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1

201.22 ESF Systems


Function of Engineered Safety Features System

Protect the public by controlling the release of fission products and limiting the release of fission products and radiation IAW federal regulations.

 

Methods Used:

Design core in conjunction with reactor protection system to insure fuel rod integrity

Retain fission products in Reactor Coolant System (RCS)

Retain fission products in Containment

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201.22 ESF Systems


List accidents for which ESFs are designed

Loss of Coolant Accident (LOCA)

Steam Break

Fuel Handling Accident

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201.22 ESF Systems


ESF design bases

Seismic Category I - Classification assigned to those structures, systems, and components that are safety-related and designed to withstand the effects of the safe shutdown earthquake and remain functional.

 

Redundant – Use of multiple trains and instrumentation channels

 

Independent – ESF trains stand alone

 

Separate – Physically and electrically separated

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201.22 ESF Systems


Single Failure Criteria

Fluid and electric systems are considered to be designed against an assumed single failure if neither:

a single failure of any active component (assuming passive components function properly)

NOR

a single failure of a passive component (assuming active components function properly)

results in a loss of the capability of the system to perform its safety function.

 

An occurrence which results in the loss of capability of a component to perform its intended function.

Multiple failures resulting from a single occurrence are considered to be a single failure.

Train “A” ECW Pump fails to start on SI signal so the associated D/G cannot perform its function.

 

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201.22 ESF Systems


10 CFR 50.67 Site Criteria

1.An individual located at any point on the boundary of the exclusion area for any 2-hour period following the onset of the postulated fission product release, would not receive a radiation dose in excess of 25 rem total effective dose equivalent (TEDE).

 

2. An individual located at any point on the outer boundary of the low population zone, who is exposed to the radioactive cloud resulting from the postulated fission product release (during the entire period of its passage), would not receive a radiation dose in excess of 25 rem total effective dose equivalent (TEDE).

 

3. Adequate radiation protection is provided to permit access to and occupancy of the control room under accident conditions without personnel receiving radiation exposures in excess of 5 rem total effective dose equivalent (TEDE) for the duration of the accident.

 

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201.22 ESF Systems


Difference between an active and passive failure

Active failure - failure of a powered component to perform it’s function (e.g. pump fails to start, valve fails to re-position)

Passive failure - failure of a static component (e.g. a pump seal fails, pipe leak)

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201.22 ESF Systems


Which systems make up the Engineered Safety Features System?

Emergency Core Cooling (ECCS) - HHSI (1560 psig), LHSI(300 psig), SI Accumulators (600-650 psig)

Containment Isolation

Containment Heat Removal - Containment Spray, RCFCs

Containment Combustible Gas Control - Recombiners, Supplementary Purge

Electrical Aux. Bldg. and Control Room Envelope HVAC

Fuel Handling Building Exhaust HVAC

Auxiliary Feedwater

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201.22 ESF Systems


What are the Engineered Safety Features support systems?

Ultimate Heat Sink (ECW Pond)

ECW

CCW

Standby D/Gs

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201.22 ESF Systems


ESF general loading sequence for Mode I actuation 

MODE I - SI ONLY

Offsite power available

All equipment operating prior to the MODE I actuation remains in service (load shed signal not generated)

Diesel generators start, but do not connect to the buses

Sequencers start non-operating equipment as required

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201.22 ESF Systems


ESF general loading sequence for Mode II actuation

MODE II - Loss of Offsite Power (LOOP)

All equipment operating prior to the MODE II actuation is terminated by load shed signal

Diesel generators start and connect to the buses within 10 seconds to restore power

Sequencer starts loads

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201.22 ESF Systems


ESF general loading sequence for Mode III actuation 

MODE III - SI and LOOP

All equipment operating prior to the MODE III actuation is terminated by load shed signal

Diesel generators start and connect to the buses within 10 seconds to restore power

Mode III sequence is the same as Mode I after the load center breakers are sequenced on at 1 second.

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201.22 ESF Systems


What will cause an SI?

Low PZR Pressure - 1857 psig 2/4

2 switches on CP-005 can block if PZR < 1985 psig, both req.

Reset with 1 switch or > 1985 psig

Containment pressure Hi-1 - 3.0 psig 2/3

Low Compensated Steam Line Pressure - 735 psig 2/3 in 1/4 steam lines

2 switches on CP-005 can block if PZR < 1985 psig, both req.

Reset with 1 switch or > 1985 psig

Blocking enables MS Isolation on rate decrease > 100 psig / 50 sec

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201.22 ESF Systems


What causes an SI Auto Recirc?

SI present and Lo Lo RWST Level (75,000 gal)

HHSI and LHSI Miniflow valves close

Once 1 valve in each pair is closed, containment sump to SI suction header opens for that train

RWST to SI suction header valves must be manually closed by control room operator