Fire Endurance Test Acceptance Criteria for Fire Barrier Systems Used to Separate Redundant Safe Shutdown Trains Within the Same Fire Area (Supplement 1 to Generic Letter 86-10)
March 25, 1994
TO: ALL HOLDERS OF OPERATING LICENSES OR CONSTRUCTION PERMITS FOR
NUCLEAR POWER REACTORS
SUBJECT: FIRE ENDURANCE TEST ACCEPTANCE CRITERIA FOR FIRE BARRIER SYSTEMS
USED TO SEPARATE REDUNDANT SAFE SHUTDOWN TRAINS WITHIN THE SAME
FIRE AREA (SUPPLEMENT 1 TO GENERIC LETTER 86-10, "IMPLEMENTATION
OF FIRE PROTECTION REQUIREMENTS")
PURPOSE
The U.S. Nuclear Regulatory Commission (NRC) is issuing Supplement 1 to
Generic Letter (GL) 86-10, "Implementation of Fire Protection Requirements,"
April 24, 1986, to disseminate the review guidance contained in Enclosure 1,
"Fire Endurance Test Acceptance Criteria for Fire Barriers Used to Separate
Redundant Safe Shutdown Trains Within the Same Fire Area." This guidance will
be used by the staff to review and evaluate the adequacy of fire endurance
tests and fire barrier systems proposed by licensees or applicants in the
future to satisfy existing NRC fire protection rules and regulations. This
guidance refines and clarifies the fire barrier testing acceptance criteria
specified by GL 86-10, for application in that specific (future review)
context.
BACKGROUND
On April 24, 1986, the NRC issued GL 86-10 in order to give the industry
additional guidance on implementing NRC fire protection requirements. The
guidance in GL 86-10 did not change the requirement to separate one safe
shutdown train from its redundant train with either a 1-hour or a 3-hour fire
rated barrier. In Enclosure 2 to GL 86-10, the NRC staff responded to
industry questions. Question 3.2.1 of the enclosure provided the staff
position on fire endurance test acceptance criteria for fire barrier cable
tray wraps. In its response, the staff stated that Chapter 7, "Tests of
Nonbearing Walls and Partitions," of National Fire Protection Association
(NFPA) Standard 251, "Standard Methods of Fire Tests of Building
Construction," was applicable to cable-tray fire wraps.
On July 30, 1991, the NRC established a special review team to identify and
evaluate technical issues related to the Thermo-Lag 330-1 fire barrier system.
On August 6, 1991, the NRC issued Information Notice (IN) 91-47, "Failure of
Thermo-Lag Fire Barrier Material to Pass Fire Endurance Test." This IN gave
licensees information on the fire endurance test performed by Gulf States
Utilities Company on a Thermo-Lag 330-1 fire barrier installed on a wide
aluminum cable tray and the associated fire test failure. On
December 6, 1991, the NRC issued IN 91-79, "Deficiencies in the Procedures for
Installing Thermo-Lag Fire Barrier Material," which gave information on
deficiencies in procedures that the Thermo-Lag vendor (Thermal Science,
Incorporated) provided for constructing Thermo-Lag 330-1 fire barriers. In
9403240197.response to concerns about the indeterminate qualifications of
Thermo-Lag 330-1 fire barriers, on June 23, 1992, the NRC issued IN 92-46,
"Thermo-Lag Fire Barrier Material Special Review Team Findings, Current Fire
Endurance Tests, and Ampacity Calculation Errors." The staff found the
following problems with Thermo-Lag 330-1 fire barriers: incomplete or
indeterminate fire test results, questionable ampacity derating test results
and a wide range of documented ampacity derating factors, some barrier
installations that were not constructed in accordance with vendor-recommended
installation procedures, incomplete installation procedures, and as-built fire
barrier configurations that may not have been qualified by valid fire
endurance tests or evaluated in accordance with the guidance of GL 86-10.
After reviewing INs 91-47 and 91-79, Texas Utilities (TU) Electric Company
initiated a fire endurance test program to qualify the Thermo-Lag raceway fire
barrier systems for Comanche Peak Steam Electric Station. Under this program,
TU Electric performed an initial fire barrier test series during the weeks of
June 15 and 22, and August 19, 1992. Notwithstanding the fire test acceptance
criteria guidance specified in GL 86-10, TU Electric followed the guidance of
American Nuclear Insurers (ANI) as specified in ANI Information
Bulletin 5(79), "ANI/MAERP Standard Fire Endurance Test Method to Qualify a
Protective Envelope for Class 1E Electrical Circuits," July 1979.
As a result of NRC interaction with TU Electric regarding its test program,
the NRC concluded that there was uncertainty on the part of licensees as to
whether or not the ANI test method established a level of fire barrier
performance equivalent to that established by the GL 86-10 acceptance
criteria. In addition, the NRC staff recognized that the 1-hour and 3-hour
raceway fire barrier systems are unique and that additional guidance on the
proper implementation of the GL 86-10 acceptance criteria would be useful.
AREAS OF CONCERN
The experiences with Thermo-Lag fire barrier systems at TU Electric recounted
above raised the following general concerns:
(1) The fire endurance test acceptance criteria used by other fire barrier
vendors, applicants, and licensees may not meet the acceptance criteria
of GL 86-10, and may not fully demonstrate the fire barrier performance
intended.
(2) Certain past cable functionality testing (i.e., circuit integrity
monitoring) may not fully demonstrate the capability of protected
circuits to function during and after a postulated fire.
FIRE ENDURANCE CAPABILITY
NRC Qualification Requirements and Guidance for Fire Barriers
Section 50.48 of 10 CFR requires that each operating nuclear power plant have
a fire protection plan that satisfies General Design Criterion (GDC) 3. GDC 3
requires that structures, systems, and components important to safety be
designed and located to minimize, in a manner consistent with other safety
requirements, the probability and effects of fires. Fire protection features
required to satisfy GDC 3 include features to ensure that one train of those
systems necessary to achieve and maintain shutdown conditions be maintained
free of fire damage. One means of complying with this requirement is to
separate one safe shutdown train from its redundant train with a fire-rated
barrier. The level of fire resistance required of the barrier, 1-hour or
3-hours, depends on the other fire protection features in the fire area.
The NRC issued guidance on acceptable methods of satisfying the regulatory
requirements of GDC 3 in Branch Technical Position (BTP) Auxiliary and Power
Conversion Systems Branch (APCSB) 9.5-1, "Guidelines for Fire Protection for
Nuclear Power Plants;" Appendix A to BTP APCSB 9.5-1; BTP Chemical Engineering
Branch (CMEB) 9.5-1, "Fire Protection for Nuclear Power Plants;" and GL 86-10.
In the BTPs and in GL 86-10, the staff stated that the fire resistance ratings
of fire barriers should be established in accordance with NFPA Standard 251,
"Standard Methods of Fire Tests of Building Construction and Materials," by
subjecting a test specimen that represents the materials, workmanship, method
of assembly, dimensions, and configuration for which a fire rating is desired
to a "standard fire exposure."
Some licensees have used the acceptance criteria of ANI Bulletin No. 5(79), to
evaluate the performance of their fire barrier systems. The ANI test
methodology, which ANI issued for insurance purposes only, requires that
cables within the fire barrier test specimen be monitored for circuit
integrity while the test specimen is subjected to a test fire that follows the
standard time-temperature curve specified in American Society of Testing and
Materials (ASTM) Standard E-119, "Standard Methods of Fire Tests of Building
Construction and Materials," and to a hose stream test. Under this criterion,
the fire barrier system is evaluated by monitoring the capability of the
cables inside the fire barrier to pass a low voltage circuit integrity test.
During the fire and hose stream tests, if cable circuit integrity is
maintained, the tests are considered successful. The ANI test methodology
does not specify the following GL 86-10 acceptance criteria:
(1) The fire barrier design has withstood the fire endurance test without
the passage of flame or the ignition of cotton waste on the unexposed
side for a period of time equivalent to the fire-resistance rating
required of the barrier.
(2) Analysis of temperature levels recorded on the unexposed side of the
fire barrier demonstrates that the maximum temperature rise does not
exceed 139 �C [250 �F] above ambient temperature.
(3) The fire barrier remains intact and does not allow water to be projected
beyond the unexposed surface during the hose stream test.
Enclosure 1, "Interpretations of Appendix R," to GL 86-10, provided additional
guidance with respect to the term "free of fire damage" as used in Appendix R.
Interpretation 3, "Fire Damage," stated: "In promulgating Appendix R, the
Commission has provided methods acceptable for assuring that necessary
structures, systems, and components are free from fire damage (see
Section III.G.2a, b, and c), that is, the structure, system or component under
consideration is capable of performing its intended function during and after
the postulated fire, as needed."
The review guidance provided in Enclosure 1 (1) clarifies the applicability of
the test acceptance criteria stated in GL 86-10 to raceway fire barrier
systems, (2) specifies a set of fire endurance test acceptance criteria which
are acceptable for demonstrating that fire barrier systems can perform the
required fire-resistive function and maintain the protected safe shutdown
train free of fire damage, (3) specifies acceptable options for hose stream
testing, and (4) specifies acceptable criteria for functionality testing of
cables when a deviation is necessary, such as when the fire barrier
temperature rise criteria are exceeded or the test specimen cables sustain
visible damage.
The test methods and acceptance criteria specified in Enclosure 1 are
acceptable for determining the adequacy of fire barrier systems proposed by
licensees or applicants in the future to satisfy NRC fire protection rules and
regulations. Applicants or licensees may propose alternative test methods and
acceptance criteria to demonstrate an equivalent level of protection; the
staff will review such proposals on a case-by-case basis. Enclosure 2 is a
summary comparison of this review guidance against the GL 86-10 acceptance
criteria.
Evaluation and Application of Fire Endurance and Functionality Test Results
The fire endurance qualification test is successful for a raceway fire barrier
if the following conditions are satisfied (see Enclosure 3, "Fire Barrier
Testing Acceptance Criteria/Logic Diagram"):
(1) The average internal temperature of the fire barrier system, as measured
on the exterior surface of the raceway or component, did not rise more
than 139 �C [250 �F] above its initial temperature; and
.(2) When cables or components are included in the test specimen, a visual
inspection of the protected cables or components revealed no signs of
degraded conditions from the thermal effects of the fire exposure;
and
(3) The fire barrier system remained intact during the fire exposure and
hose stream tests without developing any openings through which the
protected component, raceway, or cables are visible.
For raceway fire barrier systems, the staff adopted the hose stream testing
methodology specified in NUREG-0800, "Standard Review Plan (SRP) for the
Review of Safety Analysis Reports for Nuclear Power Plants," Section 9.5.1,
"Guidelines for Fire Protection for Nuclear Power Plants," Revision 2,
July 1981, Position 5.a. This SRP position established the acceptability of
using the fog nozzle method for hose stream testing of fire barrier
penetration seals. The fog nozzle hose stream test method is an acceptable
option for tests of the entire raceway fire barrier system under the new staff
position.
Licensees that propose to use fire endurance test results that deviate from
the acceptance criteria as the bases for qualifying and installing fire
barrier configurations, should request a deviation from the acceptance
criteria based on a engineering evaluation acceptable to the staff, such as
demonstrating cable functionality. For those licensees required to comply
with Section III.G to Appendix R, the engineering evaluation justifying the
deviating conditions should be submitted with the exemption request. The
review guidance provided in Enclosure 1 provides specific guidance for
demonstrating cable functionality, including subjecting the cables to Megger
and high-potential tests. The results of these tests can be used to determine
the insulation-resistance characteristics of the thermally damaged cable and
to determine if the cable insulation would have been sufficient to maintain
circuit functionality during and after the fire exposure.
IMPLEMENTATION
This section describes how the NRC plans to use the review guidance contained
in Enclosure 1. After this supplement to GL 86-10 is issued, except in those
cases in which an applicant or licensee has proposed an acceptable alternative
fire endurance test method and acceptance criteria that demonstrates an
equivalent level of fire protection, the NRC will use the methods and the
criteria specified in the enclosed review guidance to (1) evaluate fire
endurance testing programs proposed by licensees or applicants in the future
for demonstrating compliance with pertinent NRC fire protection rules and
regulations and (2) review the adequacy of the fire barrier systems proposed
in the future by applicants or licensees.
ACTIONS REQUESTED
None.
REPORTING REQUIREMENTS
None.
BACKFIT DISCUSSION
The guidance transmitted by this generic letter supplement will be used by the
staff for review and evaluation of the adequacy of fire barrier systems and
fire endurance tests that may be proposed in the future to satisfy NRC fire
protection rules and regulations. This guidance refines and clarifies the
guidance specified in Generic Letter 86-10 for application in that future
review context; specifically it (1) clarifies the applicability of the test
acceptance criteria stated in GL 86-10 to raceway fire barrier systems, (2)
specifies a set of fire endurance test acceptance criteria which are
acceptable for demonstrating that fire barrier systems can serve the required
fire-resistive function and maintain the protected safe shutdown train free of
fire damage, (3) contains acceptable options for hose stream testing, and (4)
specifies acceptable criteria for functionality testing of cables when a
deviation would be necessary, such as if the fire barrier temperature rise
criteria are exceeded or the cable sustains visible damage.
No generic or plant-specific backfitting is intended or approved at this time
in connection with issuance of this review guidance. The staff may consider
the need for further generic action in that regard, if the industry guidance
currently under development for addressing the pertinent fire protection
issues is substantively inconsistent with this staff review guidance; but such
action would be separately justified in accordance with the criteria of 10 CFR
50.109 and existing NRC backfit procedures. Similarly, if plant-specific
backfits are proposed by the NRC staff consistent with this review guidance,
the proposed backfits would be justified on a case-by-case basis in accordance
with the criteria of 10 CFR 50.109 and existing NRC backfit procedures.
.If you have any questions about this matter, please contact one of the
contacts listed below or the appropriate Office of Nuclear Reactor Regulation
project manager.
Sincerely,
/s/'d by LAReyes
Luis A. Reyes
Acting Associate Director for Projects
Office of Nuclear Reactor Regulation
Enclosures:
1. NRC Staff Review Guidance and Fire
Endurance Test Acceptance Criteria
for Fire Barrier Systems Used To
Separate Redundant Safe Shutdown
Trains Within the Same Fire Area.
2. Comparison of Staff Position on Fire
Endurance Test Acceptance Criteria
for Fire Barrier Systems Used To
Separate Redundant Safe Shutdown
Trains Within the Same Fire Area
to the Acceptance Criteria of GL 86-10.
3. NRC Fire Testing Acceptance Criteria
Logic Diagram.
Technical contact: Patrick M. Madden, NRR
(301) 504-2854
Lead Project Manager: Marsha K. Gamberoni, NRR
(301) 504-3024
. FIRE ENDURANCE TEST ACCEPTANCE CRITERIA FOR
FIRE BARRIER SYSTEMS USED TO SEPARATE REDUNDANT SAFE SHUTDOWN TRAINS
WITHIN THE SAME FIRE AREA
I. BACKGROUND
In 1975, the Browns Ferry Nuclear power plant experienced a serious electrical
cable tray fire. This fire had a significant impact on operator response to
the event from a safety perspective. The fire caused spurious instrumentation
indications and affected the control of several safety systems. As a result
of this fire, the NRC issued the following fire protection guidelines and
regulations concerning fire protection programs at nuclear power plants:
May 1, 1976 Branch Technical Position (APCSB) 9.5-1, "Fire
Protection Program."
February 24, 1977 Appendix A to Branch Technical Position
APCSB 9.5-1, "Guidelines for Fire Protection for
Nuclear Power Plants Docketed Prior to July 1,
1976."
February 19, 1981 10 CFR 50.48, "Fire Protection."
February 19, 1981 Appendix R to 10 CFR Part 50, "Fire Protection
Program for Nuclear Power Facilities Operating
Prior to January 1979."
July 1981 NUREG-0800, Standard Review Plan (SRP), 9.5.1,
"Fire Protection for Nuclear Power Plants."
In addition to the above fire protection guidance and regulations, the NRC, in
an effort to clarify its fire protection requirements to the industry, issued
Generic Letter (GL) 81-12, "Fire Protection Rule (45 FR 76602,
November 19, 1980)," February 20, 1981; GL 83-33, "NRC Position on Certain
Requirements of Appendix R to 10 CFR 50," October 19, 1983; and GL 86-10,
"Implementation of Fire Protection Requirements," April 24, 1986. GL 86-10,
which took precedence over previous staff guidance, provided staff
interpretations to Appendix R and answers to industry questions regarding the
implementation of Appendix R. The NRC, in an effort to give the licensees
flexibility to make changes to its plant specific fire protection program,
issued GL 88-12, "Removal of Fire Protection Requirements From Technical
Specifications," August 2, 1988. Through the implementation and the adoption
of a standard license condition, a licensee can make changes which do not
adversely affect the ability to achieve and maintain post-fire safe shutdown
to its fire protection program in accordance with 10 CFR 50.59.
The aforementioned NRC documents provided NRC staff guidance concerning fire
barriers separating plant fire areas, including the fire resistance
(endurance) ratings for the barriers and the qualification tests that
establish their fire resistance ratings. In addition, the documents provided
guidance on combustibility of structural materials and tests for demonstrating
low flame spread properties.
The following sections of this document provide the objective for providing
safe shutdown related fire barriers in nuclear power plants, definition of
fire protection terms related to fire barriers, and the NRC fire endurance
test acceptance criteria for fire barriers used to separate safe shutdown
functions within the same fire area.
II. OBJECTIVE OF FIRE BARRIERS USED TO SEPARATE SAFE SHUTDOWN FUNCTIONS
WITHIN THE SAME FIRE AREA
Fire rated barriers are used in nuclear power plants to provide fire area
separation between redundant safety-related components and safe shutdown
functions. They provide fire resistance protection, as required by
Appendix R, to one safe shutdown train in those fire areas which contain
both trains. The objective of the safe shutdown related Appendix R fire
barrier is to ensure that a safe shutdown train is conservatively protected
from fire-related thermal damage. The necessity for these fire barriers has
been verified by multiple probabilistic risk assessments (PRAs). These PRAs
indicated that, even with fire barriers installed, fires are a major
contributor to core melt probabilities.
It is the position of the NRC that fire endurance ratings of building
construction and materials are demonstrated by testing fire barrier assemblies
in accordance with the provisions of the applicable sections of NFPA 251,
"Standard Methods of Fire Tests of Building Construction and Materials," and
ASTM E-119, "Fire Test of Building Construction and Materials." Assemblies
that pass specified acceptance criteria (e.g., standard time-temperature fire
endurance exposure, unexposed side temperature rise, and hose stream
impingement) are considered to have a specific fire resistance rating.
Enclosure 1 to GL 86-10, "Interpretations of Appendix R," provided additional
guidance with respect to the term "free from fire damage." Interpretation 3,
"Fire Damage," states, "In promulgating Appendix R, the Commission has
provided methods acceptable for assuring that necessary structures, systems,
and components are free from fire damage (see Section III.G.2a, b, and c),
that is, the structure, system or component under consideration is capable of
performing its intended function during and after the postulated fire, as
needed."
GL 86-10, Response 3.2.1, also stated that, "The resulting 325 �F cold side
temperature criterion is used for cable tray wraps because they perform a fire
barrier function to preserve the cables free from fire damage. It is clear
that cable that begins to degrade at 450 �F is free from fire damage at
325 �F." (Emphasis added.) In addition, the staff response stated that, "for
newly identified conduit and cable trays requiring such wrapping new materials
which meet the 325 �F criterion should be used, or justification should be
provided for the use of material which does not meet the 325 �F criterion.
This may be based on an analysis demonstrating that the maximum recorded
temperature is sufficiently below the cable insulation ignition temperature."
(Emphasis added.)
The basic premise of the NRC fire resistance criteria is that fire barriers
which do not exceed 163 �C [325 �F] cold side temperature and pass the hose
stream test provide adequate assurance that the shutdown capability is
protected without further analyses. If the temperature criteria is exceeded,
sufficient additional information is needed to perform an engineering
evaluation to demonstrate that the shutdown capability is protected.
III. DEFINITIONS
In order to support the understanding of the technical terms used throughout
this document, the following definitions are provided.
Combustible Material - Material that does not meet the definition of non-
combustible.
Fire Barrier - Those components of construction (walls, floors and their
supports), including beams, joists, columns, penetration seals or closures,
fire doors, and fire dampers that are rated by approving laboratories in hours
of resistance to fire and are used to prevent the spread of fire.
Fire Resistance Rating - The time that materials of a test assembly have
withstood a standard ASTM E-119 fire exposure and have successfully met the
established test acceptance criteria (fire barrier test acceptance criteria
refer to Sections IV, V, and VI).
Noncombustible Material - (a) Material which, in the form in which it is used
and under the conditions anticipated, will not ignite, burn, support
combustion, or release flammable vapors when subjected to fire or heat; (b)
Material having a structural base of noncombustible material, with a surfacing
not over 1/8-inch thick that has a flame spread rating of not higher than 50
when measured in accordance with ASTM E-84, "Surface Burning Characteristics
of Building Materials." (There is an exception to this definition as defined
by BTP Appendix A, Position D.1.d. This position allows the use of
combustible interior finishes when listed by a nationally recognized test
laboratory, such as Factory Mutual or Underwriters Laboratories, Incorporated,
for a flame spread, smoke and fuel contribution of 25 or less in its use
configuration.)
Raceway - Cable trays, conduits, junction boxes, and other components used to
support and route cables from circuit termination to circuit termination.
Raceway Fire Barrier - Nonload bearing partition type envelope system
installed around electrical components and cabling that are rated by test
laboratories in hours of fire resistance and are used to maintain safe
shutdown functions free of fire damage.
IV. FIRE ENDURANCE TEST ACCEPTANCE CRITERIA FOR FIRE BARRIER WALLS, FLOORS,
CEILINGS, AND FREE STANDING EQUIPMENT ENCLOSURES USED TO SEPARATE SAFE
SHUTDOWN FUNCTIONS WITHIN THE SAME FIRE AREA
To demonstrate the adequacy of fire barrier walls, floors, ceilings, and
enclosures, barrier designs should be verified by fire endurance testing. NRC
fire protection guidance refers to the guidance of NFPA 251 and ASTM E-119 as
acceptable test methods for demonstrating fire endurance performance.
The fire endurance test acceptance criteria for the subject fire barriers are:
The fire barrier design has withstood the fire endurance test without
the passage of flame or the ignition of cotton waste on the unexposed
side for a period of time equivalent to the fire resistance rating
required of the barrier;
The temperature levels recorded on the unexposed side of the fire
barrier are analyzed and demonstrable that the maximum temperature does
not exceed 139 �C [250 �F] above ambient; and
The fire barrier remains intact and does not allow projection of water
beyond the unexposed surface during the hose stream test. (For
acceptable hose stream test methods and time of application - See
Section VII.)
If the above criteria are met for fire barrier walls, floors, ceilings, and
free standing equipment enclosures separating safe shutdown functions within
the same fire area, the barrier is acceptable.
NRC fire protection guidance also ensures that door and ventilation openings
and penetrations are properly protected. The guidance requires that these
openings be protected with fire doors and fire dampers which have been fire
tested and listed by a nationally recognized test laboratory (e.g., Factory
Mutual or Underwriters Laboratories, Incorporated). In addition, the
construction and installation techniques for door and ventilation openings and
other penetrations through these fire barriers should be qualified by fire
endurance tests.
The guidance of NFPA 251 and ASTM E-119 should be consulted with regard to
construction, materials, workmanship, and details such as dimensions of parts,
and the size of the specimen(s) to be tested. In addition, NFPA 251 and
ASTM E-119 should be consulted with regard to the placement of thermocouples
on the specimen.
V. FIRE ENDURANCE TEST ACCEPTANCE CRITERIA FOR ELECTRICAL RACEWAY AND
COMPONENT FIRE BARRIER SYSTEMS FOR SEPARATING SAFE SHUTDOWN FUNCTIONS
WITHIN THE SAME FIRE AREA
The NRC provided guidance in Appendix A to Branch Technical Position 9.5-1,
Position D.3.(d), for cable tray fire barriers. This fire protection guidance
states that the design of fire barriers for horizontal and vertical cable
trays should, as a minimum, meet the requirements of ASTM E-119, "Fire Test of
Building Construction and Materials," including hose stream test. On
November 19, 1980, the NRC issued Appendix R to 10 CFR Part 50. The technical
basis for Section III.M, "Fire Barrier Penetration Seal Qualification," states
that "Fire barriers are `rated' for fire resistance by being exposed to a
`standard test fire.' This standard test fire is defined by the American
Society of Testing and Materials in ASTM E-119." In addition, this technical
basis stated that "[i]f specific plant conditions preclude the installation of
a 3-hour fire barrier to separate the redundant trains, a 1-hour fire barrier
and automatic fire suppression and detection system for each redundant train
will be considered the equivalent of a 3-hour barrier." Appendix R to
10 CFR Part 50, Section III.G, "Fire protection of safe shutdown capability,"
provides what the NRC views as equivalent means for ensuring that one safe
shutdown train remains free of fire damage.
In 1984 Appendix R workshops held with industry, and later in GL 86-10, the
staff provided guidance related to fire barrier designs for raceways. In
Enclosure 2, "Question and Answers," to this GL, Question 3.2.1., "Acceptance
Criteria," the staff provided guidance on the cold side temperature for fire
barrier cable tray wraps. In response to this question the staff stated that
the acceptance criteria contained in Chapter 7 of NFPA 251, "Standard Methods
of Fire Tests of Building Construction and Materials," pertaining to non-
bearing fire barriers was applicable to cable tray fire barrier wraps.
Chapter 5 of NFPA 251 explains the conduct of the fire test.
The following is the NFPA 251 acceptance criteria:
- The wall or partition withstood the fire endurance test without
the passage of flame or gases hot enough to ignite cotton waste,
for a period equal to that for which classification is desired;
- The wall or partition withstood the fire and hose stream tests
specified in Chapter 5, without the passage of flame, gases hot
enough to ignite cotton waste, or the hose stream. The assembly
failed the hose stream test if an opening develops that permits
the projection of water from the stream beyond the unexposed
surface during the hose stream test; and
- Transmission of heat through the wall or partition during the fire
endurance test did not raise the temperature on the unexposed
surfaces more than 139 �C [250 �F] above their initial
temperatures.
The staff considers the fire endurance qualification test for fire barrier
materials applied directly to a raceway or component to be successful if the
following conditions are met:
- The average unexposed side temperature of the fire barrier system,
as measured on the exterior surface of the raceway or component,
did not exceed 139 �C [250 �F] above its initial temperature; and
(Staff Guidance: NFPA 251 and ASTM E-119 allow this temperature
to be determined by averaging thermocouple temperature readings.
For the purposes of this criterion, thermocouple averaging can be
used provided similar series of thermocouples (e.g., cable tray
side rail) are averaged together to determine temperature
performance of the raceway fire barrier system. In addition,
conditions of acceptance are placed on the temperatures measured
by a single thermocouple. If any single thermocouple exceeds
30 percent of the maximum allowable temperature rise (i.e., 139 �C
+ 42 �C = 181 �F [250 �F + 75 �F = 325 �F]), the test exceeded the
temperature criteria limit.)
- Irrespective of the unexposed side temperature rise during the
fire test, if cables or components are included in the fire
barrier test specimen, a visual inspection should be performed.
Cables should not show signs of degraded conditions resulting
from the thermal affects of the fire exposure; and
(Staff Guidance: For those cases where signs of thermal
degradation are present, the fire barrier did not perform its
intended fire-resistive function. For those barriers which are
not capable of performing their intended function, a deviation
based on demonstrating that the functionality of thermally
degraded cables or component was maintained and that the cables or
component would have adequately performed their intended function
during and after a postulated fire exposure may be granted. The
attachment to this position provides a methodology for
demonstrating the functionality of cables during and after a fire
test exposure. The purpose of the functionality tests is to
justify observed deviations in fire barrier performance. For
those fire barrier test specimens that are tested without cables,
an engineering analysis justifying internal fire barrier
temperature conditions greater than allowed can be based on a
comparison of the fire barrier internal temperature profile
measured during the fire endurance test to existing cable specific
performance data, such as environmental qualification (EQ) tests.)
- The cable tray, raceway, or component fire barrier system remained
intact during the fire exposure and water hose stream test without
developing any openings through which the cable tray, raceway, or
component (e.g., cables) is visible. Section VII identifies
acceptable hose stream test methods.
The test specimen should be representative of the construction for which the
fire rating is desired as to materials, workmanship, and details such as
dimensions of parts, and should be built under representative conditions.
Raceway fire barrier systems being subjected to qualification fire endurance
tests should be representative of the end use. For example, if it is intended
to install a cable tray fire barrier system in the plant without protecting
the cable tray supports, then the test program should duplicate these field
conditions. In addition, the fire test program should encompass or bound
raceway sizes and the various configurations for those fire barrier systems
installed in the plant. It should be noted that several test specimens will be
required in order to qualify various sizes of horizontal and vertical runs of
cable trays and conduits, junction boxes and pull boxes, etc. The cable tray
or raceway design used for the tests should be constructed with materials and
configurations representative of in plant conditions (e.g., the mass
associated with typical steel conduits and cable trays, representative
internal and external penetration seals). If cables are included in the
raceway fire barrier test specimen, these cables should be representative of
the installed plant-specific cables.
Measuring cable temperatures is not a reliable means for determining excessive
temperature conditions which may occur at any point along the length of the
cable during the fire test. In lieu of measuring the unexposed surface
temperature of the fire barrier test specimen, methods which will measure the
surface temperature of the raceway (e.g., exterior of the conduit, side rails
of cable trays, bottom and top of cable tray surfaces, junction box external
surfaces) can be considered as equivalent if the raceway components used to
construct the fire test specimen represent plant specific components and
configurations. The metal surfaces of the raceway, under fire test
conditions, exhibit good thermal conductivity properties. Temperatures
measured on these surfaces provide a indication of the actual temperature rise
within the fire barrier system.
In 1979, American Nuclear Insurers (ANI) issued a fire endurance test method
for raceway fire barrier systems for insurance purposes. This method, "Fire
Endurance Protective Envelope Systems for Class 1E Electrical Circuits,"
specified that cable temperatures be monitored by thermocouples. Industry
considers this the proper location for determining the temperature rise within
the raceway fire barrier system. Since cable jackets have a low thermal
conductivity, the actual local temperatures of the cable jackets indications
of barrier failure and internal fire barrier temperature rise conditions
during the fire exposure are masked. Monitoring cable temperatures can give
indications of low internal fire barrier temperature conditions during the
fire endurance test. Using this temperature monitoring approach, cable damage
can occur without indication of excessive temperatures on the cables. This,
linked with no loss of circuit integrity, would give indications of a
successful test. The staff considers monitoring the cable temperature as the
primary means of determining cable tray or raceway fire barrier performance to
be nonconservative. Therefore, the staff has incorporated the provision for a
post-fire visual inspection of cables that are installed in fire barrier test
specimens. As discussed above, temperatures monitored on the exterior surface
of the raceway provide a more representative indication of fire barrier
performance.
Fire endurance tests of raceway fire barrier systems should be without cables.
This method is preferred because by excluding cables from the test specimen it
eliminates bias in the test results created by the thermal mass of the cables.
Without this thermal mass, the internal temperature conditions measured by the
test specimen thermocouples during the fire exposure will provide a more
accurate determination of fire barrier thermal performance.
Thermocouple Placement - Test Specimens Containing Cables
The following are acceptable placements of thermocouples for determining the
thermal performance of raceway or cable tray fire barrier systems that contain
cables during the fire exposure:
Conduits - The temperature rise on the unexposed surface of a fire
barrier system installed on a conduit should be measured by placing the
thermocouples every 152 mm [6 inches] on the exterior conduit surface
underneath the fire barrier material. The thermocouples should be
attached to the exterior conduit surface located opposite the test deck
and closest to the furnace fire source. Thermocouples should also be
placed immediately adjacent to all structural members, supports, and
barrier penetrations.
Cable Trays - The temperature rise on the unexposed surface of a fire
barrier system installed on a cable tray should be measured by placing
the thermocouples on the exterior surface of the tray side rails between
the cable tray side rail and the fire barrier material. In addition to
placing thermocouples on the side rails, thermocouples should be
attached to two AWG 8 stranded bare copper conductors. The first copper
conductor should be installed on the bottom of the cable tray rungs
along the entire length and down the longitudinal center of the cable
tray run. The second conductor should be installed along the outer top
surface of the cables closest to the top and towards the center of the
fire barrier. The bare copper wire is more responsive than cable
jackets to temperature rise within the fire barrier enclosure. The
temperature changes measured along the bare copper conductors provide
indication of joint failure or material burn through conditions.
Thermocouples should be placed every 152 mm [6 inches] down the
longitudinal center along the outside surface of the cable tray side
rails and along the bare copper conductors. Thermocouples should also
be placed immediately adjacent to all structural members, supports, and
barrier penetrations.
Junction Boxes (JB) - The temperature rise on the unexposed surface of a
fire barrier system installed on junction boxes should be measured by
placing thermocouples on either the inside or the outside of each JB
surface. Each JB surface or face should have a minimum of one
thermocouple, located at its geometric center. In addition, one
thermocouple should be installed for every one square foot of JB surface
area. These thermocouples should be located at the geometric centers of
the one square foot areas. At least one thermocouple should also be
placed within 25 mm [1 inch] of each penetration connector/interface.
Airdrops - The internal airdrop temperatures should be measured by
thermocouples placed every 305 mm [12 inches] on the cables routed
within the air drop and by a stranded AWG 8 bare copper conductor routed
inside and along the entire length of the airdrop system with
thermocouples installed every 152 mm [6 inches] along the length of the
copper conductor. The copper conductor should be in close proximity
with the unexposed surface of the fire barrier material. Thermocouples
should also be placed immediately adjacent to all supports and barrier
penetrations.
With the exception of airdrops, the installation of thermocouples on
cables is optional and is left to the discretion of the licensee, test
sponsor, or test laboratory. Cable thermocouples are to be used for
engineering purposes only. Cable thermocouples alone are not acceptable
for the demonstration of fire barrier performance. However, cable
thermocouples may support fire barrier deviation conditions.
Temperature conditions on the unexposed surface of the fire barrier material
during the fire test will be determined by averaging the temperatures measured
by the thermocouples. In determining these cable tray or raceway temperature
conditions, the thermocouples measuring similar fire barrier areas of
performance should be averaged together and the basis of acceptance will be
based on the individual averages. The following method of averaging should
be followed:
Conduits - The thermocouples applied to the outside metal surface of the
conduit should be averaged together.
Cable Trays - The thermocouples on each cable tray side rail should be
averaged separately. For example, thermocouples placed on one side rail
will be averaged separately from the other side rail. In addition, the
temperature conditions measured by thermocouples on the two bare copper
conductors should be averaged separately.
Junction Boxes - For small JBs which have only one thermocouple placed
on each JB surface, the individual JB surface thermocouples should be
averaged together. For larger JBs which have more that one thermocouple
placed on each JB surface, the thermocouples on the individual JB
surfaces should be averaged together.
Airdrops - The thermocouples placed on the outer cable(s) routed in the
airdrop fire barrier should be averaged together.
The averages of any thermocouple group during the fire test should not exceed
139 �C [250 �F] above the unexposed side temperature within the fire barrier
test specimen at the onset of the fire endurance test. In addition, the
temperature of each individual thermocouple will be evaluated. Individual
thermocouple conditions should not exceed the 139 �C [250 �F] temperature rise
by more than 30 percent.
Thermocouple Placement - Test Specimens Without Cables
The following are acceptable thermocouple placements for determining the
thermal performance of raceway or cable tray fire barrier systems that do not
contain cables:
Conduits - The temperature rise of the unexposed surface of a fire
barrier system installed on a conduit should be measured by placing
thermocouples every 152 mm [6 inches] on the exterior conduit surface
between the conduit and the unexposed surface of the fire barrier
material. These thermocouples should be attached to the exterior
conduit surface opposite of the test deck and closest to the furnace
fire source. The internal raceway temperatures should be measured by a
stranded AWG 8 bare copper conductor routed through the entire length of
the conduit system with thermocouples installed every 152 mm [6 inches]
along the length of the copper conductor. Thermocouples should also be
placed immediately adjacent to all structural members, supports, and
barrier penetrations.
Cable Trays - The temperature rise on the unexposed surface of a fire
barrier system installed on a cable tray should be measured by placing
thermocouples every 152 mm [6 inches] on the exterior surface of each
tray side rails between the side rail and the fire barrier material.
Internal raceway temperatures should be measured by a stranded AWG 8
bare copper conductor routed on the top of the cable tray rungs along
the entire length and down the longitudinal center of the cable tray run
with thermocouples installed every 152 mm [6 inches] along the length of
the copper conductor. Thermocouples should be placed immediately
adjacent to all structural members, supports, and barrier penetrations.
Junction Boxes - The temperature rise on the unexposed surface of a fire
barrier system installed on junction boxes should be measured by placing
thermocouples on either the inside or the outside of each JB surface.
Each JB surface or face should have a minimum of one thermocouple,
located at its geometric center. In addition, one thermocouple should
be installed for every one square foot of JB surface area. These
thermocouples should be located at the geometric centers of the one
square foot areas. At least one thermocouple should also be placed
within 25 mm [1 inch] of each penetration connector/interface.
Airdrops - The internal airdrop temperatures should be measured by a
stranded AWG 8 bare copper conductor routed inside and along the entire
length of the airdrop system with thermocouples installed every 152 mm
[6 inches] along the length of the copper conductor. The copper
conductor should be in close proximity with the unexposed surface of the
fire barrier material. Thermocouples should also be placed immediately
adjacent to all supports and penetrations.
Temperature conditions on the unexposed surfaces of the fire barrier material
during the fire test will be determined by averaging the temperatures measured
by the thermocouples installed in or on the raceway. In determining these
temperature conditions, the thermocouples measuring similar areas of the fire
barrier should be averaged together. Acceptance will be based on the
individual averages. The following method of averaging should be followed:
Conduits - The thermocouples applied to the outside metal surface of the
conduit should averaged together.
Cable Trays - The thermocouples on each cable tray side rail should be
averaged separately. For example, thermocouple placed on one side rail
will be averaged separately from the other side rail. In addition, the
temperature conditions measured by thermocouples on the bare copper
conductor should be averaged separately from the side rails.
Junction Boxes - For JBs that have only one thermocouple on each JB
surface, the individual JB surface thermocouples should be averaged
together. For JBs that have more that one thermocouple on each JB
surface, the thermocouples on the individual JB surfaces should be
averaged together.
Airdrops - The thermocouples placed on the copper conductor within the
airdrop fire barrier should be averaged together.
The average of any thermocouple group should not exceed 139 �C [250 �F] above
the unexposed side temperature within the fire barrier test specimen at the
onset of the fire endurance test. In addition, the temperature of each
individual thermocouple will be evaluated. Individual thermocouple conditions
should not exceed the 139 �C [250 �F] temperature rise by more than
30 percent.
If a fire barrier test specimen without cables does not meet the average or
maximum single point temperature criteria, then the internal raceway
temperature profile as measured by the instrumented bare copper conductors
during the fire exposure can be used to assess cable functionality through air
oven tests of plant specific cable types and construction.
VI. HOSE STREAM TESTS
NFPA 251 and ASTM E-119 allow flexibility in hose stream testing. The
standards allow the hose stream test to be performed on a duplicate test
specimen subjected to a fire endurance test for a period equal to one-half of
that indicated as the fire resistance rating, but not for more than 1 hour
(e.g., 30 minute fire exposure to qualify a 1-hour fire rated barrier).
For safe shutdown related fire barrier systems referenced in Section IV and
duplicate electrical cable tray or raceway and component fire barrier test
specimens that have been exposed to the �-duration test fire exposure, the
staff finds the hose stream application specified by the NFPA 251 acceptable.
NFPA 251 requires the stream of water to be delivered through a 6.4 cm [2�-
inch] hose discharging through a standard 2.9 cm [1�-inch] playpipe nozzle
onto the test specimen after the fire exposure test. The stream is applied
with the nozzle orifice positioned 6.1 meters [20 feet] away from the center
of the test specimen at a pressure of 207 kPa [30 psi]. The application of
the stream is to all exposed parts of the specimen for a minimum duration of 1
minute for a 1-hour barrier and 2� minutes for a 3-hour barrier.
As an alternate for electrical raceway fire barrier test specimens, the
application of the hose stream test can be performed immediately after the
completion of the full fire endurance test period. If this method is used to
satisfy the hose stream test criteria, the following hose stream applications
are acceptable:
- The stream applied at random to all exposed surfaces of the test
specimen through a 6.4 cm [2�-inch] national standard playpipe
with a 2.9 cm [1�-inch] orifice at a pressure of 207 kPa [30 psi]
at a distance of 6.1 meters [20 feet] from the specimen.
(Duration of the hose stream application - 1 minute for a 1-hour
barrier and
2� minutes for a 3-hour barrier); or
- The stream applied at random to all exposed surfaces of the test
specimen through a 3.8 cm [1�-inch] fog nozzle set at a discharge
angle of 30 degrees with a nozzle pressure of 517 kPa [75 psi] and
a minimum discharge of 284 lpm [75 gpm] with the tip of the nozzle
at a maximum of 1.5 meters [5 feet] from the test specimen.
(Duration of the hose stream application - 5 minutes for both
1-hour and 3-hour barriers); or
- The stream applied at random to all exposed surfaces of the test
specimen through 3.8 cm [1�-inch] fog nozzle set at a discharge
angle of 15 degrees with a nozzle pressure of 517 kPa [75 psi] and
a minimum discharge of 284 lpm [75 gpm] with the tip of the nozzle
at a maximum of 3 meters [10 feet] from the test specimen.
(Duration of the hose stream application - 5 minutes for both 1-
hour and 3-hour barriers.)
VII. FIRE BARRIER COMBUSTIBILITY
The NRC's fire protection guidelines and requirements establish the need for
each nuclear power plant to perform a plant-specific fire hazard analysis.
The fire hazard analysis should consider the potential for in-situ and
transient fire hazards and combustibles. With respect to building materials
(e.g., cable insulation and jackets, plastics, thermal insulation, fire
barrier materials), the combustibility, ease of ignition, and flame spread
over the surface of a material should be considered by the fire hazards
analysis. One method of determining combustibility is by subjecting a sample
of the fire barrier material to a small scale vertical tube furnace as
described by ASTM E-136. The flashover ignition temperature of the material
(as determined by ASTM D-1929) and the flame spread characteristics of the
material (as determined by ASTM E-84) should also be evaluated. The potential
heat release of the material (as determined by ASTM D-3286 or NFPA 259),
should also be factored into the fire hazards analysis.
Fire barrier materials used as radiant energy heat shields inside containment
and used to achieve a combustible free zone are required to be noncombustible
as defined in Section III.
VIII. REFERENCES
U.S. Nuclear Regulatory Commission
May 1, 1976 Branch Technical Position (APCSB) 9.5-1, "Fire Protection
Program."
February 24, 1977 Appendix A to the Branch Technical Position APCSB
9.5-1, "Guidelines for Fire Protection for Nuclear
Power Plants Docketed Prior to July 1, 1976."
February 19, 1981 10 CFR 50.48, "Fire protection."
February 19, 1981 Appendix R to 10 CFR Part 50, "Fire Protection for
Nuclear Power Plants."
February 20, 1981 Generic Letter 81-12, "Staff Position - Safe Shutdown
Capability."
July 1981 NUREG - 0800, Standard Review Plan, 9.5.1, "Fire
Protection for Nuclear Power Plants."
October 19, 1983 Generic Letter 83-33, "NRC Positions on Certain
Requirements of Appendix R to 10 CFR 50."
April 24, 1986 Generic Letter 86-10, "Implementation of Fire
Protection Requirements."
American Society for Testing and Materials
ASTM E-84, "Surface Burning Characteristics of Building Materials."
ASTM E-119, "Fire Test of Building Construction and Materials."
ASTM E-136, "Behavior of Materials in a Vertical Tube Furnace at 750�C."
ASTM D-1929, "Test Method for Ignition Properties of Plastics."
ASTM D-3286, "Test Method for Gross Calorific Value of Solid Fuel by the
Isothermal-Jacket Bomb Calorimeter."
American Nuclear Insurers (ANI)
July 1979, ANI Information Bulletin No. 5 (79) test criteria for "Fire
Endurance Protective Envelope Systems for Class 1E Electrical Circuits."
National Fire Protection Association (NFPA)
NFPA 251, "Standard Methods of Fire Tests of Building Construction and
Materials."
NFPA 259, "Standard Test Method for Potential Heat of Building Materials."
. ACCEPTABLE METHODS FOR DEMONSTRATING FUNCTIONALITY OF
CABLES PROTECTED BY RACEWAY FIRE BARRIER SYSTEMS
DURING AND AFTER FIRE ENDURANCE TEST EXPOSURE
I. INTRODUCTION
The NRC considers fire barrier systems that meet the acceptance criteria
adequate under NRC fire protection regulations. The licensee, where the
criteria are not met, should submit an engineering analysis to the staff that
clearly demonstrates the functionality of the protected cables. This
engineering analysis should consider the cable insulation type, actual voltage
and current conditions, cable function, and thermal affects on the cable and
its ability to function. This evaluation should also consider cable operating
temperatures within the fire barrier at the onset of the fire exposure.
II. CABLE CIRCUIT INTEGRITY TESTS
In 1979, American Nuclear Insurers (ANI) issued a fire endurance test method
for raceway fire barrier systems for insurance purposes. This method, "Fire
Endurance Protective Envelope Systems for Class 1E Electrical Circuits,"
specified a circuit integrity test. The intent of this test was to identify
the onset of fire damage to the cables within the raceway fire barrier test
specimen during the fire endurance test period. The circuit integrity test
voltage is 8 to 10 volts DC; therefore the loss of circuit integrity under
these voltage conditions may occur only as a result of a dead short or open
circuit.
During fire tests of raceway fire barrier systems, thermal damage to the
cables has been observed. This thermal damage has led to cable jacket and
insulation degradation without the loss of circuit integrity as monitored
using ANI criteria. Since cable voltages used for ANI circuit integrity tests
do not replicate cable operating voltages, loss of cable insulation conditions
can exist during the fire test without a dead short occurring. It is expected
that if the cables were at rated power and current, a fault would propagate.
The use of circuit integrity monitoring during the fire endurance test is not
a valid method for demonstrating that the protected shutdown circuits are
capable of performing their required function during and after the test fire
exposure. Therefore, circuit integrity monitoring is not required to satisfy
NRC acceptance criteria for fire barrier qualification.
III. EQUIPMENT QUALIFICATION
Comparison of the fire barrier internal time-temperature profile measured
during the fire endurance test to existing cable performance data, such as
data from environmental qualification (EQ) tests, could be proposed to the
staff as a method for demonstrating cable functionality. EQ testing is
typically performed to rigorous conditions, including rated voltage and
current. By correlating the EQ test time-temperature profile to the fire test
time-temperature profile, the EQ test data would provide a viable mechanism to
ensure cable functionality. A large body of EQ test data for many cable types
exists today. The use of EQ data represents a cost-effective approach for
addressing cable functionality for fire tests for those cases where the 163 �C
[325 �F] limit is exceeded.
The staff agrees that a comparison of fire test temperature profiles to
existing EQ and Loss of Cooling Accident (LOCA) test results or air oven test
results is an acceptable approach to demonstrate cable functionality provided
the subject analysis incorporates the anticipated temperature rise due to self
heating effects of installed power cables with the fire test results.
IV. CABLE INSULATION TESTS
The two principal materials used as cable insulation and cable jackets by the
nuclear industry are thermoplastics and thermosetting polymeric materials. A
thermoplastic material can be softened and resoftened by heating and
reheating. Conversely, thermosetting cable insulation materials cure by
chemical reaction and do not soften when heated. Under excessive heating
thermosetting insulation becomes stiff and brittle. Electrical faults may be
caused by softening and flowing of thermoplastic insulating materials at
temperatures as low as 149 �C [300 �F]. Thermosetting electrical conductor
insulation materials usually retain their electrical properties under short-
term exposures to temperatures as high as 260 �C [500 �F]. Insulation
resistance (Megger) tests provide indications of the condition of the cable
insulation resistance, whereas the high potential (Hi-Pot) test provides
assurance that the cable has sufficient dielectric strength to withstand the
applied rated voltage. A cable insulation failure usually results from two
breakdown modes: one failure mode is excessive dielectric loss which is due
to low insulation resistance, and the other failure mode is overpotential
stress which is due to loss of dielectric strength of the insulation material.
If Megger tests are not performed at frequent intervals during the fire
exposure, indications of insulation damage in insulation may go undetected.
When removed from elevated temperatures, insulation will reset. Megger tests
of insulated cables after the fire endurance test and after the cable has
sufficiently cooled may not detect degradation in the insulation resistance.
Therefore, wet or dry Megger of cables after a fire exposure does not provide
reasonable assurance that the cables would have functioned as intended during
the fire exposure.
To provide reasonable assurance that the cables would have functioned during
and after the fire exposure, Megger tests need to be performed before the fire
test, at multiple time intervals during the fire exposure (i.e, every 20
minutes during the 1-hour fire test and every hour during the 3-hour fire
test) for instrumentation cables only, and immediately after the fire
endurance test to assess the cable insulation resistance levels. This testing
will assure that the cables will maintain the insulation resistance levels
necessary for proper operation of instruments.
The Megger tests (pre-fire, during the fire [if performed], and immediately
after the fire test conditions) should be done conductor-to-conductor for
multi-conductor and conductor-to-ground for all cables. The minimum
acceptable insulation resistance (IR) value, using the test voltage values as
shown in the table below, is determined by using the following expression:
IR (Mega-ohms) > {[K+1 Mega-ohm ] * 1000 (ft) }
Length (ft)
Where K = 1 Mega-ohm/KV * Operating Voltage (expressed in KV)
In addition, to determine the insulation resistance levels required for
nuclear instrumentation cables, an assessment of the minimum insulation
resistance value (e.g., one mega-ohm) and its potential impact on the
functionality of these cables should be evaluated. An ac or dc high potential
(Hi-Pot) test for power cables greater than 1000 volts (V) should also be
performed after the post-fire Megger tests to assess the dielectric strength.
This test provides assurance that the cable will withstand the applied voltage
during and after a fire. The high potential test should be performed for a 5
minute duration at 60 percent of either 80 V/mil ac or 240 V/mil dc (e.g.,
125 mil conductor insulation thickness x 240 V/mil dc x 0.6 = 18,000 V dc).
The table below summarizes the Megger and Hi-Pot test voltages which, when
applied to power, control and instrumentation cables, would constitute an
acceptable cable functionality test.
OPERATING MEGGER TEST HIGH POTENTIAL
TYPE VOLTAGE VOLTAGE TEST VOLTAGE
Power > 1000 V ac 2500 V dc 60% x 80 V/mil (ac)
60% x 240 V/mil (dc)
Power < 1000 V ac 1500 V dc* None
Instrument < 250 V dc 500 V dc None
and < 120 V ac
Control
* A Megger test voltage of 1000 V dc is acceptable provided a Hi-Pot
test is performed after the Megger test for power cables rated at less
than 1000 V ac.
The electrical cable functionality tests recommended above are one acceptable
method. Alternate methods to assess degradation of cable functionality will
be evaluated by the staff for acceptability on a case-by-case basis. The
above table summarizing the Megger and Hi-Pot test voltages are "typical" and
the applicant can follow the applicable industry standards and manufacturer's
recommendations for the specific cable application in the performance of the
insulation resistance and Hi-Pot tests.
V. AIR OVEN TESTS
Air oven tests can be used to evaluate the functionality of cables for those
cable tray or raceway fire barrier test specimens tested without cables. This
testing method consists of exposing insulated wires and cables at rated
voltage to elevated temperatures in a circulating air oven. The temperature
profile for regulating the temperature in the air oven during this test is the
temperature measured by the AWG 8 bare copper conductor during the fire
exposure of those cable tray or raceway test specimen which were tested
without cables.
The staff finds the test method described by UL Subject 1724, "Outline of
Investigation for Fire Tests for Electrical Circuit Protective Systems", Issue
Number 2, August 1991, Appendix B, "Qualification Test for Circuit Integrity
of Insulated Electrical Wires and Cables in Electrical Circuit Protection
Systems", with the following modifications, acceptable:
1. During the air oven test the cables are to be energized at rated
voltage. The cables are to be monitored for conductor-to-
conductor faults in multi-conductor cables and conductor-to-ground
faults in all conductors.
2. The cables being evaluated should be subjected to the Megger and
high potential tests, recommended above in Section IV, "Cable
Insulation Tests."
3. The impact force test, which simulates the force of impact imposed
on the raceway by the solid stream test, described in UL 1724,
Appendix B, paragraph B3.16, is not required to be performed.
VI. CABLE THERMAL EXPOSURE THRESHOLD
The following analysis, which is based on determining whether a specific
insulation material will maintain electrical integrity and operability within
a raceway fire barrier system during and after an external fire exposure, is
an acceptable method for evaluating cable functionality. In order to determine
cable functionality, it is necessary to consider the operating cable
temperatures within the fire barrier system at the onset of the fire exposure
and the thermal exposure threshold (TET) temperature of the cable. For
example, if the TET of a specific thermoplastic cable insulation (Brand X) is
149 �C [300 �F] and the normal operating temperature within the fire barrier
system is 66 �C [150 �F], then the maximum temperature rise within the fire
barrier system should not exceed 83 �C [150 �F] during exposure to an external
fire of a duration equal to the required fire resistance rating of the
barrier. For this example the TET limit for Brand X cable is 83 �C [150 �F]
above the cable operating temperatures within the fire barrier system at the
onset of the external fire exposure. The cable TET limits in conjunction with
a post test visual cable inspection and the Hi-Pot test described above should
readily demonstrate the functionality of the cable circuit during and after a
fire.
The normal cable operating temperature can be determined by loading cable
specimens installed within a thermal barrier system in the test configuration
with rated voltage and current. The TET temperature limits for most cable
insulation may be obtained from the manufacturer's published data which is
given as the short-circuit rating limit. With the known TET and normal
operating temperature for each thermal barrier system configuration, the
maximum temperature rise limit within a fire barrier system may then be
determined.
. COMPARISON OF FIRE ENDURANCE TEST CRITERIA
FOR FIRE BARRIER SYSTEMS USED TO SEPARATE
SAFE SHUTDOWN FUNCTIONS WITHIN THE SAME FIRE AREA
GL 86-10, SUPP. 1.GL 86-10.RATIONALE FOR
CLARIFICATION.Temperature, as
measured on the
external surface of the
Raceway, should not
exceed 163 �C [325 �F]
(Note 1).
This temperature is
determined by averaging
temperature readings of
similar series of
thermocouple (e.g.,
cable tray side rail)
(Note 2).
Barrier Condition -
Fire barrier should
remain intact. No
visible signs of
component, raceway or
cables after fire and
hose stream test.
Hose Stream Test -
solid stream test as
specified in NFPA 251
on second test specimen
after being subjected
to a fire exposure of
1/2 duration (Note 4)
or a fog stream after
the full fire exposure.
.Temperature, as
measured on the
unexposed side of the
fire barrier material,
should not exceed
163 �C [325 �F].
Barrier Condition - The
barrier should have
withstood the fire and
hose stream test
without the passage of
flame or hot gasses hot
enough to ignite cotton
waste.
Hose Stream Test -
solid stream test as
specified in NFPA 251.
.Temperature - Difficult
to measure a uniform
temperature on the fire
barrier material
surface. Raceway temps
provide good indication
of internal temp-rise
and potential barrier
failure locations
during the test.
Barrier Condition -
Cotton waste has not
been used in raceway
fire barrier testing as
an indicator of barrier
failure. Visual
inspection process
provides a better
indication of barrier
condition after the
fire and hose stream
test.
Hose Stream Test - To
reflect alternative
methods found
acceptable (Note 3).
The use of a fog nozzle
for the hose stream at
the end of a full
duration of the fire
test provides a good
method for testing
erosion and cooling
effects.
.GL 86-10, SUPP. 1.GL 86-10.RATIONALE FOR
CLARIFICATION.Cable condition - When
cables are included in
the test specimen,
post-fire condition
must be visually
inspected. Cables
should show no signs of
degraded conditions
resulting from the
thermal affects of the
fire exposure..Cable condition - No
consideration given to
determining the
material condition of
the cable.
.Cable condition - The
objective of these fire
barriers is to assure
that thermal damage to
protected safe shutdown
cables or components
does not occur.
GUIDANCE FOR ENGINEERING EVALUATIONS JUSTIFYING DEVIATIONS FROM THE FIRE
BARRIER ACCEPTANCE CRITERIA
Functionality should be
demonstrated if any of
the preceding criteria
are exceeded (Note 5).
Methods when cables are
excluded from test
specimen:
Comparison of internal
temp. profiles to EQ
and LOCA test data.
Air oven test of cables
at rated voltage with
Megger and Hi-Pot tests
(Note 6)
Method when cables are
in test specimen
include megger and
Hi-Pot testing (Note 7)
Demonstration of
functionality should
also consider operating
temperature of the
cables inside the fire
barrier at the onset of
the fire exposure. .Functionality - No
guidance provided. Up
to licensees to
demonstrate by
engineering analysis.
Analysis kept on file
for NRC review.
Engineering analysis
generally based on
internal temperature
below the ignition
temperature. No
consideration given
cable operating
temperatures within the
barrier at the onset of
the fire exposure. .Functionality is
considered to be a
deviation from the
acceptance criteria and
must be justified on a
case-by-case basis
which includes an
assessment of cable
jacket material.
Note 1: The 163 �C [325 �F] temperature condition was established by
allowing the internal temperature on the raceway surface to rise a
maximum of 139 �C [250 �F] above the initial temperature of the
test specimen (assumed to be 24 �C [75 �F]).
Note 2: NFPA 251/ASTM-E119 allows the temperature condition to be
determined by averaging the thermocouple readings. The conditions
of acceptance are also placed on the temperature conditions
measured by a single thermocouple. Under these conditions of
acceptance, if any single thermocouple exceeds 30 percent above
the maximum allowable temperature rise (i.e., max. allowable
139 �C + 42 �C = 181 �C [250 �F + 75 �F = 325 �F]) the test is
considered to have exceeded the criteria temperature limit.
Note 3: SRP 9.5.1 recognizes the use of a fog stream as an alternative
hose stream testing method for qualifying fire barrier penetration
seals.
Note 4: This hose stream test method provides assurance that the cable
tray or raceway fire barrier system has sufficient structural
integrity to resist minor fire related barrier breaches caused by
falling objects.
Note 5: A fire barrier system that does not meet the acceptance criteria
is not considered a rated fire barrier. For those conditions
(e.g., high raceway temperature, barrier openings, water
projection, cable damage) which deviate from the acceptance
criteria, an engineering analysis which clearly demonstrates the
functionality of the protected components or cables should be
submitted to the staff for review. The purpose of the recommended
functionality tests is to justify observed deviations in fire
barrier performance. Engineering analyses justifying these
deviations should not rely substantially upon the equipment (e.g.,
cable) qualification as the basis for acceptance. Deviations will
be evaluated by the staff on a case-by-case basis.
Note 6: For fire barrier systems tested without cables, plant-specific
cable types should be subjected to air oven tests when the fire
barrier temperature rise criteria are exceeded. These cables will
be exposed to a temperature profile as determined by the internal
raceway thermocouples during the fire test. Cables will be tested
at rated voltage. Megger and Hi-Pot testing should be performed
in a consistent manner to those tests performed for cables
included in a fire barrier test specimen and subjected to the fire
endurance test.
Note 7: Megger tests of cables included in the fire test specimen should
be performed before, during (instrumentation cables only) and
immediately after the fire exposure and subjecting power cables
which have voltage ratings > 1000 volts ac to a Hi-Pot test (60
percent) immediately after the fire exposure
Page Last Reviewed/Updated Tuesday, March 09, 2021