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W13 – Advancing the State of the Art in Fire PRA through Research
High Energy Arcing Faults – Insights from the OECD/NEA FIRE Project and the Resulting Experimental Project
Dr. Marina Roewekamp
Gesellschaft fuer Anlagen‐ und Reaktorsicherheit (GRS) gGmbH, GERMANY
Discussion Topics – Current Status of International HEAF Project
• Project initiation
• Project purpose and goals
• Test methodology
• Test results to date
OECD/NEA FIRE Database Project (1)• Topical Report No. 1 “Analysis of
High Energy Arcing Faults, HEAF”, NEA/CSNI/R(2013)6http://www.oecd‐nea.org/nsd/docs/2013/csni‐r2013‐6.pdf
– Non‐negligible contribution of HEAF fire events
• 48 out of 415 fire events collected in the International NPP database up to mid‐2012 represent HEAF induced fire events (over 10 %)
– Need for future testing realized
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OECD/NEA FIRE Database Project (2)• Topical Report No.3 “Event
Combinations of Fires and Other Events”, NEA/CSNI/R(2016)7http://www.oecd‐nea.org/nsd/docs/2016/csni‐r2015‐7.pdf
– More than 10 % of the events in the Database are event combinations
• Approx. 6 % are combinations involving HEAF
• ¼ of these are event chains
– Underpins risk significance
– Need for improvements recognized
OECD/NEA Task HEAFCSNI WGIAGE Task on High Energy Arcing Faults (2009 – 2013)
• Task Report “A Review of Current Calculation Methods Used to Predict Damage from High Energy Arcing Fault (HEAF) Events”, NEA/CSNI/R(2015)10http://www.oecd‐nea.org/nsd/docs/2013/csni‐r2015‐10.pdf
– Insights from operating experience with partly significant HEAF events
– Literature study on methods for predicting HEAF consequences
HEAF Project – Testing 2014 – 2016Purpose and Objectives
• Experimental program to investigate the HEAF phenomena
• Primary objective
– Perform experiments to obtain scientific fire data on HEAF phenomena known to occur in nuclear power plants (NPP) through carefully designed experiments
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HEAF Project – Test Methodology
• 26 full scale experiments conducted
• HEAF events exhibit two damage phases:
1. Short, rapid release of electrical energy
• Catastrophic failure of the electrical enclosure
• Ejection of hot projectiles and/or fire(s)
• Damage to overhead cable trays or nearby panels2. Ensuing fire• Ignition of combustible material within the HEAF
zone of influence (ZOI)
HEAF Test Parameters • Experimentally controlled parameters – Nominal Voltage
– Nominal Current
– Nominal Event Duration
– Arc Location
• Measured Parameters – Heat Release Rate (HRR)
– Temperature
– Heat Flux
– Pressure
– Damage Zone • Blast Damage vs. Enduring Fire Damage
– Furthest extent of damage• Thermal (i.e. ensuing fire damage / smoke damage)
• Physical ( i.e. thrown cabinet door, shrapnel)
Test conditions:
• 10 kV
• 15 kA
• 3 s
• Oil was removed before the test due to safety concerns
Test Results Enclosure 15 – Oil Filled Breaker (Oil Removed; Copper Bus)
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Test Results Enclosure 23 – Breaker(Aluminum Bus)
Test conditions:
• 480 V
• 40 kA
• 7 s
Test conditions:
• 4160 V
• 26 kA
• 3.5 s
Test Results Enclosure 26 – Bus Duct(Copper Bus; Aluminum Enclosure)
Main Test Results – Significance of Arc Duration • Increased duration arcing
events were more likely to create an ensuing fire
• Experiments with arc durations less than 2 s did not result in ensuing fires
• All medium voltage enclosures, 4.16 kV and above, maintained the arc for more than 2 s
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Main Test Results – Material Impact of Aluminum• Potentially much
larger ZOI
• Potentially greater likelihood of maintaining arcing at low voltage levels
• Higher risk of fire propagation
• Conductive Aluminum byproducts coated facility after testing
• Shorting out equipment and causing damage to electrical circuits
• Operating experience also shows these phenomena
Main Test Results – Potentially New Failure Mode: Conductive Byproducts
Test 23 Test 26
HEAF Project – Key Observations
• Significantly more severe physical damage to equipment if experiments involve aluminum components
• Most severe damage to electrical enclosure observed in an enclosure with aluminum bus bars as a result of a low voltage(480 V) HEAF
• Dependency between arc duration and likelihood of ensuing fire(s)
• New, previously unidentified failure mechanism: Conductive Al byproduct coating enclosure environment caused short circuits and unintended current paths in electrical systems