ML20056G995
| ML20056G995 | |
| Person / Time | |
|---|---|
| Issue date: | 07/16/1993 |
| From: | Marcus G Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20056G921 | List: |
| References | |
| GL-86-10, NUDOCS 9309080054 | |
| Download: ML20056G995 (37) | |
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7590-01 NUCLEAR REGULATORY COMMISSION Proposed Generic Letter 86-10, Supplement 1,
" Fire Endurance Acceptance Criteria for Fire Barrier Systems Used to Separate Redundant Safe Shutdown Trains Within the Same Fire Area" AGENCY: Nuclear Regulatory Commission.
ACTION: Notice of opportunity for public comment.
SUMMARY
The Nuclear Regulatory Commission (NRC) is proposing to issue Generic Letter 86-10, Supplement 1.
A generic letter is an NRC document that
- 1) requests licensees to submit analyses or descriptions of proposed corrective actions, or both, regarding matters of safety, safeguards, or environmental significance, or 2) requests licensees to submit information to the NRC on other technical or administrative matters, or, 3) transmits information to licensees regarding approved changes to rules or regulations, the issuance of reports or evaluations of interest to the industry, or changes to NRC administrative procedures. This draft generic letter supplement disseminates to licensees the NRC position on fire endurance test acceptance criteria for fire barrier systems used to separate redundant safe shutdown trains within the same fire area.
The NRC is seeking comment from interested parties regarding both the technical and regulatory aspects of the proposed generic letter supplement presented under the Supplementary Information heading.
This proposed generic letter supplement and supporting documentation were discussed in meeting number 243 of the Committee to Review Generic Requirements (CRGR). The relevant information that was sent to the CRGR to support their review of the proposed generic letter supplement is available in i
i the Public Document Rooms under accession number 9307160137.
This includes a summary of the comments received based on the November 19, 1992, public meeting with the Nuclear Management and Resources Council (NUMARC) at which l
the NRC staff presented a copy of its proposed position on fire endurance test 9309080054 930716 ~
PDR ORG NRRB
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acceptance criteria to MARC.
Some meeting attenders a d -if they could provide written comments.
The-NRC staff indicated that major written comments could be submitted, but that any comments received would not be addressed i
i prior to publishing the proposed generic letter in the Federal Reaister. A summary of the comments received to date is available in the Public Document l
.f Rooms under accession number 9307I60137. The NRC will consider these I
comments, os well as any other comments received from interested parties in 1
the final evaluation of the proposed generic letter supplement. The NRC's l
?'
final evaluation will include a review of the technical position and, when l
appropriate, an analysis of the value/ impact on licensees.
Should this generic letter supplement be issued by the NRC, it will become available for public inspection in the Public Document Rooms.
j DATES:
Comment period expires [ Insert"date 3'O days-after thelFRNLis D
published).
Comments submitted after this date will be considered if it is l
practical to do so, but assurance of consideration cannot be given except for comments received on or before this date.
ADDRESSES:
Submit written comments to Chief, Rules and Directives Review Branch, U.S. Nuclear Regulatory Commission, Washington, DC 20555.
Written a
comments may also be delivered to Room P-223, Phillips Building, 7920 Norfolk Avenue, Bethesda, Maryland, from 7:30 am to 4:IS pm, Federal workdays.
Copies of written comments received may be examined at the NRC Public Document Room,
)
2120 L Street, NW. (Lower Level), Washington, DC.
l FOR FURTHER INFORMATION CONTACT:
Patrick M. Madden (30I) 504-2854.
SUPPLEMENTARY INFORMATION:
T0:
ALL HOLDERS OF OPERATING LICENSES OR CONSTRUCTION PERMITS FOR i
i NUCLEAR POWER REACTORS
SUBJECT:
FIRE ENDURANCE TEST ACCEPTANCE CRITERIA FOR FIRE BARRIER SYSTEMS USED TO SEPARATE REDUNDANT SAFE SHUTDOWN TRAINS WITHIN THE SAME
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a FIRE AREA (5CPPLEMENT 1 TO GENERIC LETTER 86 (0, " IMPLEMENTATION t
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OF FIRE PROTECTION REQUIREMENTS")
1 PURPOSE l
The U.S. Nuclear Regulatory Commission.(NRC) is issuing this supplement to Generic Letter (GL) 86-10, " Implementation of Fire Protection Requirements,"
l l
of April 24, 1986, to disseminate review guidance contained in Enclosure A, l
i
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" Fire Endurance Test Acceptance Criteria for Fire Barriers Used to Separate Redundant Safe Shutdown Trains Located Within the Same fire Area".
This i
guidance will be used by the staff for review and evaluation of the adequacy of fire endurance tests and fire barrier systems that may be proposed by licensees or applicants in the future to satisfy NRC fire protection' rules and I
i regulations.
This guidance refines and clarifies the fire barrier testing
{
acceptance criteria specified by GL 86-10, for application in that specific i
(future review) context.
BACKGROUND
{
J On April 24, 1986, the NRC issued GL 86-10 in order to give the industry 3
additional guidance on implementing NRC fire protection requirements.
The 3
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 i
position on fire endurance test acceptance criteria for fire barrier cable tray wraps.
In its response, the staff referenced Chapter 7, " Tests of Nonbearing Walls and Partitions," of National Fire Protection Association (NFPA) Standard 251, " Standard Methods of Fire Tests of Building 1
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Construction," as being applicable to cable-tray fire wrWis.
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 t1aterial to Pass Fire Endurance Test." This IN gave licensees information on the fire endurance test performed by Gulf States Utilities Company on a Therma-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 l
Installing Thermo-Lag Fire Barrier Material," which gave information on i
deficiencies in procedures that the Thermo-Lag vendor (Thermal Science, Incorporated) provided for constructing Thermo-Lag 330-1 fire barriers.
In response to concerns about the indeterminate qualifications of Thermo-Lag 330-1 fire barriers, on June 23, 1992, the NRC issued IN 92-46, l
l l
l 1
"Thermo-Lag fire Barrier Material Special Review Team Findings, Current Fire Endurance Tests, and Ampacity Calculation Errors." The staff found the l
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 l
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 that the staff issued in GL 86-10.
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After reviewing ins 91-47 and 91-79, Texas Utilities (T;) Electric instituted l
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a fire endurance test program to,ualify its Thermo-Lag eIectrical raceway fire barrier systems for its Comanche Peak Steam Electric Station. Under this program, TV Electric performed its initial fire barrier test series duiing the weeks of June 15 and 22, and August 19, 1992. Notwithstanding the fire test acceptance criteria guidance specified in GL 86-10, TV Electric followed the guidance of American Nuclear Insurers (ANI) as described in ANI Information Bulletin No. 5 (79), "ANI/MAERP Standard Fire Endurance Test Method to Qualify a Protective Envelope for Class 1E Electrical Circuits," July 1973.
As result of NRC interaction with TU Electric regarding its fire tests, the NRC concluded that there was uncertainty on the pari 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 TV Electric recounted above raised the following general concerns:
1 (1)
The fire endurance test acceptance criteria used by other fir'. barrier vendors, applicants, and licensees may not meet the acceptance criteria of GL 86-10, and may oct fully demonstrate the fire barrier performance j
intended.
l (2)
Certain pcst cable functionality testing (i.e., circuit integrity monitoring may not fully demonstrate the intended capability of i
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protected circuitTto function during and after a Kstulated fire.
FIRE ENDURANCE CAPABILITY NRC Oualification Recuirements 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 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 complyirg with this requirement is to separate one safe shutdown train from its redundant train with fire-rated barriers.
The level of fire resistance required of the barriers, 1-hour or 3-hours, depends on the other fire protection features in the fire area.
l 1
The NRC issue. 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
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to a " standard fire exp'ofure.'"
Some licensees have used the acceptance criteria of ANI Information Bulletin No. 5 (79), to evaluate the performance of their fire barrier systems. The ANI test methodology requires the 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 of the American Society of Testing and Materials (ASTM) Standard E119, " 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 cabics 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 (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.
American Society for Testing and Materials (ASTM) Standard E119 was adopted by NFPA as NFPA Standard 251.
n, "InterpretTi. ions of Appendix R," to GL 86-0g, 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 Ccmmission 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 neeCed."
The review guidance provided in Enclosure A (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) specifies 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 and the cable sustains visible damage.
The test methods and acceptance criteria specified 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 regulation.
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 B is a comparison of this review guidance against the GL 86-10 acceptance criteria.
Fire Endurance and Functionality Tests - Evaluation anj Apolication of Test Resul t s
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The fire endurance qualTfication test is succes' ^U if tT!E following conditions are satisfied (see Enclosure C, "Fi.e Barrier Testing Acceptance Criteria / Logic Diagram"):
(1)
The 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;2 or 3
(2)
The thermal limits specified under (1), above, were exceeded and a visual inspection of the protected component or cables 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, 2 The 163 "C
[325 "F] temperature condition specified in GL 86-10 was established by allowing the internal temperature to rise 139 *C [250 *F] above ambient laboratory air temperature which was assumed to be 24 *C [75 "F] during the fire test.
3 When the temperature criterion is exceeded, component operability at the temperature conditions experienced by the component during the fire test must be assessed.
That is, the fire endurance test results that are judged acceptable on the basis of a visual inspection of certain components may not be applied to other components without a specific evaluation.
1
' Examples of thermal degradation of cable jacket and insulation materials are: swollen, split, cracked, blistered, melted, or discolored jacket; exposed shield; exposed, degraded, or discolored conductor insulation; and exposed copper conductor.
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" Guidelines for Fire Pritection for Nuclear Power Plants 7 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 method is an acceptable option for tests of the entire raceway fire barrier system under the new staff position.
The review guidance provided in Enclosure A clarifies that, if cables show signs of thermal degradation during the fire test, the licensee can submit to the staff for review a deviation based on a demonstration of the functionality of the thermally degraded cables and 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 l
l This section describes how the NRC plans to use the review guidance contained in Enclosure A.
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 demonstrate an equivalent level of fire protection, the NRC will use the methods and the i
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.
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BACKFIT DISCUSSION j
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The guidance transmitted by this generic letter supplement will be used by the j
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staff for review and evaluation of the adequacy of fire barrier systems and j
fire endurance tests that may be proposed in the future to satisfy NRC fire e
protection rules and regulations. This guidance refines and clarifies the j
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) l specifies a set of fire endurance test acceptance criteria which are acceptable for demonstrating that fire barrier systems can serve the required j
i fire-resistive function and maintain the protected safe shutdown train frce of l
fire damage, (3) contains acceptable options for hose stream testing, and (4) specifies acceptable criteria for functionality testing of cables when a i
deviation would be necessary, such as if the fire barrier temperature rise criteria are exceeded and the cable sustains visible damage.
I No generic or plant-specific backfitting is intended or approved at this time
- i in connection with issuance of this review guidance. The staff may consider-l the need for further generic action in that regard, if the industry guidance currently under development for addressing the pertinent fire protection f
issues, is substantively inconsistent with this staf f 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-l
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O nm specific backfits are p7oposed by the WRC staff consiste7fC with this review guidance, the proposed backfits would be justified on a 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 the contact listed below or the appropriate Office of fluclear Reactor Regulation project manager.
Enclosures:
1.
f4RC Staff Position on Fire Endurance Test Acceptance Criteria for Fire Barrier Systems Used To Separate Redundant Safe Shutdown Trains Within the Same Fire Area with Attachment to Proposed Generic Letter 86-10, Supplement 1 FIRE Ef4DURAf4CE TEST ACCEPTAf4CE 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:
(}
g May 1, 1976 Branch Technical Position KPCSB) 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 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 relating to the implementation of Appendix R.
The NRC, in an effort to give the licensees more flexibility to make changes to their plant specific fire protection program, issued GL 88-12, " Removal of Fire Protection Requirements from Technical Specifications." Through the implementation and the adoption of a
A standard license condit*In, a licensee can make changes Mich do not adversely affect plant ability to achieve and maintain post-fire safe shutdown to their fire protection program in accordance with 10 CFR 50.59.
The aforementioned NRC documents provided the industry with NRC staff guidance concerning fire carriers separating plant fire areas, including the fire resistance (endurance) ratings for these barriers and the qualification testing that establishes their fire resistance ratings.
In addition, these documents orovided guidance on combustibility of structural materials and the testing required to demonstrate 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 testing 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 S
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 5
For advanced reactor designs, redundant safe shutdown functions are required to be located in separate 3-hour fire areas.
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beenverifiedbymultipTJprobabalisticriskassessments7PRAs).
These PRAs indicate, even with these fire barriers installed, fires provide a major contribution 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 which 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. to GL S6-10, 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 beains to dearade at 450 *F is free from fire damage at 325 "F."
(Emphasis added.)
In addition, the staff's 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
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should be provided for tire use of material which does noHeet the 325 *F
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criterion. This may be based on an analysis demonstrating that the maximum j
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 f
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, l
sufficient additional information is needed to perform an engineering 3
evaluation to demonstrate that the shutdown capability is protected.
Ill.
DEFINITIONS In order to support the understanding of the technical terms used throughout j
this document, the fellowing definitions are provided.
1 i
Combustible Material - Material that does not meet the definition of non-combustible.
Fire Barrier - Those components of construction (walls, floors and their l
i supports), incit, ding beams, joists, columns, penetration seals or closures, i
i fire doors, and fire dampers that are rated by approving laboratories in hours of resistarace to fire and are used to prevent the spread of fire.
Raceway Fire Barrier - Non-load bearing partition type envelope system installed around el'ectrical components and cabling that are rated by approving l
t laboratories in hours of resistance to fire and are used to maintain safe j
shutdown functions free from fire damage.
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Fire Resistance Ratina 5"The time that materials of a teTT' assembly have withstood a standard ASTM E-Il9 fire exposure and have sucessfully met the established test acceptance criteria (Fire Barrier Testing 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 using ASTM E-84 Test " Surface Burning Characteristics of Building Materials."
(Note - There is an exception to this definition as I
defined by BTP Appendix A, Position D. 1. d.
This position allows the use of combustible interior finishes when listed by a nationally recognized testing laboratory, such as Factory Mutual or Underwriters Laboratories, Inc. for a flame spread, smoke and fuel contribution of 25 or less in its use configuration.)
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IV.
FIRE ENDURANCE TESTING ACCEPTANCE CRITERIA FOR FIRE BARRIER WALLS, FLOORS, AND CEILINGS USED TO SEPARATE SAFE SHUTDOWN FUNCTIONS WITHIN THE SAME FIRE AREA To demonstrate the adequacy of fire barrier walls, floors, ceilings, and onclosures, barrier designs should be verified by fire endurance testing. NRC fire protection guidance refers to the guidance of NFPA 251 and ASTM E-Il9 as acceptable test methods for demonstrating fire endurance performance.
The following are the fire endurance testing acceptance criteria for the subject fire barriers:
The fire barrier design has withstood the fire endurance test without the passage of flame or the ignition of cotton waste on the unexposed i
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.)
l If the above criteria are met for fire barrier walls, floors, and ceilings separating safe shutdown functions within the same fire area, the barrier is
l consideredtobeacceptqade.
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i 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 testing laboratory (e.g.,
Underwriters Laboratories or Factory Mutual).
In addition, the construction t
and installation techniques for door and ventilation openings and other f
penetrations through these fire barriers should be appropriately qualified by j
fire resistive testing.
The guidance of NFPA 251 and ASTM E-119 should be consulted with regard to 1
construction, materials, workmanship, and details such as dimensions of parts, i
and the size of the specimen (s) to be tested.
In addition, NFPA 251 and ASTM i
E-119 should be consulted with regard to the placement of thermocouples on the specimen.
i V.
ELECTRICAL RACEWAY A."C i,0MPONENT FIRE BARRIER SYSTEMS FOR SEPARATING SAFE SHUTDOWN FUNCTIONS WITHIN THE SAME FIRE AREA i
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 i
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 P
a
' standard test fire.'
is standard test fire is definedTy the American Society of Testing and Materials in ASTM E-Il9."
In addition, this technical basis stated that "If specific plant conditions preclude the installation of a 3-hour fire barrier to separate the redundant trains, a 1-hour fire barrier l
and automatic fire suppression and detection system for each redundant train will be considered the equivalent of a 3-hour barrier."
In 1984 kimndix R workshops held with industry, and later in GL 86-10, the staff provided guidance related to fire barrier designs for raceways.
In, 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.
j Chapter 5 of NFPA 251 explains the conduct of the fire test.
The iollowing is the NFPA 251 acceptance criteria:
The wall or partition shall have 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 shall have withstood the fire and hose stream test as specified in Chapter 5, without passage of flame, or gases hot encugh to ignite cotton waste, or of the hose stream.
The assembly shall be considered to have failed the hose stream test if an opening develops and permits projection of water from
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the stream M yond the unexposed surface dur1W the hose stream test; and Transmission of heat through the wall or partition during the fire endurance test shall not have been such as to raise the temperature on its unexposed surface more than 139 *C [250 "F]
above its initial temperature.
The staff considers the fire endurance qualification test to be successful if the following conditions are met:
The internal temperature of the fire barrier system, as measured on the exterior surface of the raceway or component, did not 6
exceed 139 *C [250 *F] above its initial temperature ; or (Staff Guidance: NFPA 251/ ASTM-E119 allows 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, the conditions of acceptance are also placed on the temperatures measured by a single thermocouple.
Under the conditions of acceptance, if any single thermocouple exceeds 30 percent of the maximum allowable temperature rise (i.e., 139 *C + 42 *C = 181 *K [250 "F + 75 *F -
325 *F] the test is considered to have exceeded the criteria
- The 163 C [325 F] temperature condition was established by allowing the internal temperature on the raceway to rise 139 *C (250 "F) above ambient laboratory air temperature, assumed to be 24 "C (75 'F), during the fire test.
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temperature'PTmit.)
Where the above thermal limits are exceeded, a visual inspection 7
of the cables is required.
Cables when inspected shall not show 8
signs of degraded conditions resulting from the thermal affects of the fire exposure; and (Staff Guidance: For those cases where signs of thermal degradation to the cables is present, it is considered that 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 was maintained and that these cables would have adequately performed their intended function during and after a postulated fire exposure may be granted. Attachment 1 to this proposed position provides a suggested methodology for demonstrating the functionality of safe shutdown cabling during and after a fire test exposure.)
The raceway fire barrier system shall have remained intact during the fire exposure and water hose stream test without developing any openings through which the electrical conductor or raceway is visible.Section VII identifies acceptable hose stream test methods and the time of application.
7 For components, when the temperature criteria is exceeded, an assessment of component operability at the temperature conditions which would be experienced by the component during the fire test is required that is, raceway fire endurance tests which are judged acceptable on the basis of a visual inspection of certain components may not be applied to other components without a specific evaluation.
8 Examples of thermal cable degradation are:
jacket swelling, splitting, cracking, blistered, melted, or discoloration; shield exposed; conductor insulation exposed, degraded, or discolored; bare copper conductor exposed.
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i The test specimen shall be representative of the construction for which the l
1 fire rating is desired, as to materials, workmanship, and details such as 1
dimensions of parts, and shall be built under representative conditions.
Raceway fire barrier systems being subjected to qualification fire endurance I
testing 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
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these field conditions.
In addition, the fire testing program should encompass the ractway sizes and the various configurations for those fire
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barrier systems inctalled 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 raceway design used for testing should be constructed with materials and configurations representative of in plant conditions (e.g., mass associated l
with typical steel conduit, steel cable trays).
i Measuring cable temperatures is not considered 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 L
unexposed surface temperature of the fire barrier test specimen, methods which will adequately 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 l
plant specific components and configurations. The metal surfaces of the I
raceway, under fire test conditions, exhibit good thermal conductivity properties. Temperatures measured on these surfaces provide a conservative indication of the actual temperature rise within the fire barrier system.
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ANIcriteriafortestiny"firebarriersrecommendstheca3?etemperaturesbe 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 1
barrier performance to be nonconservative. As discussed above, temperatures monitored on the exterior surface of the raceway orovide a more representative indication of fire barrier pcrformance.
The following are acceptable placements of thermocouples on raceway fire barrier enclosures:
Conduits - measure the temperature of the conduit by placing the thermocouples every 6-inches on the conduit surface underneath the fire barrier material.
Cable Trays - measure temperature rise of cable tray by placing the thermocouples on the exterior surface of the tray side rails underneath the fire barrier material.
In addition to placing thermocouples on the side rails, thermocouples shall be attached to two 14 gage bare copper conductors.
The first copper conductor will be installed on the bottom of the cable tray rungs along the entire length of the cable tray run.
g The second condu or shall be installed along theTuter 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 shall be placed every 6-inches along the cable tray side rails and along the bare copper conductors.
1 In addition, thermocouples shall be placed every 12-inches on the l
surface of the outer cables nearest to the raceway and on the surface of the cables nearest to the underside of the top of the fire barrier.
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Temperature conditions on the raceway during the fire test will be determined by averaging the temperatures measured by the thermocouples.
In determining the raceway temperature conditions, the thermocouples measuring similar fire barrier areas of performance shall be averaged together and the basis of acceptance will be based on these individual averages.
The following method i
of averaging shall be followed:
Conduits - The thermocouples applied to the outside metal surface of the conduit will be averaged together.
Cable Trays - The thermocouples on each cable tray side rail shall 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 bare copper conductors shall be averaged separately,
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Cables - The theri"Jcouples used to measure indiviaW1 cable temperatures will be used for engineering purposes and shall not be used for evaluating the performance of the fire barrier system.
For each thermocouple group, the averages shall not exceed 139 *C [250 *F]
above the initial temperature at the onset of the fire endurance test.
In addition, the temperature of each individual thermocouple will be evaluated.
Individual thermocouple conditions shall not exceed the 139 *C [250 *F]
temperature rise by more than 30 percent.
VI.
HOSE STREAM TESTING NFPA 251 and ASTM E-119 allow some 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 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> (e.g., 30 minute fire exposure to qualify a 1-hour fire rated barrier).
For safe shutdown related fire barrier systems, 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 gauge]. The application of the
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stream is to all exposed parts of the specimen for a minimum duration of I minute for a 1-hour barrier and 2\\ minutes for a 3-hour barrier.
As an alternate, the application of the hose stream test on the test specimen
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can be performed immediMely after the completion of the ull fire endurance test period.
If this method is used to satisfy the hose stream testing criteria, the following hose stream applications are considered acceptable:
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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]
I at a distance of 6.1 meters [20 feet] from the specimen (duration i
of the hose stream application - 1 minute for a 1-hour barrier and i
2h minutes for a 3-hour barrier); or i
The stream applied at random to all exposed surfaces of the test j
specimen through a 8.3 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 2841pm [75 gpm] with the tip of the nozzle l
ll at a maximum of 1.5 meters [5 feet] from the test specimen i
(duration of the hose stream application - 5 minutes for both 1-hour and 3-hour barriers); or
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The stream applied at random to all exposed surfaces of the test j
l specimen through 8.3 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 1pm [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).
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-VII.
FIRE BARRIER COMBUSTIBILITY j
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NRC fire protection guidelines and requirements establish the need for each nuclear power plant to perform a plant-specific fire hazard analysis.
The l
fire hazard analysis shall consider the potential for in-situ and transient I
fire hazards and combustibles. With respect to building materials (e.g.,.
cable insulation and jackets, plastics, thermal insulation, fire barrier r
materials), the combustibility, ease of ignition, and flame spread over the surface of a material shall 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, as determined by ASTM-D1929, and-the flame spread characteristics, as determined by ASTM E-84, of the fire I
barrier material shall be evaluated.
The potential heat release of the material shall also be determined and factored into the fire hazards analysis.
i The heat release of the material can be determined by testing to the l
provisions of ASTM D-3286 or NFPA 259.
i 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 Nuclear Reaulatory Commission 1,
May 1, 1976 Branch Technical Position (APCSB) 9.5-1., " Fire Protection Program."
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2.
February 24, 197 P Appendix A to the Branch TTEhnical Position APCSB 9.5-1, " Guidelines for Fire Protection for Nuclear Power Plants Docketed Prior to July 1, 1976."
3.
Februar.y 19, 1981 10 CFR 50.48, " Fire protection."
4.
February 19, 1981 Appendix R to 10 CFR 50, " Fire Protection for Nuclear Power Plants.
5.
February 20, 1981
" Staff Position - Safe Shutdown Capability,"
6.
July 1981 NUREG - 0800, Standard Review Plan (SRP), 9.5.1,
" Fire Protection for Nuclear Power Plants."
7.
October 19, 1983 "NRC Positions on Certain Requirements of Appendix R to 10 CFR 50," (Generic Letter 83-33).
8.
April 24, 1986
" Implementation of Fire Protection Requirements," (Generic Letter 86-10).
4 American Society for Testina and Materials (ASTM) 1.
ASTM E-84 Test " Surface Burning Characteristics of Building Materials."
2.
ASTM E-119, " Fire Test of Building Construction and Materials."
3.
ASTM E-136, " Behavior of Materials in a Vertical Tube Furnace at 750*C."
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4.
ASTM D-1929, " Test" Method for Ignition Properties 75' Plastics."
5.
ASTM D-3286, " Test Method for Gross Calorific Value of Solid Fuel by the Isothermal-Jacket Bomb Calorimeter."
American Nuclear Insurers (ANI) 1.
July 1979, ANI Information Bulletin No. 5 (79) test criteria for " Fire Enc ance Protective Envelope Systems for Class lE Electrical Circuits."
National Fire Protection Association (NFPA) 1.
NFPA 251, " Standard Methods of Fire Tests of Building Construction and Materials."
2.
NFPA 259, " Standard Test Method for Potential Heat of Building Materials."
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Attachment I to 2Tclosure 1 to Generic Letter 86-Ml Supplement 1 ACCEPTABLE METHODS FOR DEMONSTRATING FUNCTIONAllTY OF CABLES PROTECTED BY RACEWAY FIRE BARRIER SYSTEMS DURING AND AFTER FIRE ENDURANCE TEST EXPOSURE a.
INTRODUCTTON The NRC considers fire barrier systems that meet the acceptance criteria adequate under NRC fire protection regulations.
The licensee, where the criteria are not int, can 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 shall also consider cable operating temperatures within the fire barrier at the onset of the fire exposure.
b.
CABLE CIRCUIT INTEGRITY TESTING ANI Criteria In 1981, American Nuclear li surers (ANI) developed a fire endurance test criteria for raceway fire barrier systems.
This criteria, " Fire Endurance Protective Envelope Systems for Class IE Electrical Circuits,"
l specifies 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
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circuit integritMest voltage is 8 to 10 volts DSherefore the loss of circuit integrity under these voltage conditions may only occur as a result of a dead short or open circuit.
During actual fire testing conditions of raceway fire barrier systems thermal damage to the cables has resulted.
This thermal damage has led to cable jacket and insulation degradation without the loss of circuit integrity as monitored using ANI criteria.
Since cable vnltages used for ANI circuit integrity testing do not replicate cable operating voltages, loss of cable insulation conditions can exist during the fire test withat.t dead short occurring.
It is expected that if the cables were at rated powar and current a fault would propagate.
Therefore, the use of ANI circu integrity monitoring during the fire endurance test is not considn ca a valid method for demonstrating that the protected shutdowr. circuits are capable of performing their required function during ind after the test fire exposure.
c.
CABLE INSULATION TESTING Th, two principal materials used as cable insulation and cable jackets by the nuclear industry are thermoplastics and thermosettint polymeric materials.
A thermoplastic material can be sof tened and resoftened by heating and reheating.
Conversely, thermosetting cable insulation materials cure by chemical reaction and do not sof ten 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
t temperatures as h as 260 *C [500 *F].
Insulat resistance (Megger)
I testing provides an indication of the condition of the cable. insulation -
resistance, whereas the high potential (Hi-Pot) test provides assurance t
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
.l which is due to low insulation resistance, and the other failure mode is l
overpotential stress which is due to loss of dielectric strength of the l
r insulation material.
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I If megger tests are not performed at frequent intervals during the fire f
1 exposure, indications of insulation damage may go undetected.
Insulation, when removed from elevated tr oeratures will reset. Megger_
testing of insulated cables after the fire endurance test and after the' cable has sufficiently cooled may not detect degradation in the
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i insulatir, resistance. Therefore, wet or dry megger of cables after a I
i fire exposure does not provide reasonable assurance that the cables l
would hava runctioned as intended during the fire exposure.
j To provide rea-
. 'e assurance that the cables would have functioned l
during and after t' ire exposure, megger tests need to be performed 4
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 j
hour during the 3-hoiar fire test) for instrumentation cables only, and after the fire endurance test to assess the cable insulation resistance levels.
This testing will assure that the cables will maintain sufficient insulation resistance levels necessary for proper operation of instruments.
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The megger tests Tere-fire, during the fire [if pe7 Formed), and immediately after the fire test conditions) should be done conductor-to-
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conductor for multi-conductor anc conductor-to-ground for all cables.
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The minimum acceptable insulation resistance (IR) value, using the test voltage values as shown in the table below, is determined by using the following exprassion:
IR (Mega-ohms) > 1[(1 Meaa-ohm per KV) +11w 1000 (ft) 1 1
Length (ft)
Additionally, in determining 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 shall be evaluated.
In addition, an AC or DC high potential (4i-Pot) test for power cables greater than 1000 volts shall 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 shall be performed for a 5 minute duration at 60 percent of either 80 volts / mil ac or 240 volts / mil dc (e.g., 125 mil conductor insulation thickness x 240 volts dc x 0.6
=18,000 volts 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.
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OPERAENG MEGGER TEST HIGH POTE RIAL TYPE VOLTAGES VOLTAGE TEST VOLTAGE POWER 2 1000 vat 2500 vdc 60% x 80 V/ mil (ac) 60% x 240 V/ mil (dc)
POWER
< 1000 vac 1500 vdc #
NONE INSTRUMENT s 250 vdc 500 vdc NONE AND 5 120 vac CONTROL
- A megger test voltage of 1000 vdc will be acceptable provided a Hi-Pot test is performed af ter the megger test for power cables rated at less than 1000 vac.
d.
CABLE THERMAL EXPOSURE THRESHOLD I
The following is an acceptable analysis method for evaluating the cable 1
functionality.
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This analysis is based on determining whether a specific insulation material will maintain the electrical integrity and operability of protected cables within a raceway fire barrier system during and after an external fire exposure. 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 tiermoplastic 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 shall not exceed 81.*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 cir m t during and after a fire.
The cable normal 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.
Dated at Rockville, Maryland, this / d day of July, 1993.
FOR THE NUCLEAR REGULATORY COMMISSION 6%
Gail H. Marcus, Chief Generic Communications Branch Division of Operating Reactor Support Office of Nuclear Reactor Regulation