1. RESOLUTION OF GENERIC SAFETY ISSUE 191
Strainer Bypass Testing NEI Workshop
October 18 and 19, 2012
Steve Smith
Office of Nuclear Reactor Regulation

2. Strainer Bypass Testing - Introduction
Importance of Bypass Quantification
Test Conditions
Debris Prep and Addition
Flow Rate/Velocity
Debris Collection
Tank/Flume Conditions
Termination Criteria
Evaluation of Results
Other Considerations

3. Strainer Bypass Quantification Importance
Staff initially not focused on strainer bypass
Bypass amount higher than anticipated
Initial quantification vs. new reactors
Downstream sensitivity
In-vessel limits lower than anticipated

4. Strainer Bypass Testing - Test Conditions
Test Conditions – similar to head loss testing
Debris preparation
Use standard debris prep
NEI method
Other accepted vendor methods
Debris introduction
Small well diluted batches
Agglomeration
Sensitivity of bypass to concentration
Most transportable debris first or all fines
May not need full load
Particulate debris not required

5. Strainer Bypass Testing – Test Conditions
Tank/Flume Conditions
Stirring
No effect on bed formation
Early formation could reduce bypass
Bed disturbance could increase bypass
Tests that allow near field settling
Velocity and turbulence conservative with respect to plant
Same requirements as strainer testing

6. Strainer Bypass Testing – Test Conditions
Flow Velocity
Higher is generally conservative
Sacrificial area
Number of strainers
Number of pumps
Uniform flow vs. Non-uniform design
Area
Larger is conservative for testing
Area vs. velocity tradeoff not understood
Likely depends on strainer design

7. Strainer Bypass Testing – Test Conditions
Debris Collection
Use full flow filter
Ensure no bypass (through or around)
Changeable on line
Careful control of filter pre and post test
Weight considerations
Drying
More frequent grab sampling may supplement filter results for trending

8. Strainer Bypass Testing – Test Conditions
Termination Criteria
Base on filter results
May have to run test long since results not immediately available
Release may continue after bed formed
Near field tests may have delayed transport

9. Strainer Bypass Testing – Result Evaluation
Low upstream loads may bypass higher percentage
At some load bypass should stop or approach zero
Define bypass per screen area for various loads?
Maximum design basis value simpler
More complex for risk-informed or time based evaluations
Time based results-interim collections
How to estimate timing in plant?
Can plant conditions influence bypass?
Securing or starting pumps
Changing strainer flow rate

10. Strainer Bypass Testing – Results Evaluation
Repeatability
Extrapolation and interpolation
If sensitivities understood
Unlikely to accept extrapolation significantly beyond test conditions

11. Strainer Bypass Testing – Other Considerations
Testing may be done in groups
Strainer design
Manufacturer
Hole Size
Velocity
Debris load
Licensees validate applicability
Sensitivity testing
Water chemistry
Debris concentration

12. Strainer Bypass Testing – Other Considerations
Uniform vs. non-uniform flow strainers
Variations in approach velocity
Variations in debris bed formation
Changing parameters may affect uniform and non-uniform strainers differently
Debris loading
High and low debris loads may behave differently under varying conditions
Water chemistry
Use prototypical or evaluate sensitivity