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) | |
Text
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 (SMiRT26) 17thInternational 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 NRC Endorses Reg Guide 1.205 Prescriptive requirements NFPA-805 Endorses NUREG/CR-for nuclear fire protection 6850
1980 2001 2004 2005 2006 2010
NFPA-805 NUREG/CR-6850 NUREG/CR-6850 Performance-based Supplement 1 standard for nuclear fire 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 HEAF Research Awesome ServicesMotivation
to perform experiments for obtaining Phase I Test 23 -potential for comprehensive scientific fire data on the increased ZOI where aluminum is HEAF phenomena known to occur in NPPs involved through carefully designed experiments 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 50% of units had SAT FCTs of 2 Typically located in the main bus bars and primary cable seconds or less compartment Awesome ServicesPhysical Testing
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 spectral emissions Served as benchmark cases for CFD oxidation 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
AdditonalGuidance
-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