ML21098A131
| ML21098A131 | |
| Person / Time | |
|---|---|
| Issue date: | 04/06/2021 |
| From: | Glover A, Kenneth Hamburger Office of Nuclear Regulatory Research, Sandia |
| To: | |
| Kenneth Hamburger | |
| Shared Package | |
| ML21098A124 | List: |
| References | |
| Download: ML21098A131 (10) | |
Text
HEAF Target Fragility Progress Kenneth Hamburger, P.E. (NRC)
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