Nuclear Regulatory Authority Experimental Program to Characterize and Understand High Energy Arcing Fault (HEAF) Phenomena (NUREG/IA-0470, Volume 1)

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Publication Information

Manuscript Completed: August 2016
Date Published: August 2016

Prepared by:
S. Tsuchino*, H. Kabashima*, S. Turner**, S. Mehta, D. Stroup, N. Melly, G. Taylor, F. Gonzalez

*Regulatory Standard and Development Department
Secretariat of Nuclear Regulatory Authority (S/NRA/R)
Tokyo, Japan 106-8450

**Leidos, Inc.
301 Laboratory Road
Oak Ridge, TN 37830

M. H. Salley, NRC Project Manager

Division of Risk Analysis
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

Prepared as part of:
The Agreement between NRC and NRA in the Area of Fire-Related Research

Published by:
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

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Abstract

A High Energy Arcing Fault (HEAF) occurred in a high-voltage (6.9 kV) switchgear (SWGR) in Unit 1 of the Onagawa Nuclear Power Plant of the Tohoku Electric Power Company on March 11, 2011 during the Great East Earthquake in Japan. HEAF events are not common and have occurred in nuclear power plants (NPP) worldwide. The operating experience seen from the Onagawa event illustrate that HEAFs can present a potential threat to the safe operation of NPPs. As a result, the nuclear power industry has placed a new emphasis on understanding and developing evaluation methods for these events.

To investigate the HEAF event sequence and to understand the phenomena, the Regulatory Standard and Research Department, Secretariat of the Nuclear Regulation Authority (S/NRA/R) (Japan) conducted HEAF tests by simulating the design and operating conditions of the SWGR HEAF at Onagawa NPP in addition to simulating the HEAF energy effects using a "Rocket Fuel Arc Simulator" (RFAS). Tests of 480 V Motor Control Center (MCC) and Distribution Panel (DP) cabinets were also conducted to understand HEAF characteristics.

The results of the HEAF tests simulating the SWGR at Onagawa NPP showed similar damage to the actual HEAF with respect to the duration time, energy level, and ensuing cable fires. However, the overall structural damage and extent of the internal fire damage was much less severe than Onagawa. The tests for the MCC and the DP provide insight on HEAF behavior and ensuing fires in low voltage systems. Data such as temperature, heat flux, heat release rate during the arc and ensuing fires due to HEAF conditions were successfully simulated by the RFAS test.

The results were generally consistent with the previously observed behavior. However, the tests also provided a new appreciation for and recognition of the high thermal energy from the oxidation of aluminum bus bars, such as those used in the SWGR tests. Since aluminum is sometimes used in bus bars, the energetic effects of an arc involving this material should be considered when analyzing HEAF effects.

This report provides the results of the S/NRA/R tests that, in combination with operating experience and other HEAF test data, will be used by international teams to develop consensus conclusions on HEAF behavior, understand the potential for HEAF damage including ensuing fires, establish HEAF evaluation criteria to support Fire Hazards Analyses (FHA), and recommend protection measures.