1. NON-TRACER GAS METHODS TO EVALUATE ISOLATION DAMPER LEAKAGE Peter Lagus, Ph.D., CIH Lagus Applied Technology, Inc Joe Bendyk Exelon Limerick Station NHUG Chicago, Illinois July 2008
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2. ALTERNATIVE TEST(S) FOR ISOLATION DAMPER LEAKAGE
For reconnaissance test we want “simple” go/no-go test
Want less expensive and less procedurally intensive test than a tracer gas test
Ideally, test to be performed by plant personnel
For reconnaissance test, need not have the precision and accuracy needed during inleakage testing.
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3. CRH ISOLATION DAMPERS
Occur singly or in pairs within a given ventilation train
Provide isolation from unfiltered or normal OS Air intakes
Provide isolation of CREVS from adjacent (non-safety) systems
Can contribute significant unfiltered inleakage
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4. MAJOR TYPES OF CRH ISOLATION DAMPERS
Butterfly
Parallel Blade
Opposed Blade
Expandable Bladder
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5. DAMPER LEAK RATES
Bubble-tight damper spec (ANSI N510) implies SCFM allowable leakage
A 0.01 inch opening between two flat 24 inch damper blades will leak roughly 3-4 SCFM with a 5 in. w.g. differential pressure
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6. DAMPER PAIR LEAKAGE TEST
Qleak
Interval Volume, V
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7. DAMPER PAIR LEAKAGE TEST
Close both dampers and use volume between them as a test chamber
Methods based on ANSI N510
Direct Flow Rate Measurement
Pressure Decay Measurement
Caveat: Testing both dampers simultaneously may INOP the CREVS/CRE.
Depends on system design and plant specs
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8. DIRECT FLOW RATE MEASUREMENT
Provide measured flow rate at appropriate (low) delivery pressure (usually the System Design dP)
Flow for 10 minutes
Record flow rate every 30 seconds
Compute average flow rate.
Required components
Compressed air source
Delivery regulator
Low pressure (pancake) regulator
Flow Meter
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9. PRESSURE DECAY METHOD
Pressurize volume to 1.25x System Design Pressure
Measure pressure decay at 1 minute intervals for 15 min (or until pressure decays to 75% of design value)
Measure gas temperature in volume at beginning and end
VERY Sensitive to Temperature Changes
1 Deg F dT can cause approx 10% change in calculated flow!!
Calculate leakage rate
Required components
Compressed air source
Temperature sensor
Pressure sensor
Absolute pressure readings are better
Pressure readings should be corrected for barometric drift
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10. LEAK RATE CALCULATION Qav=Average Leak Rate (SCFM)
Pi,Pf=Initial and Final Pressures (lb/ft2)
Ti,Tf=Initial and Final temperatures (Deg R)
RA=Gas Constant ft-lb/(lb Deg R)
dt = time interval (min)
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12. WHAT ABOUT A SINGLE ISOLATION DAMPER?
Previous tests use two dampers to create test volume
Works great if neither damper leaks
If either damper leaks then need a method to measure flow across each separately
Infrequently isolation can be provided by a single damper
Very rare
Test can be qualitative or semi-quantitative test
Use simple test gear
No major intrusion into ductwork/damper area
Short duration test(s)
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13. SINGLE DAMPER LEAKAGE TESTS
Source and Receptor Tests
Use smoke, aerosol, visible light as source
Use appropriate sensing equipment/element
Traverse Tests
Use flow through damper opening to detect leak
Measure flow directly or measure another characteristic of the flow
Feeler Gauge along Sealing Surfaces
Need access
May affect dP conditions
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14. CAVEATS No warranty implied or expressed
Some of the following test techniques/test equipment have not been used in the nuclear industry
Some of these test techniques/test equipment are used in other industries to find leakage sites
Other test equipment may be more useful or usable than the equipment shown in the following
Theoretically all of the following test techniques should be capable of finding a leaking damper
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15. SINGLE DAMPER LEAKAGE TESTS (SOURCE & RECEPTOR TESTS)
Smoke Generator plus Borescope (+ light source)
DOP Generator plus Light Scattering Photometer
Light Source plus Photometer
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16. SINGLE DAMPER LEAKAGE TEST
SAMPLE
Qleak
SOURCE
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19. LIGHT SOURCE FOR GE BORESCOPE
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20. SMOKE GENERATOR FOR DAMPER TEST
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22. AEROSOL GENERATORS
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23. LASKIN NOZZLE AEROSOL GENERATOR
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24. VISIBLE LIGHT PHOTOMETER
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25. LED LIGHT SOURCE
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26. SINGLE DAMPER LEAKAGE TESTS (TRAVERSE TESTS)
Ultrasonic Probe
At 5 in. w.g. differential across at a 24 inch long by 0.01 inch crack the flow velocity is several thousand FPM
Probe is “tuned” for air leak frequencies
Hot Wire Anemometer Flow Traverse
MUST hold anemometer probe perfectly still!!
Measurement uncertainty is large, but because of the high sensitivity the measurement shows which damper(s) leaks
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27. ULTRA SONIC PROBE IN USE
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28. ULTRA SONIC PROBE
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29. HOT WIRE TRAVERSE Measure flow at several traverse points
Any indication of flow indicates a leak if the probe is stationary
Probe MUST be stationary
Use Vent Lok with Thermocouple fitting to clamp the probe
Hot Wire anemometer exhibits sensitivity as low as 5 FPM.
In a 1 ft2 duct this is 5 CFM!
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30. HOT WIRE TRAVERSE TEST VENT LOK WITH SWAGE THERMOCOUPLE FITTING DUCT
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31. HOT WIRE ANEMOMETERS
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32. RECOMMENDATIONS If possible, test dampers pair-wise
Careful NOT to INOP System
If leakage is unacceptable, then use single damper tests to find out which one (or both) is leaking
Single damper tests need not be quantitative since a leak indication is all you are looking for
If you find a “leaker” you gotta bite the bullet and fix it.
Joe Bendyk at Limerick--ask about borescope and smoke test
Kevin Fleming for details about DOP + L. S. Photometer test
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