ML20151E723
| ML20151E723 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 06/30/1988 |
| From: | Krieg J, Shea T, Simmons J EBASCO SERVICES, INC., STONE & WEBSTER ENGINEERING CORP., TENNESSEE VALLEY AUTHORITY |
| To: | |
| Shared Package | |
| ML20151E713 | List: |
| References | |
| TAC-62260, NUDOCS 8807260184 | |
| Download: ML20151E723 (24) | |
Text
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QA .. Record 822 b8 0617 016/? !
Tun TENNESSEE VALLEY AUTHORITY Aut Division of Nuclear Engineering fi','Or, /
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EVALUATION OF BROWNS FERRY NUCLEAR PLANT CABLE INSTALLATION CONCERNS
SUMMARY
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. I EVALUATION OF BROWNS FERRY NUCLEAR PLANT ,
CABLE INSTALLATION CONCERNS
SUMMARY
REPORT PREPARED FOR TENNESSEE VALLEY AUTHORITY DIVISION OF NUCLEAR ENGINEERING JUNE 1988 8
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TABLE OF CONTENTS Page
1.0 INTRODUCTION
.................................................... I 1.1 Background ................................................ I 1.2 Purpose ................................................... I 1.3 Approach .................................................. 2 1.4 Report format ............................................. 3 2.0 CABLE INSTALLATION REQUIREMENTS .......'......................... 4 3.0 CABLE MATERIAL EVALUATION ...................................... 8 4.0 CABLE INSTALLATION EVALUATION .................................. 9 5.0 SPECIFIC ISSUE RESOLUTION ...................................... 11 5.1 Sidewall Pressure ......................................... 11 5.2 Pullbys ................................................... 12 5.3 Jamming ................................................... 14 5.4 Ve r t i cal Cabl e Suppor t s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 5.5 Cable Bend Radil ................................... ...... 16 5.6 Pulling Cable Around 90-Degree Condulets and Through Mid-Run Flexible Conduit .................... 17 6.0
SUMMARY
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7.0 REFERENCES
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1.0 INTRODUCTION
1.1 Background .
During the summer of 1986, the U.S. Nuclear Regulatory Commission (NRC) began a review of concerns relating to the adequacy of construction practices at the Tennessee Valley Authority's (TVA)
Watts Bar Nuclear Plant (WBN). The review identified that many of the concerns centered on potential damage to electrical cables due
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to alleged improper or inadequate cable installation practices.
Accordingly, the NRC performed a comprehensive review to determine if significant damage had occurred to cables during-their installation at WBN. Since TVA's Sequoyah (SQN) and WBN plants arn based on the same overall design, the NRC extended the evaluation of the cable installation concerns to the SQN plant. The Technical Evaluation Report (TER) describing the NRC evaluation, conclusions, and recommendations regarding the concerns relating to potential abuse of electrical cable from installation practices at SQN was provided to TVA via reference 1.
TVA performed an extensive and comprehensive evaluation of those SQN issues for which the TER determined implementation was required prior to startup of that plant (rn'erence 2). These issues were successfully resolved at SQN and its cable installation practices in these areas were demonstrated to have resulted in adequate cable installation (reference 3).
As a result of generic reviews of the Condition Adverse to Quality Reports (CAQRs) issued to document the potential conditions at SQN, these same cable installation concerns have been identified at Browns Ferry Nuclear Plant (BFN).
In order to evaluate the extent to which these concerns applied to BFN and to determine whether significant damage had occurred to cables during their installation, TVA implemented an individual indepth review on BFN. This report provides the evaluations, conclusions, and recommendations from this review for resolution of the BFN specific cable installation concerns.
1.2 Purpose The BFN evaluation was performed to determine if significant cable abuse had occurred during installation. The plan was specifically intended to address the following:
. Determine if significant differences existed between the cable installation practices and procedures utilized in the construction of BFN and those utilized in the industry during the time period of BFN's construction.
. Perform plant walkdowns to review specific installation practices and assess the overall quality of the cable installation.
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. Determine the extent to which the. installed cables It BFW are enveloped by the SQN cable issue resolution progran'.' j
. Establish, as necessary, a BFN corrective action program for !
resolution of the cat'le installatiori concerns. J 1.3 Approaq .
The issues of pullbys, jamming, and vertical cable supports were resolved at SQN by performing direct current high potential tests on a selected number of installed cables. During this testing, several insulation breakdowns occurred at high voltages ranging from 7.5 to 10.8 kV dc. Subsequent testing at tne University of Connecticut's Electrical Insulation Research Center (Reference 20) and Hyle Laboratories (References 20 and 21) demonstrated that cables with insulation defects similar to those discovered in the failed cables were.in fact in a serviceable condition and could perform their intended function during the design basis accident. This raised serious questions regarding the validity of.high potential tests on installed cables. Futhermore, the NRC Advisory Committee on_ Reactor Safeguards, following its review of the SQN test program, stated ".
. . we recommend against the continued use of high-voltage testing of installed low-voltage cables" (reference 4).
Accordingly, TVA determined that the approach for resolution d the BFN cable installation concerns should be initially based upon inspection and analysis. Forming an integral element in this program would be the extensive calculations, field inspections, and results of tests performed at SQN. In order.to determine the extent to which the BFN installation is enveloped by the SQN test program, TVA performed the following:
. A review of the TVA cable installation requirements which existed ,
during the construction of BFN fer comparison against the '
requirements which exts.ted in the industry during that time period as well as at SQN during its cable installation (reference 5).
. A review of the cable materials and constructions utilized in -
safety-related applications at BFN. Special consideration was !
given to the cables durability or susceptibility with respect to the types of damage postulated in the TER. This review includes a !
comparison of the BFN cables with SQN cables, and their associated properties. The purpose of this review was to determine whether the BFN cables were more, less, or equally susceptible to installation damage when compared with the SQN cables, which were demonstrated to not have incurred installation damage I (reference 6). !
. A walkdown of selected representative cable installations to examine whether any damage had occurred and to assess the relative difficulty which the conduit configuration presented to the' cable installation (Reference 7). This walkdown was also intended to provide a basis for comparison of the as-installed cable configuration at BFN with that previously analyred and/or tested ;
at SQN. '
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4 The results of the above. reviews formed the basis for the conclusions on the BFN cable installation issues and established the corrective action plan, as necessary, for resolution of each issue.
1.4 Report Format :
The report addresses the individual cable installation issues which included: ,
Cable sidewall pressure Cable pullbys Cable jsmming Vertical cable supports Cable bend radius
, Pulling cable around 90-degree condulets and through mid-run flexible conduit Sections 2.0, 3.0, and 4.0 provide an overview of the results of the examinations of installation practices, cable materials, and installation conditions, respectively. Section 5.0 provides an individual evaluation of each of the above issues; conclusions and recommendatitns are provided within the discussion on each issue.
An overall assessment and summary of the BFN cable installation issue resolution program is provided in section 6.0. The references identified in the report are listed in section 7.0.
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6 2.0 CABLE INSTALLATION _REQUIr..HENTS The review of cable installation requir.ements (reference 5) concentrated on the period from issuance of the BFN construction permit in May 1967 to the time that the three BFN units were-brought on line in 1973, 1974, and 1976, respectively. This report recognized that for the cable installation issues of concern, the BFN installation procedures were generally silent. The sole exception was sidewall pressure for which a limitation of 100 lb/ft was stated in January 1973. However, this requirement would have had little impact on BFN, as cable installation was virtually complete on units.I and 2 by that time. In the area of cable pull tension, the~ industry recognized limit of .008 lb/cir mil was ,
identified in TVA requirements documents prior to the beginning of BFN construction. Monitoring of pe'l tension became mandatory in 1973; however, this was subsequent to the majority of BFN units 1 and 2 cable pulling. Although cable pull tension is not a specific area of concern, adherence to this requirement could help alleviate concerns such as pullby, sidewall pressure, and jamming damage.
This review has identified what today might be considered a lack of proper requirements. The purpose, however, was to compare BFN against the requirements which existed at the time of its construction. To accomplish this a detailed review of industry standards and manufacturers installation recommendations was performed.
One of the earliest sources of guidance on cable installation 1: the Underground Systems Reference Book (reference 8) which was originally published in 1931, with the first (and last) revision in 1957. As indicated in the title, the scope of this publication focused on the installation of underground cables including buried cables, cables installed in ducts, pipe-type cables and submarine cables. The discussions on installation of cables in ducts and pipe-type cables include the considerations of cable sidewall pressure, cable jam ratio and cable bend radius. These carameters appear to have been developed specifically for the installation of paper-lead cables in underground ducts and pipes. This conclusion is supporteJ by the numerous cautions, contained in the installation s n tions, regarding possible distortion or scoring of the lead sheath or distorting the oil.or gas channel in low-pressure oil- or gas-filled cables. It is interesting to note that '
the text states "Usually, no attempts are made to measure the pulling tensions imposed on low-voltage cables."
A technical paper of the same era,. "Pipe-Line Design for Pipe-Type Feeders" (reference 9) addresses the concerns of sidewall pressure and jam ratios. However these considerations are again applied specifically to pipe-type cables, which operate at very high electrical stresses and relatively high pressure with either oil or gas as the pressure medium.
The Simplex Manual (reference 10), issued in 1959, represents one of the earliest cable manufacturer handbooks. This manual, which addresses the l installation of cable in ducts and condults, provides guidance for cable sidewall pressure and bend radius. It is silent on the other cable installation issues and particular notice is taken of the lack of consideration of cable jamming.
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e In the late 1960s a working group was formed on Hire and Cable Systems in the Station Design Subcommittee of the Power Generation Committee of the IEEE Power Engineering Society. The work of this group would eventually be published as IEEE Standard 422-1977, "IEEE Guide for the Design and Installation of Cable Systems in Power Generating Stations." A draft versic.i of that document was made available in November 1970 and subsequently presented at the 1971 IEEE Hinter Power Heeting (reference 11). While again relating the industry recognized concerns on cable pull tension and sidewall pressure, with minor discussions on raceway bend radli, it contains no mention of or guidance for the '
remaining BFN installation concerns. This is especially noteworthy as it is in the time period of the major cable pulling activ.ities at BFN.
In 1971, IEEE Standard 336 was issued. Although it's title is I "Installation, Inspection, and Testing Requirements for Instrumentation and Electric Equipment During Construction of Nuclear Power Generating Plants." it contained no specific recommendations or requirements for cable insta11atica.
The mid-1970s bagan to see the formal preparation and issuance of cable manufacturer installation handbooks. In 1974 Essex issued its Control l Cable Engineering Handbook (reference 18) as a successor to their ;
Underground Cable Engineering Handbook. This manual, which as indicated by its title is directed toward control cables, addresses only the requirements for cable pull tension, sidewall pressure and bend radius. ,
The Raychem Installation Guide (reference 12) in 1976 also provides j recommendations for cable pull tansion, sidewall presstr and bend l radius, but is silent in the other areas of concern. Anaconda Cable {
Installation Manual (reference 13), first published in 76, addresses ,
these same ;onsiderations and provides the first rWrence found which !
applied the' concern of jam ratio to all cables in: .ading low voltage. It does refine the scope, however, in its statement "For one or two conductors or for a multiconductor with an overall jacket, jamming is not applicable."
IEEE Standard 422 was issued in 1977. It still contained the recommendations, previously discussed in its 1970 draft, for cable pull tension and sidewall pressure, had expanded the discussion of the bend radius of raceways and its relationship to cable radius, and provided the first industry consensus on vertical cable supports. It did not contain any recommendations or discussion on cable pullbys, jamming or pulling around 90 degree condulets or through flexible conduit.
The Okonite Company published their first bulletin (EHB-78) in 1978 (reference 14) which addressed the installation of cable systems. This manual discusses cable pull tension, sidewall pressure and bend radius and provides specific recommendations on vertical cable support. It does not address the remaining BFN issues.
The 1979 Kerite Installation data (reference 16) reflects the changing industry philosophy and provides recommendations for cable pull tension, sidewall pressure, jamm'.ng, bend radius and vertical cable supports. No guidance or cautions are provided for cable pullbys or pulls around condulets or through flexible condults. -
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The pubitcations issued in the early 1980s reflect the state-of-the-art in cable' installation today. This includes considerations of cable pull tension, sidewall pressure, jamming, vartical cable supports and bond radius. It is evidenced in the-1982 Eaton Cable Installation Guide (reference 17) and the 1984 initial issue:of IEEE 690 "IEEE Standard for the Design and Installation of. Cable Systems for Class lE Circuits in Nuclear Power Generating Stations." It is noted, however, that while IEEE 690 represents the first industry consensus standard to address cable jamming, it does so only in its appendix which is not actually part of the standard itself. The Okonite "Installation Practices for Cable Raceway Systems" (reference 15) issued in 1982 contains the most comprehensive review of installation practices found in this review. In addition to the concerns addressed in the two guides discussed in this paragraph, it includes specific prohibitions ot eable pullbys and pulling around 90 degree condulets. It represents, however, the recommendations of a single manufacturer and not on industry consensus.
The above constitutes a review of all known and readily available cable installation guides and standards. It is intended to show the origin and evolution of cable installation practices and requirements. In particular, it is utilized to determine those aspects of cable installation practice which would have clearly been agreed upon by a majority of cable installation experts at the time of BFN construction.
From this review it can be seen that when BFN was constructed, there did exist general industry guidance concerning cable pull tension and bend radius. The issue of cable sidewall pressure nad been addressed, but there was little spectfic guidance. Cable jamming and vertical cable supports had not been idet:1fied as concerns for generating station cables and no requirement. or recomm?ndations existed concerning cable pullbys or pulling cable around 90-degree condulets and through mid-run flexible conduit. Specific guidanca in these areas did not appear until the late 1970s, years after BFL commercial Opn etion, and many of the issues still lack specific guiuance and/or industry consensus support.
It is believed that these issues were adequately addressed,.as was the case at BFN, by the use of a trained and experienced workforce.
This review could find no basis for considering many of the cable installation concerns to have been industry practice around 1970, the time of major activity la BFN cable pulling. Nor was any basis found for concluding that the later requirements were determined by the industry to !
require backfit on previous plants. Nevertheless, each of these issues and their relationship to BFN, has been individually addressed in section 5.0 of this report.
The secondary purpose of the review of cable installation requirements was to determine the similarity of procedures utilized in the construction of BFN and SQN. The results (reference 5) indicate tha; 1
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cables'at both 8FN and SQN.were installed with the same requirements with the exception of sidewall pressure. .However, the SQN cable issue resolution program was performed wlthout any credit taken for'this requirement. Accordingly, from the' aspect of cable installation requirements, the results of the cable resolution program at SQN are directly applicable to BFN.
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I 3.0 CABLE MATERIAL EVALUATION A study was performed of the cable matarlais and design practices utilized at BFN in comparison with those at SQN (reference 6). The purpose of this study was to determine the type of cable' insulation and j jacket materials installed at BFN and their relative durability with respect to the specific installation concerns. In addition, the design practices utilized in selecting cable for a particular application were to be reviewed. The informatloa from each of these reviews would then be compared to the results of similar examinations on SQN to determine whether the BFN materials compared favorably with respect to application and ability to withstand the rigors of installation. The results of the ,
BFN and SQN comparison would determine whether the'recently completed cable resolution programs at SQN were representative, from a material and application standpoint, of those at BFN.
The results of these reviews indicate that BFN compares favorably with SQN. Perhaps of greatest significance is the fact that BFN does not utilize silicone rubber insulated cablos as part of the general design practice. These cables were of the most concern at SQN. At BFN they are used strictly in pigtail extension applications where they would be relatively short lengths.
The reviews indicata that most cable contracts were shared by BFN and SQN. This would generally be expected to provide for a random selection of cable types and manufacturers for each installation, at either plant.
In ada. tion, all cables of a particular insulation material were procured I to the same specification requirements, ensuring a consistent minimum level of physical properties. The installed cabies at BFH are therefore considered to be equally resistive to installation damage as those at SQN. A'ccordingly, from the aspect of cable material and application Oe results of the cable resolution program at SQN are directly applicable to BFN.
During this review, it was noted that while both plants utilize the same type of cables, BFN, due to the timeframe in which it was constructed, utilizes a greater quantity of polyethylene insulated cables. These thermoplastic cables are considered to be more susceptible to creep over time at elevated temperatures than the other widely utilized materials, I which are thermosetting. This was considered in the evaluation of the individual issues in section 5.0 of this report.
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4.0 CABLE INSTALLATION EVALUATION A walkdown team was formed to perform fleid inspections of the BFN cable installation. The purpose was to determine if significant cable abuse occurred durtrig installation as would be evidenced by the existing conduit configuration and inspections on selected representative conduits and cables. In addition, the walkdown was intended to provide a basis for comparison of the as-installed cable configuration at BFN with that of other nuclear plants of its vintage as well as that recently analyzed and/or tested at SQN. The results of this comparison would determine whether.the recently completed cable resolution programs at SQN were representative, from an installation configuration _ standpoint, of those at BFN.
The results of the walkdown were very favorable (reference 7). No significant cable damage was observed. The conduits were installed with many pullpoints, in accessible locations, which reduced the length and degree of bends of each pull, Good craftmanship was generally exhibited, particularly in the use of cable pulling lubricant. There appeared to be a good knowledge of cable installation practices, especially with respect to the installation and routing of conduits. The compact nature of the plant, the limited number of buildings containing safety-related electrical equipment, and the close proximity of much of the interconnected equipment contributed in reducing the difficulty of the individual pulls. The installed cable configuration at BFN compared favorably with that of SQN and is similar to other plants of its vintage. Accordingly, from the aspect of installed cable and conduit configuration, the results of the cable resolution program Tt SQN are directly applicable to BFN.
The probability of accidents related to common mode failures from cable installation problems as postulated in the SQN TER (reference 1) is significantly reduced by the BFN cable routing practices inside the !
primary containment (drywell). In this area, Division I cables were generally installed in trays except where they drop from the tray to i their end devices, or where a direct conduit route to the end device is '
shorter than the distance required to access the tray. Therefore, although Division II cables are installed only in conduit inside primary l containment, it is not expected that cables of both divisions could be '
subjected to the same installation deficiencies.
In addition, all cables located in the three worst case harsh environment i areas (drywell, steam tunnel, and heat exchanger rooms) and required for -
the mitigation of a design basis event that creates a harsh environment are being replaced prior to restart (see reference 7, sections 5.E.2 and 5.4.2). These replacements will be made in accordance with all presently applicable standards and specifications.
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The walkdowns were performed in accordance with the issued procedure which identified specific attributes for -inspection. These included '
conduit and cable data, accessibility of pull points, useoof lubricant, conduit configuration, and the existence of any cable damage. The walkdown, however, was -not restricted to only those conduits, attributes, or issues in the original procedure. Rather the walkdown team scanned the installation as a whole in all plant areas inspected, which resulted in the. addition of conduits into the review for concerns such as excess bends between pull points, condulet sizing, and(4-kV cable bend radius.
The walkdowi; results, therefore, represent an inspection even more comprehensive than originally outlined.
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- 5.0 SPECIFIC ISSUES 5.1 Sidewall Pressure .
5.1.1 Issue Description The issue of cable sidewall pressure (SWP) is concer'ned'with possible damage to cable shielding or insulation due to excessive radial force exerted on the_ insulation and jacket of a cable at a bend point, during pulling operations. A detailed description of
. sidewall pressure requirements, contributing factors and failure mechanisms is provided in paragraph 5.1.1 of the Cable _ Issues Walkdown Report (Reference 7).
This issue has been addressed at BFN, primarily by the walkdown effort which. observed conduit and cable installations. The effort determined the extent or possibility of cable damage due to sidewall pressure an addition, a comparison of installation requirements and cable insulation and jacket materials, between BFN and SQN plants, was performed to assess the applicability of SQN calculation results to BFN. The calculations-performed at SQN indicated that no damage due to SHP occurred during the cable installation.
5.1.2 Conclusions
.As discussed in paragraph 5.1.1 of the Cable Issues Walkdown Report (Reference 7), acceptable limits for sidewall' pressure have changed with time and vary significantly between various cable types and constructions. Earlier limits for sidewall pressure, established by cable manufacturers and the industry, have been significantly increased. TVA has performed independent tests to determine sidewall pressure limits for the types of cables used in their Nuclear Program. These results are documented in TVA QA Record "Cable Sidewall Bearin )ressure Tests" (Reference 22).
The TVA tests have verified rei,tively high limits are acceptable for cables used at BFN. ,
The results of tne Cable Issues Walkdown Report indicate that the possibility of damage to cables installed at BFN due to excessive sidewall pressure is not of concern. The walkdown evidence indicates goort workmanship as reflected in the use of an adequate number and location of pullpoints and also that the pullpoints were utilized during cable. installation. The installed conduit i configurations were similar in severity to those analyzed in the l SQN SHP calculations. Calculations performed on the worst-case ;
observed conduits at BFN indicated that allowable SHP was not exceeded.
Cable materials analyzed for potential damage due to SNP at SQN )
are similar to those used at BFN and have simliar durability with '
respect to SHP damage. This is demonstrated by the Haterials Evaluation Report (Reference 6).
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Overall conc 16sions drawn from the above is that the possibility of damage to : ables due to sidewall pressure is not of concern based on SQN calculation results, their applicability' to BFN, and the BFN walkdown conclusions.
5$1.3 Recommendations ,
No further corrective action is required for the issue of cable sidewall pressure.
5.2 Pullbys .
5.2.1 Issue Description A pullby is the pulling of one or more new cables past previously installed cables in a condult. A pullback is the removal of one or more (but not necessarily all) cables previously installed in a condult. Depending upon the conduit conditions and nature of the pull (removal), it could be possible for' the pulled (removed) cables to "saw through" the irsulation of the previously installed cables. .For the purposes of this report, the term.pui'.by refers to the concerns for pullbys and pullbacks. 'A detailed description of the pullby issue, contributing factors, and failure mechanisms is provided in Paragraph 5.2.1 of the Cable Issues Walkdown . Report (Reference 7).
The issue of pullbys has been addressed at-BFN-by the performance of inspection walkdowns and by comparison of BFN installation requirements / practices and cable materials to those utilized at SQN to determine a'pplicability of SQN test results.
5.2.2 Conclusions The SQN TER (Reference.1) raises specific concerns regarding the pulling of abrasive manila, or braided synthetic pull lines, and thermosetting jacketed cables over previously installed.
thermoplastic insulated / jacketed cables. BFN walkdown observations found no evidence of braided pullropes being used for pullbys. This was supported by the high incidence of left-in-place insulated pull wires. Although the authors of this report do not condone use of pull = wires / rop?s that were installed with previous cables, it was observed that the BFN pra:tice of using No.10 AHG insulated wire as pull' wire is preferrible to other more abrasive options. -
Due to the time frame of TVA's revision to cable procurement specifications (i.e., transition from polyethylene type cables to cross-linked cables in 1975), it is obvious that'the majority of post commercial operation maintenance / modification pullbys vould result in thermosetting cables being pulled over thermoplastic-cables.
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s The authors of this report agree with conclusions drawn in the SQN TER that the most important consideration in preventing pullby-damage is adequate use of lubrication. The Cable Issues Walkdown Report identified cable lubricant in more abundance at pullby, inspection points than in non-pullby condulets. This indicates that BFN craftsmen understood the need to provide abundant lubrication when performing pullbys.
In addition, the Cable Issues Walkdown Report found no evidence of pullby damago. Conduit installation practices utilized limited distances and number of bends between pull points, which is a favorable factor in preventing pullby damage. All walkdown evidence indicated that installed pull points were utilized. In addition, the Cable Issues Walkdown Report indicates that pullbys were limited to control cable installations.
SQN pullby test results addressed a wide range of cable types / materials including thermoplastic insulation / jacket -
materials (See Reference 19). Based upon review of the SQN test results, the installed configurations and the Materials Evaluation Report (Reference 6), it was concluded that the SQN pullby tests encompassed the pullby situations at BFN.
It should also be noted that all cables idcated in the three worst case harsh environment areas (Drywell, steam tunnel and heat exchanger rooms) and required for the mitigation of a design basis event that creates a harsh environment shall be placed prior to restart in conformance with presently' applicable standards and specifications. (See References 23-26.)
5.2.3 Recommendations '
Based on the conclusions stated abovr recommendations regarding the pullby issue are as follows:
TVA should ensure thit specifications and site procedures achieve the following:
- 1. Provide direction to.not use previously installed pull wires or cables as pull lines. Pull lines should be non-abrasive.
- 2. Length of pullby cable should be limlied.
- 3. A high quality, flowable, pull lubricant such as "Polywater J" should be utilized for pullbys.
TVA has, in place, a program to identify any adverse trend of cable failures that could result from pullby cable damage. This program should be continued with appropriate actions to be initiated in the event of cable failures resulting from pullby damage.
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5.3 Jamming 5.3.1 Issue Description .
> When the ratio of the inside diameter of a conduit to the cable diameter is close.to 3.0, one c' the_ cables in a pull of three .;.
cables of equal diameter could slip oetw'een the two others and'cause s
them to' wedge in the condult. By3 definition this results in a s sudden large increase in tension and.the pull would;be stopped. If not, the tensicn would incr,ase to the point where either.the pulling line breaks or the insulation is crushed or deformed, thereby releasing the tension and rendering the cable useless.
A more detailed discussion on jamming may ti found in Paragraph 5.3.1 of the Cable Issues Walkdown Report (Reference 7). '
5.3.2 Conclusions The results of the Cable Issues Walkdown Report show that the possibility of damage to cables at BFN due to jamming is not of s concern. The two companion reports indicate..that the cables at SQN and BFN were installed under similar specifications and the materials are similar in durability with respect to jamming damage.
In addition, 45 conductors of,the same kind were HVDC tested at SQN without any failures.
5.3.3 Recommendations 1
No further corrective action is required for the issue of cable jamming at BFN.
5.4 Vertical Cable Supports 5.4.1 Issue Gescription ;
The issue of vertical ca' Ele supports addresses concerns regarding cable damage due to excessive strain resulting from improperly-supported cables in a vertical section.of condult. Of special concern are instances where a conduit fitting, box, or termination device is located at the top of a vertical section of a conduit which can result in damage to cable jacket and insulation due to the cable being forced to conform to sharp changes in direction at edges of the fittings. A detailed description of the vertical cable supports issue is presented in the Cable Issues WalkdoWn Report (Reference 7) paragraph 5.4.1.
The issue of vertical cable supports at BFNP has been addressed by performance of inspection walkdowns and bv comparison of BFN installation requirements and practices and cable materials to thore utilized at SQN to determine applicability of SQN cable te: ting. l 1
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5.4.2 Conclusions Analysis of the SQN csble tests for the vertical cable supports
.lssue and the Materials Evaluation Report reveals that the SQN tests are not applicabl( td BFN due to differences in cable insulation materials.
The Cable Installation Requirements Report (Reference 5) shows the requirements for-vertical' cable supports were not,in effect at either BFN or SQN until after commercial operation of both plants, therefore the cables were installed under similar conditions.
The Cable Issues Walkdown Report identified a potential for cable damage due to this issue. Also the walkdown sample did not include medium voltage cables.
5.4.3 Recommendations Based on the walkdown results for the inspected cable, it is recommended that all conduit containing medium voltage (5 kV and i above) Class 1E cables be walked down to verify that vertical I sections are properly supported to the current TVA' General Construction Specification G-38 criteria. Vertical sections of l cable not properly supported should be HVDC tested at the ;
maintenance voltage levels specified in IFEE Standard 400 and -'
supports added if the cable passes the test. This recommendation is based on the increased potential for electrical fault in'these cables due to the higher voltage stresses that could occur at 1 jacket / insulation deformations. This is a pre-restart recommendation. ,
l With respect to low-voltagk power and control .ctrcuits, it 'Is '
recommended that the original walkdown effort described in the Cable i Issues Walkdown Report (Reference 7, paragraph 5.4.2) be continued.
This will identify situa.tlons with cable deformations or substantial strain on cables in a condulet or similar fl.tting. These cables should be tested by insulation resistarice tekting ?n accordance with IEEE Standard 690 (see Paragraph 1.3, "Approhch" fcr the reservations about high-voltage de testing) and supported if the '
cable passes the test. This recommendation is post-restart.
However. it is felt by the authors of this report that TVA management shouid pursue resolution of this matter within a reasonable time frame of two years. The authors of this report feel that the recommendation for post-restart completion of the walkdown of low-voltage power and control cables in vertical runs'is justified for the following reasons:
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1 Low-voltagepowerandchntrolcablesgenerallyoperate-ator '
below temperature ratings,.below voltage ratings, and with low-voltage stress.
1 Multi-conductor control cables have the protection of sheaths 'and the added protection of binders.
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The major area of concern is the effect of.a DBE on thermoplastic insulation in vertical run situations, with condulets at the top and located in containment and steam tunnel areas. All cables located in the three worst case harsh environment areas (Drywell, !
, steam tunnel and heat exchanger rooms) and required for the mitigation of a design basis event that creates a harsh environment shall be replaced prior to restart in conformance i with presently applicable standards and.specif1 cations. (See ,i References 23-26.) l TVA has in place a program that would identify an adverse trend of cable failures thaticould result from insulation damage due to inadequately supported cables in vertical condult. l 1
5.5 Cable Bend Radii l 5.5.1 Issue Description The Cable Bend Radil issue' addresses the concern regarding bending j of cables beyond a specified limit. Cable manufacturers have i assigned minimum bend radius values to preclude any possibility of damage to the cable. The effects of exceeding the bend radius are different for medium (5 kV and above)-than for low voltage power, control and instrumentation cables. This is discussed further in the Cable Issues Walkdown Report (Reference 7, paragraph 5.5.1). l
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5.5.2 Conclusions The Cable Issues Walkdown Report revealed cases of cable bend radius )
violations. Violations were found in .instrunantation, control, and l power cables. In general, any degradation of instrument cables due to bend radius deficiencies will be detected as a-result of routine i instrument calibration and' maintenance. Therefor 0, no corrective I action for these cables is necessary. 1 Low voltage power and control, as well as instrumentation cables, which exceed manufacturer's recommended bend radius are not likely to experience failures other than of a random nature since they-generally operate below temperature ratings,' voltage ratings, and with low voltage stress. Medium voltage cables which exceed bend radius limits are of concern due to the possibility of corona discharge initiated failure.
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5.5.3 Recommendations Based on tne results of the Cabla. Issues Walkdown Report (Reference 7, paragraph 5.5.3), the comparison of materials-in the Haterials Evaluation Report (Reference 6) and the Cable Installation Requirements Report (Reference 15) the recommended action for closure of the cable bend radius: issue is the performance of a walkdown of Class IE medium voltage cables. This walkdown should inspect these medium voltage cables using G-38 requirements as acceptance-criteria. Any cables which do not meet this criteria will be technically justified or replaced to ensure compliance with G-38 requirements. This is a pre-restart recommendation.
5.6 Pulling Through 90 Degree Condulets ard Mid-Rua Flexible Conduit 5.6.1 Issue Description According to the SQN TER (Reference 1), cable being pulled through flexible conduit is subjected to additional sidewall pressures due to the reduced internal surface area caused by the convolute structure of the flexible conduit. The TER also states that a cable that stops moving during a pull will tend to have its surface locked into the corrugations of the flex conduit, causing additional stress on the cable when the pull is resumed. The TER further states that sidewall pressure is substantially increased when a cable is "pulled under tension around the inside edge of a 90 degree condulet".
5.6.2 Conclusions The results of the walkdown (Cable Issues Walkdown Report, ,
Reference 7, paragraph 5.6.3) indicates minimal use of mid-run flexible conduit at BFN. Where flexible conduit was used, it was observed at locations adjacent to a pull point that would have allowed the flexible conduit to be installed over the cable for the initial pull. No indications of cable damage from pulls around condulets were observed.~ Discussion with BFN electricians verified 1 that condulets were being used as pullpoints.
5.6.3 Recommendations i Based on the walkdown results, no further corrective action is required for this issue.
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6.0
SUMMARY
The cable installation concerns at BFN. arose from a review of concerns at other TVA facilities. An examination of the evolution of the requirements which form the basis for the concerns indicates that many were not in effect, and would not have clearly been agreed upon by a majority of cable installation experts, at the time of BFN construction.
Furthermore, no basis was found for concluding that the later requirements were determined by the industry to require backfit on previous plants. This appears to be justified by the excellent operating history of electrical cables with respect to installation concerns. This is true not only in the nuclear , industry as a whole but also specifically at BFN, which in its decade of operation has a reported random failure rate for control and low voltage power cables near zero. NUREG/CR4257, Appendix B (Reference 27) "Representative Failure Modes and Causes for Cables Screened from LER Data Base" does not show any failures caused by the type of cable installation deficiencies listed in the TER.
The above information notwithstanding, TVA implemented an extensive and comprehensive review of each of the concerns as it applied to BFN.
Mindful of the concerns and cautious of many. senior members of the cable industry and the NRC Advisory Committee on Reactor Safeguards, the BFN program was structured to provide a firm basis for its conclusions j without resorting to the type of high potential testing performed at i SQN. However, it was recognized that the SQN program represented one of I the most indepth evaluations of installed cables performed in-the nuclear industry.
The BFN cable resolution program was therefore designed to utilize the knowledge and results gained in the SQN experience. This information was applied to BFN, however, only when technically justifi'ed from an individual review on each issue. This review included an examination of the installation practices and procedures utilized at each plant during construction as well as the properties of the cable materials with respect to susceptibility to installation damage. In addition, an extensive walkdown was perform'ed to gather BFN specific installation information and to provide a basis for determining.the comparableness i between BFN and SQN. l l
The results of the BFN program represent an effort equal to the SQN program in the depth and breadth of physical and literature examination 1 and technical support. The walkdown effort alone far exceeded that on j which the original SQN TER concerns were based, both in the extent of the attributes, and the scope of the installations, examined.
This report has demonstrated the integrity c# cables installed at BFN.
Implementation of the recommendations contained herein, along with 'he separate upgraded installation procedures recently issued, will ensure that this integrity is maintained.
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7.0 REFERENCES
- 1. ' Letter from B. J. Youngblood -(USNRC) to S. A. White (TVA) dated March 9, 1987 (A02 870312 023).
(L44'870731 803).
' dated March 15, 1988 (843 880617 701).-
- 5. Project Topical Report Cable Installation Requirements dated June 17, 1988 (B22 880617 015).
- 6. Materials Evaluation and Comparison of Safety-Related Cable and Conduit Materials Used at-Sequoyah and Browns Ferry Nuclear Plants,-
Revision 1. June 1988~(B22.880617 017).
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- 7. Cable' Issues Halkdown Report,' Revision 1, June 1988 (822 880617 018).
- 8. Underground Systems Reference Book, Copyright 1957 by the Edison
, Electric Institute, New York, NY. '
- 9. Pipe-Line Design fhr Pipe-Type Feeders, R. C. Rifenburg, Paperf53-389 Presented at the AIEE. Fall General Meeting, Kansas City, MO, November 2-6, 1953 (843 880617 702).
- 10. The Simplex Manual, Copyright 1959, Simplex Hire & Cable Co...
Cambridge, MA (843 880617 703).
- 11. Working Group Report for Design and Installation of Hire and Cable Systems in Power Generating Stations, Paper 71 TP 83-PHR presented at the IEEE~ Hinter Power Meeting, New York, NY, January 31-February 5, 1971 (843 880617 704).
- 12. Installation Guide for Raychem Flamtrol Insulated Instrume'tation, n Control and Power Cables, and Coaxial and Triaxial Cables, Raychem Corporation,' January 1976 (843 880617 705).
- 13. Cable Installation Manual, Publication PC-7600, The Anaconda Company, 1976 (843 880617 706).
- 14. Engineering Data for Copper and Aluminum Conductor Electrical Cables,-
Bulletin EHB-78, The Okonite Company,. 1978 (843 880617.707).
- 15. Installation Practices for Cable Raceway Systems, The Okonite Company, May 1982 (843 880617 708).
- 16. Kerite Installation Data, The Kerite Company, March 1979 (843 880617 709).
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- 17. Cable Installation Guide, Eaton Industrial Polymer Products Division, Eaton Corporation, Revision 0, September'15, 1982 (843 880617 710).
- 18. Essex Control Cable Engineering Handbook, Copyright 1974. Essex International, Inc., Power Conductor Division'(843 880617 711).
- 19. Memorandum.from J. B. Hosmer, SQN Project Engineer, to M. R. Harding, Manager, Site Licensing Staff, dated November 13, 1987 (B25 871113 046).
- 22. Memorandum from H. A. Taff to H. S. Raughley dated June 4, 1986 (E13 860604 001).
- 23. QIR EQP86016 Rl; Quality Information Release from R. S. Martin to D. F. Faulkner dated November 20, 1986; The Environmental Qualification of BFN Unit 2 RHCU Heat Exchanger Room Cable.
- 24. QIR EQP86019 Rl; Quality Information Release from R. S. Martin to D. F. Faulkner dated November 20, 1986; The Environmental Qualification of BFN Unit 2 Steam Tunnel Cable.
- 25. QIR E0P87063 R2; Quality Information Release from R. S. Martin to D. f. Faulkner dated May 4, 1987; BFN Unit 2 Cables Potentially Requiring Replacement Under ECN P3208.
- 26. QIR EQP86011; Quality Information Release from E. D. Hill to D. F. Faulkner dated August 5, 1986; The Environmental Qualification of BFN Unit 2 Primary Containment Cable to 10CFR50.49.
- 27. NUREG/CR4-257, Inspection Surveillance and Monitoring of Electrical Environment Inside Containment of Nuclear Power Plants with Application to Electrical Cables.
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K Enclosure 2 .!
List of Commitments
- 1. Conduit containing medium voltage Class .1E cable wl'll be walked down tol <
verify that vertical sections of cable are properly' supported in ,'
accordance with current G-38 acceptance' criteria. Cable bend radit which do not meet the G-38 criteria will be technically justified or replaced to ensure compliance with G-38. Vertical sections of cable not properly .
supported will be, HVDC tested at the maintenance . voltage levels specified in IEEE Standard 400 and supports added if the cable passes the test. The above actions will be completed before restart of each respective unit on those cables required for operation of the unit.
- 2. Conduits containing Class lE low voltage power and control circuits will be walked down to identify vertical cable : support situations with cable deformations or substantial strain on cables in a condulet or similar fitting. Vertical sections of cable not properly supported will be tested by insulation resistance testing in accordance with IEEE Standard 690 and resupported. The above is scheduled to be completed on the' cables associated with each unit within approximately two years of restart of the respective unit.
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