ML21098A131

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: ML21098A125 ML21098A126 ML21098A128 ML21098A129 ML21098A131
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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