ML21098A131: Difference between revisions

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{{#Wiki_filter:HEAF Target Fragility Progress Kenneth Hamburger, P.E. (NRC)
{{#Wiki_filter:}}
Austin Glover (SNL)
Sandia National Laboratories is a multimission laboratory managed and operated by National Technology &
Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S.
Department of Energys National Nuclear Security Administration under Contract DE-NA0003525.
SAND2021-3959-PE
 
===Background===
* 2017 Phenomena Identification and Ranking Table (PIRT) identified the assessment of target fragility as a high research priority
      - Classical fire failure metrics (e.g.,
internal jacket temperature of a cable exposed to a fire) are based on low heat flux, long duration exposures
      - HEAF exposures are high heat flux, short duration exposures, and target response is not well characterized                              https://www.nrc.gov/docs/ML1803/ML18032A318.pdf HEAF Research Working Group Update - April 6th, 2021                  2
 
Objectives
* The goal of this effort is to evaluate the fragility of targets exposed to the environmental conditions after a HEAF
      - Tests at high heat flux/short duration exposures are needed to gain insight on relevant physics and failure modes
* After working group review of possible targets, the test effort was focused on cable targets
      - As in other areas of fire PRA, two categories of cable (thermoset and thermoplastic) were addressed HEAF Research Working Group Update - April 6th, 2021  3
 
Test Facility
* Tests were conducted at the Solar Furnace at the National Solar Thermal Test Facility at Sandia National Laboratories in Albuquerque, NM.
      - Concentrates sunlight to generate thermal environments reaching 6 MW/m2 on a spot ~5 cm in diameter
* The heliostat (top) reflects sunlight through an attenuator onto a large reflective parabolic dish (bottom) to concentrate heat flux onto a target HEAF Research Working Group Update - April 6th, 2021 4
 
Hypothesis
* A literature review was conducted to evaluate relevant phenomena
* The ignition threshold of blackened cellulose as a function of heat flux and total energy was evaluated in the 1960s by Stan Martin
      -  This includes bifurcation of the ignition region into two subregions: transient and persistent ignition.
* This work has been extended to several different materials through test data collected at the Solar Furnace and/or Solar Tower
* A preliminary lumped-material model of a cable was derived for the high heat flux exposure conditions resulting from a HEAF
* This model was compared to full-scale test data as a proof-of-concept, which yielded encouraging results
* The tests at the Solar Furnace would be used to gather data on the material properties of different cables with respect to the ignition model HEAF Research Working Group Update - April 6th, 2021              5
 
Test Plan
* The objective of testing was to establish, in conjunction with theory, an ignition model that robustly accounts for the variation of cable material properties found in nuclear power plants.
* A three-phase approach was taken to test planning
      -  Phase 0 - Exploratory tests to evaluate the validity of the approach
      -  Phase 0B - Exploratory tests to evaluate the feasibility of achieving persistent ignition at the Solar Furnace scale
      -  Phase 1 - Tests to support data collection for development of persistent ignition model
* For each test phase, electrical and thermal instrumentation was used to monitor the cable response to the exposure
* Additionally, high-speed video was taken to evaluate transient and persistent ignition HEAF Research Working Group Update - April 6th, 2021                                                  6
 
Results
* Phase 0
      - A single cable sample was used as the target
      - Exploratory tests yielded positive results on spontaneous ignition
      - However, sustained ignition was not observed during this test phase
* The exposure profile did not account for heat feedback from heat sinks or surrounding cables after the initial exposure.
* Phase 0B
      - A three-cable bundle was used to evaluate if sustained ignition is possible.
      - Also, the heat flux profile was modified so that a secondary heat flux was provided after the initial exposure to simulate heat feedback
      - Additional tests were run with a single cable and the secondary heat flux
      - All tests yielded persistent ignition HEAF Research Working Group Update - April 6th, 2021          7
 
Results (contd)
* Phase 1
      - Test plan originally developed to support persistent ignition model for both thermoset and thermoplastic cables
* Based on results from Phase 0B, it was decided that a single cable would be sufficient since it yielded persistent ignition with secondary heat flux
* A modified profile was used, which captured insight from thermal monitoring instrumentation from the full-scale tests at KEMA
      - Daily meetings were held with the working group to discuss the results from the previous day and any modifications needed to the test plan based on results
* Initial test results did not yield sustained ignition results, so working group decided to probe other failure modes
                    -    Electrical Failure
                    -    Sub-jacket temperature
                    -    Jacket Damage
                    -    Sustained ignition events were also observed in the later tests
* Additionally, a three-cable bundle was introduced with shorter samples for the later tests HEAF Research Working Group Update - April 6th, 2021                              8
 
Results (contd)
* Phase 1 (contd)
      -  Gathered data for both thermoset and thermoplastic cables
      -  Sustained ignition data (bottom)
      -  Damage as a function of total energy
      -  Electrical failure of cables
      -  Sub-jacket temperature HEAF Research Working Group Update - April 6th, 2021                9
 
Path Forward
* The working group is utilizing the test data to define a method to determine the fragility of cables exposed to a HEAF
* Use of data/insights from multiple sources
      -  Full Scale Tests
      -  Operating Experience
      -  Phase 0, Phase 0B, and Phase 1 Tests at the Solar Furnace
      -  International Data
* Evaluation of all phenomena to determine fragility
      -  Jacket Damage
      -  Persistent Ignition
      -  Electrical Failure
      -  Sub-jacket temperature
      -  Etc.
* The group is currently working on determining the fragility of targets so that it may be combined with the source term to determine the ZOI HEAF Research Working Group Update - April 6th, 2021                10}}

Revision as of 21:40, 17 January 2022

1G - Fragility
ML21098A131
Person / Time
Issue date: 04/06/2021
From: Glover A, Kenneth Hamburger
Office of Nuclear Regulatory Research, Sandia
To:
Kenneth Hamburger
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ML21098A124 List:
References
Download: ML21098A131 (10)
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