ML25267A030

Fire Damper Functionality Ril Pdf Final

ML25267A030
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Issue date:	09/30/2025
From:	Albert Lee NRC/RES/DE
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RIL 2025-07
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RIL 2025-07 FIRE DAMPER FUNCTIONALITY Final Report Date Published: September 2025 Prepared by:

A. Lee Division of Risk Analysis Office of Nuclear Regulatory Research (RES)

U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 Adam Lee, NRC Project Manager Research Information Letter Office of Nuclear Regulatory Research

ii Disclaimer Legally binding regulatory requirements are stated only in laws, U.S. Nuclear Regulatory Commission (NRC) regulations, licenses, including technical specifications, or orders, not in Research Information Letters (RILs). A RIL is not regulatory guidance, although the NRCs regulatory offices may consider the information in a RIL to determine whether any regulatory actions are warranted.

iii ABSTRACT This report presents a comprehensive review of fire damper operating experience (OE),

regulatory guidance, industry standards, and probabilistic risk assessment (PRA) considerations, with a focus on the implications for PRA realism and surveillance practices in the nuclear industry. A key challenge identified is the lack of consistent, quantitative data on fire damper performance, emphasizing the need for industrywide data collection efforts to support PRA realism.

Fire dampers account for a small portion of fire protection equipment failures, but issues such as blade damage, improper installation, corrosion, and obstructions may not be reliably detected by visual inspection alone. Functional testing, in combination with visual inspections, may better capture these failure modes. Regulatory requirements establish general fire protection requirements but lack specificity regarding damper surveillance methods and frequencies.

Furthermore, regulatory guidance does not adequately address functional testing under static or low-flow conditions, where failures have been observed, revealing a potential gap.

A literature review of associated studies and PRA methodologies provided qualitative and quantitative information. Risk insights from PRA methodologies and studies, including NUREG/CR-6850, Fire PRA Methodology for Nuclear Power Facilities, Volume 2, Detailed Methodology, indicate that fire damper failures generally have minimal impact on core damage frequency (CDF). Additional relevant studies suggest that intact ventilation ducts may, under specific conditions, provide sufficient protection without fire dampers; however, these findings do not address risks from heat, smoke, or gas transfer. Additionally, the Electric Power Research Institute (EPRI) guidance can be utilized to make risk-based decisions for fire damper surveillance. However, when using insights from this report, the plants licensing basis and regulatory commitments must be understood and considered.

In conclusion, this report highlights important information regarding the regulatory requirements, OE failure mechanisms, and fire damper surveillance practices for fire dampers. It provides information for enhancing PRA realism through the discussion of relevant reports and suggests that further data collection can help drive the PRA realism forward.

Keywords Damper, fire damper, fire barrier

iv TABLE OF CONTENTS LIST OF FIGURES................................................................................................................... vii LIST OF TABLES.................................................................................................................... viii EXECUTIVE

SUMMARY

........................................................................................................... ix ACKNOWLEDGMENTS............................................................................................................. x ABBREVIATIONS AND ACRONYMS....................................................................................... xi 1 Introduction.........................................................................................................................1-1 1.1 Defense in Depth and the Role of Fire Dampers..........................................................1-1 1.2 Background..................................................................................................................1-3

1.3 Purpose and Scope

......................................................................................................1-4 2 Fire Damper History............................................................................................................2-1 2.1 History of Fire Dampers................................................................................................2-1 2.2 Damper Type and Component Design..........................................................................2-2 2.2.1 Common Heat-Responsive Devices....................................................................2-3 2.2.2 Common Fire Damper Blade Types....................................................................2-4 2.2.3 Additional Damper Components..........................................................................2-4 2.3 Static and Dynamic Fire Dampers................................................................................2-5 3 Review of Fire Damper Operating Experience..................................................................3-1 3.1 Electric Power Research Institute.................................................................................3-1 3.1.1 EPRI Compilation of Institute of Nuclear Power Operations Operating Experience and Significant Event Reports...........................................................3-1 3.1.2 EPRI-Compiled Data from License Event Reports..............................................3-2 3.2 Institute of Nuclear Power Operations Industry Reporting and Information System Database.................................................................................................................3-3 3.3 NRC Documents..........................................................................................................3-8 3.3.1 NRC Inspection Findings.....................................................................................3-8 3.3.2 NRC License Event Reports................................................................................3-8 3.4 Summary of Findings....................................................................................................3-9 4 Qualification Tests and Standards for Fire Dampers.......................................................4-1 4.1 Underwriters Laboratories Standard for Safety for Fire Dampers (UL 555)...................4-1 4.1.1 UL 555, Seventh Edition (2006)..........................................................................4-1 4.1.1.1 Fire Endurance and Hose Stream Test............................................................. 4-2 4.1.1.2 Cycling Test........................................................................................................ 4-3 4.1.1.3 Salt Spray Exposure Test.................................................................................. 4-3 4.1.1.4 Spring Closing Force Test.................................................................................. 4-3 4.1.1.5 Dynamic Closure Test........................................................................................ 4-3 4.1.2 UL 555, Third Edition (1979)...............................................................................4-4 4.1.3 UL 555, First Edition (1968).................................................................................4-4

v 4.2 National Fire Protection Association Standards............................................................4-4 4.2.1 NFPA 80, Standard for Fire Doors and Other Opening Protectives...................4-4 4.2.1.1 Operational Testing Requirements.................................................................... 4-5 4.2.1.2 Periodic Inspection and Testing Requirements................................................. 4-5 4.2.1.3 Exception to Periodic Testing for Fully Ducted Fire Damper............................ 4-6 4.2.2 NFPA 90A, Standard for the Installation of Air Conditioning and Ventilating Systems.............................................................................................................4-6 4.3 Summary of Findings....................................................................................................4-7 5 NRC Fire Protection Regulations, Guidance, and Generic Communications for Fire Dampers.....................................................................................................................5-1 5.1 Background..................................................................................................................5-1 5.2 BTP APCSB 9.5-1, Guidelines for Fire Protection for Nuclear Power Plants..............5-1 5.3 10 CFR 50.48 and Appendix R to 10 CFR Part 50.......................................................5-2 5.4 NUREG-0800, Section 9.5.1.1, Fire Protection Program and NUREG-2191, Generic Aging Lessons Learned for Subsequent License Renewal, (GALL-SLR)........................................................................................................................5-3 5.5 Regulatory Guidance 1.189, Fire Protection for Nuclear Power Plants.......................5-4 5.6 NRC Generic Communications.....................................................................................5-5 5.6.1 Generic Letter 86-10...........................................................................................5-5 5.6.2 Information Notice No. 83-69, Improperly Installed Fire Dampers at Nuclear Power Plants.........................................................................................5-5 5.6.3 Information Notice No. 89-52, Potential Fire Damper Operational Problems............................................................................................................5-5 5.7 Technical Requirements Manual..................................................................................5-6 5.8 Summary of Findings....................................................................................................5-7 6 Technical Analysis of Fire Dampers..................................................................................6-1 6.1 Review of Studies on Fire Damper Removal................................................................6-1 6.1.1 Study on Eliminating Fire Dampers to Maintain Process Confinement................6-1 6.1.2 Fire Hazard Analysis of Rocky Flats Building 776/777 Duct Systems..................6-1 6.1.3 Key Findings from the Literature Review.............................................................6-2 6.1.3.1 Direct Flame Impingement................................................................................. 6-2 6.1.3.2 Flame Radiative Zone........................................................................................ 6-2 6.1.3.3 Plume Impingement........................................................................................... 6-2 6.1.3.4 Upper Gas Layer................................................................................................ 6-3 6.1.3.5 Duct and Hanger Integrity Considerations......................................................... 6-3 6.1.4 Summary of Literature Review Findings..............................................................6-3 6.2 NUREG/CR-6850, Fire PRA Methodology for Nuclear Power Facilities, Volume 2, Detailed Methodology........................................................................................6-4 6.3 EPRI, Fire Protection Equipment Surveillance Optimization and Maintenance Guidance................................................................................................................6-5 6.4 Summary of Findings....................................................................................................6-6 7 Conclusions........................................................................................................................7-1 8 References..........................................................................................................................8-1

vi APPENDIX A Institute of Nuclear Power Operations IRIS Event Reports and NRC Documents................................................................................................. A-1

vii LIST OF FIGURES Figure 1-1. SSD, the third objective of defense in depth, highlighting separation (firewalls) as one of the many methods for achieving SSD................................1-2 Figure 2-1. Drawing of first fire damper patent (Gross 1993)....................................................2-1 Figure 2-2. Fully ducted fire damper installation (left) and nonducted fire damper (right)..........2-2 Figure 2-3. Side view of curtain-style fire damper in the closed position...................................2-3 Figure 2-4. Fusible links (left), redrawn with reference (Ruskin 2010) and ETL (right),

redrawn with reference (SR Products 2007)......................................................2-3 Figure 2-5: Curtain-type fire damper (left) and multiblade type fire damper (right),

redrawn from reference (Maune 2013)..............................................................2-4 Figure 2-6. Smoke damper (left) and a combination fire smoke damper (right), redrawn from reference (Maune 2013)............................................................................2-5 Figure 3-1. INPO OE and SER events involving fire protection equipment reliability, maintenance, testing, and inspection. Data used to represent this pie chart was collected in the 1980s. (EPRI 2003)..................................................3-2 Figure 3-2. Fire protection systems identified in LERs between 1984 and 1990 (EPRI 2003)................................................................................................................3-3 Figure 3-3. Types of fire barriers identified in LERs between 1984 and 1990 (EPRI 2003)................................................................................................................3-3 Figure 3-4. Count of INPO IRIS event reports organized by manufacturer...............................3-6 Figure 3-5. Top five manufacturers by number in INPO IRIS event reports..............................3-7 Figure 3-6. Percentage of static and dynamic dampers in INPO IRIS event reports.................3-7 Figure 4-1. Time-temperature curve referenced in ASTM E-119 (ASTM 2020). Figure was taken from NUREG-1805 (Iqbal and Salley 2004).....................................4-2 Figure 6-1. Temperature versus steel yield strength (Jeans 1984)...........................................6-3

viii LIST OF TABLES Table 3-1. Categorized event reports by INPO-defined performance descriptions...................3-4 Table 3-2. Summary of failure cause and recommended inspection type............................... 3-10 Table 4-1. Required tests for different fire dampers, recreated from UL 555 (UL 2020)............4-1 Table 5-1. Surveillance Type per Technical Requirements Manual (TRM)...............................5-7 Table 6-1. Barrier types and their failure probabilities (Nowlen, Najafi, et al. 2005)..................6-4 Table 6-2. EPRI fire damper visual inspection frequency survey results from figure B.8 (EPRI 2003)......................................................................................................6-5

ix EXECUTIVE

SUMMARY

PRIMARY AUDIENCE: Fire protection, electrical, and probabilistic risk assessment engineers conducting or reviewing fire hazard analysis or fire risk assessments.

SECONDARY AUDIENCE: Engineers, reviewers, utility managers, and other stakeholders who conduct, review, or manage fire protection programs and need to understand the underlying technical basis for fire dampers.

KEY RESEARCH QUESTIONS: What are the current industry practices for functional testing of fire dampers; how well do functional, compared to visual, tests account for damper failures; what issues are related to their performance; what are the regulations governing fire damper surveillance testing; and how can this information be used to inform PRA realism?

RESEARCH OVERVIEW The goal of this research was to better understand the background, design characteristics, operating experience (OE), and inspection/testing requirements related to rated fire dampers used in in-duct and through-wall applications.

Recently, the question of functionally testing fire dampers arose during inspections at several nuclear power plants, resulting in an unresolved item concerning whether a visual inspection provides reasonable assurance that fire dampers would perform as intended. Additional concerns were raised about the potential effects of degradation on the fire dampers ability to close and latch properly, which could affect the intended safety function of the damper in the fire area.

This research was divided into four distinct sections: (1) a literature review of fire dampers and how they function, (2) a collection and analysis of OE data on fire dampers, (3) regulatory and nonregulatory documents pertaining to fire dampers, and (4) information to consider regarding fire damper surveillance practices.

KEY FINDINGS This research revealed qualitative insights into how fire dampers are failing, the current standards for industry practices and testing requirements, the regulatory requirements regarding fire dampers, and information to consider regarding fire damper surveillance practices.

WHY THIS MATTERS This report reviews available OE data, relevant regulatory documents, standards, and risk information to support nuclear power plant engineers in performing and reviewing fire modeling analyses and fire probabilistic risk assessments involving fire dampers.

HOW TO APPLY RESULTS Engineers and scientists implementing and maintaining a site fire protection program should focus on sections three, five, and six of this report.

x ACKNOWLEDGMENTS The author is grateful for the valuable feedback, comments, and information provided by Jay Robinson, Charles Moulton, Naeem Iqbal, Gabe Taylor, Nick Melly, and Kelly Sullivan during the development of this report.

xi ABBREVIATIONS AND ACRONYMS

°C degrees Celsius

°F degrees Fahrenheit APCSB Auxiliary Power Conversion Systems Branch ASB Auxiliary Systems Branch ASTM American Society for Testing and Material BTP branch technical position Btu British thermal unit(s)

CCDP conditional core damage probability CDF core damage frequency CFAST Consolidated Fire and Smoke Transport (model)

CFR Code of Federal Regulations CMEB Chemical Engineering Branch DWPF Defense Waste Processing Facility EDG emergency diesel generator EN event notification EPRI Electric Power Research Institute ETL electro thermal link FHA fire hazard analysis FPP fire protection program ft foot/feet GDC general design criterion/criteria GL generic letter hr hour HRR heat release rate HVAC heating, ventilation, and air conditioning INPO Institute of Nuclear Power Operations IR inspection report IRIS Industry Reporting and Information System kW kilowatt(s)

LER license event report LWR light-water reactor m

meter(s)

NFPA National Fire Protection Association NPP nuclear power plant NRC U.S. Nuclear Regulatory Commission NRR NRC Office of Nuclear Reactor Regulation OE operating experience PRA probabilistic risk assessment RBHVAC reactor building heating, ventilation, and air conditioning RCFC reactor coolant fan cooler

xii RES NRC Office of Nuclear Regulatory Research RG regulatory guide RIL research information letter SER significant event report SMACNA Sheet Metal and Air Conditioning Contractors National Association SSC structures, systems, and components SSD safe shutdown SRP standard review plan TRM technical requirements manual TS technical specifications UL Underwriters Laboratories URI unresolved item USNRC U.S. Nuclear Regulatory Commission WGE work group evaluation WSRS Westinghouse Savannah River Site

1-1 1 INTRODUCTION The U.S. Nuclear Regulatory Commission (NRC) requires all operating commercial nuclear power plants (NPPs) to have a fire protection program (FPP)1 that satisfies General Design Criterion (GDC) 3, Fire protection.2 The primary objective of a FPP is to minimize both the likelihood and the consequences of fire. To meet these objectives, the FPPs are designed to provide reasonable assurance, through defense in depth that a single fire will not prevent the necessary safe shutdown (SSD) functions from being performed and that radioactive releases to the environment in the event of a fire will be minimized.

Rated fire barriers confine fire effects to a single compartment or area, minimizing adverse impacts on redundant safety-related structures, systems, and components. Confinement allows for the assessment of potential fire damage through a fire hazards analysis (FHA) to SSD equipment based on a single fire. A fire area is a portion of a building or plant that is separated from other areas by fire barriers, including components of construction such as beams, joists, columns, penetration seals or closures, fire doors, and fire dampers.

Redundant SSD components may be separated by fire-resistant walls, floors, enclosures, or other types of barriers. However, penetrations through fire-resistant barriers are required for ventilation and must be protected by fire dampers to maintain barrier integrity during fire conditions.

1.1 Defense in Depth and the Role of Fire Dampers Defense in depth is defined as creating multiple independent and redundant layers of defense to compensate for potential human and mechanical failures so that no single layer, no matter how robust, is exclusively relied upon (USNRC 2021). Title 10 of the Code of Federal Regulations (10 CFR) 50.48, Fire protection, (U.S. CFR 1956) applies the concept of defense in depth to protect the health and safety of the public from fires at NPPs. Defense in depth is applied to fire protection in fire areas important to safety, with the following objectives: (1) to prevent fires from starting, (2) to detect rapidly, control, and extinguish promptly those fires that do occur, and (3) to provide protection for structures, systems, and components (SSCs) important to safety so that a fire that is not promptly extinguished by the fire suppression activities will not prevent the SSD of the plant (U.S. CFR 1980).

The third objective, SSD, ensures that one path of systems relied on for reactor safety is free of fire damage. As shown in figure 1-1, fire-rated walls are an avenue for providing reasonable assurance of SSD, given the plant fire is not prevented or rapidly suppressed. Firewalls can help separate redundant safety equipment into fire areas, such that it would be impacted only by a single fire, with the assumption that fire barriers, such as fire doors, dampers, walls, etc.,

function as intended. Proper maintenance of rated fire dampers ensures continuity of the fire barrier, thereby preserving redundant safety equipment.

1 Title 10 of the Code of Federal Regulations (10 CFR) 50.48(a) 2 10 CFR Part 50, Domestic Licensing of Production and Utilization Facilities, Appendix A, General Design Criteria for Nuclear Power Plants, GDC 3, Fire protection.

1-2 Figure 1-1. SSD, the third objective of defense in depth, highlighting separation (firewalls) as one of the many methods for achieving SSD.

To confine a fire and limit fire damage, licensees divide NPP buildings into separate fire areas.

These are generally rooms or plant areas that have fire-rated walls and fire-rated floor-ceiling assemblies. These fire-rated walls and floor-ceiling assemblies (i.e., structural fire barriers) are rated to withstand fire hazards in the fire area and outside the fire area. Most NPP fire barriers are constructed of reinforced concrete and have a fire-resistance rating of 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> (see section 5.3).

Penetrations are openings in the structural fire barriers that allow piping, ventilation, instrument tubing, and cable trays to pass from one fire area to another. Creating openings in fire barriers defeats the design function; therefore, penetration seals and fire dampers are used to preserve barrier continuity during fire conditions. For ventilation openings, fire-rated barriers at NPPs are typically protected with rated fire dampers to prevent the passage of fire and fire products from one side of the rated barrier to the other. Fire-rated dampers provide a method for protecting the integrity and continuity of fire barriers containing penetrations.

Unlike penetration seals and structural fire barriers, fire dampers have moving parts that can affect the functionality and effectiveness of the fire damper. Nonfunctional fire dampers may fail to isolate one fire area from another, potentially compromising the plants ability to achieve and maintain SSD conditions during a fire.

Fire dampers are not unique to the nuclear industry. In fact, they are used widely in many industries, both commercial and residential, and are a universally accepted building component that is crucial to fire protection and heating, ventilation, and air conditioning (HVAC) systems.

Many fire damper manufacturers that serve commercial and residential industries also supply the nuclear industry. Therefore, many of the testing and installation standards are similar. For example, all rated fire dampers have the Underwriters Laboratories (UL) certification, which is

1-3 obtained by performing tests under UL 555, Standard for Fire Dampers. The National Fire Protection Association (NFPA) has standards for installation, testing, and maintenance of fire dampers, such as NFPA 90A, Standard for the Installation of Air-Conditioning and Ventilating Systems, and NFPA 80, Standard for Fire Doors and Other Opening Protectives (see section 4).

Fire dampers are designed to help contain a fire within the fire area by providing protection and maintaining the integrity of the overall fire barrier. The significance of fire barriers may depend on many factors, such as the as the number of dampers; the importance of the equipment in the fire area (and adjacent areas); the configuration and location of fuel packages, if any, in the areas and adjacent areas; the potential for fire growth in the areas; the other fire protection features installed in the areas; and the accessibility of the areas to the plant fire brigade.

1.2 Background

For many licensees, the surveillance requirements for fire dampers are embedded within the plants licensing basis and may be specified in licensee-controlled documents such as the technical requirements manual (TRM). However, even this can vary between plants and appear in other licensee-controlled documents. Fire damper surveillance requirements vary by plant licensing basis. For example, some plants TRMs address functional testing requirements for fire dampers, while others may only specify visual inspection. As a baseline, visual inspections are typically required per the plants licensing basis.

Recently, the question of functionally testing fire dampers arose during inspections at several NPPs. An unresolved item (URI) stemmed from concerns that a visual inspection might not provide reasonable assurance that fire dampers would remain functional; the associated URI 05000458/2022010-02, can be found in Inspection Report (IR) 05000458/2023004, dated January 30, 2024 (USNRC 2024). The URI was resolved without identifying a performance deficiency. The fire dampers were installed according to the NFPA 90A 1974 edition, which lacks functional testing requirements for fire dampers. Additionally, the Office of Nuclear Reactor Regulation (NRR) staff noted that the manufacturer's installation directions do not require periodic functional testing. Annual testing was included in maintenance instructions but was not part of the licensing basis (USNRC 2024). However, in the URI, both the regional inspectors and NRR staff noted that while the licensees strategy of conducting visual-only inspections of fire dampers is consistent with the licensing basis, it may not be sufficient to detect degraded conditions which could interfere with fire damper functionality during an event (USNRC 2024).

The Generic Aging Lessons Learned for Subsequent License Renewal (GALL-SLR) Report (NUREG-2191, Volume 2), section XI.M26, Fire Protection, (USNRC 2025) provides fire protection aging management program (AMP) guidance on periodic visual inspections for fire damper housings to verify the integrity of the pressure boundary. However, license renewal does not address the degradation of active components with moving parts; the GALL-SLR Report AMP is not intended to assess the functional performance of dampers. Since degradation may affect the intended safety function of the damper in the designated fire area and active components of the damper may not be functionality tested, this may present a potential gap in which active components may degrade to the point of inoperability.

1-4

1.3 Purpose and Scope

The purpose of this research information letter (RIL) is to provide background, design characteristics, operating experience (OE), and surveillance insights for rated fire dampers used in in-duct and through-wall applications. This work is divided into seven main sections: (1) the purpose and scope of the research, (2) background on fire damper components, (3) existing industry OE, (4) a literature review of qualification tests and standards pertaining to fire dampers, (5) a literature review of NRC fire protection regulations and historic generic communications pertinent to fire dampers, (6) quantitative and qualitative information on fire damper functionality, and (7) a summary of the overall findings and conclusions.

2-1 2 FIRE DAMPER HISTORY 2.1 History of Fire Dampers The first U.S. patent for fire dampers was filed in March 1953. As noted in the patent document, the invention of the fire damper relates to devices for impeding the spread of fire in a frame structure along a plastic pipe or through an opening in such a structure where a pipe existed previously (Gross 1993). Other similar and earlier devices closed off the pipe by providing a means of closing and compressing the interior of the pipes. The fire damper differed by using a guillotine-type shutter for closing off an opening occupied by a melting plastic pipe (Gross 1993). The early patent design for the fire damper consists of a base and a disk-like gate. The base can be mounted to a structural member, and the disk-like gate has a slightly larger surface area than the opening of the pipe. Torque is applied in the direction of the pipe, with the mounting base as the hinge connection and the disk-like gate as the arm. The fire damper is armed using a spring, and the gate is pressed up against the pipe, as shown in figure 2-1.

During a fire, the lower portion of the plastic pipe becomes malleable, allowing the gate to crush the softened pipe and thereby cutting off the flow of hot gases and isolating the area through the pipe.

Figure 2-1. Drawing of first fire damper patent (Gross 1993).

The proposed patent for the fire damper consists of a frame, movable blades, an activation device, and a fusible link; current models of fire dampers still contain many of these basic parts.

NFPA 80 defines a fire damper as a device, installed in an air-distribution system, that is designed to close automatically upon detection of heat to interrupt migratory airflow and to restrict the passage of flame (NFPA 2022). Simply, many current fire damper designs consist of an outer frame, blades for restricting the passage of flames, a heat-sensitive device, and springs. The following sections discuss these components and their purposes in detail.

2-2 2.2 Damper Type and Component Design Fire dampers are typically installed in two configurations: with ductwork and without ductwork.

This depends on the rooms ventilation design. In many cases, ductwork is required for HVAC.

To allow forced air to flow from one room to another, ductwork often penetrates fire-rated walls, as shown in figure 2-2. The ducting material consists of steel, warped into rectangular shapes, and installed in accordance with the standards of the Sheet Metal and Air Conditioning Contractors National Association (SMACNA). In many buildings, the HVAC ducting penetrates fire barriers and therefore fire dampers are installed within the ductwork and in-plane with the firewall to maintain fire barrier continuity. Rooms that rely on natural airflow typically lack ductwork, as shown in figure 2-2. This type of ducting is typical for many buildings with HVAC.

Figure 2-2. Fully ducted fire damper installation (left) and nonducted fire damper (right).

Many accordion-style fire dampers, discussed in 2.2.2, function by having the heat-sensitive device act as an opposing force to the spring or gravity (if a spring is not present in the design).

The spring acts as an additional force for shutting down the accordion-style damper blades. In a fire, the heat-sensitive device releases the blades, and the spring forces them closed. Figure 2-3 shows a side view of a curtain-style fire damper. The curtain-or accordion-style blades are folded on top of each other. Gravity or spring provides a force downward to unfold the blades and shut the damper. Additionally, as labeled in figure 2-3, the heat-sensitive device upholds the damper blades in a closed position by attaching to both sides of the damper curtains.

Fire-rated wall Duct Curtain-style fire damper (closed)

Fire-rated wall Curtain-style fire damper (closed)

2-3 Figure 2-3. Side view of curtain-style fire damper in the closed position.

2.2.1 Common Heat-Responsive Devices A fire damper activates through a heat-sensitive device, typically a fusible link or an electro thermal link (ETL). A fusible link is a heat-actuated device that triggers at a specific temperature.

It consists of two strips of metal held together by solder that melts at a specific temperature.

Heat from a fire would melt the solder and activate the fusible link. An ETL functions like a fusible link. However, it can also be triggered by applying an electrical signal that heats the core of the link and causes it to separate. Both fusible links and ETLs contain notches that latch to both ends of the fire damper to hold the curtain-style blades in a closed and tensioned position.

Once the temperature threshold is reached, or an electrical signal is sent (to an ETL), the fusible link breaks apart and releases that tension, thereby allowing the curtain blades to unfold.

Figure 2-4. Fusible links (left), redrawn with reference (Ruskin 2010) and ETL (right), redrawn with reference (SR Products 2007)

Folded curtain blades Fusible link or ETL

2-4 2.2.2 Common Fire Damper Blade Types The movable blades are typically of two styles: an accordion curtain blade or multiblade type.

The accordion curtain blade style consists of metal blades folded together within the fire dampers track and frame. When the fusible link is activated, the curtain-style blades unfold along the inner track of the frame, latching and closing the opening of the fire damper. The multiblade type consists of multiple blades that are horizontally positioned, allowing airflow through the damper. When activated, the blades rotate such that the opening is closed. Figure 2-5 (Maune 2013) shows a curtain-style fire damper (left) and a multiblade-type fire damper (right).

Figure 2-5: Curtain-type fire damper (left) and multiblade type fire damper (right), redrawn from reference (Maune 2013).

2.2.3 Additional Damper Components Additional components of a fire damper include the damper housing, sleeve, S-hook, spring, and actuators. The housing provides structural support, as well as guiding the closure of the blades. The sleeve allows the damper housing to fit snuggly within the openings of the fire barrier wall. For fire dampers that are installed in a duct network, an S-hook is used to connect the duct to the sleeve of the damper. The S-hook provides a breakaway connection so that if the duct falls, the damper sleeve and housing remain fitted to the fire barrier and are not dragged down by the falling duct. The spring provides an additional closure force and is discussed in sections 2.2 and 4.1.1.4.

Damper actuators, either pneumatic or electric, are used to control the opening and closing of a damper. Actuators, as shown in figure 2-6, are typically found in smoke dampers and smoke/fire hybrid dampers and have a temperature threshold that activates the closing of the damper. Fire dampers are typically designed to activate using a fusible link or ETL; these dampers often do not contain actuators.

2-5 Figure 2-6. Smoke damper (left) and a combination fire smoke damper (right), redrawn from reference (Maune 2013).

2.3 Static and Dynamic Fire Dampers Fire dampers fall into two categories: static and dynamic. The difference between static and dynamic fire dampers varies slightly depending on the source of the definition. A common misconception is that static dampers lack a spring to aid in closing. Although some sources indicate that a static, curtain-style fire damper closes only by gravity and a dynamic damper utilizes a spring, the difference between a static and dynamic damper ultimately depends on whether it is rated to close under airflow. Based on UL 555, fire dampers for static systems are defined as having HVAC systems that are automatically shut down in the event of a fire or for air transfer openings in walls or partitions (UL 2020). Fire dampers for dynamic systems are for HVAC systems that are operational in the event of a fire (UL 2020). Therefore, static fire dampers are defined as being rated to close when the airflow to the HVAC system has shut off, and dynamic fire dampers can be defined as qualified to shut and latch at a specific airflow velocity.

This definition of static and dynamic systems is commonly used throughout the industry. For example, in NFPA 80, static and dynamic systems are defined as follows:

• Static System: An HVAC system designed to stop the movement of air within the system at the indication of a fire. (NFPA 2022)

• Dynamic System: An HVAC system designed to maintain the movement of air within the system at the indication of a fire. (NFPA 2022)

The key difference is that dynamic dampers are designed to close with airflow present, while static dampers close only when airflow is absent.

3-1 3 REVIEW OF FIRE DAMPER OPERATING EXPERIENCE A variety of sources were used to determine the types of fire dampers commonly used in U.S. NPPs. Three main sources were used to compile a set of industrywide data. These data are derived from both industry experience and NRC data. The first set of data comes from the Institute of Nuclear Power Operations (INPO) and was reported by the EPRI. The second set of data was independently parsed by NRC staff and includes a wider range of data found in the INPO Industry Reporting and Information System (IRIS) database. Finally, the third set of data was derived from NRC IRs, event notifications (ENs), and license event reports (LERs). All three sets of data were integral in developing observations and qualitative conclusions on fire dampers. Aggregating data for holistic, unbiased insights was challenging due to the lack of industrywide survey data. Regardless, the following section summarizes and describes the observations from each set of data.

3.1 Electric Power Research Institute In 2003, EPRI released TR-1006756, Fire Protection Equipment Surveillance Optimization and Maintenance Guidance (EPRI 2003), intended to provide a comprehensive review of fire protection equipment and associated failure data. The data were collected from a variety of sources but are compiled in such a way that trending and interpretation of all the collected data can provide insights into maintenance, surveillance, and testing practices of fire protection equipment.

3.1.1 EPRI Compilation of Institute of Nuclear Power Operations Operating Experience and Significant Event Reports A key source of data was INPO OE reports and Significant Event Reports (SERs), compiled in TR-1006756 (EPRI 2003). Ranging from the mid-1980s to 1990s, the 61 reports contain information about fire protection equipment reliability, maintenance, testing, and inspection.

However, the EPRI report does not mention the screening criteria or metrics used to decide which reports were included. It is also important to note that events pertaining to failed fire protection equipment were included; this is not to be confused with events that pertain to the ignition, growth, and decay of a fire (a fire event). The EPRI report does note that events documented by INPO OEs and SERs are generally of a significant nature or have a potential industry-wide impact (EPRI 2003). Therefore, this database likely does not capture less significant degradation and impairments of systems, and care should be taken when drawing any significant conclusions from this source. Figure 3-1 shows a breakdown of the data collected in the 1980s from INPO OE and SER events. Five different systems were observed in the OE and SER reports: the water supply, portable extinguishers, gaseous suppression, barriers, and water-based suppression systems. Fire barrier systems represent 15 % of reports that have some relevancy to equipment reliability, maintenance, testing, and inspection.

There are only two instances of fire damper impairments, which are noted in 9-2 of the EPRI report. Events 34 and 58 involved fire dampers that failed to fully close. The summaries and causes (EPRI 2003) are as follows:

Event 34: Fire dampers were unable to fully close due to deflection in the ducting, which was caused by an expansion of foam seal around the damper penetration. The cause was determined to be an installation deficiency.

(EPRI 2003)

3-2 Event 58: Fire dampers failed to fully close because of the power source to the ETLs for the damper not being adequately sized to melt the links. The cause was determined to be a design deficiency of the dampers.

(EPRI 2003).

Therefore, only two of the 61 INPO OE and SER reports (~3%) involved fire dampers.

Figure 3-1. INPO OE and SER events involving fire protection equipment reliability, maintenance, testing, and inspection. Data used to represent this pie chart was collected in the 1980s. (EPRI 2003).

3.1.2 EPRI-Compiled Data from License Event Reports LERs were compiled in EPRI report TR-1006756 (EPRI 2003). The LERs involving fire protection systems date from 1984 to 1990. Although dated, these reports can provide further insights into fire damper OE. Specific LERs were not available or were not specified in the EPRI report. However, EPRI does note that there were downward trends in barrier issues; this is attributed to better awareness of barrier issues and a reduction in missed compensatory actions (EPRI 2003). Many of the degradation and failure issues in the LERs were caused by either design or human error (EPRI 2003).

Figure 3-2 presents a breakdown of the different fire protection systems. The EPRI report does not mention the total number of LERs reviewed and presented in this dataset. However, barriers contributed to 54 % of LERs from 1984 to 1990 (EPRI 2003). Barriers are further subcategorized into different groups, shown in figure 3-3, such as fire dampers, walls, fire wraps, penetration seals, doors, and other. Fire dampers make up approximately 13 % of all LERs pertaining to barriers. Therefore, LERs involving fire dampers make up approximately 7 percent of the total LERs reviewed from 1984 to 1990. The total number of LERs reviewed Gasseous [sic]

Suppression 32%

Portable Extinguishers 3%

Water Supply 20%

Barriers 15%

Water-Based Suppression 30%

3-3 between 1984 and 1990 is unknown. Therefore, caution is warranted when drawing conclusions solely from the percentage of fire damper failures in this dataset.

Figure 3-2. Fire protection systems identified in LERs between 1984 and 1990 (EPRI 2003).

Figure 3-3. Types of fire barriers identified in LERs between 1984 and 1990 (EPRI 2003).

3.2 Institute of Nuclear Power Operations Industry Reporting and Information System Database The INPO IRIS database contains valuable information for determining failure and manufacturing data on fire dampers, such as information on the failure mechanism, the component that failed, and the manufacturer of the failed component. This information helps identify the types of fire dampers used in the industry and common failure mechanisms. An additional benefit of including the INPO IRIS data is that it provides a larger sample size and Unspecified 14%

Detection 10%

Suppression 22%

Barriers 54%

Fire Dampers 13%

Penetration Seals 42%

Unspecified 9%

Fire Wraps 7%

Hatches 1%

Walls 2%

Doors 26%

3-4 therefore is more representative of the industry. The failures reported in the INPO IRIS database were identified by direct and indirect equipment surveillances.

Three steps were used to compile relevant fire damper data from the INPO IRIS database. The dataset was developed by first performing a search using the INPO IRIS database search function. The search used keywords such as fire damper and filtered through components that fell under the Valves, damper category. This search returned a total of 116 different event reports. The second step was to filter and screen reports for relevancy. Each event report contains detailed information that can be used to gather insight into the types of dampers in the industry, such as the description, abstract, and components involved in the event. This information was used to identify relevant events and the components involved in the failure.

Events that did not actually pertain to the mechanical failure of a fire damper closing and latching were also considered. For example, various events mentioned a fire damper actuating and closing, which may have resulted in another component or system being impaired; these events were screened out if the fire damper was found to be fully closed, latched, and intact.

Additionally, events were screened out when the fire damper received an unintended actuation signal, but the fusible link or heat-responsive device worked as intended and the damper fully closed. In both cases, the physical damper still managed to mechanically close and fully latch.

The final step was to categorize the event reports based on the failure types of each fire damper. The event report performance descriptions indicated how components failed, allowing similar events to be grouped.

After screening the events, 55 of the initial 116 events, as shown in table 3-1, were determined to be relevant. The performance description column conveys the performance state of the failed damper. General observations and descriptions were derived from the binned events, as well as the number of events per bin. Common general observations, regardless of the performance description, were mechanical binding of the blades and obstructions that blocked the full closure of the damper.

Table 3-1. Categorized event reports by INPO-defined performance descriptions.

INPO-Reported Performance Description General Description of Similarly Binned Events General Observations Count Failed to Close on Demand The damper did not close (i.e., move from the open position at all) on a demand (i.e., heat source or electrical signal).

Mechanical binding of the blades and track Obstructed by object(s) 23 Failed to Remain Open The damper drifted to a closed or semiclosed position.

Failure of fusible link or ETL in combination with degraded blades and/or obstructions by object(s) 15 Failed to Close within Setpoint Tolerance The damper did not close and latch fully within the design conditions.

In some events, fire dampers did not close fully under the designed airflow 5

3-5 The event reports also list the manufacturer and model of the fire dampers involved. This is a representative sample of 116 INPO event reports and does not imply that one manufacturer has a higher failure rate, since the total number of dampers per manufacturer is unknown. For example, if manufacturer A experiences 10 failures and manufacturer B experiences 20 failures, this does not mean that manufacturer B experiences twice the percentage of failures. In fact, if the failure rates were the same and there were a larger number of overall fire dampers manufactured by manufacturer B than A, then manufacturer B would obviously have a higher number of fire dampers that fail.

Manufacturer data from all 116 event reports were analyzed to provide a larger sample of the types of dampers and manufacturers used within the nuclear industry. This data includes all component types labeled as Valves, dampers in the INPO IRIS database. Therefore, the manufacturer data may include other items besides dampers, such as valves. However, because of the keyword search for fire dampers that was applied in the initial INPO IRIS database search, many of the results have specific relevancy to fire dampers.

Figure 3-4 shows a breakdown of all the manufacturers that appear in the event reports. The names of the manufacturers in figure 3-4 are presented based on how the information was reported to the INPO database.

INPO-Reported Performance Description General Description of Similarly Binned Events General Observations Count Due to binding, damaged blades, and/or degraded springs Partially Closed on Demand (Not Stuck Open)

The damper may have actuated on a demand and initiated closure but did not close fully or latch as designed.

Interference of ETL, spring, or other object(s)

Due to dirt and lacked lubrication of tracks 10 Discovered to Be Unable to Close The damper was discovered through the review of adjacent documents (i.e.,

review of maintenance practices) and not through testing or indication.

Identified broken components (i.e., damper blades and springs) 2

3-6 Figure 3-4. Count of INPO IRIS event reports organized by manufacturer.

The top five manufacturers, as shown again in figure 3-5. Of the 116 reports, the top three contributors were Ruskin Company, contributing to 25 % of the event reports; Air Balance, Inc.,

contributing to 23%; and American Warming and Ventilating, Inc., contributing to 11%. The INPO event reports show some components as Not yet determined. This contributed to 18% of the event reports. All other manufacturers are grouped in the Other category and contribute 23%.

It is important to note that many of the event reports include data on manufacturer fire dampers, as well as valves and other related components. Because INPO component labels include Valves, dampers, it would have been a tedious challenge to distinguish the other components from the dampers. This task could have been performed by parsing specific manufacturer information, such as the specification sheets and other information found on the manufactures website. This posed a challenge because legacy data on the components are not always publicly available. However, valves listed in the components section seemed to contribute little to the overall batch of event reports and would not bias the sample size.

0 5

10 15 20 25 30 35 Air Balance Custom Fabricated American Warming & Ventilating, Inc Valvex Not yet determined N/A for subcomponent Ruskin Company Press Mechanical Inc Not available from site data or walk downs Tyco Fire & Integrated Solutions (Wormald)

Pullman Const Industries Buffalo Forge Co.

Advance Air (Allied Therm.)

Richards Wilcox Mfg Co SR Products Inc Target Rock Corp SSM Industries Johnson Svs Co ITT General Controls Honeywell Inc Count Manufacturer Count of Manufacturers in Event Reports

3-7 Figure 3-5. Top five manufacturers by number in INPO IRIS event reports.

The product specifications for each listed model can be located on the manufacturers web page. There were 60 different models, with each product specification sheet listing whether the fire damper was rated as a static or dynamic fire damper. Some models identified in the event reports are no longer listed on manufacturers websites and were categorized as unknown.

Figure 3-6 presents a sample taken from the top three manufacturers (Air Balance, Ruskin Company, and American Warming & Ventilating, Inc.); the fire damper models were categorized as static, dynamic, or unknown based on the product sheet. Static dampers make up 62 % of the sample. Dynamically rated fire dampers account for 8 percent, and fire dampers with an unknown rating contribute 30 % of the sample. Most dampers in the INPO IRIS event database appear to be static, even if all unknown-rated dampers are assumed to be dynamic.

Figure 3-6. Percentage of static and dynamic dampers in INPO IRIS event reports.

23%

25%

11%

18%

23%

Top Five Manufacturers Air Balance Ruskin Company American Warming & Ventilating, Inc.

Not yet determined Other 62%

8%

30%

Static and Dynamic Dampers Static Dynamic Unknown

3-8 3.3 NRC Documents This section reviews the aggregated data from NRC-related documents such as inspection findings, ENs, and LERs. This dataset does not provide many data points because the threshold for these items is higher than an INPO IRIS event report. Therefore, the NRC reports alone do not capture many of the recurring or common low-level problems, and caution should be taken when drawing conclusions from this dataset alone.

3.3.1 NRC Inspection Findings NRC inspection finding documents from 1990 to 2024 were reviewed. This review included key search words such as fire damper and damper. By expanding the search to generic dampers, the NRC staff was able to return a larger number of IRs. However, this meant that all searches with the keyword damper would return reports that are not explicitly relevant to this review. Therefore, each inspection finding was parsed for relevancy. Relevant scenarios include events in which a damper, not necessarily a fire damper, activates but fails to close fully and latch. Additionally, the inspection finding descriptions were reviewed to ensure that the damper described functions similarly to the curtain-style fire damper (i.e., accordion blades and tracks).

Using the keyword fire damper in the search resulted in 19 total inspection findings from 2000 to 2024. After review, only 10 of these inspection finding reports were relevant; all were of green (low) safety significance. However, using the keyword damper resulted in 143 total inspection findings from 1990 to 2024; these inspection findings were also of green (low) safety significance. A subset of 18 of the 143 reports remained after screening and accounting for duplicates. The total number of relevant inspection findings is 28. Many of the findings noted that the damper actuated but failed to close fully. The inspection finding reports do not always thoroughly explain the cause of the damper failure. Common causes of failure included improper resetting, incorrect component installation, corrosion, or combinations of these factors.

It was unclear whether the corrosion of components was age related or due to a lack of preventive maintenance practices. However, it is important to note that many manufacturers recommendations and certification standards consider possible corroded components.

Appendix A lists all the inspection findings.

3.3.2 NRC License Event Reports LERs were reviewed for events relevant to fire dampers. Since LERs typically contain more detailed information on a reporting event, they were reviewed instead of ENs to avoid duplicative effort. A search using the keywords fire damper was performed and resulted in a total of 8 LER reports, ranging from 2000 to 2016. However, after reviewing the event descriptions, only one LER event description described fire damper(s) not fully closing. The cause of this was a bent blade and the improper installation of the ETLs. It is important to note that the reporting requirements for ENs and LERs are specifically outlined in 10 CFR 50.72, Immediate notification requirements for operating nuclear power reactors, and 10 CFR 50.73, License event report system. Therefore, the low number of LERs concerning failure of fire dampers to fully close can be attributed to the reporting requirements. A fire damper closure failure would not necessarily require an EN and LER from the licensee, unless a fire damper contributed to an event that would require notification in accordance with 10 CFR 50.72 and 10 CFR 50.73.

The search criteria were expanded to include the word damper. However, the results of that analysis are not included here because of the lack of information pertaining to that search.

3-9 Although searching by the more general term damper returned a higher number of LERs, the information often lacked detail on the damper component failure mechanism. As mentioned earlier, because the criteria for an EN are specified in 10 CFR 50.72 and 10 CFR 50.73, the event details often reflect those reporting requirements and exclude information about subcomponents, such as dampers or fire dampers. Additionally, many of the LERs did not contain enough detail to determine if the damper functioned in a similar manner to a fire damper.

3.4 Summary of Findings This section summarizes the findings from reviewing fire damper OE within the industry. Fire dampers contribute a minor portion of total fire protection equipment failures, as shown from the data compiled in the EPRI report (EPRI 2003). Based off the reviewed data, the majority of fire dampers that appeared in the event reports are static fire dampers (i.e., operate under no airflow).

Common failure mechanisms were qualitatively assessed by a review of INPO IRIS event reports3 and NRC IRs.4 A review of all OE results in the following bins for causes of failure:

failure of actuation device (i.e., ETL or fusible link) improper resetting or installation of the fire damper damaged or missing components (i.e., curtain blades) corrosion, debris, and components obstructing or binding fire damper components objects or components blocking the path of curtain closure Table 3-2 summarizes the resulting common failure mechanisms and recommended inspection type (visual or functional) to address those failures. Many of the causes of failures listed in table 3-2 are not independent of each other. One observation made by the NRC staff when reviewing OE is that some INPO IRIS events had failures with objects or components blocking the path of curtain closure damaged coinciding with improper resetting or installation of the fire damper.

Improper resetting or installation of the fire damper may lead to looser or unaligned components and thus obstruction of the closure path of the damper. Also, the failure of actuation device (i.e., ETL or fusible link) coincided with the damaged and/or missing components (i.e., curtain blades) failure; this was simply due to a handful of event reports that noted fusible links or ETLs being damaged or missing, which applied to both categories.

3 For additional information on the number of INPO IRIS event reports that fall into each category, see table A-2.

4 For additional information on binned causes of failure in NRC IRs, see table A-1.

3-10 Table 3-2. Summary of failure cause and recommended inspection type.

Although this review of OE provided some additional insights into failure mechanisms, there are some limitations. First, the failure rates of the data cannot be determined because the total number of surveillances performed and fire dampers per reactor, site, fleet, and/or nuclear industry are completely unknown. Additionally, non fire dampers were included to provide additional insights and data points, and it was not always completely clear whether the damper functioned in a similar manner to a fire damper. Hence, it was left to the interpretation of the NRC staff to determine if the damper functioned and failed in a manner similar to a fire damper.

In addition, NRC IRs rarely reported the cause of the issue; the cause was often inferred based on the description in the IR. Without surveying the nuclear industry, a qualitative assessment provides the best insight into determining failure causes.

Cause of Failure Recommended Inspection Type Comments Failure of actuation device (i.e., ETL or fusible link)

Visual A visual inspection reveals linkage failure (fusible or ETL) because it can confirm whether the link has been degraded or broken.

Improper resetting or installation of the fire damper Visual and functional Functional tests revealed failures where improper resetting of the fire damper caused components to shift out of place and obstruct the full closure of the damper. A component may appear to be properly reset but can shift out of place when the damper activates.

Damaged and/or missing components (i.e., curtain blades)

Functional Because curtain-style fire dampers have blades that fold onto themselves in the open position, a functional test reveals any damaged or missing blades that cannot be inspected visually.

Corrosion, debris, and components obstructing and/or binding fire damper components Visual and functional A functional test reveals additional sticking and binding of the damper blades that would not have been detected by a visual inspection. There were events in which functionally testing the damper resulted in complete binding of the blades (they stayed in the open position).

Objects or components blocking the path of curtain closure Visual and functional Functional tests revealed failures where components shifted out of place and obstructed the full closure of the damper. Although visual inspection can catch obstructions in the path of the damper, components can shift in the closure path of the damper during activation.

4-1 4 QUALIFICATION TESTS AND STANDARDS FOR FIRE DAMPERS This section covers the testing requirements for fire dampers and the maintenance practices outlined in UL and NFPA standards. Because many NPPs were built in the 1950s and 1960s, understanding the history of these documents is essential to evaluating test, installation, and maintenance practices of that period. Additionally, an analysis was performed to determine any discrepancies in testing requirements or standards between editions.

4.1 Underwriters Laboratories Standard for Safety for Fire Dampers (UL 555)

This section of the report summarizes the various testing requirements outlined in UL 555. The standard is currently in its seventh edition, but the first edition was published in 1968.

Understanding the history and evolution of this standard is important because fire dampers manufactured before 1968 may not have undergone standardized testing. Therefore, this section will examine the tests in each edition, highlight the differences between each edition, and provide a simple gap analysis.

4.1.1 UL 555, Seventh Edition (2006)

Published in July 2006 and last revised in October 2020, the 7th edition of UL 555 is the industry standard test used to determine the rating of fire dampers. Fire dampers are rated in minutes or hours and are subjected to tests outlined in UL 555. According to UL 555, 7th edition (UL 2020), all fire dampers must undergo three tests (described in sections 4.1.1.1 to 4.1.1.3):

(1) Fire endurance and hose stream (2) Cycling (3) Salt spray exposure As stated in 1.2 of UL 555, fire dampers are evaluated for either static or dynamic systems.

Static fire dampers are designed for HVAC systems that are automatically shut down in the event of a fire or for air transfer openings in walls or partitions (UL 2020). Dynamic fire dampers are designed for HVAC systems that are operational in the event of a fire (UL 2020). In the event of a fire, both static and dynamic fire dampers are intended to activate and close automatically upon a signal from either a fusible link or a heat-response device. Depending on whether the fire damper is static or dynamic, the damper is subjected to a spring closing force or dynamic closure test, respectively, as shown in table 4-1.

Table 4-1. Required tests for different fire dampers, recreated from UL 555 (UL 2020).

Test Static Fire Damper Dynamic Fire Damper Fire Endurance and Hose Stream X

X Cycling X

X Salt Spray Exposure X

X Spring Closing Force X

Dynamic Closure X

4-2 4.1.1.1 Fire Endurance and Hose Stream Test The fire endurance and hose stream test are used to determine the rating of a fire damper.

Similar to structural fire barriers, fire dampers are rated in hours or minutes. The tested fire damper is installed in a representative wall assembly, as specified by the manufacturers installation instructions. Two samples of the fire damper are installed and tested. One sample is installed such that the upstream side is facing the furnace, and the other sample is installed such that the downstream side is facing the furnace. The fire damper assembly is exposed to the standard time-temperature curve, as presented in the American Society for Testing and Materials (ASTM) Standard Test Methods for Fire Tests of Building Construction and Materials (ASTM E119-20), (ASTM 2020) shown in figure 4-1.

Figure 4-1. Time-temperature curve referenced in ASTM E-119 (ASTM 2020). Figure was taken from NUREG-1805 (Iqbal and Salley 2004).

At least nine thermocouples are symmetrically installed to measure temperatures across the assembly. The fire test is continued until the desired rating is reached or until the fire damper fails to comply with the acceptance criteria. Immediately after the exposure portion of the test, the assembly is subjected to the impact, erosion, and cooling effects of a hose stream, as specified in sections 10.3.9, 10.3.10. and 10.3.11 of UL 555 (UL 2020).

Section 10.1 of UL 555 specifies the acceptance criteria for this test. The acceptance criteria state that the fire damper must remain within the assembly during the fire exposure and hose stream test. The fire damper must also completely close and latch upon activation of the heat-responsive device. Additionally, all the blades, latching mechanisms, and blade guides shall remain engaged. Any movement or warping of the fire damper assembly shall not result in

4-3 an excess of the specified width of visible openings between various fire damper components, as specified in section 10.1.3 of UL 555. Fire-rated barriers, which have limits on the average and individual point temperature on the unexposed surface, undergo testing described in UL 263, Standard for Safety Fire Tests of Building Construction and Materials (UL 2011). For fire dampers, acceptance criteria require that no flaming occurs on the unexposed side of the assembly. Unlike UL 263, UL 555 does not specify an upper threshold on the temperature of the unexposed side for fire dampers; the testing standard does not specify the reason for not having this acceptance criterion.

4.1.1.2 Cycling Test The cycling test ensures that the damper can repeatedly open and close without failure. Section 11 of UL 55 fully describes the test. Dampers that utilize an actuator, such as a combination fire smoke damper, have requirements for how many strokes need to be tested to ensure reliability.

This includes mechanically operating the damper (close and reopen) for 20,000 strokes, or if intended to be used as a volume control damper, then the damper must be operated for 100,000 strokes. For a fire damper that does not have an actuator, the number of full-stroke operations is 250, cycled manually.

4.1.1.3 Salt Spray Exposure Test The salt spray exposure test is intended to simulate dust and debris that accumulate on a fire damper and determine the performance of the fire damper. Section 12 of UL 555 describes this test. To pass this test, the fire damper must completely close and latch automatically following a specified time of exposure to the salt spray. The salt spray consists of a common salt (sodium chloride) and distilled water mixture, which is applied in accordance with ASTM B117, Standard Practice for Operating Salt Spray (Fog) Apparatus (ASTM 2019). After exposure to the mixture, the fire damper is removed from the chamber and dried and cured for the specified time and temperature. It is then placed in the open position and tested for closing and latching (UL 2020).

The salt spray exposure test is of particular interest to damper functionality because it proactively addresses the concern about dirt, debris, and degradation of the damper by emulating those conditions.

4.1.1.4 Spring Closing Force Test This test applies only to static fire dampers, as detailed in section 13 of UL 555 (UL 2020). The spring closing force test ensures the spring is adequately sized to close and latch the damper blades from fully open to closed. The springs are fully detached from the damper, and the force required to close and latch the fire damper is measured at a series of different positions, ranging from fully open to closed (latched). The force available from the action of the spring or springs is required to be 2.5 times the measured force used to close and latch the fire damper.

4.1.1.5 Dynamic Closure Test The dynamic closure test, detailed in sections 14 and 14.2 of UL 555, is used for dynamic fire dampers only (UL 2020). This test is designed to ensure that the dynamic fire damper can close under tested airflow conditions. Incremental airflow, pressure, and heat values are predetermined and listed in table 14-1 of UL 555 (UL 2020). Under specified airflow and pressure conditions, the samples of fire dampers are required to latch (when a latch is provided) and close without damage to the damper or its components. The fire damper is tested so that airflow is in both directions. Section 14.3 of UL 555 outlines an alternative to the dynamic

4-4 closure test. The alternative method develops a velocity profile, as described in UL 555, section 14.3.2 (method 1) or section 14.3.3 (method 2).

4.1.2 UL 555, Third Edition (1979)

The third edition of UL 555 (UL 1979) was published in 1979. The following tests are described in both the seventh edition (UL 2020) and the third edition (UL 1979) of UL 555:

• fire endurance and hose stream

• cycling

• salt spray exposure However, UL 555, third edition, states the following:

Fire dampers for the protection of wall openings, without ducts, are not covered in this standard but are investigated in accordance with Standard UL 10B, Tests of Door Assemblies. (UL 1979)

The description of fire dampers for the protection of wall openings, without ducts, may be applicable to some fire dampers in NPPs because of an abundance of large open rooms. Some fire dampers in NPPs may therefore have been qualified under UL 10B, Standard for Safety Fire Tests of Door Assemblies. Because the 1979 edition of UL 10B is not publicly available, NRC staff could not review its required tests.

4.1.3 UL 555, First Edition (1968)

Similarly, UL 555, the first edition, is not publicly available for review. It is unknown what tests were required in the first edition or whether the salt spray test, as discussed in section 4.1.1.3, was a required test. This test simulates dust and debris accumulation, addressing one of the common failure mechanisms observed in fire dampers that failed to fully close. Therefore, review of the first edition may provide some additional insights into whether this issue was addressed and considered for fire dampers manufactured around or before 1968.

4.2 National Fire Protection Association Standards Various editions of the applicable NFPA standards were reviewed to understand the functional testing and installation guidance of fire dampers. Reviewing various editions of these standards provides a broader perspectivebeyond the nuclear industryon how functional testing is addressed. This section discusses the history and development of these standards. There are two main standards that involve functional testing of fire dampers: NFPA 80 and NFPA 90A.

4.2.1 NFPA 80, Standard for Fire Doors and Other Opening Protectives To reiterate, and as defined in section 2.1, fire dampers are a device, installed in an air-distribution system, that is designed to close automatically upon detection of heat to interrupt migratory airflow and to restrict the passage of flame (NFPA 2022). The first introduction of fire dampers in NFPA 80 occurred in the 2007 edition (NFPA 2007). There was a name change for NFPA 80 during that time. Previously known as the Standard for Fire Doors and Fire Windows, the name of the standard was changed to Standard for Fire Doors and Other Opening Protectives in the 2007 edition. Before 2007, standards for fire dampers were found in a

4-5 different set of NFPA standards, which is discussed in this section. In the 2007 edition of NFPA 80, the origin and development section state the following:

The 2007 edition includes a major reorganization in accordance with the Manual of Style for NFPA Technical Committee Documents and a title change to accommodate the broader scope of the document. New chapters on fabric fire safety curtains and the installation, testing and maintenance of fire dampers have been added (NFPA 2007).

4.2.1.1 Operational Testing Requirements Chapter 19 of NFPA 80, 2007 edition, contains the installation testing and maintenance requirements for fire dampers. Furthermore, section 19.3 states the operational test requirements. Section 19.3.1.1 states that after the installation of damper is completed, an operational test shall be conducted (NFPA 2007). It is important to note that the section 19.3.1 heading includes the label Dynamic Fire Dampers. It is unclear if the section is meant to apply to dynamic fire dampers only, or if it was simply an oversight in the first reorganized edition of NFPA 80. However, the 2022 edition of NFPA 80 provides further insight into the operational testing requirements, and it can now be concluded that the operational testing requirements were meant for all fire dampers, both static and dynamic. A comparison of the 2007 and 2022 NFPA 80 editions for section 19.3.1 statement supports the above conclusion and is shown below:

19.3.1 Dynamic Fire Dampers. After the installation of a damper is completed, an operational test shall be conducted. (NFPA 2007) 19.3.1 Fire Dampers. After the installation of a damper is completed, an operational test shall be conducted. (NFPA 2022)

For the operational test to succeed, the damper shall fully close from the open position. The test also ensures that there are no obstructions to the operation of the damper; for dynamic dampers, it shall be verified that the airflow is within the velocity rating of the damper.

4.2.1.2 Periodic Inspection and Testing Requirements The 2022 edition of NFPA 80 specifies the periodic testing requirements in section 19.5. It requires that one year after installation, the fire damper is to be tested and inspected. After this initial inspection, the test and inspection frequency are every four years. For occupancies classified as hospitals, the functional testing frequency for fire dampers is every six years (NFPA 2022). The same requirements are mentioned in the 2007 edition in sections 19.4.1.1 (NFPA 2007).

Section 19.4.5 in the 2007 edition states, the operational test of the damper shall verify that there is no damper interference due to rusted, bent, misaligned, or damaged frame or blades, or defective hinges or other moving parts (NFPA 2007). However, this statement is not in the 2022 edition of NFPA 80, although a similar statement regarding rust and damaged blades is included.

Section 19.6.2 of NFPA 80, 2022 edition, states that all exposed moving parts of the damper shall be dry lubricated as required by the manufacturer (NFPA 2022). The appendix to this

4-6 section further explains that each damper should be examined to ensure that it is not rusted or blocked, with attention given to hinges and other moving parts (NFPA 2022).

Both editions of NFPA 80 consider rust and other moving parts. However, the 2007 edition specifically states that the operational test is used to verify that the fire damper can fully close without interference. The 2022 edition does not explicitly state the above but instead states that the fire damper must be maintained to ensure that it can close fully.

4.2.1.3 Exception to Periodic Testing for Fully Ducted Fire Damper In the 2022 edition of NFPA 80, section 19.5.1.3 contains a statement regarding not having to periodically test a single fire damper if it is not accessible and if it lays in a fully ducted HVAC system and sits within a rated barrier or shaft. This statement is further explained in appendix A.19.5.1.3 to NFPA 80, 2022 edition; the appendix recognizes that some dampers are inaccessible for various reasons and that the inability to test a single damper might not pose a significant risk to the performance of the system when the system is fully ducted (NFPA 2022).

Although the appendix explanatory statement does not give technical justification, NFPA standards are consensus-driven and reflect the qualitative collective judgment of experienced committee members. Therefore, while the basis for this addition to the code is not documented or presented, it is assumed that the above statement represents quality information.

4.2.2 NFPA 90A, Standard for the Installation of Air Conditioning and Ventilating Systems Before the revision of NFPA 80 in 2007, NFPA 90A governed the testing and maintenance standards of fire dampers. Therefore, many of the installation, testing, and maintenance requirements for fire dampers before 2007 are found in this standard. Although many licensees may not be committed to NFPA 90A or NFPA 80, the requirements in NFPA 90A are discussed below to highlight common practices in the fire damper industry during that time.

Chapter 3, Fire Integrity of Building Construction, in NFPA 90A, specifies many of the required fire protection assemblies, including fire dampers. Section 3-3.7.1 states the following:

Fire dampers used for the protection of openings in firewalls, or walls and partitions having a fire resistance rating of 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> or more, shall possess a 3-hour fire protection rating in accordance with UL 555, Standard for Fire Dampers and Ceiling Dampers, 3rd Edition. (NFPA 1985)

It is important to note that the 1985 edition of NFPA 90A references the third edition of UL 555 (UL 1979). This implies that many, if not all, fire dampers manufactured would have been subjected to the UL 555 standard tests, whether used in the nuclear industry or not.

However, NFPA 90A does not outline any specific maintenance and installation requirements.

Section 3-3.7.2.2 states fire dampersshall be installed in accordance with the condition of their listing and the manufacturers installation instructions (NFPA 1985). Appendix B-7 states the following:

Each door or damper should be examined once a year, giving attention to hinges and other moving parts, to see that it is in good operable condition. Remove fusible links (where applicable), operate door or damper, check latch (if provided) and lubricate moving parts if necessary. It is desirable to operate doors or

4-7 dampers with normal system airflow to assure that they are not held open by the air stream (NFPA 1985).

The Appendixes to the standard bring attention to possible deficiencies in fire dampers and how to properly address them, but the deficiencies are not explicitly addressed in the body of the standard as they are in NFPA 80. Later editions of NFPA 90A discuss where fire dampers shall be installed and required per the standard, but the actual installation, maintenance, and testing practices (i.e. surveillance type, periodicity, etc.) are not discussed.

4.3 Summary of Findings The salt spray exposure test, as detailed in section 4.1.1.3, is an important test for assessing damper functionality because it simulates conditions similar to some of the failure mechanisms observed from OE. Given that corrosion and debris can obstruct or bind fire damper components (section 3.4), this test effectively addresses these failure mechanisms. It was noted that the seventh and third editions contain the requirements for the salt spray test. However, it is unknown whether Standard UL 10B or UL 555, first edition, have the salt spray test requirement. Since most nuclear power plants were constructed and licensed before 1990, it can be assumed their fire dampers were subject to either the first or third edition. Regardless of the UL edition, many of the OE cases described in section 3 report instances of binding due to debris and dust. This indicates that failures continue to occur regardless of whether earlier editions included the salt spray requirement. Although not essential, information on whether the first edition of UL 10B or UL 555 required the salt spray test could provide additional insight into the causes of observed failure mechanisms (e.g., maintenance practices or design).

Although many licensees may not be committed to NFPA 90A, the testing and maintenance practices in the standards provide a context for fire damper industry norms. Analysis of the requirements in NFPA 90A suggests that fire dampers manufactured around 1985 were subjected to the testing and certification requirements of UL 555, third edition (UL 1979), which includes the testing requirements mentioned in section 4.1.1. Additionally, many of these testing requirements ensure adequate fire ratings through fire endurance and hose stream testing.

Additionally, the salt spray exposure test addresses dust and debris concerns. NFPA 80 contains specific maintenance practices for addressing rust and damaged parts; NFPA 90A addresses these topics in the appendix, which is not a requirement in the standard.

5-1 5 NRC FIRE PROTECTION REGULATIONS, GUIDANCE, AND GENERIC COMMUNICATIONS FOR FIRE DAMPERS

5.1 Background

NRC requirements and guidelines for fire protection are contained in several documents. In 1971, the Atomic Energy Commission released Appendix A to 10 CFR Part 50 (U.S. CFR 1971). GDC 3 in Appendix A states the following:

Structures, systems, and components important to safety shall be designed and located to minimize, consistent with other safety requirements, the probability and effect of fires and explosions. Noncombustible and heat-resistant materials shall be used wherever practical throughout the unit, particularly in locations such as the containment and control room. Fire detection and fighting systems of appropriate capacity and capability shall be provided and designed to minimize the adverse effects of fires on structures, systems, and components important to safety. Firefighting systems shall be designed to assure that their rupture or inadvertent operation does not significantly impair the safety capability of these structures, systems, and components (U.S. CFR 1971).

The Atomic Energy Commission did not discuss the specific requirements for fire barriers, such as fire dampers, or guidelines for implementing the requirements in GDC 3. As a result of the Browns Ferry Nuclear Plant fire, which occurred on March 22, 1975, the NRC received two recommendations from the Special Review Group that investigated the event (Collins, et al.

1976). These recommendations ensured that the FPPs at operating NPPs conformed to GDC 3 (Bajwa and West 1996).

The first recommendation was that the NRC develop specific guidelines or recommendations for implementing GDC 3. In response, the NRC developed Branch Technical Position (BTP)

Auxiliary Power Conversion Systems Branch (APCSB) 9.5-1, Guidelines for Fire Protection for Nuclear Power Plants (USNRC 1976), and Appendix A to BTP APCSB 9.5-1 Guidelines for Fire Protection for Nuclear Power Plants Docketed Prior to July 1, 1976 (USNRC 1977). The second recommendation was that the NRC review the FPP at each operating plant and compare it to the specific implementing guidance mentioned above, BTP APCSB 9.5-1 (USNRC 1976) or Appendix A to BTP APCSB 9.5-1 (USNRC 1977).

5.2 BTP APCSB 9.5-1, Guidelines for Fire Protection for Nuclear Power Plants BTP APCSB 9.5-1 describes the acceptable guidelines for implementing GDC 3. Although BTP APCSB 9.5-1 does not explicitly define fire dampers, a general definition of fire barriers is as follows: Fire Barrierthose components of construction (walls, floors and roofs) that are rated by approving laboratories in hours for resistance to fire to prevent the spread of fire (USNRC 1976).

Additionally, Appendix A of BTP APCSB 9.5-1 states that penetrations for ventilation systems should be protected by a standard fire door damper where required. (Refer to NFPA 80, Fire Doors and Windows.) (USNRC 1977). Although Appendix A of BTP APCSB 9.5-1 requires fire dampers and its functionality, there is no language that specifies a method, frequency, or inspection type (i.e., visual versus functional). For example, the guidance references NFPA 80 as one example of a standard that would satisfy the guidances requirements but does not

5-2 recommend that licensees/applicants commit to it. Additionally, as discussed in section 4.1, NFPA 80 editions prior to 2007 do not mention fire damper testing or maintenance requirements. Before 2007, fire damper installation and maintenance guidance was in the NFPA 90A standard. Therefore, even if licensees were to refer to the guidance in Appendix A BTP APCSB 9.5-1, the appropriate reference for fire damper requirements is in NFPA 90A for editions before 2007. Hence, depending on the version and year, a gap may exist within the initial fire damper guidance for those referencing Appendix A BTP APCSB 9.5-1. Note that the correct reference, NFPA 90A, is fixed in revision three of NUREG-0800, Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants: LWR Edition (USNRC 1981).

5.3 10 CFR 50.48 and Appendix R to 10 CFR Part 50 The Special Review Groups second recommendation was that the NRC should review the FPP of each operating plant and compare it to the agency guidance in BTP APCSB 9.5-1 (USNRC 1976). In review, it was found that most licensees complied with most of the implementing guidance, BTP APCSB 9.5-1. However, the staff and some licensees disagreed on several issues. To resolve the disputed issues, NRC introduced 10 CFR 50.48, Fire protection, (U.S.

CFR 1956) and Appendix R to 10 CFR Part 50 (U.S. CFR 1980).

The basic fire protection regulation for NPPs is 10 CFR 50.48. In part, the regulation requires that each operating plant with an operating license under 10 CFR Part 50 Domestic Licensing Of Production And Utilization Facilities (U.S. CFR 1956) or 10 CFR Part 52, Licenses, Certifications, and Approvals for Nuclear Power Plants, (U.S. CFR 1989) have a fire protection plan that satisfies GDC 3. However, neither GDC 3 nor 10 CFR 50.48 explicitly address fire dampers.

The introduction of Appendix R was intended to resolve the disputes on fire protection issues (Bajwa and West 1996). However, the Commission decided to retroactively apply the requirements for fire protection of three sectionsfire protection of SSD capability, emergency lighting, and reactor coolant pump oil collection systemsto all plants in operation before January 1, 1979, even if the NRC staff had already approved alternative approaches. The remaining sections of Appendix R were backfit to plants only to the extent required to resolve the disputed issues (Bajwa and West 1996). There are three sections that discuss fire barriers, with some relevance to fire dampers, but Appendix R does not explicitly address fire dampers.

The following sections of Appendix R refer to fire barriers:

Appendix R (II)(C)(4)Fire barriers or automatic suppression systems or both shall be installed as necessary to protect redundant systems or components necessary for safe shutdown. (U.S. CFR 1980)

Appendix R (II)(C)(7)Surveillance procedures shall be established to ensure that fire barriers are in place and that fire suppression systems and components are operable. (U.S. CFR 1980)

Appendix R (III)(G)(2)(a)Separation of cables and equipment and associated non-safety circuits of redundant trains by a fire barrier having a 3-hour rating.

Structural steel forming a part of or supporting such fire barriers shall be protected to provide fire resistance equivalent to that required of the barrier.

(U.S. CFR 1980)

5-3 Fire protection features proposed or implemented by plants prior to February 19, 1981, and accepted by NRC staffwhether they meet the provisions of Appendix A BTP 9.5-1 or were accepted prior to 1976, before the issuance of Appendix A BTP APCSB 9.5-1are considered compliant under 10 CFR 50.48(b)(1) and do not require Appendix R except for specified sections of Appendix R. Although fire barrier requirements are not explicitly referenced in 10 CFR 50.48, fire damper requirements are incorporated in Appendix A BTP 9.5-1 and/or through the licensing basis at the time the licensee/applicant was approved.

Plants that did not receive approval for, or did not implement, fire protection features prior to 1981or were not reviewed against Appendix A BTP 9.5-1are subject to Appendix R, including its fire barrier requirements under 10 CFR 50.48(b). A review of both Appendix R and Appendix A BTP 9.5-1, shows that while both documents generally address fire barrier requirements and operability, they do not specify methods for surveillance or surveillance frequency.

5.4 NUREG-0800, Section 9.5.1.1, Fire Protection Program and NUREG-2191, Generic Aging Lessons Learned for Subsequent License Renewal, (GALL-SLR)

Following 1979, fire protection guidance documents underwent various names and versions such as BTP 9.5-1 Auxiliary Systems Branch (ASB), Revision 1, "Guidelines for Fire Protection for Nuclear Power Plants, (USNRC 1979); BTP 9.5-1 Chemical Engineering Branch (CMEB)

(July 1981), (USNRC 1981), and NUREG-0800, (150:234) Chpt [sic] 9, Section 9.5.1, Rev. 3, Fire Protection Program, of the Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants. LWR Edition, (USNRC 1981). These guidance documents, or standard review plans (SRP), established criteria to help NRC staff review and evaluate whether applications meet NRCs regulations.

Most plants that were licensed to operate after January 1, 1979, committed to either (1) meet the combination of guidance of Appendix A to BTP APCSB 9.5-1 and the criteria of certain sections of Appendix R as licensing commitments (Bajwa and West 1996) or (2) committed to BTP 9.5-1 Chemical Engineering Branch (CMEB) (July 1981), (USNRC 1981), an early version of what is now known as NUREG-0800, Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants: LWR Edition, section 9.5.1.1, Fire Protection Program (USNRC 2009). NUREG-0800 incorporates the guidance of Appendix A to BTP 9.5-1 and the criteria of Appendix R (Bajwa and West 1996). Therefore, plants licensed to operate after January 1, 1979, can implement NUREG-0800 to establish a fire protection program that complies with 10 CFR 50.48 (U.S. CFR 1956) and GDC 3 (U.S. CFR 1971) inherently.

BTP 9.5-1 Chemical Engineering Branch (CMEB) (July 1981), (USNRC 1981) mentions the need for fire dampers and refers to NFPA 90A. Additionally, it does mention that the plant is responsible for design, maintenance, surveillance, and quality assurance of all fire protection features (e.g., detection systems, suppression systems, barriers, dampers, doors, penetration seals, and fire brigade equipment) (USNRC 1981). So, although maintenance and surveillance of fire dampers are mentioned, it was up to the decision of the licensee/applicant to adopt standards such as NFPA 90A, leaving the frequency or method of surveillance up to the choice of the licensee/applicant and the approval of NRC staff.

NUREG-0800 identifies fire barrier design and ventilation system design as elements of the licensees or applicants FPP for review but does not explicitly reference fire dampers. However, Appendix B, Supplemental Fire Protection Review Criteria for License Renewal, to

5-4 NUREG-0800, section 9.5.1.1, lists damper housings as a passive and long-lived fire protection component that would be subject to an aging management review (USNRC 2009). It is important to note that, in the context of licensee renewal, NUREG-0800 explicitly addresses the damper housing (i.e., the frame of the damper) but does not discuss other active components of the fire damper such as the blades and springs that are outside the scope of the AMPs. This is consistent with NUREG-2191, section XI.M26, Fire Protection, in which the scope of the fire protection AMP encompasses only fire damper housings (USNRC 2025). As part of detecting aging effects, NUREG-2191 states visual inspections to detect cracking and loss of material for fire damper housings, but aging management of active components of the fire damper are outside the scope of license renewal AMPs.

5.5 Regulatory Guidance 1.189, Fire Protection for Nuclear Power Plants Regulatory Guide 1.189 (USNRC 2023), section 2.4, recommends that fire barriersincluding dampers, doors, and penetration sealsbe routinely inspected. For penetration seals, inspections may be conducted on a sample basis, with frequency and sample size determined by the total number of penetrations and observed failure rates.

Section 4.2.1.3 of the same guide emphasizes that building design should ensure ventilation openings are protected with fire-tested dampers. These dampers, along with the construction and installation of ventilation penetrations through fire barriers, should be qualified by fire endurance testing. NFPA 90A further requires that fire dampers be installed in all air transfer openings within rated walls, particularly for barriers rated at 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> or more.

Historically, UL 555, Standard for Fire Dampers, has been the primary industry standard for fire damper design, fabrication, and testing. However, it is stated in RG 1.189 that UL 555 evaluates damper performance only in the closed position under fire conditions and does not assess whether dampers will close under actual airflow conditions. As a result, traditional testing methodssuch as visual inspections or drop testing with duct access panels openmay not accurately reflect damper operability during real airflow scenarios. To address this, surveillance testing is recommended under airflow conditions to verify that dampers will fully close when required. This can be achieved by:

Type testing under worst-case airflow conditions for plant-specific configurations, Testing all dampers installed in required fire barriers under airflow conditions, or Administratively shutting down ventilation systems upon fire confirmation, as outlined in plant emergency procedures.

In reviewing the current language of RG 1.189, there are two areas of ambiguity that may present a potential gap. The first is that RG 1.189 states that UL 555 dampers are not tested for closure under airflow conditions. This is true for dampers that are designed for static closure, but for dampers that are dynamically rated, UL 555 specifies the dynamic closure test (section 4.1.1.5). Therefore, it is ambiguous if the RG is referring to static or dynamic dampers and may imply that static dampers may be used in airflow conditions as long as type testing under worst-case airflow conditions for plant-specific configurations or testing all dampers installed in required fire barriers under airflow conditions is performed (USNRC 2023). Additionally, there are no references to test standards or additional information to ensure that the tests performed are similar, or have considered, similar test requirements of UL 555 for a damper to be certified under airflow.

5-5 The second area of ambiguity is that RG 1.189 states that a third option to verify dampers close under airflow conditions can be achieved by administratively shutting down ventilation systems upon fire confirmation, as outlined in plant emergency procedures (USNRC 2023). This does not imply functional testing of the damper under non-airflow conditions, only that airflow conditions are shutdown. Hence, current guidance does not address functional testing of fire dampers under non-airflow conditions, where some operational failures have been observed.

This represents a potential gap in surveillance practices, as dampers may fail to operate correctly in static or low-flow environmentsconditions that are not currently simulated in standard testing protocols.

5.6 NRC Generic Communications The NRC issued three relevant pieces of generic communication. One a generic letter (GL),

which included NRC responses related to the implementation of fire protection requirements, and two INs related to fire dampers. The first, IN 83-69, addresses improper installation of fire dampers (USNRC 1983). The second, IN 89-52, Potential Fire Damper Operational Problems, dated June 8, 1989, (USNRC 1989) focuses on operational issues under airflow. However, neither IN addresses fire damper reliability concerning degraded conditions.

5.6.1 Generic Letter 86-10 In 1984, the Commission held a series of regional workshops on the implementation of NRC fire protection requirements at NPPs. The staff developed a package of recently developed NRC guidance, which included NRC responses to industry questions about the implementation of fire protection requirements, and issued it through GL 86-10, Implementation of Fire Protection Requirements, dated April 24, 1986 (USNRC 1986). This GL does not explicitly address fire dampers, except through its reference to Information Notice (IN) 83-69, Improperly Installed Fire Dampers at Nuclear Power Plants, dated October 21, 1983, (USNRC 1983).

5.6.2 Information Notice No. 83-69, Improperly Installed Fire Dampers at Nuclear Power Plants The NRC issued this IN in 1983 to all nuclear power reactor facilities holding an operating license or construction permit. The purpose of this IN was to notify licensees of potential generic problems involving the improper installation of fire dampers (USNRC 1983). The first identified problem was that the design drawings required a 3 hour3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> fire rating for the dampers, and over 50 fire dampers did not meet the required fire rating. The second issue was that the fire dampers installed were not properly located within the duct system. Many of these dampers were installed within the ducts inside the fire area and not within the firewall penetration.

Improper installation could permit the passage of fire through a fire barrier.

5.6.3 Information Notice No. 89-52, Potential Fire Damper Operational Problems The second IN (USNRC 1989) addressed all holders of an operating license or a construction permit for nuclear power reactors. This IN addresses the potential problems of curtain-type fire dampers closing reliably under system operational airflow conditions. There were multiple reports to the NRC of curtain-type fire dampers failing to close during the ventilation duct airflow test. The IN states the following:

The standard [UL 555 (1979)] does not evaluate whether fire dampers will close under airflow conditions. If licensees depend on the UL product listing and do

5-6 not sufficiently model airflow during surveillance testing, they cannot be sure that the dampers will close fully when called upon to do so unless airflow is stopped first (USNRC 1989).

5.7 Technical Requirements Manual The TRM is one of the many licensee-controlled documents that typically contain surveillance requirements for fire dampers. The TRM is a licensee-controlled document, separate from the technical specifications (TS), that contains surveillance requirements for a variety of components. Originally found in TS, fire protection requirements in four major areas (fire detection, fire suppression systems, fire barriers, and fire brigade staffing) were removed from technical specification requirements as addressed in GL 86-12, Removal of Fire Protection Requirements from Technical Specifications, dated August 2, 1988 (USNRC 1988). Given that the TRM is not a regulatory required document, there is a general lack of TRMs accessible to NRC staff, which has posed a challenge in conducting a comprehensive review.

Some licensees perform functional testing of their fire dampers. All obtainable TRMs were reviewed to gain insights into licensee surveillance testing, such as frequency and type (visual, functional, or both). Because TRMs are licensee-controlled, not all TRMs were available to the NRC staff, and some may not be the most up-to-date version. For each NPP unit reviewed, it was determined whether the licensee had transitioned to NFPA 805, Performance-Based Standard for Fire Protection for Light Water Reactor Electric Generating Plants (NFPA 2001);

whether the TRM was available; whether the TRM requires a visual inspection; the frequency of the visual inspection; whether a functional test is performed according to the TRM; and the functional testing frequency.

TRMs corresponding to a total of 57 plants, housing a total of 98 reactors, were searched within the Agencywide Documents Access and Management System (ADAMS). However, only 23 plants, a total of 41 reactors, had corresponding TRMs in ADAMS. Additionally, 25 plants, or 44 reactor units, are licensed under the performance-based fire protection rule (10 CFR 50.48(c),

NFPA 805); 32 plants, or 54 reactor units, are licensed under the deterministic fire protection rule (10 CFR 50.48(a)(1) and 10 CFR 40.48(b)).

Of the 25 plants that are licensed under NFPA 805, nine had TRMs accessible by the NRC staff, and 3 of these TRMs mention visual inspection. However, only two plants mention visual and functional testing in their TRM. Of the 32 plants that are non-NFPA 805 plants, 14 plants had TRMs accessible to the NRC staff. Only seven of these plants TRMs mention visual inspection of fire dampers, and no TRMs mention functional testing. Table 5-1 illustrates the breakdown of the reviewed TRM data.

It is also important to note that the discussion of TRMs may not be a complete representation of which units do and do not functionally test their fire dampers. The data presented are limited because the TRMs are licensee-controlled, and only some TRMs were readily accessible to the NRC staff. Additionally, the surveillance procedures for fire dampers may reside in other licensee-controlled documents not readily available to NRC staff.

5-7 Table 5-1. Surveillance Type per Technical Requirements Manual (TRM).

5.8 Summary of Findings The NRCs regulation for fire protection originated from GDC 3 Appendix A to 10 CFR Part 50, which requires that structures, systems, and components important to safety be protected from the effects of fire. However, GDC 3 does not provide specific requirements for fire dampers.

Following the 1975 Browns Ferry fire, the NRC developed BTP APCSB 9.5-1 and its Appendix A to BTP APCSB 9.5-1 to provide implementation guidance for GDC 3. While these documents reference fire dampers and recommend the use of standards such as NFPA 80, they do not mandate specific testing methods, frequencies, or inspection types. Furthermore, early versions of Appendix A to BPT 9.5-1 refer to NFPA 80 for fire damper information. However, earlier editions of NFPA 80 did not include fire damper testing requirements and were instead found in NFPA 90A prior to 2007. The NRC has issued generic communications related to fire dampers, including INs 83-69 and 89-52, which highlight issues with improper installation and operational failures under airflow, but not necessarily failures under static or low-flow conditions, which is also evidenced in RG 1.189. TRMs were identified for 57 plants (98 reactor units), and 23 (41 units) had accessible TRMs and were reviewed. Only a few licensees explicitly included fire damper surveillance requirements. Of the 25 plants licensed under NFPA 805, only two mention functional testing in their TRMs. Among the 32 non-NFPA 805 plants, none of the accessible TRMs mention functional testing. Because TRMs and related surveillance procedures are licensee-controlled, they are not always accessible to NRC staff, and thus the full extent of damper testing practices remains unclear.

In summary, NRC regulations such as GDC 3, 10 CFR 50.48, and Appendix R address fire barrier requirements and operability, but do not specify specific requirements for surveillance methods or surveillance frequency, leaving many of the specific fire damper requirements to be incorporated in Appendix A BTP 9.5-1 and/or through the specific licensing basis at the time the licensee/applicant was approved. RG 1.189, while recommending damper testing under airflow conditions, introduces ambiguity by not clearly distinguishing between static and dynamic dampers and by failing to reference specific testing standards for airflow conditions, such as the dynamic closure test in UL 555. This lack of clarity may lead to inconsistent testing practices, and inconsistent verification of fire damper operability, across plants. Additionally, current guidance does not address functional testing of fire dampers under non-airflow conditions, where some operational failures have been observed. This represents a potential gap in surveillance practices, as dampers may fail to operate correctly in static or low-flow environmentsconditions that are not currently simulated in standard testing protocols.

Additionally, AMPs outlined in NUREG-2191 address the damper housing only. Therefore, unrealized degradation of active components may affect the intended safety function of the damper. This may lead to situations in which active components, such as blades and springs, Licensing Track Reactor Units Plants TRM Available (plants)

Visual Inspection Only (plants)

Visual and Functional Testing (plants)

Undetermined Surveillance Protocol (plants) 10 CFR 50.48(a)(1) 10 CFR 40.48(b) 54 32 14 7

0 7

10 CFR 50.48(c) 44 25 9

1 2

6 Total 98 57 23 8

2 13

5-8 may degrade to the point of inoperability, further emphasizing the potential gap in surveillance practices. As part of an ongoing effort, these failure potentials will be captured in future fire event database updates, ensuring quantitative plant data and root cause analyses are available to support potential regulatory revisions.

6-1 6 TECHNICAL ANALYSIS OF FIRE DAMPERS This section provides risk insights associated with fire damper testing, providing qualitative and quantitative information that may help drive PRA realism. A literature review on relevant studies and methodologies, such as the Study on Eliminating Fire Dampers to Maintain Process Confinement (Patel, Strunk and Walling 1991) and NUREG/CR-6850, Fire PRA Methodology for Nuclear Power Facilities, Volume 2, Detailed Methodology (Nowlen, Najafi, et al. 2005), was conducted to identify key insights and factors that could enhance PRA realism, with a focus on fire damper performance under (1) localized fire conditions and (2) hot gas layer scenarios. This section also references EPRI, Fire Protection Equipment Surveillance Optimization and Maintenance Guidance (EPRI 2003), which provides guidance on using performance-based test and inspection methods in lieu of prescriptive surveillance practices. Insights and conclusions from this report may further highlight well established and reliable practices for optimizing fire damper surveillances and achieving PRA realism.

It is important to note that the information presented in this report should only be applied within the plants licensing basis and commitments. For example, while most facilities have removed fire protection surveillance requirements from their Technical Specificationsallowing for changes to testing and inspection protocols without prior NRC approval under the standard fire protection license conditionsome may still have binding commitments tied to comply with guidance such as BTP APCSB 9.5-1 and 10 CFR 50 Appendix R, or related exemptions and deviations. Therefore, the information in this section and throughout the report is informational in nature and should be applied solely within the context of the plants established licensing basis.

6.1 Review of Studies on Fire Damper Removal Fire dampers are traditionally installed to maintain fire barrier integrity in the event of a fire.

However, in some facilities, the presence of fire dampers may conflict with other safety objectives, such as maintaining process confinement. This section reviews two studies that assess the risk of eliminating fire dampers ductwork and evaluates the thermal and structural performance of ducts under various fire conditions. The goal is to determine whether ducts can provide sufficient protection and to inform fire PRA modeling.

6.1.1 Study on Eliminating Fire Dampers to Maintain Process Confinement The Study on Eliminating Fire Dampers to Maintain Process Confinement (Patel, Strunk and Walling 1991) assessed the risk of removing fire dampers where their closure could compromise the integrity of the process confinement system within the Defense Waste Processing Facility (DWPF) at the Westinghouse Savannah River Site (WSRS). For context on their fire protection system, the WSRS incorporated NFPA 90A in the design and many of the fire barrier ratings are between 0.2 and 0.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />, unlike the 3 hour3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> fire rating barriers required for many NPPs. The acceptance criteria for UL ensures that there is no flaming of the fire damper assembly material on the unexposed side (see section 4.1.1.1). The analysis determined whether intact ducts could prevent flame penetration through a damper but does not discuss heat or smoke transfer. The conclusion was that ducts could serve as effective barriers if structural integrity near the damper opening is maintained.

6.1.2 Fire Hazard Analysis of Rocky Flats Building 776/777 Duct Systems The study, Fire Hazard Analysis of Rocky Flats Building 776/777 Duct Systems (DiNenno, et al. 1988), conducted FHAs of Buildings 776/777 at the Rocky Flats site, where fire

6-2 dampers were not initially installed. The study evaluated the likelihood of duct collapse and the potential for fire spread through penetrations. It emphasized the importance of duct and hanger integrity and used analytical methods to assess exposure to flame, plume, and hot gas layers.

Like the DWPF study, it concluded that intact ducts could prevent flame passage, though heat and smoke transfer were not addressed.

6.1.3 Key Findings from the Literature Review Both studies discuss key considerations when assessing the integrity of the duct. The following sections summarize these topics.

6.1.3.1 Direct Flame Impingement Flame impingement occurs when flames directly contact a surface, such as duct components and the duct exterior. The position and type of fuel, such as when the fuel package(s) are located beneath the duct, can influence if the flame is impinged. For a fire at steady state, the flame height can be calculated through the empirically derived Heskestad correlation (Heskestad 1988), with the flame height increasing near walls and corners due to reduced air entrainment. To account for these effects5, it is standard practice to multiply the heat release rate (HRR) by a factor, depending on if the fire is adjacent to a wall or corner (Custer 2008).

DiNenno, et al. (1988) assumed that flame temperatures typically range from 926-1,126 degrees Celsius (°C) (1,700-2,060 degrees Fahrenheit (°F)).

6.1.3.2 Flame Radiative Zone A portion of the heat transfer from a fire is radiative, with the intensity decreasing as the distance from the flame increases. Therefore, if the flame is close enough to the duct, radiative effects can affect ducts even without direct contact. For ignition to occur, the heat flux must be greater than a critical value; this is known as the critical heat flux. If the heat flux is less than the critical value, then ignition will not occur. The critical distance, where the target receives more than its critical heat flux, can be determined using the point source fire irradiation model (Iqbal and Salley 2004). For reference, Patel, Strunk and Walling (1991) estimated the radiative heat flux to be approximately 200 kilowatts per square meter (kW/m2) (63,442 British thermal units per hour per square foot [Btu/hr/ft2]) for their assumed fire scenario.

6.1.3.3 Plume Impingement There are two key parts of a fire plume, the plume right above the flame and the plume jet. Both can transfer significant heat to surrounding surfaces through convective means. Correlations, such as those developed by Alpert and Heskestad (Heskestad 1988), are used to estimate plume temperatures and radial dispersion distance. Regarding the fire plume, it is assumed that the duct is the same temperature as the plume at the location in question (Patel, Strunk and Walling 1991).

5 RIL 2020-04, The Influence of Walls, Corners, and Enclosures on Fire Plumes, issued April 2020, includes certain changes to the classical fire protection assumption (McGrattan, Selepak and Hnetkovsky 2018).

6-3 6.1.3.4 Upper Gas Layer During a fire, hot combustion products rise to the ceiling and fill the compartment from ceiling to floor. As hot combustion gases accumulate near the ceiling, an upper gas layer can form and heat the surrounding area. The upper gas layer temperature and depth are of interest because ducts located below the ceiling will not be significantly heated until the layer drops to the level of the duct (Patel, Strunk and Walling 1991).The upper gas layer temperature and depth depends on the room size, fire size, and room ventilation. The layer depth and temperature at a given time requires an energy and mass transfer balance of the room. Zone models, such as the Consolidated Fire and Smoke Transport (CFAST) model, can take advantage of these energy and mass transfer balances, which can be used to determine the temperature and height of the upper gas layer before it reaches a steady state. In large compartments, the average hot upper layer gas temperature may not be valid (DiNenno, et al. 1988).

6.1.3.5 Duct and Hanger Integrity Considerations Both studies assume that ducts and their associated supports are thermally thin, and the material strength is correlated to temperature. Therefore, the critical temperature at which the duct, and/or components, fail can be determined when the yield strength of the material is reduced until it nearly equals the design strength and the factor of safety approaches unity (Patel, Strunk and Walling 1991). Figure 6-1 shows the relationship between steel strength and temperature. For example, if a hanger is loaded to 60 % of its design strength, the temperature at which the yield strength is 60 % of its nominal strength would be the critical temperature of the material. Referencing figure 6-1, at a 60 % design strength and based off the yield strength, the steel hanger would fail at a critical temperature of around 538°C (1,000°F). Both studies note that duct warpage can create gaps at penetrations, allowing hot gas passage, though neither explores this effect in detail (DiNenno, et al. 1988) (Patel, Strunk and Walling 1991).

Figure 6-1. Temperature versus steel yield strength (Jeans 1984).

6.1.4 Summary of Literature Review Findings These studies identify key variables for evaluating whether ducts can effectively substitute for fire dampers, supporting more realistic fire modeling and PRA. While ventilation ducts may provide sufficient protection under certain conditions, their performance is influenced by specific fire conditions, structural loading, and material properties. Additionally, this information should be applied solely within the context of the plants established licensing basis and plants should

6-4 ensure that their licensing commitments and basis are clearly understood before making any changes.

6.2 NUREG/CR-6850, Fire PRA Methodology for Nuclear Power Facilities, Volume 2, Detailed Methodology The joint report published by the NRC and EPRI (NUREG/CR-6850, Fire PRA Methodology for Nuclear Power Facilities, Volume 2, Detailed Methodology, issued September 2005), outlines a fire modeling process for multicompartment scenarios (Nowlen, Najafi, et al. 2005).

NUREG/CR-6850 assumes that a multicompartment fire can occur solely on the formation of a hot gas layer in the exposing compartment. The general process outlined in NUREG/CR-6850 includes (1) screening for multicompartment scenarios (determining if a hot gas layer can form and become a multicompartment fire), and then (2) evaluating target damage in multicompartment fire scenarios that are not screened.

If not initially screened with a CDF value of 0.1, the CDF of a multicompartment fire scenario can be developed by multiplying the barrier failure probability, the nonsuppression probability, severity factor, ignition frequency, weighting factor, and conditional core damage probability (CCDP). Table 6-1 lists the barrier failure probabilities by type (Nowlen, Najafi, et al. 2005). A component count of each barrier type is then summed and multiplied by the appropriate failure barrier probability.

Table 6-1. Barrier types and their failure probabilities (Nowlen, Najafi, et al. 2005).

The resulting equation for calculating the CDF for a hot gas layer scenario is

=

=3 (1) where:

Barrier Type Barrier Failure Probability/Demand Type 1fire, security, and watertight doors 7.4x10-3 Type 2fire and ventilation dampers 2.7x10-3 Type 3penetration seals, firewalls 1.2x10-3

= core damage frequency for a hot gas layer scenario

= ignition frequency for the postulated ignition source group

= weighting factor for the likelihood that the fire occurs in a specific ignition source or plant location

= a severity factor reflecting percentage of fires large enough to generate the postulated damage if left unsuppressed

= nonsuppression probability that the fire goes unsuppressed long enough that the target set is damaged

6-5 Due to the linear nature of the CDF equation, variables like CCDP, ignition frequency, and severity factor dominate its value, while the impact of fire damper count and barrier failure probability is minimalunless their values are relatively high. Hence, the influence of fire damper count and barrier failure probability on the overall CDF value will vary from plant to plant.

6.3 EPRI, Fire Protection Equipment Surveillance Optimization and Maintenance Guidance As discussed previously, the contribution of type 2 barriers to a plants CDF in hot gas layer scenarios can vary based on several factors. Therefore, adjusting surveillance methods and intervals to reflect their actual risk significance may be appropriate in achieving PRA realism.

Depending on the plants licensing basis and commitments, plants may be able to utilize the EPRI, Fire Protection Equipment Surveillance Optimization and Maintenance Guidance, (EPRI 2003) to implement or revise a performance-based surveillance program. This section summarizes key elements of that guidance related to fire damper surveillance and EPRI recommended surveillance methods and intervals.

The EPRI guidance outlines a framework of major elements for implementing a performance-based surveillance program in section 10.3 (EPRI 2003). The four main elements of the framework include:

1. Establishing a program framework (section 11.1)

2. Data collection and evaluation (section 11.2)

3. Reliability and uncertainty analysis (section 11.3)

4. Program implementation (section 11.4)

For a baseline, EPRI performed a large-scale survey to collect data about which tests are being performed, what inspections are being done, and at what frequency. A total of 37 plants and 56 operating units participated in the survey. For fire dampers, only visual inspection testing was reported, although it is unclear whether functional testing was considered in the survey. Table 6-2 shows the periodicity at which visual fire damper inspections are performed.

Table 6-2. EPRI fire damper visual inspection frequency survey results from figure B.8 (EPRI 2003)

Operating Cycle Annually 18 months 24 months 5%

5%

18%

72%

= conditional core damage probability, which is the probability that given loss of the target set, operators fail to achieve SSD and the core is damaged

= barrier failure probability given the type of barrier (i.e., type 1, 2, and 3), with the barrier type denoted as i

= the total number of barrier components of the given type (i.e., type 1, 2, and 3),

with the barrier type is denoted as i

6-6 Additionally, the Fire Protection Equipment Surveillance Optimization and Maintenance Guidance, Appendix N, Fire Barrier Maintenance Guidelines, (EPRI 2003), contains recommended inspections, tests, and maintenance practices for fire barriers, specifically for fire dampers. The EPRI guidance recommends that dampers are visually and functionally tested every 18-24 months. In section N.5, it is stated that the purpose of the functional test is to confirm the ability of the damper to close under the conditions in which it is expected to operate (with or without airflow) (EPRI 2003). However, this does not consider observed failures of fire dampers under static or low-flow conditions. In section N.4.3, for visual inspections, the failure criteria is the inability of the damper to close and prevent the spread of fire from one area or zone to another (EPRI 2003). While the EPRI guide lists failure examples, it does not include dirty or damaged blades or improper resetting of the dampera failure mode that is likely to be detected through functional testing.

6.4 Summary of Findings This section provided a review of studies and methodologies, including the DWPF and Rocky Flats analyses, NUREG/CR-6850, and EPRI guidance. Several important insights were identified to support more realistic fire PRA and inform performance-based surveillance practices.

The literature review regarding the removal of fire dampers at the DWPF and Rocky Flats demonstrated that, under certain conditions, intact ventilation ducts may provide sufficient protection in lieu of fire dampers, particularly when structural integrity is maintained and fire conditions are accounted for. However, these conclusions are highly dependent on specific fire conditions, duct material properties, and the performance of supporting components such as hangers. While UL 555 criteria focus on flame penetration, they do not address heat, smoke, or toxic gas transferfactors that may still pose risks in the absence of functional dampers.

A PRA approach for modeling multicompartment fires, as outlined in NUREG/CR-6850, was discussed. It was determined that variables like ignition frequency, severity factor, and CCDP have a dominant influence on CDF. In contrast, the contribution of fire damper failure probability is generally minimal unless damper count or failure rates are relatively high. However, this assumption is derived from analytically examining the overall CDF equation and the true effect of each variable will depend on a case-by-case basis evaluation. Nevertheless, for some plants, this may support adopting or modifying performance-based surveillance practices for fire dampers.

The EPRI guidance provides a structured framework for implementing performance-based surveillance programs, emphasizing establishing a framework, data collection, reliability analysis, and program implementation. Regarding fire dampers, while visual inspections are commonly practiced (EPRI recommendation is 18-24 months), functional testing may be necessary to detect failure modes such as dirty or damaged blades, which are not always evident through visual means alone.

Regarding the information and conclusions presented in this report, any changes to fire damper surveillance practices must be evaluated within the context of the plants licensing basis and regulatory commitments. Where flexibility exists, performance-based approachessupported by technical justification and risk insightscan enhance PRA realism. The findings in this report are intended to inform such efforts and should be applied accordingly.

7-1 7 CONCLUSIONS This report reviews fire damper OE, regulatory guidance, industry standards, and PRA considerations, highlighting their potential impact on PRA realism and surveillance practices in the nuclear industry. A large challenge was the lack of consistent quantitative data on fire dampers. Hence, the development of collection efforts on industrywide quantitative data could further enhance realism in PRA applications.

Fire dampers have observed failure mechanisms that may be uncaptured by visual inspection alone. Failures such as damaged actuation devices, improper installation or resetting, physical damage, corrosion, and obstructions have been observed in the available OE. Some of these failure mechanisms may be more easily captured with functional testing and visual inspections as opposed to just visual inspections.

From a regulatory perspective, while NRC requirements such as GDC 3 and 10 CFR 50.48 establish the need for fire protection barriers, they do not prescribe specific surveillance methods or frequencies for fire dampers. Additionally, the lack of specificity and guidance in RG 1.189 does not adequately address functional testing under non-airflow conditions, despite evidence that such conditions can lead to operational failures. This possibly represents a gap in surveillance practices, as degradation of active components may go undetected, potentially compromising the dampers intended function. As part of an ongoing effort, these failure potentials will be captured in future fire event database updates, ensuring quantitative plant data and root cause analyses are available to support potential regulatory revisions.

Two studies were reviewed, which suggest that under certain conditions, intact ventilation ducts may offer sufficient protection in lieu of fire dampers, though this depends on fire severity, duct materials, and duct support components. The basis for these two studies is that UL 555 addresses flame penetration as an acceptance criterion. However, a gap not addressed in the scope of these studies is heat, smoke, or hot gas layer transfer to adjacent compartments, which can remain potential risks. Additionally, PRA multicompartment analysis methods from NUREG/CR-6850 show that fire damper failure generally has minimal impact on CDF, supporting the case for an approach to PRA realism such as performance-based surveillance methods for some plants. EPRI guidance outlines a structured approach for implementing and/or modifying such programs. Per EPRI guidance, functional testing is performed for assessing functionality under airflow conditions only. For non-airflow conditions, OE review suggests that functional testing may be able to identify issues like dirty or damaged blades that are not always captured in visual inspections.

In conclusion, the information presented in this report is informational only. Any changes to fire damper surveillance practices should be assessed within the framework of the plants licensing basis and regulatory commitments. Although this report is informational, its findings on fire damper operating experience, regulatory guidance, industry standards, and PRA considerations provide a foundation for guiding future data collection and enhancing PRA realism.

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Patel, J.B., A.J. Strunk, and R. C. Walling. 1991. Study on Eliminating FIre Dampers to Maintain Process Confinement (U). Aiken, GA: Bechtel National, Inc.

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A-1 APPENDIX A INSTITUTE OF NUCLEAR POWER OPERATIONS IRIS EVENT REPORTS AND NRC DOCUMENTS This section contains the full list of inspection findings that were reviewed and discussed in section 3.3. A set of five generic failure causes was developed and identified from reviewing the INPO IRIS event reports and U.S. Nuclear Regulatory Commission (NRC) documents. The following five generic failures were identified:

(1) Failure of actuation device (i.e., ETL or fusible link)

(2) Improper resetting or installation of the fire damper (3) Damaged and/or missing components (i.e., curtain blades)

(4) Corrosion, debris, and components obstructing or binding fire damper components (5) Objects or components blocking the path of curtain closure Table A-1 provides additional information on which NRC inspections fell under each cause of failure. Each NRC IR can show multiple causes of failure. For example, event ID 28 falls under the Failure of actuation device (i.e., ETL or fusible link) and the Failure of actuation device (i.e., ETL or fusible link) categories.

Table A-2 references the number of INPO IRIS event reports, as discussed in section 3.2 that fall under the appropriate failure cause. Because each failure cause is not independent of each other, some events may have been binned in multiple causes of failures.

Table A-1. NRC inspections binned by cause of failure.

Cause of Failure NRC Inspection Event ID (See Table A-3)

Failure of actuation device (i.e., ETL or fusible link) 21, 24, 28 Improper resetting or installation of the fire damper 8, 9, 10, 11, 12, 13, 16, 21, 24, 26, 28 Damaged and/or missing components (i.e., curtain blades) 2, 5, 17, 19 Corrosion, debris, and components obstructing or binding fire damper components 1, 6, 15, 20 Objects or components blocking the path of curtain closure Table A-2. INPO IRIS event report count sorted by cause of failure.

Cause of Failure INPO IRIS Event Report Count Failure of actuation device (i.e., ETL or fusible link) 9 Improper resetting or installation of the fire damper 10 Damaged and/or missing components (i.e., curtain blades) 13

A-2 Cause of Failure INPO IRIS Event Report Count Corrosion, debris, and components obstructing or binding fire damper components 12 Objects or components blocking the path of curtain closure 5

A-3 Table A-3. NRC inspection findings related to damper failures.

Event ID Inspection Finding Title Stated Cause in the Inspection Report Link 1

Failure to Correct Degraded Isolation Dampers Associated with the Unit 3 Supplemental Leak Collection and Release System The licensee determined that the auxiliary building air inlet damper (3HVR*AOD35A) and the main steam valve building ventilation support damper (3HVV*MOD51C) were degraded and did not fully close during the surveillance test, which was identified to be the direct cause of the test failure.

ML22318A030 2

Inadequate Preventive Maintenance for Service Water Bay Ventilation Dampers During a 6-year inspection of the 2SWV9 (30276511) on January 25, 2021, operators found the damper failed in the closed position with a broken main bracket, several bent linkages, and all of the linkage pivot pins or swivels seized or corroded.

ML21229A025 3

Inadequate Relay Replacement Frequency Causes Momentary Loss of Secondary Containment Vacuum The shutoff damper failed to close because electrical contacts on the Agastat time delay relay associated with the west RBHVAC

[Reactor Building HVAC] train exhaust fan stuck closed when the fan was secured, which allowed a solenoid associated with the damper positioner to remain energized, which kept the damper open.

ML20038A340 4

Failure to Establish Procedural Steps that Ensure 480-Volt Switchgear Room Ventilation Remained Functional The inspectors observed the licensees maintenance personnel using significant force (two hands) to free movement of two blades, which were stuck in the closed position. The third blade, which was identified as stuck in a 10 degrees open position, was freed using one hand.

ML19214A263 5

Failure to Promptly Identify and Correct a Condition Adverse to Quality Associated with Reactor Containment Fan Coolers During the inspection of RCFC [reactor containment fan cooler] Fan 21B and backdraft damper, the cause of the failure to close was determined to be a failed ribbon spring. After the maintenance technicians completed their inspection, the inspectors felt the spring and confirmed that the spring had lost all tension and was not capable of applying the required closing force on the backdraft damper.

ML18131A014 6

Failure to Identify Degraded Condition of Unit 1 Electrical Equipment Room Supply Fan Gravity Dampers Following the identification of this concern by the team, the licensee assessed the condition by shutting down one operating fan and observed that the gravity damper of the nonoperating fan remained fully opened. The same observation was made when the second supply fan was shut down. The licensee was also unable to ML16103A379

A-4 Event ID Inspection Finding Title Stated Cause in the Inspection Report Link manually close the dampers by applying force to their counterweights.

7 Failure to Identify and Correct a Condition Adverse to Fire Protection Specifically, the inspectors identified that the ventilation dampers used to maintain the environmental conditions of the No. 2 diesel fire pump room and needed for pump protection were damaged and not functional for an extended period of time.

ML15134A499 8

Failure to Conduct Adequate Post maintenance Testing The inspectors found that the damper was prevented from going to the full closed position due to the position of a stop rod adjustment nut. This stop rod had been manipulated in the wrong direction when the damper was rebuilt in June 2012. Because the limit switches for the damper position indication were actuated by the damper operator (rather than the actual damper position), the damper would indicate closed even though not fully closed.

ML13129A370 9

Failure to Provide Maintenance Procedures for Control Room Emergency Ventilation System Dampers The inspection determined that the failure of the damper was due to improper setup of the linkage, which resulted in a slip at one of the linkage connections. Performance of an inspection of the linkages likely misaligned the linkages and subjected the swivels to excessive spring forces causing them to slip over a period of time.

ML13039A078 10 Failure to Correctly Assemble Diesel Generator Ventilation System Damper Resulted in Inoperable Diesel Generator The licensee completed an equipment apparent cause evaluation for the damper failure and concluded that maintenance craftsmen had failed to sufficiently tighten a locknut on the coupling when the hydra motor was replaced, due to inadequate guidance in the maintenance procedure.

ML12310A499 11 Failure to Correct the Reactor Auxiliary Building Emergency Exhaust System Dampers Failure to Close A significant root cause investigation was conducted in 2001 after the repetitive failures of AV-D11SA and AV-33SA. The investigation found no root cause, but the lack of lubrication was identified as a contributing factor. During the investigation associated with AR #322771, the licensee found eight other damper failures and concluded that the problem would be alleviated by lubrication and cycling of the dampers. The licensee also concluded in the same Adverse Condition Investigation that, for some dampers, the failure was likely due to the degradation of the actuator springs, particularly in dampers with small available margin between the ML12121A549

A-5 Event ID Inspection Finding Title Stated Cause in the Inspection Report Link actuator spring minimum closing torque and damper required torque.

12 Failure to Incorporate Adequate Clearance Guidance Prevents Full Operation of the Unit 1 Emergency Control Room Ventilation Makeup Air Supply Damper Upon investigation, the licensee determined that the CV-7910 damper could not operate as designed because the temporary modification interfered with the damper blade.

ML111330725 13 Inadequate Procedural Guidance Results in Damaged Emergency Control Room Ventilation System Air Damper An investigation revealed that the maintenance performed the day before, on September 16, 2010, to rebuild the damper actuator resulted in the bent damper condition. This temporary modification consisted of bolting a blank flange on the damper housing. Due to the damper housing not being very deep, the damper, when opened, does extend beyond the housing. During the maintenance, the damper was stroked and contacted the blank flange and became bent without being detected by the licensee.

ML111330725 14 Inadequate Evaluation of Operating Experience Contributes to a Unit 2 Reactor Trip The licensee determined that an increase in the degradation of the failed damper was due to the increased turbulent flow to which the dampers had been subjected. The licensee identified that the inspection frequency and criteria did not consider that the fans were sometimes operated in parallel with the increased flow.

ML110400363 15 Failure to Follow Procedures Results in Repetitive Malfunction of Electrical Auxiliary Building Air Handling Unit 21B Smoke Purge Inlet Damper The apparent cause evaluation concluded that the cause of the stuck damper was infrequent cycling of these dampers with oil-impregnated bushings in a high-humidity operating environment, which renders them susceptible to sticking. The evaluation determined that a design change in 2002, when the licensee changed the damper blades from carbon steel to stainless steel to prevent excessive corrosion from degrading the damper performance, resulted in mechanical interference between the damper blade linkage arm and a bearing housing stud.

ML101300540 16 Inadequate Modification Contributes to Failure of Control Room Isolation Damper During installation of this fire damper, the licensee discovered that the bolts used to attach the hinges of the operating shaft to the damper had been pulled out of the damper, causing the operating ML071280850

A-6 Event ID Inspection Finding Title Stated Cause in the Inspection Report Link shaft to become detached from the damper, and two of the hinges had fallen beneath the damper plate.

17 Inadequate Corrective Actions Result in Repeat Failure of a Solenoid Valve The immediate cause of the failure was determined to be a sticking actuator solenoid valve, which prevented the damper from closing.

The solenoid valve was replaced, and the damper was returned to service.

ML060270428 18 Failure to Perform Preventative Maintenance of Reactor Building Ventilation Fire Damper 9 (66FD-9)

A revision was issued to visually inspect fire dampers every 24 months, taking out functionality tests. As part of the impact review, fire dampers will receive preventive maintenance. This maintenance activity will include cleaning and lubrication of the track, springs, and other moving parts. IR 04448166 stated that on November 16, 2010, the James A. FitzPatrick Nuclear Power Plant retired the preventive maintenance task for fire dampers. The WGE

[work group evaluation] did not consider the input from action item 9 of IR 04448166, in that other stations do perform functional testing of fire dampers. The inspectors determined that FitzPatrick correctly identified the problem and captured the issue in IR 04448166; however, the plant did not adequately assess and evaluate functionality.

ML22125A105 19 Fire Zone Separation Not Maintained The licensee condition evaluation found the lower edge of the damper blade was mushroomed to a larger thickness causing the damper to become lodged in the damper housing when pushed all the way up during post-test resetting. With the fire damper stuck in the damper housing, there was no motive (gravity) force on the link to the carbon dioxide pop-off. The damper did not drop under its own weight because it was mechanically stuck in its track as the result of the mushroomed damper blade.

ML22129A205 20 Halon System Damper Failure Based on door fan pressurization testing for the room (RER SNC1147178), eight dampers are required to close to maintain halon concentration limits when the system is actuated.

Two of the eight dampers did not close when the event occurred (dampers 2-121-116-04 and 2-121-116-05). Further investigation discovered that one damper (2-121-116-04) was mechanically ML21211A513

A-7 Event ID Inspection Finding Title Stated Cause in the Inspection Report Link bound in the open position and the other damper (2-121-116-05) remained open because of debris preventing actuation of the ETL.

21 Failure to Ensure Fire Barrier Penetrations (Including Fire Dampers) in Fire Zones Protecting safety-related areas shall be functional in accordance with NFPA 805 Section 3.11.3, Fire Barrier Penetrations Fire dampers 1-188-332-01 and 1-188-332-02 in the A and B SWIS battery rooms were improperly installed based on their design drawing U164049, and the B train battery room fire damper failed to shut during a surveillance drop test on July 20, 2018.

Specifically, the angle clip bracket was not installed with the 90-degree leg pointed away from the damper skirt, which caused the damper skirt to not drop and seal off the barrier penetrations between the battery rooms (deterministic fire areas) and SWIS switchgear rooms (performance-based fire areas). In the case of fire dampers 1-188-332-01 and 1-188-332-02, all four 11/2-hour rated curtain-type fire dampers were equipped with SRDs and fusible links, not ETLs. SRDs are not Underwriters Laboratories (UL) listed/labeled, but ETLs are UL listed/labeled. The referenced electrical elementary design drawings reflected use of ETLs, not SRDs.

ML18256A251 22 Failure to Perform Required Surveillances on Multiple Fire Dampers (section 1R05.2b)

Specifically, Procedure CPS 9601.01, Fire Rated Assemblies and Penetration Sealing Devices, section 2.1.1, requires that fire dampers and associated hardware be verified operable at least once per 48 months (allowing an additional [25 %] grace period) by visual inspection. Specifically, the licensees failure to inspect the fire barrier dampers could result in not identifying degraded dampers, which could affect their ability to prevent a fire from spreading from one fire area to another.

ML17150A434 23 Failure to Implement the Design Change Process when Modifying the Safety-Related Fire Dampers In 2008, the Sequoyah Nuclear Plant identified a trend of spurious, partial closures of the emergency diesel generator (EDG) room inlet fire dampers due to pressure surges at the start of two diesel building exhaust fans. The plant modified the EDG rooms inlet fire dampers, applying jumper brackets to connect the four quadrants of each damper to address this condition. These design changes were made by revising the vendor manual for the fire dampers, thereby circumventing the design change process.

ML16210A482

A-8 Event ID Inspection Finding Title Stated Cause in the Inspection Report Link 24 Improper Orientation of Fire Dampers in Auxiliary Building During an inspection of the selected fire areas, the inspectors noted that several fire dampers in fire areas adjoining the 6.9-kilovolt Shutdown Board Room A (FAA 067) were installed with their fusible links oriented downward, approximately 18 inches from the floor.

Based on this information, the inspectors concluded that the dampers fusible link would not have melted as required, and thus the dampers were not functional.

ML14108A377 25 Failure to Maintain Design Control of the Power Supplies for the Emergency Switchgear and Battery Room Fire Dampers On June 10, 2013, during a surveillance of the division 2 carbon dioxide fire damper actuation system, 10 division 1 switchgear and battery room cooler fire dampers were inadvertently closed.

Electricians investigated and found that a common ground existed between the divisions 1 and 2 emergency switchgear and battery room damper control panels.

ML13331B343 26 Failure to Follow Procedure When Adjusting EDG Intake Fire Damper On August 24, 2007, while inspecting the EDG 2A intake fire damper, a fire operations foreman found the damper to be improperly aligned. Instead of initiating a minor maintenance work order, as required by appendix A to Procedure SPP-6.1, Work Order Process Initiation, Revision 4, the foreman classified the misaligned damper as tool pouch maintenance, which did not require a work order, and instructed two fire operators to adjust it.

While the operators were making the adjustment, the damper closed and, because a ventilation exhaust fan was running, this caused a high crankcase pressure lockout of EDG 2A. Because of the improper use of tool pouch maintenance, the control room was not notified before work began, and the EDG subsequently was inoperable for approximately 2.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />.

ML072990357 27 Surveillance Did Not Include Technical Specification Requirements The defense in depth elements included the fire endurance capabilities of the undampered duct, the limited fire exposure to the assembly, the fire protection features in the areas, and the expected response by the fire brigade. The undampered duct assembly was constructed of heavy gauge sheet metal. The fire protection defense in depth elements, identified in ENG-ME-437, were previously considered during the NRC staffs review and approved as documented in the significant event report dated ML063040357

A-9 Event ID Inspection Finding Title Stated Cause in the Inspection Report Link September 6, 1979, and did not provide any additional information that justified not installing the fire-rated damper.

28 Failure to Demonstrate the Fire Resistance Rating of 3-Hour Duct Wrap While manual actuation of the halon system in the emergency switchgear and relay room in response to a fire condition would signal these dampers in the ventilation system to close, the team found that there were no smoke or fire detection actuation devices to signal them to shut during a fire in the main control room.

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