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

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

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

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

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

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

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

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

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

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

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

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