ML21022A206

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RIC 2021 Heaf_Flat
ML21022A206
Person / Time
Issue date: 03/08/2021
From:
Office of Nuclear Regulatory Research
To:
Kenneth Hamburger
Shared Package
ML21022A205 List:
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Download: ML21022A206 (14)
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Office of Nuclear Regulatory Research High-Energy Arcing Faults Involving Aluminum:

A Path to Resolution Office of Nuclear Regulatory Research Division of Risk Analysis Fire and External Hazards Analysis Branch

Exhibit Overview

1) Background of HEAF 3) Technical and Regulatory Program Paths to Resolution Brief overview of the origins of the Next steps in the research and NRCs HEAF Research Program. regulatory approach and incorporation of enterprise risk management strategies.
2) Progress of the Joint Working Group 4) Live Q&A Session Updates on the progress of the NRC staff will be available to NRC/Electric Power Research Institute answer questions or take (EPRI) working group, including hazard comments during a live Q&A modeling and probabilistic risk assessment session.

(PRA) methodology.

What Is a HEAF?

A. Upper right: Damage to a bus

  • Sustained discharge of duct caused by a HEAF at Columbia in 2009.

electric current across a B. Lower left: Damage to an gap between two electrical enclosure caused by conductors with different a HEAF at Prairie Island in 2001.

C. Lower right: Damage to a bus voltages. duct caused by a HEAF at Diablo Canyon in 2000.

  • Typically observed in switching equipment with voltages of 440 volts and higher and bus ducts.
  • Generates significant heat, light, and pressure, which have the potential to damage surrounding equipment.

Existing HEAF Models The original hazard model for HEAFs, documented in Appendix M to NUREG/CR-6850, was based largely on the 2001 event at the San Onofre Nuclear Generating Station.

Damage caused by the 2001 San Onofre.

HEAF event, upon which the current model is based.

Idealized graphic depicting the current zone of influence (ZOI) for a HEAF in an electrical enclosure.

HEAFs Reexamined OECD/NEA International Fire Incident Records Exchange (FIRE) Program

  • HEAFs often associated with complicated shutdowns.
  • Hazard model in use had few supporting data.

Left: The cover of NEA/CSNI/R(2013)6OECD Fire Project Topical Report No. 1.

needed.

Above: An excerpt from the executive summary highlighting key conclusions of the report.

Confirmatory Research - Phase I Damage from a 480-volt test at 35 kA for Damage from a 600-volt test at 40 kA Damage from a 4160-volt test at 27 kA for 4 seconds, copper conductors with aluminum 8 seconds, copper conductors. Energy for 7 seconds, aluminum conductors. housing. Aluminum oxidation effects observed.

release largely in agreement with existing Energy release exceeds existing models. models.

Confirmatory ResearchFocus on Aluminum Experiments at three scales: A. Upper left: Small-scale test apparatus at Sandia National Laboratories.

  • Small-scale testing to B. Upper right: Posttest photo of investigate aluminum open-box test 4 at KEMA Laboratories.

oxidation and morphology. C. Lower left: Small-scale microscopy results of

  • Medium-scale open-box aluminum particulate morphology and oxidation.

testing to investigate the D. Lower right: Enclosure breach temperature and spectral during full-scale testing at emissions of the arc column. KEMA Laboratories, medium-voltage with aluminum conductors.

  • Large-scale testing to investigate enclosure breach and energy distribution.

Joint NRC/EPRI Working Group Working Group Goal Statements: Major Working Group Tasks:

  • Characterize the primary factors that influence
  • EPRI survey of U.S. nuclear the occurrence and severity of arcing fault fleet.

events (arc flash, arc blast, or HEAF).

  • Hazard modeling and
  • Develop tools and methods to assess the risk validation.

posed by arcing fault events based on experimental data, operating experience, and

  • Updated PRA guidance.

engineering judgment.

  • Target fragility testing and
  • Analyze the plant impact of, and quantify the characterization.

change in risk from, arcing fault events involving copper and aluminum.

EPRI Survey Types of Information Collected:

  • General plant information.
  • The number of plants with aluminum in equipment susceptible to HEAFs.
  • Types of equipment containing aluminum, including medium-voltage switchgear, low-voltage switchgear, load centers, nonsegregated bus ducts, and isophase bus ducts.
  • Information on equipment containing aluminum, including manufacturer, model, voltage, enclosure material, location of aluminum, and bus bar insulation.
  • Electrical design information, including unit auxiliary transformer lineup and fault clearing times.

Multiphysics Modeling A simulation of test 2-24 (medium-voltage switchgear with aluminum bus bars) Simulated results from the SIERRA modeling framework showing local performed in the Fire Dynamics Simulator. temperatures at the electrodes.

Updated PRA Methodology

  • Aimed at improving the realism and fidelity of the hazard model.
  • Includes an evaluation of U.S. operating experience, updated fire ignition frequencies, and updated nonsuppression probabilities.
  • Also incorporates the configuration of plant electrical distribution systems.

Sample analysis of a plant electrical distribution system for updated PRA methodology.

Target Fragility Testing The response of common PRA targets is being tested for HEAF-like exposures at Sandia National Laboratories Solar Furnace test facility.

This damage model can be coupled with the hazard and PRA models to comprehensively and realistically assess the risk of Left: Reflective surface at Sandia National Laboratories Solar Furnace test facility.

HEAFs.

Above: Pre- and post-test cable samples showing damage caused by thermal exposure.

Right: Sample fragility model based on critical target parameters.

Regulatory Treatment

  • The NRC is pursuing an enterprise risk management approach to achieve timely resolution of the aluminum HEAF issue.
  • This approach will apply an NRC screening method using EPRI insights to bin plants of interest for further evaluation.
  • The screening method will consider factors such as the fidelity of the fire PRA model, the conditional core damage probability of aluminum HEAF, and the change in core damage frequency.
  • The screening method will also take into account EPRI best practices and potential mitigation using Diverse and Flexible Coping Strategies (FLEX) equipment as appropriate.

Contact Information Nicholas Melly, P.E. Kenneth Hamburger, P.E.

Nicholas.Melly@nrc.gov Kenneth.Hamburger@nrc.gov Gabriel Taylor, P.E.

Gabriel.Taylor@nrc.gov HEAF Web Site https://www.nrc.gov/about-nrc/regulatory/research/fire-research/heaf-research.html

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