ML20212C038
| ML20212C038 | |
| Person / Time | |
|---|---|
| Site: | Summer  |
| Issue date: | 10/19/1997 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20212C035 | List: |
| References | |
| NUDOCS 9710280360 | |
| Download: ML20212C038 (8) | |
Text
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k S UNITED STATES NUCLEAR REGULATORY COMMIESION WA$HINGTON, D.C. 30046 4001
(*ess e ENCLOSURE SAFETY EVALVATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION DEVIATION FROM FACILITY OPERATING LICENSE CONDITION, PARAGRAPH 2.C.(18) -
FIRE PROTECTION OF SAFE SHUTDOWN CAPABILITY VIRGIL C. SUMMER NUCLEAR STATION DOCKET NO, 50-395
1.0 INTRODUCTION
Appendix R. " Fire Protection Program for Nuclear Power Facilities Operating Prior to January 1, 1979," to Title 10 of the Code of Federal Reculations (10 CFR) Part 50, establishes fire protection features required to satisfy General Design Criterion 3. " Fire protection." of Appendix A to 10 CFR Part 50 with respect to certain generic issues for nuclear power pl6nts licensed to operate prior to January 1, 1979. By letter dated October 17, 1996, as supplemented by letter dated Ma 1, 1997, South Carolina Electric & Gas Company, the licensee for Virgi C. Summer Nuclear Station, (VCSNS) requested a deviation from its commitment to meet th> technical requirements of Section 1,II.G of Appendix R to 10 CFR, Part 50, to the extent that it. specifies the separation of certain redundant safe shutdown circuits with fire-rated barriers. Alternatively, the licensee proposes to use Rockbestos Firezone R Appendix R cables to replace portions of certain shutdown circuits. The staff issued a request for additional information (RAI) by letter dated March 17, 1997. By letter dated May 1, 1997, the licensee resoonded to the RAI. The licensee supplemented its response to the staff's RAI by letter dated September 17, 1997, 2.0 DEVIATION REQUESTED Paragraph I!!.G.2.c of Section III.G. " Fire protection of safe shutdown capability." of Appendix R to 10 CFR Part 50, specifies:
Enclosure of cable and equipment and associated non-safety circuits of one redundant train in a fire barrier having a 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> fire rating. In addition, fire detectort and an automatic fire suppression system shall be installed in the fire area.
The licensee requested a deviation from its commitment to meet these requirements to allow the use of fire resistant cables instead of enclosing the cables in fire barriers having a 1-hour fire resistance rating. The-licensee proposed to use Rockbestos firezone R pendix R fireproof cable to protect circuits that are required for meeting pendix R shutdown criteria.
A deviation is needed because the Firezone R ca es do not meet the literal requirements of Section III.G of Appendix R.
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1 2 I 3.0 -DISCUSSION The Rockbestos Firezone R Appendix R fireproof cable has been tested by Unde writers Laboratories Inc. (UL) in order to provide data on the electrical characteristics of the fire resistant cable under controlled fire exposure conditions and during an extended cool down period. The testing program, which is documented in Underwriters Laboratories Report en Fire Resistant cables. File R10925 1, dated April 10, 1984, investigated fire ,
resistant electrical cables installed in trays, conduits and air drops beneath a floor / ceiling assembly. Several firezone R cables were tested and were subjected to a 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> fire endurance test with the furnace temperature ;
controlled in accordance with the ASTM Standard E-119. " Standard Test Methods for Fire Tests of Building Construction and Materials." Imediately before beginning the large scale fire test, the cables (which included 3/C #14 AWG :
and 3/C #6 AWG both sheathed and unsheathed) were energized with a steady- !
state current. Each cable remained energized with a steady state current of '
about 4_ amperes throughout the fire endurance test exceat for a 10 second
, period immediately preceding an inrush current test witi approximately 17 amperes. Following the fire endurance test, the cables were (1) de energized and subjected to a water hose stream test, (2) re-energized with steady state electrical currents throughout a 93 hour0.00108 days <br />0.0258 hours <br />1.537698e-4 weeks <br />3.53865e-5 months <br /> cooldown period except for a 10 second period just prior to the a) plication of 4 supplemental inrush current tests. (3) subjected to a second lose stream test, and (4) subjected to a final inrush current test. The cables were monitorea for electrical feults during the test. An automatic data logger scanned each circuit and provided a printed record to show electrical faults. The analysis of this printed record by UL concluded that no electrical faults occurred. Further, analyses of the measured values recorded for electrical currents, insulation resistances, and ,
dielectric withstand voltag s provide additional evidence that the tested cables remained electricall functional during the one hour fire endurance test and during the extende cooldown period.
The cables to be installed at VCSNS are larger gauge (2 AWG vs. 6 and 14 AWG) than those tested by UL. Mechanical and electrical comparisons of cable r performance are presented below.
4 4.0 EVALUA110N 4.1 Mechanical Performance Comoarison During the UL fire endurance test, the Firezone R cables present in the cable tray retained their mechanical strength and supported the dead weight of the
" fuel load" cables and failed tray system - '
In the case of the Firezone R cable'to be installed at VCSNS in a cable tray, the larger 2 AWG cable being used would be expected to exceed mechanical
- strength of the smaller 6 and 14 AWG cable used in the UL test. A total of nine 3C 2AWG fire' rated cables with stainless steel (SS) sheath (armor) will be installed in cable tray 3088. Cable tray 3088 transitions from 18" wide to 12" wide along its route. In comparison, a 24" wide cable tray was used in the UL test with approximately 41.5 percent cable fill including the potential
3 fuel contributing cable. Cable tray 3088 does contain conve1tional IEEE 383 cable in the tray with Firerone R cable and is less than fully loaded.
Considering the larger 3C 2AWG SS sheathed cables and smaller tray system and lower fill level of conventional cable, the mechanical performance would be expected to exceed that of the tray in the UL test report.
The stainless steel ties used in the UL test will not be used in the VCSNS installation. This omission would minimize the stress on the Firezone R cable during a fire cMdition should the cable tray system fail in the fire as the Firezone R cable would only be carrying its own weight.
The largest conduit used in the UL fire test was 3" diameter. The Firezone R cable to be installed by the licensee will be routed in 3-1/2" diameter and 4" diameter steel galvanized conduit. The mechanical aerformance of the cables in these conjuits would be expected to exceed tlat of the UL fire tests !
on the same basis as that described above for cable tray 3088. '
Based on the above, the mecharical performance of the Firezone R cables to be installed by the licensee is considered to be bounded by the UL fire test results.
4.2 Electrical Performance In the fire endurance test conducted by UL. the cables were considered to remain electrically functional during the 1+ hour duration of the test.
Numerous electrh.al checks were satisfactorily performed on cables during the fire test. The material construction of the 3C-2 AWG cable is equivalent to that of the cables used in the UL fire tests only ir, that they have the same number of conductors. Otherwise. the cable has a larger gauge conductor and a greater insulatic, thickness. The 3C-2 AWG cable contains a substantially greater heat sink than the cables in the UL test due to the increased thermal mass Due to the larger mass, greater heating of the copper conductor can occur. and -
this could possibly subject the cable jacketing and insulation to a greater heat flux during a fire exposure. This could lead to premature degradation of 1 the cable insulation.
The licensee's design uses two to three parallel conductors as individual leads. With exception to the Firezone R cables being used for DGE4A and DGE32A, an internal cable fault between conductors would be inconsequential.
DGE4A end DGE32A use a single 3C Firezone R cable while the remaining cables use a single thrce conductor cable for each required lead, Since the ,
installation of these cobles uses this multi-cable approach in all cases !
except DGE4A and DGE32A, a fire induced conductor to conductor fault within those cables will not necessarily result in the loss of the cable's functionality In the case of DGE4A and DGE32A. the replacement Firezone R cable is significantly oversized in comparison to the conventional cable previously used (1-3-2 AWG vs. 1-2-10 AWG and 1 2-6 AWG).
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l 4- i 4.3 Fire Hazards Analysis Cable tray 3083, currently wrapped in Thermo Lag 330-1, is a> proximately 80 feet long and runs both horizontally and vertically through :1re Sub Zones IB-25.1.2 and 18 25.6.2. Fire Sub Zone IB 25.1.2 is located in the western portion of the Intermediate Building and extends from the floor at elevation 412 to the underside of the floor at elevation 436. This sub zone contains mainly 'B' train equipment and cabling. For a fire in this sub zone, shutdown would be achieved from the control room using 'A' train equipment. Fire Sub .
Zone 18 25.6.2 is also in the western portion of the Intermediate Building and extends from the floor at elevation 436 to the underside of the floor at
- elevation 463. This sub zone contains mainly 'A' train equipment and cabling.
For a fire in this sub zone, shutdown would be achieved from the control room using 'A' train equipment. There is on open hatch between Fire Sub Zones IB- ,
25.1.2 and 18 25.6.2.
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four safe shutdown 'A' train cables in cable tray 3088 within Fire Sub Zone IB 25.6.2 need to be protected to ensure that they remain functional during a ;
fire in Fire Sub Zone 18-25.1.2 due to the open hatch. ,
Cable Tray 3088 is located near the open equipment batch. Therefore, there is .
a concern for >otential damage to the four A train safe shutdown cables in '
this tray (wit 11n zone 1B 25.6.2) as the result of a fire within Fire Sub Zone 18-25.1.2. However, as explained below, there is reasonable assurance that a fire within Fire Sub-Zone IB 25.1.2 will not damage the 'A' train cables needed for safe shutdown that are located within Fire Sub Zone 18 25.6.2.
provided the cables in cable tray 3088 are adequately protected.
The fire loading in both the sub-zones is moderate, and consists mostly of cable insulation. The physical characteristics of the zones involved will not support the development of a hot gas layer at the ceiling during a fire due to the large area involved, high ceilings and an open ecuipment hatch between the elevations. In the unlikely event that a fire shoulc occur. an automatic fire :
detection system which alarms in the control room is arovided for these fire i
- zones. The fire detection system will also actuate tie automatic preaction suppression system which partial coverage for SubZone provides full coverage 18-25.6.2. forthe including Sub cable Zone IB-25.1.2 tray locationsand near the equipment hatch. In addition. hose stations and portable fire extinguishers are provided for manual fire fighting activities in both sub-zones.
Cable tray 3088 contains 14 cables, four of which are required for safe shutdown. In lieu of separation, through the provision of a 1-hour rated fire barrier and automatic suppression and detection. the licensee 3roposes to provide Rockbestos Firezone R fire rated cable (in the open ca)le tray) for the four-safe shutdown circuits. The existing automatic suppression and detection systems will be maintained. !
Conduit XX-7177A is a aingle 3" diameter horizontal rigid steel conduit approximately 5 feet long and 11 located in the south end of room CB 12-04 approximately 9 feet above floor level. This conduit will be replaced by 2 1
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5 conduits, a 4" diameter conduit (XX 7637A) and a 3.5" diameter conduit (XX-7638A). lhese conduits will be routed from the west wall of the Intermediate Building to the west wall of room CB 12 04 through fire rated penetrations, similar to the original XX 7177A conduit. The conduits will contain 4 cables.
three of which are required for safe shutdown. The licensee proposes to install Rockbestos firezone R cable for the three safe shutdown circuits.
The conduits will reside in fire area CB 2. which is the 'B' train east basement chase of the control building located at elevations 412' and 425*.
It also includes the east )ortion of the electrical pit at elevation 400'.
The area mainly contains ' r train cabling and no equipment. The three safe shutdown 'A' train cables in the conduits and within fire area CB 2 need to be protected so that they remain functional during a fire.
The area has a very high fire loading, and is primarily composed of cable insulation and stored combustibles. The physical characteristics of fire area CB 2 does not support the development of a hot gas layer at the elevation of the conduits until substantial fire growth has occurred. The fire area has a small floor area; however, the ceiling height is approximately 24 feet. In the unlikely event that a fire should occur, an automatic fire detection system which alarms in the main control room is provided in the fire area.
The fire detecticn system will also actuate an automatic preaction suppression system which provides full coverage in the area. Hose stations and portable fire extinguishers are available for manual fire fighting activities.
4.4 Sbonorts s The staff was concerned a fire could directly damage the cables or damage structures surrounding and/or supporting the cables which could damage the cables themselves. This could affect the ability to achieve and maintain post-fire safe shutdown.
4.4.1 Cable Trav 3088 in the unlikely event that a fire should occur, the combustible quantity / fire size would have to be sufficient to result in temperatures in excess of 1058'F at more than one unprotected horizontal support location to result in damage to the tray support system (i.e.. failure of a single horizontal support, all of the vertical supports or a single section of the tray would not result in mechanical failure of the entire tray system).
The UL fire test demonstrated that a limited mechanical failure of the tray system can occur without compromising the capability of the cable. Tray 3088 runs over the normal access route to the battery and battery charger rooms located on the 412 elevation. Such route would normally not have a high fire loading. It is unlikely therefore, without a high fire loading. that a fire of the necessary .ceverity could develop and damage or degrade the structura; integrity of the cable tray support system. Should a fire occur. there is a reasonable assurance that the automatic preaction sprinkler system would
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operate, cooling the supports and controlling the fire. Therefore there is reasonable assurance that the tray's support structure would not fail in the event of a fire.
4.4.2 Conduits XX-7637A and XX-7638A The area above the new 3-1/2" and 4" conduits is open to the ceiling. A vertical cable tray and its support structure are the only significant items located above the new conduit locations. The support structure for the tra is located approximately 6 feet above where the conduit is to be installed.y In the event of a fire, the support could fail and impact the conduits containing the Rockbestos Firezone R cables. However, given the fire hazards
) resent in the area, it is ur',ikely that the cable tray suppcrt would be leated to the point of failure. In addition, even in the unlikely case of cable tray support failure leading to the impacting of the cable tray on the conduits, the 3 1/2" and 4" steel galvanized conduits would be expected to absorb the impact of such an event without failure.
4.5 Cable Size and Loding The size difference between the tested cables (#6 AWG) and the cables proposed to be installed (#2 AWG) is appreciable. In a request for additional information and in discussions with licensee engineering personnel, the staff questioned whether or not the cables that the licensee proposes to install are bounded by the UL fire test, used to justify the 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> rating of the cables, fhe concern ex)ressed by the staff was the degradation of cable insulation due to additional 1 eat flux present in the larger co)per conductor material of the larger cable. This could lead to a failure in tie functionality of the cable.
The UL fire test energized the cables tested with a steady : tate ac electrical current. The cables were also energized with a dc voltage and monitored for electrical faults. The steady state current measured in the 3/C #6 AWG cables was 30 Amps (A), while in-rush current tests energized the cable with 118 A for 30 seconds.
The licensee proposes to install 13 total Firezone R cables to replace ths foliowing cables carrying a continuous load current of between 1 and 10 Amps and a nominal voltage of 125 Volts: DGE4A, DGE14A, DGE32A, ESE31A, ESE32A, and ESE33A. For cable EMC83A the licensee has proposed to use three 3 conductor Firezone R cables. size'2 AWG (3/C 2AWG) to carrying a continuous total lead current of 94.6 A at a nominal voltage of 480 Volts. The circuit will utilize three conductors per phase, whicn means that each conductor of each )hase will carry approximately 30 amps, The size 2AWG Rockbestos Firezone R ca)1e is rated for 85 amperes with an 1800'F conductor temperature in a 1700'F ambient (fire condition). The Firezone R cables that the licensee has proposed to use to replace portions of their safe shutdown circuits fall within the design parameters of the cable.
Postulated fires in the Fire Sub-Zones in which the Firezone R cable is to be installed would most l1kely be slowly developing cable fires involving cable insulation. Such a fire would generate a significant amount of smoke in its l
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early stages. The automatic fire detection system in conjunction with the automatic suppression system provides reasonable assurance of rapid detection and control of a fire in its early stages. Should the automatic suppression system fail to fully extinguish th fire, the detection system provides reasonable assurance that there wiil be an early response by the plant fire brigade to extinguish the fire manually prior to significant propagation.
Based on the automatic detection and preaction suppression systems coverage provided for the cables in the fire sub zones, and fire brigade response for manual fire fighting activities. there is reasonable assurance that postulated fires in the fire sub zones discussed would be detected, controlled, and extinguished prior to temperatures rising to a level that could challenge the structural support capabilities of the fire resistant cables cable tray network, and overhead conduits.
Following from the discussion above, and on the bases of the ASTM E119 test results for the 3/C #6 AWG Firezone R cable as contained in the UL report, and the proposed installation configurations for the cables, the staff concludes that the electrical functionality of the proposed 3/C #2 AWG Firezone R cables would be equivalent to that whicn was tested in the UL fire test. Further, the staff concludes that the Firezone R cables would provide an equivalent electrical functionality as would be provided by enclosing cables in a 1-hour fire rated barrier for the licensee's proposed application with the exception noted above.
As part of its evaluation, the staff reviewed similar exemption and deviation requests and found that it had previously approved the use of Firezcne R cables in lieu of 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> fire rated barriers at other facilities.
The Rockbestos firezone R Appendix R fireproof cables meet the unrierlying purpose of Appendix R Section Ill.G.2.c criteria for a 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> fire barrier, for the cables mentioned herein, which is to ensure that one train of systems nccessary to achieve and maintain hot shutdown conditions is free of fire damage.
S.0 CONCLUSION On the basis of the its evaluation, the staff concluded that there is a reasonable assurance that replacement of the following cables with Firezone R cables as proposed by the licensee will allow these cables to remain functional during postulated fires at Summer and. therefore, postulated fires would not prevent plant operators from achieving and maintaining safe shutdown:
DGE4A DGE14A DGE32A ESE31A ESE32A ESE33A EMC83A 1