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, Gabriel Taylor, Mark Henry Salley 26thInternational Conference on Structural Mechanics in Reactor Technology (SMiRT 26) 17th International Post-Conference Seminar on 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 2001 NRC Endorses NFPA-805 2005 Reg Guide 1.205 Endorses NUREG/CR-6850 1980 Appendix R Prescriptive requirements for nuclear fire protection 2004 2010 2006 NUREG/CR-6850 Fire PRA Methodology NUREG/CR-6850 Supplement 1 Includes bus ducts NFPA-805 Performance-based standard for nuclear fire protection
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
Awesome Services to perform experiments for obtaining comprehensive scientific fire data on the HEAF phenomena known to occur in NPPs through carefully designed experiments Phase I Test 23 - potential for increased ZOI where aluminum is involved HEAF Research Motivation
Development of a CFD Model for predicting a wide variety of electrical and equipment configurations Survey of the US Nuclear Fleet to ensure that full-scale experiments are representative Physical Testing to support the development and validation of the CFD model Fragility Testing to assess target damage from HEAF events Research Activities Overview The NRC developed a comprehensive project plan, consisting of five main tasks:
PRA Method Development to improve the realism of the model and update fire 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-effective and flexible approach.
Low Voltage Switchgear 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 Switchgear Style 83% of switchgear use horizontal draw-out style; the remainder use vertical-lift style Presence of Aluminum Typically located in the main bus bars and primary cable compartment SAT Fault Clearing Times 50% of units had SAT FCTs of 2 seconds or less Bus Bar Insulation MV bus bars primarily insulated; LV bus bars are usually not Conducted by the Electric Power Research Institute (3002020692)
Awesome Services Small-Scale Medium-Scale Full-Scale Aluminum/copper particle size distributions, rates of particle production, particle morphology, and oxidation Direct observation of the arc, enclosure breach, material loss, arc spectral emissions Enclosure breach, event progression, pressure rise, thermal/visual imaging.
Served as benchmark cases for CFD model.
Physical Testing
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