ML22307A236
| ML22307A236 | |
| Person / Time | |
|---|---|
| Issue date: | 10/21/2022 |
| From: | Coyne K, Kenneth Hamburger, Mcgrattan K, Nick Melly, Markhenry Salley, Gabe Taylor NRC/RES/DRA |
| To: | |
| References | |
| Download: ML22307A236 (1) | |
Text
26thInternational Conference on Structural Mechanics in Reactor Technology (SMiRT26) 17thInternational Post-Conference Seminar on FIRE SAFETY IN NUCLEAR POWER PLANTS AND INSTALLATIONS Development of Improved High Energy Arcing Fault (HEAF) Target Damage Thresholds and Zone of Influence (ZOI) Models Kevin Coyne, Gabriel Taylor, Kenneth Hamburger, Nicholas Melly, Kevin McGrattan, Mark Henry Salley ZOI Development Comprised of three major research activities
Updated Fragility CFD Simulations Confirmatory ZOI Modeling FDS development and Analysis Physical testing and application to large matrix Independent confirmation operating experience to of configurations using modified IEEE arc flash develop fragilities for model electrical cables Cable Fragility Experiments
SNL Solar Furnace Facility
Heliostat and parabolic reflector, generating up to 6 MW/m2over a 5 cm circle
Varied heat flux, duration, cable material, and exposure profile
Objective was to develop metrics for evaluating cable failure and quantify threshold criteria Solar Furnace Testing Methodology
Test 1-22 (7 MJ/m2): Surface damage to jacket only
Test 1-32 (24 MJ/m2): Sub-jacket shielding visible
Test 1-09 (206 MJ/m2): Cable insulation and bare wire exposed Solar Furnace Testing Results
Total of 38 tests conducted, and categorized by damage extent:
jacket damage, insulation exposure, conducting wire exposure
Results for initial heat fluxes of >1 MW/m2 are shown (upper plot thermoplastic, lower plot thermoset)
Fragility Working Group Process for data analysis and consensus building
1 2 3
Proposal Weekly Meetings Consensus Development Proposals presented to full Technical evaluators and
Two teams developed working group and integrators caucused to proposals to address the resource experts for reach agreement on path specific technical issues feedback forward for each issue Fragility Working Group Conclusions
The threshold for electrical Incident failure/damage of thermoplastic jacketed Energy cables is 15MJ/m² and the threshold for thermoset jacketed cables is 30MJ/m²
Sustained ignition is assumed for cables Sustained within the enclosure of origin (e.g. Ignition
internal cables and components within switchgear and load centers)
Protective Features 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> (or greater) rated Electrical Fire Raceway Barrier System (ERFBS) will prevent ignition inside the enclosure of origin, and damage in the ZOI FDS Inputs
Source Term (HRR)
Radiative Volumetric HRR to Fraction represent the arc Relative convective/radiative fraction of HRR
Mass of electrode vaporized during arc Electrode Mass Q Particle size Loss Rate distribution and extent of oxidation Metal Oxidation Heat Release Rate Development
Volumetric HRR Definition
FDS does not include models for electrical/magnetic fields, dissociation of molecules at high temperatures, or formation of plasma
Total arc energy can be accounted for using arc voltage, current, and duration
A volume was defined in FDS to approximate the arcing region with the same total arc energy Radiative Fraction & Electrode Mass Loss
Data from Literature
Cressaultdeveloped radiative fraction correlations for electrical arcs as a function of electrode material (aluminum, copper) and arc power
Stanback developed electrode mass loss rate correlations as a function of electrode material (aluminum, copper) and arc current Metal Oxidation
Experimental Data
SNL conducted experiments in a closed calorimeter with scaled current densities
Experiments determined vapor fraction of lost electrode and extent of particle oxidation
Nozzles defined in FDS to emit metal particles with defined oxidation rates at each conductor in the arc volume FDS Validation
Full-scale experiments used for model validation; unbiased FDS predictions plotted against experimental temperatures for MV switchgear shown at right Processing the FDS Run Matrix
Scripted Automation
A matrix of FDS simulations was created to vary the important inputs: energy profile, geometric configuration, electrode material, housing material, and arc initiation location
In total, 130+ simulations were run
A Python script, FDS template, and parameter file were used to programmatically swap the relevant variables in and out and reduce the chance of human error FDS Results & Conclusions
FDS simulations allowed the determination of the distances where 15 MJ/m2 and 30 MJ/m2 would be exceeded.
Sample results shown for medium-voltage switchgear with arc initiated at the main bus bars and a 15 MJ/m2 fragility threshold
Dominant factor in ZOI is total arc energy.
Switchgear are sensitive to arc initiation location and geometry. Bus ducts are sensitive to housing material (aluminum vs. steel)
Results not sensitive to electrode composition (aluminum vs. copper)
Confirmatory ZOI Analysis Using a modified model based on IEEE guide 1584-2018
Base Current Enclosure Decay Model & Breach Current Voltage
Base model developed to Base model uses bolted Base model does not Arc energy profile estimate incident energy fault current, modified to assume a barrier between developed for generator-at various distances from use arc current. Arc source and target. fed faults during coast an arc flash for personnel voltage obtained from Modified model down following a trip safety CIGRE-602 model incorporates a time to breach before target receives energy Modified IEEE & FDS Models Compared
Modified IEEE model results are generally within 20 cm of FDS results. IEEE Max ZOI FDS Max ZOI MV Switchgear (15 MJ/m2) 1.6 m 1.3 m MV Switchgear (30 MJ/m2) 1.06 m 0.97 m NSBD Aluminum (15 MJ/m2) 1.2 m 1.41 m NSBD Aluminum (30 MJ/m2) 0.77 m 0.95 m Considering vastly different NSBD Steel (15 MJ/m2) 1.18 m 1.33 m nature of the models NSBD Steel (30 MJ/m2) 0.76 m 0.89 m (empirical vs. CFD) the ZOIs are in fairly good agreement and provide confidence in the results THANK YOU!
https://www.nrc.gov/about-nrc/regulatory/research/fire-research/heaf-research.html