ML25191A208
| ML25191A208 | |
| Person / Time | |
|---|---|
| Issue date: | 07/14/2025 |
| From: | Albert Lee, Gabe Taylor NRC/RES/DRA/FXHAB |
| To: | |
| References | |
| Download: ML25191A208 (53) | |
Text
Response Bias of Electrical Cable Coatings at Fire Conditions and Aged Cable Coating Research RES/DRA/FXHAB Presented by:
Adam Lee Gabriel Taylor, P.E.
July 14, 2025 ADAMs Accession No. ML25191A208
Agenda 2
Phase 1
- Draft Research Information Letter (RIL) for stakeholder feedback
- Volume 1 : Fire-Retardant Electrical Cable Coatings and History of use in Nuclear Facilities
- Volume 2 : Fire Properties of Cables
- Volume 3 : Cable Functionality
- Final publication of RIL
- Draft Research Project Plan for Aged Cable Coatings Phase 2
- Testing and Draft Aged Cable Coating RIL 3
Project Overview
- Phase 3
- Use unaged and aged data to develop/update fire PRA methodology with EPRI
- NUREG/CR-6850 Appendix Q
- Phase 4
- Publish aged cable coating research in a RIL
- Publish methodology update report to NUREG/CR-6850 Appendix Q Project Overview 4
Volume 1: Fire-Retardant Electrical Cable Coatings and History of use in Nuclear Facilities 5
Short History: Non-Nuclear Expanded use of electrical cables and fire hazard
- 1800s, Cable development
- Electric telegraph and power industry
- Mining industry focused on cable coatings after large losses
- 1917 Granite Mountain Copper Mine (168 fatalities)
- Natural resins were preferred material
- Flammability was a concern
- Fire incidents indicated that insulation contributed to fire growth
- Late 1800s
- Asbestos started to be used as component to reduce hazard (marketed as non-ignitable) 6
- 1891 - Isaac Merrell patented a fireproof paint product composed of pulverized ceramics and asbestos
- 1906 - First documented health concerns from asbestos
- 1973 Environmental Protection Agency (EPA) passed a law to limit asbestos use
- Polychlorinated Biphenyl (PCB) added to polyvinyl chloride insulated cables to increase resistance to heat and flame
- 1979 EPA issued regulation to ban PCB use Short History: Non-Nuclear Use of fire-retardant coatings 7
Short History - US Nuclear Need to reduce combustible loading 1975 - Brown Ferry Nuclear (BFN) Fire
- Special Review Group (NUREG-0050)
- Suggested use of fire-retardant coatings 1976-1980
- Development of Branch Technical Positions (BTPs) per recommendations from special review group
- Research: Sandia National Laboratories and BFN cable fire tests 1998: SECY 98-058: alternative performance-based fire protection
- 2004 Rulemaking to endorse NFPA standard as alternative 2005 - NUREG/CR-6850 Fire PRA Methodology, Appendix Q: Passive Fire Barriers 8
Brown Ferry Nuclear (BFN) Plant
Short History - US Nuclear Installation of Fire-Retardant Coatings Post BFN fire, fire retardant cable coatings installed in cable tray (left) and being inspected (above).
9
- Confirm regulatory guidance
- Cable separation
- Cable coating research
- SAND 77-1424
- SAND 78-0518
- NUREG/CR-0366 Short History - US Nuclear Fire Protection Research Program, 1975 - 1987 10 Full-scale test apparatus.
Regulatory Guidance What prompted the use of fire-retardant coatings
- BTP APCSB 9.5-1 Guidelines for Fire Protection for Nuclear Power Plants
- Refers to IEEE 383 flame test criteria, as minimum
- Appendix A to BTP APCSB 9.5-1 also stated
- If IEEE 383 flame test criteria can not be met, all cable must be covered with an approved fire retardant coating
- NUREG-800 - Standard Review Plan
- Refers to IEEE 383 flame spread criteria or IEEE 1202
- Refers to IEEE 383 flame spread criteria or IEEE 1202 11
Title 10 Code of Federal Regulations (10 CFR)
- Appendix A to Part 50: General Design Criteria, Criterion 3 Fire Protection
- 50.48 Fire Protection Deterministic Fire Protection Plan
- Appendix R to 10 CFR 50 Performance-Based Fire Protection Plan
- 10 CFR 50.48(c), National Fire Protection Association Standard NFPA 805, 2001 edition
- Alternative regulation for meeting deterministic regulations or license conditions
- NRC incorporated NFPA 805 2001 edition by references, with exceptions, modifications, and supplementation US NRC Fire Protection Regulations 10 CFR 50.48 12 Illustration of defense in depth applied to fires.
Exception v
- Existing cables. In lieu of installing cables meeting flame propagation tests as required by Section 3.3.5.3 [of NFPA 805], a flame retardant coating may be applied to the electric cables,, to provide an equivalent level of protection. In addition, the italicized exception is not endorsed.
3.3.5.3 specifies that electric cables shall meet flame propagation tests as specified by AHJ Annex 3.3.5.3 identifies recognized flame spread tests, such as
- IEEE 817, Standard Test Procedure for Flame-Retardant Coatings Applied to Insulated Cable in Cable Trays [IEEE Withdrawn]
- IEEE 1202, Standard for Flame Testing of Cables for Use in Cable Tray and Industrial and Commercial Occupancies Regulatory Exception to NFPA 805 Existing cables and cable coatings 13
- NUREG/CR-6850 (EPRI 1011989)
- Joint technical document presenting methods to perform Fire PRA.
- Appendix Q, Passive Fire Protection
- Diesel Pool Fire Tests
- Guidance
- Ignition at 12 minutes
- Cable Damage
- 3 minutes for severe exposure
- 10 minutes for cable tray Fire probabilistic risk assessment (PRA)
Supports use of NPFA 805 via risk evaluations Table Q-1 of NUREG/CR-6850 14
Research Need Why perform this research?
- NUREG/CR-6850 based on limited dataset
- SNL diesel pool fire tests from the 1970s
- Expand flame retardant materials performance data
- Burning behavior
- Electrical functionality response 15 Full-scale single-tray test apparatus.
Testing Approach
- Volume 2: Fire properties of cables
- Thermal response
- Volume 3: Cable functionality
- Electrical response 16
Questions for Volume 1 17
Contact:
Gabriel.Taylor@nrc.gov Adam.Lee@nrc.gov Meeting Feedback https://feedback.nrc.gov/pmfs/
Meeting Code: 20250771 ADAMs Accession No. ML25191A208
Volume 2 : Fire Properties of Cables 18
Coatings What materials were evaluated? Why?
- Coating A (Carboline Intumastic 285)
- Intumescent
- Coating B (Flamemastic F-77)
- Thermoplastic resin
- Coating C (Vimasco 3i)
- Ablative
- Coating D (Fire Security FS15)
- Water based mastic 19
Electrical Cables What is the base configuration (control)
Cable No.
Insulation Material Jacket Material Class Year Manufactured Description
- Other cables have been evaluated under past NRC research programs.
- Qualified cables - pass the flame test of the Institute of Electrical and Electronic Engineers (IEEE) standard IEEE 383-1974
- 900 #902
- 802
- 807 20
- 813
Testing Approach - Small Scale Tests What was done and how will results be used
- Modified version of standard test 21 Thermogravimetric analysis (TGA)
(Vol 2)
Fire properties of cables with/without coatings - Vol 2 Calorimetry (micro-combustion and cone calorimetry)
- Fire properties of cables with/without coatings - Vol 2 Furnace ignition tests
- Ignition temperature - Vol 2 Circuit integrity test (IEC 60331-11)*
- Cable time to circuit failure and thermal failure temperature - Vol 2, Vol 3 Cable 802 coated with Flamemastic F-77.
The completed assembly for uncoated cables.
Testing Approach - Full Scale Tests What was done and how will results be used
- Modified version of standard test 22 Penlight apparatus radiant heat test
- Cable time to circuit failure and thermal failure temperature - Vol 3 Vertical flame spread test (IEEE 1202-1991)*
- Flame spread distance -
Vol 2 Multi-tray horizontal test
- Cable time to circuit failure and thermal failure temperature - Vol 2, Vol 3 Typical configuration of uncoated cables attached to a tray.
Drawing of the vertical flame experiment apparatus.
Measurements Thermal Heat of combustion, Hc (MJ/kg)
Specific heat, c (J/g*K)
Thermal conductivity, k (W/m*K)
Reaction rate and char yield
- ASTM E1131 (TGA)
Heat release rate
- ASTM D 6113-03 (Cone calorimetry)
Ignition temperatures
- Cable temperatures (beneath cables outer jacket) 23 Oven exterior showing electrodes, gas inlets, and thermocouple wire ports.
Instrumentation of a cable segment for an uncoated experiment.
Observations - Cable Coatings TGA, Microcombustion Calorimetry
- The first at approximately 300°C (572°F).
- The second at approximately 450°C (842°F).
- Coatings do burn and leave a relatively large amount of residue.
24 TGA results for the cable coatings, expressed in terms of reaction rate.
Heat of combustion and char yield with standard uncertainty.
Observations - Coated vs Uncoated Cables Cone Calorimetry
- Doubled the ignition time.
- Halved the peak HRR.
- Doubled the total energy released.
C 25 Cone calorimeter results for cable 814. Rep. 0 denotes the uncoated sample.
Observations - Ignition Temperature for Coated vs Uncoated Cables Furnace
- Uncoated thermoplastic cables ignited at temperatures around 300°C (572°F).
- Uncoated thermoset cables ignited around 400°C (752°F).
- Coatings did not necessarily raise ignition temperature.
C 26
Observations Vertical Flame Spread Test (IEEE 1202-1991) 27
- 20 kW burn test.
- Undersized coating thickness led to upward fire spread.
- Properly applied coatings prevented repeat of fire behavior.
Photograph of experiment I-4, cable 900, uncoated.
Photograph of experiment I-8, cable 900 coated with FS15.
Observations Full-Scale Horizontal Tests Average interior cable temperature at the time of failure was approximately 300°C (572°F).
Range of failure temperatures was considerable.
- Less than 200°C (392°F) to over 500°C (932°F).
Cables in Tray 3, immersed in the hot gas layer, tended to fail at lower temperatures than the cables in Trays 1 and 2.
28 Compartment to be used for the horizontal cable experiments.
Conclusions - Fire Properties Uncoated thermoplastic cables ignited at temperatures about 300°C (572°F).
Uncoated thermoset cable ignited at about 400°C (752°F).
Coatings decrease the peak burning rate and increase the total energy released (i.e., coatings do add to the fuel load).
- The amount of additional energy released due to the application of coatings is negligible.
Coatings did not systematically increase the effective ignition temperature of the cables.
- Rather increased delay time to reach the ignition temperature.
Coatings prevented the upward spread of fire from the 20 kW burner when applied according to the manufacturers recommendations.
29
Questions for Volume 2 30
Contact:
Gabriel.Taylor@nrc.gov Adam.Lee@nrc.gov Meeting Feedback https://feedback.nrc.gov/pmfs/
Meeting Code: 20250771 ADAMs Accession No. ML25191A208
Volume 3 : Circuit Integrity 31
Measurements Electrical
- Insulation Resistance Measurement System (IRMS).
- Surrogate Circuit Diagnostic Unit (SCDU) 32 Experiment configuration: SCDU (left); data acquisition (right); experiment 3 assembly (background).
SCDU - MOV control circuit S8 S7 S3 S2 S1 3 A S1 S2 S3 AT5 G7 N/C A
N/C AT5 AT6 1800 Ohms V
A V
A V
A V
A V
A V
A V
A V
A V
P-4 P-5 SCDU CIRCUIT PATH DESIGNATION 120 V (AC)
S9 1800 Ohms 33 SCDU circuit diagram
34 Failure Data Spurious Operation, Circuit Failure FAILURE Experiment configuration BSCI-10bare cablecable 813thermosetreplicate 1.
35 Bench-Scale Tests IEC 60331-11 Photograph of a typical circuit integrity experiment.
36 Observations - Coating Thickness Thermoplastic - IEC 60331-11 Added thickness above the vendors recommended minimum typically resulted in an additional delay in time to failure.
37 Observations - Coating Thickness Thermoset - IEC 60331-11 Added thickness above the vendors recommended minimum typically resulted in an additional delay in time to failure.
Observations - Radiant Heat Penlight Apparatus Coated samples had little to no delay in electrical failure time when compared to the uncoated sample failure time.
TP cables showed little degradation until their insulation and jacket materials melted.
- Corresponds with the point of electrical failure.
TS coated cable assembly was heated and expanded, cracks in the coating developed.
- Resulted in better heat transfer.
38 Penlight apparatus.
Observations - Vertical Tests Circuit Integrity 39 Time-to-failure box plots of IEEE Standard 1202 experiments.
Observations Full-Scale Horizontal Tests 40 The full-scale series consisted of eight experiments. In each experiment, 12 cables were monitored for electrical functionality.
In all instances, the cables under experiment failed electrically.
Schematic diagram of the full-scale horizontal flame spread experiment.
Results multilayer nonqualified (cable 900).
Conclusions - Cable Functionality Delay in time to damage
- Nonqualified electrical cables coated with a fire-retardant cable coating demonstrate a delay in time to damage, regardless of coating type.
- Qualified electrical cables coated with a fire-retardant cable coating demonstrated mixed results.
- Bench-scale tests demonstrated a delay,
- Full-scale vertical flame spread testing did not demonstrate a delay.
Coating thickness
- Additional cable coating thickness beyond the manufacturers specified minimum thickness provides additional delay in time to damage Cable construction
- Cable construction attributes such as conductor size, insulation thickness, conductor count, etc., will impact the performance of a cable under fire conditions regardless of coating type.
- Important to note that the primary qualified and nonqualified cables experimented within this program are of different construction 41
Questions for Volume 3 42
Contact:
Gabriel.Taylor@nrc.gov Adam.Lee@nrc.gov Meeting Feedback https://feedback.nrc.gov/pmfs/
Meeting Code: 20250771 ADAMs Accession No. ML25191A208
Aged Cable Coating Research Plan 43
Purpose and Use of Results 44 Understand the functional performance of aged cable coatings Understand the fire protection aspects of aged cable coatings Inform how (aged) cable coatings may be credited in fire PRA Update NUREG/CR-6850 Appendix Q Not environmental qualification (EQ) testing Cable coatings showing change from their original white color.
Roles and Responsibilities 45 Name Role and Responsibilities Org.
Contact Kevin McGrattan Principle Investigator, Experimental Director NIST kevin.mcgrattan@nist.gov Adam Lee Project Manager / Test Personnel NRC adam.lee@nrc.gov Gabe Taylor Circuit Functional Testing / Test Personnel / Data Analysis NRC gabriel.taylor@nrc.gov
Schedule and Milestones 46
- 1.
Finalize Research Project Plant
- 2.
Perform TGA on coatings
- 3.
Determine accelerated age time and temperature and prepare samples
- 4. Samples aging in the oven
- 5. Gather Results and Draft Research Information Letter (RIL)
At a simulated age of 0 years At a simulated age 40 years At a simulated age of 80 years At a simulated age of 120 years Perform cone calorimetry and circuit integrity test Perform cone calorimetry and circuit integrity test Perform cone calorimetry and circuit integrity test Perform cone calorimetry and circuit integrity test
Arrhenius Model
=
47
= activation energy (eV) (1 eV = 23.06 kCal/mole) k = Boltzmanns constant = 8.617 x 10-5 eV/K ta = accelerated aging time ts = service time being simulated Ta = aging temperature (K)
Ts = service temperature (K) where:
Can be used to determine the required accelerated aging time and oven temperature that results in the simulated service time
Aging Considerations
- Simulated age is sensitive to the activation energy
- Will need the activation energy of the cables and the cable coatings
- Use the activation energy that yields the minimal target age of both cables and cable aging - ensures conservatism
- Oven temperature
- Operating service temperature assumption
- Use an oven temperature close to operating temperature
- Extends the time in the oven
- Time in the oven 48
Aged Cable Coating Research 49 Cable Class/Material TS/XPLE TP/PVC Cable Coating/Carboline Intumescent 285 Activation Energy (eV) 1.34 1.23 1.19 ta (months) ts (years) ta (months) ts (years) ta (months) ts (years) 0 0
0 0
0 0
6.83 64.4 9.7 45.4 11 40 13.7 128.8 19.4 90.8 22 80 20.5 193.1 29.1 136.2 33 120
- Values are fictious to illustrate activation energy conservatism.
Assumed Ts = 90 °C (403 K)
Assumed Ta = 130 °C (363 K)
Aged Cable Coating Research Obtain activation energy
- Obtain activation energy of coatings using TGA
- Obtain activation energy of cables from manufacturer and/or literature review Perform two tests on specimen
- Cone calorimetry
- Bench-scale circuit integrity test Specimen
- Two sets cables (TS and TP)
- Each set of cables (4 coatings + 1 bare)
- Repeat for unaged, 40, 60, 80, 120 year* accelerated aged cables 50 Cable A Cable B Class Thermoset (TS)
Thermoplastic (TP)
Insulation Material XPLE PVC Jacket Material CSPE PVC Number of Conductors 2-7 2-7 Conductor Size (AWG) 8-16 8-16 Activation Energy Obtained from manufacturer Obtained from database/literature review Similar to CAROLFIRE Number 14 5
- Accelerated aged years and intervals are expected to change as activation energy information becomes available.
Activation Energy of Coatings
- Activation energies on fire retardant coatings are not well captured in literature review
- Formula varies from manufacturer to manufacturer and from year to year
- Perform thermogravimetric analysis (TGA) to obtain specific activation energy of coatings
- ASTM E1641-18, Standard Test Method for Decomposition Kinetic by Thermogravimetry Using the Ozawa/Flynn/Wall Method
- Perform mass loss of the same coating at various heating rates 51
Aged Cable Coating Experiments
- Cone Calorimetry
- Heat release rate (HRR)
- Circuit Integrity
- Failure time (i.e., resistance monitoring using IRMS or breaker trip using SCDU)
- Temperature at time of failure 52
Questions 53
Contact:
Gabriel.Taylor@nrc.gov Adam.Lee@nrc.gov Meeting Feedback https://feedback.nrc.gov/pmfs/
Meeting Code: 20250771 ADAMs Accession No. ML25191A208