ML22307A235
| ML22307A235 | |
| Person / Time | |
|---|---|
| Issue date: | 10/21/2022 |
| From: | Coyne K, Kenneth Hamburger, Nick Melly, Markhenry Salley, Gabe Taylor NRC/RES/DRA |
| To: | |
| References | |
| Download: ML22307A235 (1) | |
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Overview of USNRC Research Activities to Update PRA Treatment of High Energy Arcing Faults Kevin Coyne, Kenneth Hamburger, Nicholas Melly, 26thInternational Conference on Structural Mechanics in Reactor Technology (SMiRT 26) 17th International Post-Conference Seminar on Gabriel Taylor, Mark Henry Salley FIRE SAFETY IN NUCLEAR POWER PLANTS AND INSTALLATIONS
HEAF Background A High Energy Arcing Fault (HEAF) is a failure mechanism postulated for equipment at 440 V and higher
- Caused by poor or degraded electrical connections, foreign material ingress, misaligned breakers
- Rapid release of energy, including ionized gases, molten metal, and overpressures. Often accompanied by ensuing classical thermal fire
Regulatory Context Appendix R Reg Guide 1.205 NRC Endorses Prescriptive requirements Endorses NUREG/CR-NFPA-805 for nuclear fire protection 6850 1980 2001 2004 2005 2006 2010 NFPA-805 NUREG/CR-6850 Performance-based NUREG/CR-6850 standard for nuclear fire Supplement 1 Fire PRA Methodology protection Includes bus ducts
Original HEAF ZOI Documented in Appendix M of NUREG/CR-6850. Based largely on 2001 HEAF at San Onofre (pictured on right)
- ZOI was 3 feet (0.9 m) horizontally and 5 feet vertically (1.5 m)
- Insensitive to parameters affecting the severity of the HEAF (voltage, current, duration, geometry, materials, etc.) - One-size-fits-all
Original HEAF ZOI Bus ducts addressed in NUREG/CR-6850 Supplement 1 as part of the FAQ process
- ZOI was sphere of 1.5 ft (0.45 m) radius, and a 30-degree right cone extending downward for 20 feet (6 m).
- Like switchgear, this model also neglected parameters affecting the severity of the HEAF (voltage, current, duration, geometry, materials, etc.) - One-size-fits-all
HEAFAwesome ResearchServices Motivation to perform experiments for obtaining Phase I Test 23 - potential for comprehensive scientific fire data on the HEAF phenomena known to occur in NPPs increased ZOI where aluminum is through carefully designed experiments involved
Research Activities Overview The NRC developed a comprehensive project plan, consisting of five main tasks:
Development of a Survey of the US Physical Testing Fragility Testing PRA Method CFD Model Nuclear Fleet to support the to assess target Development for predicting a wide to ensure that full- development and damage from HEAF to improve the variety of electrical scale experiments are validation of the CFD events realism of the model and equipment representative model and update fire configurations ignition frequencies
Development of a CFD Model Leverage experimental data and provide information for configurations that were not subject to full-scale testing. This provides a cost-Low Voltage Switchgear effective and flexible approach. Bus bar material (aluminum, copper), arc duration, arc location, arc energy 34 FDS simulations Medium Voltage Switchgear Bus bar material (aluminum, copper), arc duration, arc location, arc energy 42 FDS simulations Non-segregated Bus Ducts Duct material (aluminum, steel), bus bar material (aluminum, copper) arc duration, duct geometry, arc energy 57 FDS simulations
Survey of US Nuclear Fleet Conducted by the Electric Power Research Institute (3002020692)
Bus Bar Insulation MV bus bars primarily insulated; LV bus bars are usually not Switchgear Style 83% of switchgear use horizontal draw-out style; the remainder use vertical-lift style SAT Fault Clearing Times Presence of Aluminum Typically located in the main 50% of units had SAT FCTs of 2 bus bars and primary cable seconds or less compartment
Awesome Physical Testing Services Small-Scale Medium-Scale Full-Scale Aluminum/copper particle size Direct observation of the arc, Enclosure breach, event progression, distributions, rates of particle enclosure breach, material loss, arc pressure rise, thermal/visual imaging.
production, particle morphology, and oxidation spectral emissions Served as benchmark cases for CFD model.
Fragility Testing The need for defining fragility criteria with respect to HEAFs was a key conclusion of the 2017 Phenomena Identification and Ranking Table (PIRT).
Physical Testing Conducted at SNLs Solar Furnace facility to simulate the effects of a short duration, high heat flux exposure Engineering Analysis Data analysis, operating experience review, and consensus building to establish fragility criteria
PRA Method Development Fault Zone Analysis Location of fault within plant EDS determines maximum fault duration and provides credit for circuit protection features Generator-Fed Faults & GCB Accounts for potential generator-fed fault and provides credit for generator circuit breakers
PRA Method Development Supply vs. Load Configuration Additional specificity based on the function of the switchgear within the lineup (breaker set points)
Direction-Specific ZOIs ZOIs are formulated for each face of the enclosure (left/right, front, back, and top)
Breaker Style Refinements Additional refinements for horizontal draw-out or vertical lift breakers due to mass and position of the breaker
PRA Method Development Revised NSBD ZOI Geometry Testing and operating experience leveraged to redefine the waterfall portion of the ZOI Additonal Guidance
-Ensuing fire modeling guidance
-Updated HEAF frequencies and bins
-Updated non-suppression probabilities
https://www.nrc.gov/about-nrc/regulatory/research/fire-research/heaf-research.html