[Federal Register Volume 84, Number 125 (Friday, June 28, 2019)]
[Notices]
[Pages 31125-31126]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2019-13893]


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NUCLEAR REGULATORY COMMISSION

[NRC-2019-0118]


Refining and Characterizing Heat Release Rates From Electrical 
Enclosures During Fire

AGENCY: Nuclear Regulatory Commission.

ACTION: Draft NUREG; request for comment.

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SUMMARY: The U.S. Nuclear Regulatory Commission (NRC) is issuing for 
public comment a draft NUREG entitled, ``Refining and Characterizing 
Heat Release Rates from Electrical Enclosures during Fire--Volume 2: 
Fire Modeling Guidance for Electrical Cabinets, Electric Motors, Indoor 
Dry Transformers, and the Main Control Board'' (NUREG-2178 Volume 2/
EPRI 3002016052). This report is a joint product of the NRC and the 
Electric Power Research Institute (EPRI) collaborating under a 
memorandum of understanding for fire research. This report describes 
improved methods that can increase the realism in the modeling of 
selected ignition sources. The areas further investigated include the 
treatment of flame radiation and obstructed radiation, fire propagation 
between adjacent electrical cabinets, heat release rates (HRRs) for 
electric motors and dry transformers, fire location factor, non-
suppression probability floor values, and the modeling of the main 
control board.

DATES: Submit comments by August 27, 2019. Comments received after this 
date will be considered if it is practical to do so, but the Commission 
is able to ensure consideration only for comments received before this 
date.

ADDRESSES: You may submit comments by any of the following methods:
     Federal Rulemaking Website: Go to https://www.regulations.gov/ and search for Docket ID NRC-2019-0118. Address 
questions about docket IDs in Regulations.gov to Jennifer Borges; 
telephone: 301-287-9127; email: [email protected]. For technical 
questions, contact the individuals listed in the FOR FURTHER 
INFORMATION CONTACT section of this document.
     Mail comments to: Office of Administration, Mail Stop: 
TWFN-7-A60M, U.S. Nuclear Regulatory Commission, Washington, DC 20555-
0001, ATTN: Program Management, Announcements and Editing Staff. For 
additional direction on obtaining information and submitting comments, 
see ``Obtaining Information and Submitting Comments'' in the 
SUPPLEMENTARY INFORMATION section of this document.

FOR FURTHER INFORMATION CONTACT: David W. Stroup, Office of Nuclear 
Regulatory Research, telephone: 301-415-1649, email: 
[email protected]; or Nicholas.Melly, Office of Nuclear Regulatory 
Research, telephone: 301-415-2392, email: [email protected]. Both 
are staff of the U.S. Nuclear Regulatory Commission, Washington, DC 
20555-0001.

SUPPLEMENTARY INFORMATION:

I. Obtaining Information and Submitting Comments

A. Obtaining Information

    Please refer to Docket ID NRC-2019-0118 when contacting the NRC 
about the availability of information for this action. You may obtain 
publicly-available information related to this action by any of the 
following methods:
     Federal Rulemaking Website: Go to https://www.regulations.gov/ and search for Docket ID NRC-2019-0118.
     NRC's Agencywide Documents Access and Management System 
(ADAMS): You may obtain publicly-available documents online in the 
ADAMS Public Documents collection at https://www.nrc.gov/reading-rm/adams.html. To begin the search, select ``Begin Web-based ADAMS 
Search.'' For problems with ADAMS, please contact the NRC's Public 
Document Room (PDR) reference staff at 1-800-397-4209, 301-415-4737, or 
by email to [email protected]. The draft NUREG entitled ``Refining 
and Characterizing Heat Release Rates from Electrical Enclosures during 
Fire--Volume 2: Fire Modeling Guidance for Electrical Cabinets, 
Electric Motors, Indoor Dry Transformers, and the Main Control Board'' 
is available in ADAMS under Accession No. ML19162A406.
     NRC's PDR: You may examine and purchase copies of public 
documents at the NRC's PDR, Room O1-F21, One White Flint North, 11555 
Rockville Pike, Rockville, Maryland 20852.

B. Submitting Comments

    Please include Docket ID NRC-2019-0118 in your comment submission.
    The NRC cautions you not to include identifying or contact 
information that you do not want to be publicly disclosed in your 
comment submission. The NRC will post all comment submissions at 
https://www.regulations.gov/ as well as enter the comment submissions 
into ADAMS. The NRC does not routinely edit comment submissions to 
remove identifying or contact information.
    If you are requesting or aggregating comments from other persons 
for submission to the NRC, then you should inform those persons not to 
include identifying or contact information that they do not want to be 
publicly disclosed in their comment submission. Your request should 
state that the NRC does not routinely edit comment submissions to 
remove such information before making the comment submissions available 
to the public or entering the comment into ADAMS.

II. Discussion

    In 2005, the EPRI and the NRC's Office of Nuclear Regulatory 
Research issued a joint technical report NUREG/CR-6850 (EPRI 1011989), 
EPRI/NRC-RES Fire PRA Methodology for Nuclear Power Facilities. This 
publication documented state-of-the-art methods, tools, and data for 
conducting a fire probabilistic risk assessment (PRA) for a commercial 
nuclear power plant application. Following this publication, many 
utilities developed Fire PRAs using the guidance in NUREG/CR-6850 (EPRI 
1011989) to support risk informed applications, including the 
transition to National Fire Protection Association Standard 805 among 
others. The results obtained from the Fire PRA models have suggested 
specific elements in the fire scenario analysis where improved methods 
and/or guidance can reduce conservatism and increase realism in the 
risk estimates. Consequently, over the past fifteen years, fire PRA 
research covering the areas of fire ignition frequencies (e.g., NUREG-
2169 (EPRI 3002002936)), fire modeling (e.g., NUREG-2178 (EPRI 
3002005578)), human reliability analysis (NUREG-1921 (EPRI 1023001)), 
and spurious operations (e.g., NUREG/CR-7150) have been published and 
made available to the industry.
    The first volume of NUREG-2178 (EPRI 3002005578) was published in 
April of 2016. This document included methods focused on refining the 
modeling of fires in electrical cabinets, including updated HRR 
probability distributions and an obstructed fire plume model. During 
drafting of NUREG-2178 volume 1 (EPRI 3002005578), the joint NRC/EPRI 
working group authoring the document identified additional methods to 
further refine the modeling of selected ignition sources within the 
fire PRA for inclusion in a second volume. As in the

[[Page 31126]]

case of Volume 1 of NUREG-2178, this second volume would provide 
improved methods for achieving realism by reducing some of the 
conservatisms present in the NUREG/CR-6850 (EPRI 1011989) methods. As 
such, the guidance and methods described in these documents would not 
replace or invalidate existing methods or guidance, but rather, provide 
more realistic (usually less conservative) alternative approaches.
    This second volume of NUREG-2178 (EPRI 3002016052) includes the 
following methods that can be used for refining the modeling of 
selected ignition sources:
     Flame radiation and obstructed radiation: The document 
describes and reviews existing methods for calculating flame radiation. 
From that discussion, a modified approach for computing flame radiation 
is developed and a detailed method for determining the thermal 
radiation impact from fires inside electrical cabinets is presented. 
This approach extends the research documented in NUREG-2178 Volume 1 
(EPRI 3002005578) associated with modeling plume temperatures generated 
by fires inside electrical cabinets (i.e., the obstructed plume 
temperature model) by developing guidance on predicting thermal 
radiation that may be obstructed by vented or unvented cabinet walls.
     Fire propagation between adjacent electrical cabinets: A 
detailed approach for modeling fire propagation between vertical 
sections in a bank of electrical cabinets is described in the report. 
This method expands upon the guidance provided in Appendix S of NUREG/
CR-6850 (EPRI 1011989) which referred to this scenario as ``enclosure-
to-enclosure fire spread.''
     HRRs for electric motors and dry transformers: Appendix G 
of NUREG/CR-6850 (EPRI 1011989) recommended bounding/conservative 
values for HRRs associated with electric motors and dry transformers 
based on the values used for electrical cabinet fires. However, 
electric motors and dry transformers are different in terms of ignition 
sources, modes of ignition, and combustible configuration in comparison 
to electrical cabinets. Consequently, revised HRRs for electric motors 
(including those motors associated with pumps) and dry transformers 
based on the size (horsepower or voltage respectively) of the equipment 
were developed.
     Fire location factor: Existing guidance suggests that 
fires adjacent to walls or in corners of a room may generate elevated 
plume temperatures when compared to fires away from these surfaces 
(sometimes referred to as the wall/corner plume correction factors). 
Based on recent fire experiments, this document discusses new guidance 
for estimating plume temperatures from fires along walls or in corners. 
The guidance is applicable to both fixed and transient ignition 
sources.
     Non-suppression floor value: Appendix P of NUREG/CR-6850 
(EPRI 1011989) recommends that the non-suppression probability versus 
time curves be used subject to a floor (minimum) value of 0.001 for all 
cases. This assumption means that, in effect, 1 fire in 1000 is never 
suppressed which clearly contradicts the available data. This document 
discusses the basis and development of a lower non-suppression 
probability floor value.
     Main control board fire scenarios: Appendix L of NUREG/CR-
6850 (EPRI 1011989) described a simplified model for determining the 
severity factor and non-suppression probability for fire scenarios 
associated with the main control board based on a predefined zone of 
influence (i.e., a defined set of damage target components). Although 
easy to apply, this model limits the ability to integrate the main 
control board scenarios with other elements associated with the PRA 
quantification of fire scenarios inside the main control room. This 
document describes a comprehensive event-tree based approach for 
characterizing the fire scenario progression following ignition of a 
component in the main control board.

    Dated at Rockville, Maryland, this 25th day of June 2019.

    For the Nuclear Regulatory Commission.
Mark H. Salley,
Branch Chief, Fire and External Hazards Analysis Branch, Division of 
Risk Analysis, Office of Nuclear Regulatory Research.
[FR Doc. 2019-13893 Filed 6-27-19; 8:45 am]
BILLING CODE 7590-01-P