Vogtle UFSAR §5.1.1 -
id: TE-421-COLD
description: RCS loop 2 cold-leg temperature
sim-path: rcs.loop2.t_cold
units: degF
equipment: rcs-loop-2
source: Vogtle UFSAR §5.1.1 -
id: TE-431-COLD
description: RCS loop 3 cold-leg temperature
sim-path: rcs.loop3.t_cold
units: degF
equipment: rcs-loop-3
source: Vogtle UFSAR §5.1.1 -
id: TE-441-COLD
description: RCS loop 4 cold-leg temperature
sim-path: rcs.loop4.t_cold
units: degF
equipment: rcs-loop-4
source: Vogtle UFSAR §5.1.1 -
id: SI-PUMP-A
description: high-head SI pump A status
sim-path: ess.si_pump.a.status
units: enum[STOPPED,RUNNING,FAULT]
equipment: si-system
source: Vogtle UFSAR §6.3 -
id: SI-PUMP-B
description: high-head SI pump B status
sim-path: ess.si_pump.b.status
units: enum[STOPPED,RUNNING,FAULT]
equipment: si-system
source: Vogtle UFSAR §6.3 -
id: PZR-HTR
description: pressurizer heater bank energization status
sim-path: rcs.pressurizer.heaters.status
units: enum[OFF,ON,FAULT]
equipment: pressurizer
source: Vogtle UFSAR §5.4 -
id: PORV-456A
description: pressurizer PORV 456A position
sim-path: rcs.pressurizer.porv.456a.position
units: enum[OPEN,CLOSED,INTERMEDIATE]
equipment: pressurizer
source: Vogtle UFSAR §5.4 -
id: PORV-456B
description: pressurizer PORV 456B position
sim-path: rcs.pressurizer.porv.456b.position
units: enum[OPEN,CLOSED,INTERMEDIATE]
equipment: pressurizer
source: Vogtle UFSAR §5.4 -
id: SUB-MARGIN
description: RCS subcooling margin (T_sat at PT-455 minus hot-leg temperature)
sim-path: rcs.subcooling_margin
units: degF
equipment: rcs
source: Vogtle UFSAR §15.6