Power Operations 20-100% Flashcards Preview

LOIT 2020 GOP phase > Power Operations 20-100% > Flashcards

Flashcards in Power Operations 20-100% Deck (56)
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Why should you slowly place MSRs in service?

avoids excessive temp transients which minimizes Turbine vibrations.


What operator actions with MSRs helps maintain LP Turbine dTemperature < 50F?

  • Operate MSRs in the same Mode to maintain LP Turbine ∆T’s < 50°F.


State several items that can affect the intensity of MT vibrations during operation.

  • Lubricating oil temperature
  • Low turbine loading
  • High rates of power change
  • High rates of condenser vacuum change or approaching 2” HgA
  • ∆T across the condenser section
  • MSR operation
  • Steam drain operation
  • Thermal transients (Equipment malfunctions that direct steam or drains to the condenser)


What steady state method of turbine control maintains plant stability?

What else does this minimize with respect to the TCVs.

  • Steady state: turbine control on the load limiter. Maintains plant stability and minimize pressure surges on control valves.


What is the normal MT vibration threshold?

What is the MT trip criteria for high vibrations?

When should a reactor trip be performed with regard to high vibrations in the MT?

  • 5 mils (normal Turbine vibration)
    • Auto turbine trip at 12 mils unfiltered
  • Turbine trip criteria:
    • Filtered journal vibration > 10 mils and rapidly ↑ towards 12 mils at rated speed
    • Filtered vibration > 10 mils with a slow ↑ towards 12 mils after a 15 minute time span at rated speed
  • Reactor trip criteria (if during normal power reduction with a planned reactor trip):
    • Sudden step ↑ of 2 mils
    • Vibration ≥ 10 mils


What is the temperature limit for the following:

MT oil drain temp.

MT bearing metal temp.

LP turbine steam inlet temp change limit.

  • ≤ 170°F: Limit for Turbine oil drains during continuous operation at the hottest bearing.
  • ≤ 225°F: Normal turbine bearing metal temperature.
  • < 125°F/hour: Normal LP turbine steam inlet temperature change limit. Short term changes limited to 250°F/hour.


What operations should be avoided to minimize MT damage with regards to vibrations?

  • < 40% load with C shell ≥ 5 inches HgA (vibrations)
  • < 40% load (410 MW) and C shell > 4” to < 5” HgA for 1 hour max (vibrations)


How can breaking vacuum above 1200rpm affect the turbine? 

When is it allowed?

  • Breaking vacuum > 1200 rpm (excessive loading on Last Stage Buckets)
  • In emergencies only.


What is detrimental about maintaining vacuum without GS in service?

  • Maintaining vacuum after gland seal steam lost  can cause thermal shock to rotor by intake of cold air.


What can happen if excessive use of exhaust hood Sprays at low speeds and low loads is allowed?

erosion of last stage buckets


What minimum speed and load should be avoided with regards to the MT?


  • Operating < 800 rpm (> 5 min). (Cause packing rub, high vibes not indicated, or bowed rotor)
  • Minimize operation < 5% load (moisture erosion on last stage buckets)


What are teh exhaust hood temperature limits and what coudl happen if they are violated?

  • ≤ 125°F: rapid load changes allowed
  • 125 - 175°F: may operate continuously but change load slowly (0.5%/min) (avoids unnecessary thermal stress)
  • 200-225°F: 15 minute max operations (turbine trips at 225°F)


State the following:

rate of turbine load reductions

normal power reductions

TG operation prior to start

continuous TG operations.

  • ≤ 10%/min load reductions minimizes turbine thermal stresses.
  • Limiting normal power reductions to 20%/hour (4 hour normal shutdown) will minimize turbine vibration.
  • < 48 hours TG operation prior to turbine start may cause shaft bowing
  • Avoid long periods of TG operations. Generator field grounds may occur from copper dust build-up. (galling of windings)


With regard to Condenser backpressure:

  1. State the C shell max backpressure
  2. C shell operations that minimizes MT vibrations
  3. Reactor trip setpoints

  1. C shell max backpressure is < 5.0” HgA.
  2. C shell > 2” HgA and ≤ 4” HgA minimizes Turbine vibration.
  3. Trip reactor if load < 410 MW and > 4” HgA for > 1 hour
    • Trip reactor if load 5” HgA



Why should the condenser vacuum be maintained as close as possible to table values?

> 40% pwr


  • > 40% power: maintain average pressure as close to table values as possible (↑ turb efficiency / ↑ MWe)
  • Maintain A shell pressure above the table values (↓ erosion of condenser internals from excess steam velocities)


What actions are taken to prevent exceeding 5" HgA?

  • Reduce turbine load to prevent exceeding 5” HgA


State the ASI limits associated with LCO 3.2.5.

  • LCO 3.2.5 ASI limits:
    • COLSS Operable
      • -0.18 ≤ ASΙ ≤ 0.17 (> 50%)
      • -0.28 < ASI < 0.17 (> 20% and < 50%)
    • COLSS out of service (CPC)
      • ± 0.10 ASI (>20%)


When should ASI dampening be performed?

  • ASI dampening performed if ASI will exceed ESI by ± 0.1.


At what ASI threshold is a reactor trip performed?

  • Trip the reactor if exceeded or trending to ± 0.5 (CPC Hot Pin ASI Aux Trip).
    • ASI input to CPC aux trip depends on power
    • ≥ 51% (sum of the 3 NIs): uses actual power distribution (during power ascension)
    • ≤ 45% (sum of the 3 NIs): uses a canned value (during power reduction)


Which of the following should be used during a downpower?

Colss asi or CPC asi?

  • CPC and COLSS can calculate a large ASI difference due to design differences and calculation processes. CPCs generate an auxiliary trip prior to COLSS indicating a problem with ASI.


When is PZR boron equalization performed?

  • ≥ 50 ppm RCS Boron conc. change: perform PZR boron equalization 
    • Maintain until ≤ 10 ppm difference (RCS vs PZR)



Who is notified if Rx power is < 85% for more than 10 days?

  • Power < 85% for > 10 days: notify nuclear fuel groups for evaluation.


Who is notified if a power change is required or ASI dampening is performed and why?

When is the sample required?

  • Chemistry notified of any power change or ASI dampening (sample for iodine spikes)
  • LCO requires sample within 2-6 hours of a ≥ 15% / hour power change


What is required from section 6.1 prior to raising power > 20%?

  • 20% mode change checklist complete (ZZ11)
  • Maintain Power Ascension Rate Limits (App. A)
  • Unit Ops Manager permission required if SBCS, PLCS, PPCS, or FWCS are NOT in Auto.
  • Monitor AZTILT (LOC limit and CPC value < actual tilt)
  • Place MSRs in-service


When are both HDPs placed in service?

  • 20-25% plant power: place both HDTPs in-service


When are extr steam drains and turbine drains closed?

  • 250 MWe: close extraction steam drains and turbine drains


What happens at 30, 50 and 90% on power ascension?

  • 30%, 50%, 90%: chemistry hold points



When is the 3rd CDP started?



When is the second MFP started?

40-60% reactor power


When is RPCB placed in service and when are subgroups selected?


  • 70% reactor power: place RPCB in-service with NO subgroups selected
  • 74% reactor power: select RPCB subgroups