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)
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
HEAF Research Working Group Update - April 6th, 2021
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 2
https://www.nrc.gov/docs/ML1803/ML18032A318.pdf
HEAF Research Working Group Update - April 6th, 2021 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 3
HEAF Research Working Group Update - April 6th, 2021 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 4
HEAF Research Working Group Update - April 6th, 2021 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 5
HEAF Research Working Group Update - April 6th, 2021 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 6
HEAF Research Working Group Update - April 6th, 2021 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 7
HEAF Research Working Group Update - April 6th, 2021 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 8
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 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 9
HEAF Research Working Group Update - April 6th, 2021 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 10