ONS-2015-058, Oconee, Units 1, 2, and 3 - TIA 2014-05, Potential Unanalyzed Condition Associated with Emergency Power System

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Oconee, Units 1, 2, and 3 - TIA 2014-05, Potential Unanalyzed Condition Associated with Emergency Power System
ML15139A049
Person / Time
Site: Oconee  Duke energy icon.png
Issue date: 05/11/2015
From: Batson S L
Duke Energy Carolinas
To:
Document Control Desk, NRC/RGN-II
Shared Package
ML15139A018 List:
References
IR 2014007, ONS-2015-058, TIA 2014-05
Download: ML15139A049 (26)
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Text

ENERI~GY, Scott L. Batson Vice President Oconee Nuclear Station Duke Energy ONOI VP I 7800 Rochester Hwy Seneca, SC 29672 o: 864.873.3274 f 864.873. 4208 Scott.Batson@duke-energy.com ONS-2015-058 May 11,2015 U.S. Nuclear Regulatory Commission Document Control Desk Washington, D.C. 20555

Subject:

Duke Energy Carolinas, LLC Oconee Nuclear Station, Docket Nos. 50-269, 50-270 and 50-287 TIA 2014-05, Potential Unanalyzed Condition Associated with Emergency Power System

References:

1. Oconee Nuclear Station -NRC Component Design Bases Inspection Report 05000269/2014007, 05000270/2014007, and 05000287/2014007, dated June 27, 2014, ADAMS Accession No. ML14178A535.

The 2014 Oconee Component Design Basis Inspection (CDBI) is documented in the Reference 1 NRC Inspection Report. This report initiated Unresolved Item (URI) 05000269,270,287/2014007-05, Potential Unanalyzed Condition Associated with Emergency Power System, which describes NRC concerns related to the design and installation of 13.8 kVac emergency power cables and 125 Vac control cables within the Keowee underground concrete raceway system (Trench 3). As noted in the report, Region II has requested assistance from the Office of Nuclear Reactor Regulation (NRR) via a Task Interface Agreement (TIA) to review the emergency power system licensing basis to determine the acceptability of the design. The TIA is identified as TIA 2014-05.During the 2014 CDBI, Duke Energy staff met with the NRC inspection team on 4/28/2014 to discuss the cable design and installation.

This meeting was also attended by supporting NRR personnel and management and Region II DRS managers.

During this meeting Duke Energy discussed the planned performance of cable testing and the NRC expressed interest in reviewing the results of any such testing.The NRC staff briefed the Oconee staff on October 7, 2014, pertaining to the TIA request contents as required by NRR Procedure COM-106, Task Interface Agreements, Revision 4, Section 6.1.4.Subsequent informal discussion between Duke Energy management and NRC management confirmed continued interest in making cable testing results available to the NRC. Duke Energy recognizes that these results are an important factor to the NRC in helping to assess the URI with regards to compliance with the regulations and the Oconee licensing basis and for assessing the risk significance of any performance deficiencies that may ultimately be identified. 0 www.duke-energy.com ONS-2015-058 TIA 2014-05 May 11, 2015 Page 2 Oconee Units 1, 2, and 3 were granted Construction Permits in 1967 and Operating Licenses were issued in 1973, 1973, and 1974 respectively.

10 CFR 50 Appendix A, General Design Criteria (GDC)were issued as draft in 1967 and final in 1971. 10 CFR 50 Appendix B, Quality Assurance Criteria, was issued as draft in 1968 and final in 1970. Various letters between Duke and the NRC during the late 1960s and early to mid-1970s addressed how these appendices, their associated industry standards and endorsing Regulatory Guides would be applied to Oconee's licensing basis. Oconee was substantially built before these appendices were issued.Duke Energy developed Attachment 1, Review of the Design and Installation of Medium and Low Voltage Cables in Trench 3 at Oconee Nuclear Station, which lays out the Oconee licensing basis as it pertains to the content of the TIA request that NRC briefed with the Oconee staff on October 7, 2014.Attachment 1 is provided to help the NRC with regard to Oconee's licensing basis that spans over 40 years of operation and includes numerous plant modifications, including the emergency power system cable configurations that are the subject of the TIA. Attachment 1 compares the Oconee Trench 3 cable configuration to the Oconee licensing basis and to various NRC documents pertinent to cable design and cable faults. A key point made in Attachment 1 is the difference between the Oconee single failure licensing basis and the single failure licensing requirements to which later plants were subsequently licensed.

Based on Oconee licensing basis documents, the Attachment 2 cable testing results, the properties of the Keowee generator impedance grounding system and the Operability Determination conducted for the Trench 3 configuration, Attachment 1 demonstrates that the Trench 3 cables are capable of performing their intended functions and comply with the Oconee licensing basis.Attachment 2, UL 1569 Impact and Crush Tests on Keowee Underground Trench Power Cables, contains the results of the cable armor testing conducted at the Okonite Company's High Voltage Laboratory in Paterson, New Jersey. This testing was performed to confirm the mechanical properties of the bronze tape shieldedl3.8 kVac emergency power cables installed in Trench 3. The testing demonstrates that the cable configuration with bronze tape shield provides adequate protection to perform as armored cable per Underwriters Laboratory Test 1569, Sections 24, 25, and 26.UL 1569 Section 24 impact testing was done on each of four cable samples. Impact strike tests consisting of a 50 lb. weight dropped 12" above the cable with the cable perpendicular to a 3/4-inch diameter steel rod. For each cable type, ten impacts tests spaced 12 inches apart were performed.

The acceptance criteria were no instances of electrical continuity between the cable conductor(s) and the metallic shield. The impact tests were performed on jacketed cable samples to reflect the cable as-installed configuration.

All samples exhibited a passing result, without any continuous or momentary failures.UL 1569 Section 25 crush testing requires 10 crushes per sample, with the cable between a steel plate and a 3/4-inch diameter steel rod. Per the UL standard, the compression force is continued until there is indication that contact has occurred between the circuit conductors, or between one or more of the circuit conductors and any grounding conductor, the armor, or both. The acceptance criteria were no instances of electrical continuity between the cable conductor and the metallic shield. All cable types passed the sustained crush tests. Additional electrical tests (not required by UL 1569) were performed consisting of pre-crush and post-crush Partial Discharge testing at multiples of system operation voltage. All cables passed the additional electrical tests.

ONS-2015-058 TIA 2014-05 May 11, 2015 Page 3 UL 1569 Section 26 crush testing involved four different cable samples and a series of crushes of increasing load, with the cable positioned between a steel plate and 3/4-inch diameter steel rod. For each cable type, ten crushes spaced 9 inches apart were performed with the force on each crush increased until cable failure, i.e., continuity detected between the cable conductors and ground. The measured force at failure ranged from 2,280 lbs. to >5,000 lbs. depending on cable sample. All of the samples passed the UL acceptance criteria of exceeding 2,000 lbs.Duke Energy has also arranged for fault testing of the subject 13.8 kVac cables, which is scheduled for the fall of 2015. The schedule for this testing was driven by several factors, including test facility availability, manufacturing of cable identical to the Oconee installed cable and fabrication of a concrete raceway section representative of the Oconee installation.

The fault testing is intended to confirm conclusions made concerning the fault mechanisms and their credibility in Trench 3. The scope of work involves simulated phase-to-ground and phase-to-phase electrical faults on 13.8 kV and 4.16 kV bronze armored-shield power cables as necessary to analyze the effects on other power cables and on interlocked armored control and instrumentation cables in the same trench. The test environment will be representative of the field conditions as depicted on drawings provided by Duke Energy. The fault testing plan includes subjecting the mock-up to a 3-phase bolted end connection fault and a series of single phase-to-ground faults Duke Energy will use this testing to validate that existing cable separation requirements will not result in any adverse interaction between the faulted medium voltage power cables and any non-faulted medium voltage power cables or low voltage control cables. The results of this testing will be used to update the Oconee UFSAR to specifically address the bronze tape shielded power cables.There are no new or revised regulatory commitments being made in this submittal.

Should the NRC require any additional information or desire to witness the upcoming cable fault testing, please contact Chris Wasik, Oconee Regulatory Affairs Manager, at 864-873-5789.

Sincerely, Scott Batson Vice President Oconee Nuclear Station Attachment 1- Review of the Design and Installation of Medium and Low Voltage Cables in Trench 3 at Oconee Nuclear Station Attachment 2 -UL 1569 Impact and Crush Tests on Keowee Underground Trench Power Cables for Duke Energy Carolinas, LLC ONS-2015-058 TIA 2014-05 May 11, 2015 Page 4 xc (with attachments):

Mr. Victor McCree Administrator, Region II U.S. Nuclear Regulatory Commission Marquis One Tower 245 Peachtree Center Ave., NE, Suite 1200 Atlanta, GA 30303-1257 Mr. Eddy Crowe NRC Senior Resident Inspector Oconee Nuclear Station Mr. James R. Hall NRC Senior Project Manager (File via E-mail)U.S. Nuclear Regulatory Commission One White Flint North, M/S O-8B1 11555 Rockville Pike Rockville, MD 20852-2746 Ms. Holly D. Cruz NRC Project Manager (File via E-mail)U.S. Nuclear Regulatory Commission One White Flint North, 12E1 11555 Rockville Pike Rockville, MD 20852-2746 ONS-2015-058 TIA 2014-05 Attachment 1 Review of the Design and Installation of Medium and Low Voltage Cables in Trench 3 at Oconee Nuclear Station (22 pages, including cover page)

Review of the Design and Installation of Medium and Low Voltage Cables in Trench 3 at Oconee Nuclear Station 1. Executive Summary During the 2014 NRC Component Design Basis Inspection (CDBI) the NRC team identified an unresolved item (URI) to determine whether a performance deficiency exists related to the configuration of electrical cabling installed in the Keowee underground concrete raceway. (Potential Unanalyzed Condition Associated with Emergency Power System [05000269, 270, 287/2014007-05 URI Section[1R21.2.b.v]).

The issue was reported to the NRC as a potential unanalyzed condition in accordance with 10 CFR 50.73 (a)(2)(ii)(B) as part of Licensee Event Report 269/2014-01.

The concern expressed in the URI is that the 13.8 kV medium voltage power cables could experience a fault and interact with the low voltage instrumentation and control cables in a manner that could adversely impact the control functions.

An element of this concern is the level of protection provided by the bronze tape shield on the medium voltage cables when compared to galvanized steel interlocked armor. Duke Energy's position is that the current design configuration meets design and licensing requirements for Oconee and will not create a condition that impacts the ability of the emergency power system to perform its intended function.Duke Energy is currently pursuing testing to further validate the acceptability of the current design. This testing is being performed in two phases. The first phase performed UL1569 'Metal Clad Cables' crush and impact tests of the medium voltage cables and was completed in February 2015. The phase one testing compared the bronze tape shielded cables to galvanized steel interlocked armored cables with respect to their physical protection via UL1569 testing sections 24 (impact testing), 25 (increasing crush), and 26 (direct burial crush). All of the cable types tested, including the medium voltage cables installed in the Keowee Underground Trench, met the performance requirements of the standard for the specified tests. See the 'Cable Testing' section below for more details on the testing to-date.The second phase of the testing will involve replicating a section of the Keowee Underground Trench in a lab setting and inducing faults on the various medium voltage cables while monitoring for any effects on the non-faulted cables. This fault testing is anticipated to take place in the 4 th quarter of 2015. The purpose of this testing is to further validate the engineering analyses that have concluded the power cables will not adversely interact with the control cables in the underground trench.This paper will address both the design of Keowee Underground Trench (Trench 3) and the associated licensing basis.2. Overview of the Cable/ Trench Configuration The Trench 3 Keowee Underground power path was installed in 2000-2002 as a refurbishment project to replace the original direct-buried cables connecting the Keowee Hydro Units (KHU) to Oconee Nuclear Station (ONS) for emergency power. The installation of Trench 3 addressed cable aging issues and improved equipment reliability.

Page 1 of 21 Trench 3 currently contains the following power and control cables relating to KHU operation:

1) 13.8 kV power cables connecting one KHU to the on-site emergency power transformer CT-4 2) 13.8 kV power cables connecting the KHU to the Protected Service Water (PSW) system switchgear located in the PSW building.3) 4.16 kV power cables connecting 1TC switchgear to KHU transformer CX 4) Low voltage I&C cables consisting of supervisory functions for both KHU, one train of KHU emergency start cables, and breaker control for the PSW KPF switchgear.

Trench Box Design Trench 3 consists of pre-cast steel-reinforced concrete boxes with removable covers and duct banks engineered to withstand earthquakes and tornado missiles, and to minimize water entry. Passive drains and inspection ports are provided at trench low points. Figure 1 below shows a typical trench box and cover.Figure 1: Keowee Underground Trench Section Pre-install Cable Design The 13.8 kV Keowee underground (KUG) feeder to transformer CT-4 consists of six single-conductor shielded power cables. The circuit consists of two conductors per phase. Each cable consists of a 750 Page 2 of 21 kcmil copper conductor, 15 kV nominal voltage rating at 173% insulation level (i.e. 25 kV phase-to-phase), ethylene propylene rubber (EPR) insulation, two layers of 10 mil bronze metallic tape shield/armor with an overall Hypalon jacket. The cables were procured as OA-1 per Duke Specification OSS-139.00-00-0010 from the vendor, Okonite.Standard design for Oconee power cables are jacketed galvanized steel interlocked armor over a three-conductor cable core. For the Keowee application, using a three-conductor cable with the resulting increased cable diameter vs. a single conductor cable for the lengths needed would have resulted in cable reels of unmanageable diameter, as well as bending radius and cable training issues. Additionally, multiple splices along the route from Keowee to CT-4 would have been required.Since it was desired to avoid or minimize splices on the circuits, consistent with the original direct buried Keowee to CT-4 installation, replacement single-conductor bronze tape shield/armor cables were selected.

There are no cable splices in Trench 3. In addition to providing the required metallic insulation shield for medium voltage cables, the bronze metallic tape/armor provides mechanical protection to the cable.The KUG 13.8 kV cables are conservatively designed with substantial margins in insulation rating (15 kV nominal with 173% insulation level for a 8 kV line-to-ground operating voltage) and metallic shield thickness of 20 mils vs the 2.5 mils required by ICEA/NEMA cable standards.

The additional shield thickness provides cable armoring from the effects of external mechanical damage (see 'Cable Testing'section below for further discussion).

The KUG feeder metallic shield also has a significant margin in ground fault current carrying capacity vs.clearing times of the protective elements.

The shield cross sectional area is approximately 62 kcmils which equates to an effective conductor size between #3 and #2 AWG. For the resistance grounded KUG feeder, the shield can sustain, without damage, a phase-to-ground fault for over 15 hours1.736111e-4 days <br />0.00417 hours <br />2.480159e-5 weeks <br />5.7075e-6 months <br /> compared to the 3.2 seconds required for the associated protective relaying and circuit breaker to detect and clear the fault.The 13.8 kV power cables connecting Keowee to the PSW system are cables of identical core construction to the KUG feed to CT-4.The nominal 5 kV 250 kcmil single conductor cables used for the feed from switchgear 1TC to the Keowee CX transformer are designed with the same shield/armor design of two wraps of 10 mils bronze tape as the 750 kcmil cables.The low voltage I&C cables at the bottom of Trench 3 consist of various multi-conductor designs and are all specified with galvanized steel interlocked armor.Figure 2 below shows a cross sectional view of one of the single conductor 750 kcmil power cables. The layers consist of 1) a Hypalon jacket, 2) two layers of 10 mil bronze tape, 3) EPR insulation at 173%insulation level, and 4) the 750 kcmil copper conductor.

Page 3 of 21 Figure 2: 750 kcmil power cable cross-sectional view 1. Jacket 2. Bronze Armor 3. Insulation

4. Conductor The black layers between conductor and insulation and armor are semiconductive layers.Trench Configuration, Installation, and Separation The KUG feeder cables were installed in accordance with site design and installation criteria.

The routing system consists of concrete trenches and duct banks. The power cables are installed on separate supports above the control cables. The power cables are laid on the horizontal Unistrut supports at four foot intervals and are secured with stainless steel tie-wraps.

The physical separation creates a minimum 5" of distance between the power and control cables. The supports are bonded by grounding conductors.

In addition, the shield/armor of each cable in the trench is grounded at the cable termination points. At cable crossover points where cable separation is decreased between power cables, a fire retardant refrasil wrap was installed on the cables. See Figure 3 below for a construction photo of the uncovered trench depicting the cable configuration/layout.

Figure 4 shows a construction photo of the configuration at a cable crossover point.Page 4 of 21 Figure 3: Keowee Trench 3 Uncovered Figure 4: Trench 3 uncovered with cable cross-over shown.Page 5 of 21 Cable Testing Extensive post installation commissioning tests were performed on the medium voltage power cables to ensure that the insulation system was free from damage or defects.Off-line sinusoidal power frequency Partial Discharge (PD) post-installation testing was performed on the CT-4, CX and PSW cables. No PDs were detected in the cables.Very Low Frequency/Tan Delta (VLF/TD) was performed on the 13.8 kV cables feeding the PSW building switchgear in accordance with IEEE 400.2 (IEEE Guide for Field Testing of Shielded Power Cable Systems Using Very Low Frequency (VLF) (less than 1 HZ). The VLF/TD testing indicated that the cable insulation was in the highest (i.e. "Good") classification per EPRI guidance, and that no further study or actions were required.Cable testing was performed in February 2015 by Okonite to compare the physical protection provided by a bronze tape shield against steel interlocked armor using the methodology in UL 1569 (Metal Clad Cables). Four cables types, including both types of power cables used in Trench 3, were tested as follows: Cable Type 1: " Cable

Description:

Single conductor cable, 750 kcmil conductor, 220 mils insulation with copper longitudinal corrugated shield* Used On: Fant underground path from the Duke power delivery dip-poles to the splice box outside PSW manhole 6* System Operating Voltage: 13.8 kV phase-to-phase or 8 kV phase-to-ground Cable Type 2: " Cable

Description:

Single conductor cable, 750 kcmil conductor, 260 mils insulation with two 10 mil layers of bronze tape shielding.

  • Used On: Keowee underground (Trench 3) path to transformer CT-4; Keowee underground (Trench 3 and PSW ductbank) path to PSW building; Fant underground (PSW ductbank) path from the splice box outside PSW manhole 6 to the PSW building" System Operating Voltage: 13.8 kV phase-to-phase or 8 kV phase-to-ground Cable Type 3: " Cable

Description:

Single conductor cable, 250 kcmil conductor, 140 mils insulation with two 10 mil layers of bronze tape shielding* Used On: Underground (Trench 3) path plant feed for Keowee station service transformer CX* System Operating Voltage: 4.16 kV phase-to-phase or 2.4 kV phase-to-ground Page 6 of 21 Cable Type 4:* Cable

Description:

Three conductor cable, #2 AWG conductor, 140 mils insulation with tin coated copper tape shielding and galvanized steel interlocked armor* Used On: N/A- this cable was tested to compare the crush test resistance of cable with steel interlocked armor of similar O.D. to the cables with bronze tape armor* System Operating Voltage: 4.16 kV phase-to-phase or 2.4 kV phase-to-ground The following UL 1569 (Metal-Clad Cables) tests were performed by Okonite: 1. Impact strike tests consisting of a 50 lb. weight dropped 12" above the cable with the cable perpendicular to a % inch diameter steel rod. For each cable type, ten (10) impacts tests spaced 12" apart were performed.

The acceptance criteria were no instances of electrical continuity between the cable conductor(s) and the metallic shield. All cable types passed the impact strike test. It should be noted that the impact tests were performed on jacketed cable samples to reflect the cable as-installed configuration.

2. Sustained crush tests of 1000 lbs. for 60 seconds with the cable between a steel plate and a 3/4 inch diameter steel rod. For each cable type, three (3) crushes spaced 9" apart were performed.

The acceptance criteria were no instances of electrical continuity between the cable conductor and the metallic shield. All cable types passed the sustained crush tests. Additional (not required by UL 1569) electrical tests were performed consisting of pre-crush and post-crush PD testing at multiples of system operation voltage. All cables passed the additional electrical tests.3. Continuously increasing crush tests with the cable between a steel plate and % inch diameter steel rod. For each cable type, ten (10) crushes spaced 9" apart were performed with the force on each crush increased until cable failure (i.e. continuity detected between the cable conductors and ground). The measured force at failure ranged from 2,280 lbs. to >5,000 lbs. depending on cable sample. All of the samples passed the UL acceptance criteria of exceeding 2,000 lbs.Post-implementation cable testing and evaluation per industry standards reflects the robust and conservative Duke cable design and construction.

The cable impact and crush tests recently performed by Duke Energy confirm that the bronze tape shield provides mechanical protection that meets or exceeds UL1569 'Metal Clad Cables' test sections 24 (impact testing), 25 (increasing crush), and 26 (direct burial crush) performance requirements.

Protective Relaying Scheme Potential Keowee Hydro Station generator ground faults are detected by ground overvoltage and overload/phase fault overcurrent protection relays.1) Ground Overvoltage (59GN) -monitors High Impedance Ground Impedance Voltage (proportional to current) and provides a sensitive, inverse time based clearing of line breakers for all ground fault conditions.

Page 7 of 21

2) Overload / phase fault (50/51) -monitors phase currents and provides inverse time-based actuation based on overcurrent (long-time) and phase fault (short-time) to protect the cables from overload or un-grounded load fault conditions.

The KUG uses a high impedance neutral grounding scheme on the 13.8 kV power cables to mitigate the damage by limiting the neutral current, limiting the transient overvoltage, and to provide a sensitive means of detection of faults. A ground fault on a 13.8 kV KUG cable would be limited to 17.6A. CT-4 is a Delta/Primary transformer and therefore it will not transfer any neutral currents in the primary.3. Response to General Concerns Cable Whip From magnetostatics, there are electromagnetic forces between two or more current-carrying wires.The potential effects of magnetostatics in Trench 3 during a fault condition were conservatively analyzed in Prompt Determinations of Operability (PDO) for PIPs 0-13-8748, 0-14-2965, 0-14-3190, and 0-14-5125, as well as calculations OSC-11013, OSC-11061 and OSC-11062.

Initial electromagnetic forces (i.e.cable whip) were calculated based on a formula provided in IEC 61914 (Cable Cleats for Electrical Installations).

The ANSYS finite element program is used to determine displacements due to those initial forces. The force time history is calculated using an Excel spreadsheet.

Therefore, this is a transient analysis in time, force, geometry and current. In both cases it was determined that the cable whip would not cause a consequential failure of either KUG control channel, thus the Emergency Power System Function would remain available via the Overhead Path.The Instrumentation and Control (I&C) cables have sufficient mechanical protection such that interaction with the 750 kcmil cables will not adversely affect the insulation integrity or the function of the armored cables. The I&C cables are shielded from the effects of induced voltage if the 750 kcmil cables are in close proximity or in direct contact. The results of the calculations concluded that a power cable would not be severed due to electromagnetic forces.Bronze Armor Protection As previously stated, the two layers of bronze tape provide mechanical protection for the cables. The specified 800% of the industry minimum thickness enables the insulation shield to function as armor.URS study ONS-17-05-100-001 Rev 0 (URS Deliverables for ONS 2014 NRC CDBI) analyzed the bronze tape parameters of material, thickness, width, and application against the armor requirements of ANSI/NEMA WC 74/ICEA S-93-639 (5-46KV Shielded Power Cable for Use in the Transmission and Distribution of Electric Energy). Revision 1 to the URS study further analyzed those same parameters against IEC 60502-2. Table 1 below contains the results of Revision 0 of the URS study. Table 2 below contains the results of Revision 1 of the study.Page 8 of 21 Table 1 Bronze Tape Parameters vs NEMA WC 74 parame o s Cable for H lieragrsl 1sMtallcm NEMA WC 74 Parameters Cable Specllcaboo Recluminsd P nutm evalueoin Juernlcauon TapOe AtMa Matmail Per section 7-3.3.2: Section 2.5 of Attachinelt I oT PsOM-316-45 ard CS- Equal The srpectllcaln requred a Normiagnleic tapes can be specii-aicatn OSS-0139.1O-it0010 ttu ,.639 (referto bronze metac armor tape.rnads of alurninum, brass. requires a MetallIc WNeWd Armor Attachenest lb tme whlch meets the NEMA bronza, culprw-r4cet., Mc, or Tape to be rmade of Normagnellic (lmiltes carte am standard.stalless steel. bronze- provided wiM 2 ryers, W bronze 'ape.Thickness Per table 7-12 the nourral Section 2.5 ofAttachimernt t o Petr 01-31,.498 and C-1 Equivalent The spectUcalton required a Uitf ess oa the broize tape pect cal ,.n a .--C 139n G n 1,593$ (rear to btorme metalc armor tape per cable diameter reqluires (2) tio ten ml tape layers. Altacfares 1). th thickness o 20 airs In total calculated per Aprpnix C, OCltue cable 'was (buo x 10 mls) mth meets the the armor nust be 20 mils. prwlvded w'th 2 layers o" NEMA Standard.p0 me Bronze lae mm Peg We 7-i11, Ste nomitnal Specilfcation Pe scorrespondence fror Equivatent, Having a Wer tape generally dtcutro the bronze tape contains no tape wt'th requirement Okortte the tape'ad.tti Is affects the overa flexiblty cf based oan the cable diameter 1.25 Inches (rEr to the carle ant makes managnl calculated per Appendix C, A.tactiment

2) the cable during Installation the aimor 05us be E.L75 more dScualt Per 053-tidies nohte s139.30-0D-Ot}lO.

the appitalln reqireements orame tape are Intended to prvide smardiw ssandleattlity.

In addtuion.

lie calre was sumcessfly installed and tested after Installaaton wt no signs of damage. Therefre, Mte wider tape Is not a concern.Application and paclag Fm other annm designs like Secton 2.5 orAltacrnmenl I T Peg om--as-,49a ana Cs- Equal This specification required tape. per secltn 73.Z4. specmmcatn 0,S&G039.O0tiO-401O0 16939 tape layers; one layer applied nao meta131 tapes SMail be requlies mat te first of tape Mftmhnisit lb the Ta and a second applied heltraly In Mhe same be appliedwiflout ovramp arid malt Olutirtte cable wras overap whichi meets the, lEMA ulrealln.

Anry sap gaps a second layer of tape be pridallerd wt 2 layers cr starclarta as s 2D% of tape widtL tiverlapped a mintomrn af 12,5%. 90 wri ironrs lape helicaly with a M0% gap cc me Inner tape and a 12% verlap an the Table 2 Bronze Tape Parameters vs IEC 60502-2 COMPARISON OF STANDARDS AND SPEC REQUIREMENTS Parenstere UEKA WC 74 IEC 6050-2 Cae Speeirtoslim asoets Cable Sirmonu"apu~ti pt atmerm Parawnstam I Requirteu t Parasters Evaluation Uetasbc Taps Armor Per Section 7.3.3.2: Per 13.2 the armour Section2.5ctAltadiunent a=d'C- The spectrlcaltin required a bronzemtarac tn Nontmagrellc apes can ot single-core castes nir use 1 of spedntcaton 0 -15939. the O1nulle cable tape. Vta1ch meets NEMA IEC standas s.be moade ofa! lUrninr. o c. sysems constitat 0139.-00o-0t10 requires ws provideldt111 2 bras. browns. 0450- or Mate". a Metaofc Shied Anntr layem olritze tape.n!". Si. or tlaieless unless a special cons"luai on Tape to be made of set is chlosen. Noumaigrislc linme.Trhclawas Per tasb 7-12 he Per Sectiono 13.4 arm 135. Section 2.5 orAitasctner Per OM-31 6498 aid CS- Tre specttIcaln required a bronze met ali ncdnal of the noinrk WarlV ess or I oa t iecacoi ont-- 16939. the catle tape thickness of 213 mils In lotia (Wo x 10 mils bon.e tape per cale tape Itr a carte aim a 0139.00-03-40010 requires was pMOs sMM 2 which meets the HEMA standards, The [CC dianets; calcnltaed per flricaur7 dranmeter unidr (2) tao ten mnt tape laeysis armid rtworoe iastartar uises two layers or appioarkititey, 20 Appendix C. the amm the arnour above 30 ,m layemn tape. tape.imist be20 fnts, (1.181 51) aid less than 70 mm (2.756 In) shruld be 0.5 mnm (19.685 MIS).__.Pertain 7-11. the There is no spcaM Spectltoalkn Oss- Per courrspowiedncerromn NEmA requirements agains the actl tape v. Im nomuinia o m s're retqlrmeit o oMe tape 0i139.0-0t.1-11t1 alaon the tapewlidh IS are sealuated under study ONS-17-tI5-I O0-ti braine tape based or Wwl. cornawis no tape %Wh 1.25 snims. Rev U Me cats diamnetes; reeqirtentmr.

IC standards do not specify width requiremer s.calcula.ed per Appendrlx C. armor must be 0.875 Incies nominora.Applicatlon ad1 For rther armor Per Settor 13.7 tie tape Secion 2.5 ci Atadciene Per ON6F315,498 and CS- The specilfiction required to tape layers: wl speclsg lise tape, per s.ctr anart sh"ll be appled I oi 0W- 16939. Me sluantha ctale layer applise t dat aid a second layer wth avee 7.34, Iwi metal tapes nerally In two Layers (20 013LOO-t-iOIO requires was pFrIded With 2 slfllh Is In line wstM llse HEMA standard r ste shall be applied hetltaly mis each) no that the cutsr Utat tie firt laeir of tape layers af I0 MU ro armi tape. The NEMA starndard doeas M5 qisetlcat In the same arenan. tape Is approlxmaley be appeedwitmout tape retoally applied sM discuss me applicaton of non-magrellc tape.' Te Any %Tap gaps aresa over me gapeoflte tnrer c-ialap and Mta a second a 10% gap onthme tIner ONS spec does not sperlly te or e 20% it tape idln. lape. The gap betaeen layr of rae lie tape aid a 12o telap secoed layer agarnst te first layer. Stice lhe adjatent tims of each tape oGerlapped a irilrnum of on Me outer lape. masiornim ai',ed ap In the lEC standard Is sall not exceed 60 % CC rte 12.6%. 50%. most of ore tle will nave 20 MRit otap ?VMdl of the tape. anl sours parts 'l have 40 wiiis.Page 9 of 21 Single Failure Scenarios Oconee's design and single failure philosophy were developed prior to most of the present day industry standards.

Oconee was designed in the late 1960s before 10 CFR Part 50 Appendix A, "General Design Criteria for Nuclear Power Plants" was issued by the NRC. In addition, the NRC's Standard Review Plan (NUREG 800) was not in existence and industry standards that address the single failure criterion were not available.

In the absence of regulations and standards, Oconee and other early commercial nuclear power plants developed their own single failure criterion, using correspondence from the Atomic Energy Commission (AEC) and available mechanical and electrical codes.The original design criteria for Oconee were developed in consideration of the 70 General Design Criteria for Nuclear Power Plant Construction Permits proposed by the AEC in a proposed rule-making published for 10CFR Part 50 in the Federal Register of 11 July 1967. These 70 criteria were presented and discussed in Appendix 1A of the original FSAR, and are contained in Section 3.1 of the UFSAR. The General Design Criteria that pertain to single failure are discussed in Section 3.2.1.1.Since the original FSAR was released, the design of the station and some design criteria have been modified.

All commitments to change the design criteria are captured in licensing correspondence.

Therefore, the Oconee-Keowee design criterion, including the single failure criterion, consists of commitments made in the original FSAR plus commitments made in licensing correspondence.

There is no single industry document which, by itself, states the Duke Power/Oconee-Keowee position on the application of the Single Failure Criterion.

In a response to the NRC request for additional information regarding the design of Oconee's onsite th emergency power system dated May 13 , 1976 ONS committed that "The design of the Oconee onsite emergency AC and DC power systems conforms to the single failure requirements of IEEE 279-1971." The single failure requirements are contained in section 4.2 of IEEE 279-1971 and state "any single failure within the protection system shall not prevent proper protective action at the system level when required." The ONS UFSAR also states in section 8.3.1.2 that "the basic design criterion for the electrical portion of the emergency electric power system of a nuclear unit, including generating sources, distribution system, and controls is that a single failure of any component, passive or active, will not preclude the system from supplying emergency power when required.

Special provisions have been employed to accomplish this which include...diverse protective relaying for each circuit breaker...

physical separation and other features." ONS specification OSS-254.00-00-4013 "Design Basis Specification for the Oconee Single Failure Criterion" provides the overall site guidance on the application of the single failure criterion.

Reference is made within the single failure specification to the NRC authored information report SECY-77-439"Single Failure Criterion." The SECY-77-439 document states that "in applying the [single failure]Criterion, it is not assumed that any conceivable failure could occur... In general only those systems or components which are iudged to have a credible chance of failure are assumed to fail when the Single Failure Criterion is applied." The SECY-77-439 guidance is echoed in OSS-254.00-00-4013 Section 3.2.1.4.1

'Credible Failures' which states "Application of the single failure criterion does not require that Page 10 of 21 all failures be assumed. Only those failures with a credible chance of occurring must be considered in evaluations of system design bases (Reference

[SECY-77-439]).

It is the practice of Oconee to look at equipment operating histories and consider the equipment manufacturers' experiences when evaluating if a hypothetical failure is credible and must be considered when applying the single failure criterion." Further guidance was found in IEEE 379-2000 "Standard for Application of the Single Failure Criterion to Nuclear Power Generating Station Class 1E Systems" which states that "reliability analysis, probability assessment, operating experience, engineering judgment, or a combination thereof, may be used to establish a basis for excluding a particular failure from the single-failure analysis." IEEE 379-2000 is endorsed by NRC Regulatory Guide (RG) 1.53.Using the ONS Single Failure Design Basis Specification in addition to SECY-77-439 and IEEE 379 documents as guidance, a credibility cable failure evaluation was performed on Trench 3 as part of the PDO in PIP 0-14-3190.

This credibility based evaluation was independently supported by a second evaluation done as part of URS study ONS-17-05-100-001.

The following failure modes of the KUG feeder cables were examined: 1) A single phase-to-ground fault was deemed credible.2) A high impedance ground fault was deemed credible and would be bounded by the single phase-to-ground fault analysis.3) A double phase-to-ground fault was deemed non-credible.

This would require the simultaneous failure of the insulation between the conductor and grounded bronze tape on two separate cables and would thus go beyond the failure of a single component.

In addition, a single phase-to-ground could not propagate to a double phase to ground fault as the grounded bronze tape combined with the protective relaying logic ensures cable protection.

See Protective Relaying section above for discussion on relaying logic and ground fault magnitude.

4) A three phase-to-ground fault was deemed non-credible.

Similar to the discussion for a double phase-to-ground, extended to the simultaneous failure of a third cable.5) A phase-to-phase fault was deemed non-credible.

This fault would require failing through the insulation and bronze tape shield/armor of two separate cables in an area of close enough proximity for the bare conductors to touch. This mechanism is excluded as discussed in the double phase-to-ground fault scenario.6) Three phase-to-phase fault was deemed credible only at the terminal ends of the cable runs.ONS has analyzed this case in calculations OSC-11061, OSC-11062 and OSC-11013.

For a fault of this type occurring at other than the cable terminal ends, per NUREG/CR-6850, there is no OE in the industry for cables with grounded metallic shields. For this type of failure to occur, the entire cable systems (insulation, metallic shield and jacket) of all three phases would have to fail in close proximity to each other. Therefore, non-terminal end three-phase faults are excluded.Prior testing performed by Duke in 1977 on interlocked steel armored cable (as documented in MCM-1354.00-0029.001) haý shown that cable armoring provides excellent prevention of cable to cable faults Page 11 of 21 or failures.

While the bronze tape shield/armor cable design was outside of the scope of the 1977 testing, the robust design of the medium voltage power cables provides a commensurate level of protection from cable to cable faults or failures based on the current analysis and testing. The use of armored cable at ONS supports the credibility determinations detailed above.Further guidance on analyzing the potential of various cable failure mechanisms was gleaned from NUREG/CR-6850 (EPRI/NRC-RES Fire PRA Methodology for Nuclear Power Facilities), as endorsed by NRC RG 1.205. NUREG-6850 contains the following statements on rugged grounded shields precluding certain cable failure mechanisms:

1) "Three-phase proper polarity hot shorts on AC power systems: Case 3: Armored cable or cable in dedicated conduit. Three-phase proper polarity faults are not considered credible for armored power cable or a single triplex cable in a dedicated conduit. The basis for exclusion is that multiconductor-to-multiconductor hot shorts are not plausible given the intervening grounded barrier (i.e. the armor or conduit)." 2) "Plant specific design features can preclude certain circuit failures from occurring.

For example, the use of grounded, metallic, armored cable or dedicated conduit, shorting switches or rugged (e.g. braided metal) shielding are considered in most cases to preclude external hot shorts from further consideration." 3) "If the cable design can be verified as one that employs a rugged grounded metallic shield (e.g.armor, braid, etc.) then the analysis need only consider the effects of shorting between the conductors within the shield and shorting the conductors to ground, i.e., the effects of shorts from external sources need not be considered." NUREG-6850 also contains the following statements which support the consideration of a three phase bolted fault only at the terminations:

1) "Cable ducts: A power conductor configuration that provides a function like a bus duct but uses a length of insulated electrical cable in lieu of metal bus bars... Cable ducts may be used in application conditions similarly to either a segmented or non-segmented bus duct." The medium voltage power cables in Trench 3 meet this definition of a cable duct.2) "Because nonsegmented bus ducts (category
1) and cable ducts (category
3) have no transition points other than theterminations at the end device, no treatment of bus duct faults/fires independent from the treatment of fires for the end devices is required.

That is, arc faults for these two categories of bus ducts, 1 and 3, are inherently included in the treatment of the end device, and no further treatment is needed." 3) "segmented bus ducts (category 2), a number of the identified fire events were manifested at bus transition points (a point where two segments of the bus duct are bolted together) rather than at the bus termination points. These events were generally attributed to loose bolted connections, to failed insulators, or to the accumulation of dirt/debris/contaminants in the bus duct. The key, however, is that the effects of the fault are manifested at transition points along the bus duct length. Fire scenarios for segmented bus ducts should, therefore, be postulated to occur at duct transition points (i.e., bolted connections)." The failure mechanisms deemed credible above were evaluated at length in the operability determinations documented in PIPs 0-14-3190 and 0-14-5125, as well as calculations OSC-11013, OSC-Page 12 of 21 11061, and OSC-11062.

The results of those evaluations support that the design of Trench 3 is safe and meets industry standards and regulatory guidance.Defense in Depth The SECY-77-439 makes the overall point that the single failure criterion is only "one element of the defense in depth approach to reactor safety." ONS has a diverse range of power sources that are available to the nuclear units, as shown in the lists below and Figure 5." Unit Main Generator via Unit Auxiliary Transformer (1T, 2T, 3T)" Offsite Power via 230kV Switchyard and Start-up Transformer (CT1, CT2, CT3)" Keowee Hydro Unit Overhead Power Path" Keowee Hydro Unit Underground Power Path via Transformer CT4" Lee Combustion Turbine (7C or 8C) via Isolated Line and Transformer CT5" Offsite Power via 1OOkV Central Switchyard and Transformer CT5" Offsite Power via back charge of Main Step-up Transformer and Aux Transformer" Shared Start-up Transformer via Emergency Start-up (cross connect) Bus In addition, the following geographically diverse offsite power sources are available." Large Transmission Switchyards at ONS" 230kV Switchyard" 525kV Switchyard" Multiple separate Transmission Line Connections to ONS Switchyards" ONS Switchyards connected via Auto-bank Transformer" Jocassee Hydro and its switchyard, north of ONS, tie to ONS 230kV Switchyard" 1OOkV Central Switchyard and Feeder to ONS Transformer CT5 Figure 5: Power Sources Available to ONS Page 13 of 21 Probabilistic Risk Assessment (PRA)PRA analyses has also been done on the proposed cable failures." The probability of a fault at a connection point is estimated to be approximately 1E-04 per year" The CDF associated with a connection fault is estimated to be less than 1E-07 per year" A passive cable fault in the trench would have substantially less safety significance" If a phase to phase fault was a credible event, the CDF would be on the order of 1E-11 per year Reliance on Commercial Equipment for Protection Per Section 3.2.1.4.3 (Effects of a Non-Qualified Component Failure) of OSS-0254.00-00-4013, Oconee Single Failure Criterion: "The licensing basis for Oconee contains single failure evaluations that make no distinction between a failure of a "qualified" component and a failure of a "non-qualified" component. (Here "non-qualified" is used to represent equipment variously called control grade, non-safety, non-QA-1, etc. in Oconee documents).

The relevant distinction for application of single failure requirements is limited to whether the specific system in question is committed to be designed to handle single failures.

The components of such a system may or may not be "qualified", but that is not a factor for single failure design requirements.

This point is important because design criteria applied to plants licensed later than Oconee may assume all "non-qualified" SSCs (structures, systems, and components) fail, in addition to taking a single failure in a "qualified" system. Such assumptions do not align to Oconee's licensing basis." 4. Response to Specific Questions 1. What is the ONS licensing basis, design basis, NRC regulations for analyzing electricalfailures (single failure or otherwise) between medium voltage AC power and low voltage DC circuits?The licensing basis, design basis, and NRC regulations for the failure analysis of the Keowee Underground Trench is discussed at length in the "Single Failure Scenarios" section above.Additionally, further PRA analysis of a fault in Trench 3 is documented in the "Probabilistic Risk Assessment (PRA)" section above.An overview of the basis is as follows: ONS UFSAR section 8.3.1.4.6.2 states that "Control, instrumentation, and power cables are applied and routed to minimize their vulnerability to damage from any source" and "It is our intent wherever physically possible to utilize metallically armored and protected cables systems. By this we mean the use of rigid and thin wall metal conduit, metal sheathed cables (aluminum and other Page 14 of 21 metals), bronze armored control cables, steel interlocked armor, or metallic taped power and control cables, and either interlocked armor, served wire, or braided armored instrumentation cables." The UFSAR section 8.3.1.4.6.2 statements underlay the basis for both the design of the overall cable construction and the configuration of the trench design.The ONS UFSAR also states in section 8.3.1.2 that "the basic design criterion for the electrical portion of the emergency electric power system of a nuclear unit, including generating sources, distribution system, and controls is that a single failure of any component, passive or active, will not preclude the system from supplying emergency power when required.

Special provisions have been employed to accomplish this which include...diverse protective relaying for each circuit breaker...

physical separation and other features." Additionally, in a response to the NRC request for additional information regarding the design of th Oconee's onsite emergency power system dated May 13t, 1976 ONS committed that "The design of the Oconee onsite emergency AC and DC power systems conforms to the single failure requirements of IEEE 279-1971." The single failure requirements are contained in section 4.2 of IEEE 279-1971 and state "any single failure within the protection system shall not prevent proper protective action at the system level when required." UFSAR Table 8.4 documents the single failure analysis for the emergency electrical power system.The UFSAR 8.3.1.2 statements, as supplemented by the IEEE 279-1971 and the May 13, 1976 letter, underlay the basis for the failure analysis of the Keowee Underground Trench.ONS specification OSS-254.00-00-4013 "Design Basis Specification for the Oconee Single Failure Criterion" provides the overall site guidance on the application of the single failure criterion.

Reference is made within the single failure specification to the NRC authored information report SECY-77-439 "Single Failure Criterion." The SECY-77-439 document states that "in applying the[single failure] Criterion, it is not assumed that any conceivable failure could occur... In general only those systems or components which are iudged to have a credible chance of failure are assumed to fail when the Single Failure Criterion is applied." The SECY-77-439 guidance is echoed in OSS-254.00-00-4013 Section 3.2.1.4.1

'Credible Failures' which states "Application of the single failure criterion does not require that all failures be assumed. Only those failures with a credible chance of occurring must be considered in evaluations of system design bases (Reference

[SECY-77-439]).

It is the practice of Oconee to look at equipment operating histories and consider the equipment manufacturers' experiences when evaluating if a hypothetical failure is credible and must be considered when applying the single failure criterion." These statements underlay the basis for considerations to be taken while performing the failure analysis.Prior testing performed by Duke in 1977 on interlocked steel armored cable (as documented in MCM-1354.00-0029.001) has shown that cable armoring provides excellent prevention of cable to cable faults or failures.

While the bronze tape shield/armor cable design was outside of the scope of the 1977 testing, the robust design of the medium voltage power cables provides a commensurate level of protection from cable to cable faults or failures based on the current analysis and testing.The use of armored cable at ONS supports the credibility determinations detailed above.Page 15 of 21 Further guidance on analyzing the potential of various cable failure mechanisms was gleaned from NUREG/CR-6850 (EPRI/NRC-RES Fire PRA Methodology for Nuclear Power Facilities), as endorsed by NRC RG 1.205. NUREG-6850 contains the following statements on rugged grounded shields precluding certain cable failure mechanisms:

1) "Three-phase proper polarity hot shorts on AC power systems: Case 3: Armored cable or cable in dedicated conduit. Three-phase proper polarity faults are not considered credible for armored power cable or a single triplex cable in a dedicated conduit. The basis for exclusion is that multiconductor-to-multiconductor hot shorts are not plausible given the intervening grounded barrier (i.e. the armor or conduit)." 2) "Plant specific design features can preclude certain circuit failures from occurring.

For example, the use of grounded, metallic, armored cable or dedicated conduit, shorting switches or rugged (e.g. braided metal) shielding are considered in most cases to preclude external hot shorts from further consideration." 3) "If the cable design can be verified as one that employs a rugged grounded metallic shield (e.g.armor, braid, etc.) then the analysis need only consider the effects of shorting between the conductors within the shield and shorting the conductors to ground, i.e., the effects of shorts from external sources need not be considered." NUREG-6850 also contains the following statements which support the consideration of a three phase bolted fault only at the terminations:

1) "Cable ducts: A power conductor configuration that provides a function like a bus duct but uses a length of insulated electrical cable in lieu of metal bus bars... Cable ducts may be used in application conditions similarly to either a segmented or non-segmented bus duct." The medium voltage power cables in Trench 3 meet this definition of a cable duct.2) "Because nonsegmented bus ducts (category
1) and cable ducts (category
3) have no transition points other than the terminations at the end device, no treatment of bus duct faults/fires independent from the treatment of fires for the end devices is required.

That is, arc faults for these two categories of bus ducts, 1 and 3, are inherently included in the treatment of the end device, and no further treatment is needed." 3) "segmented bus ducts (category 2), a number of the identified fire events were manifested at bus transition points (a point where two segments of the bus duct are bolted together) rather than at the bus termination points. These events were generally attributed to loose bolted connections, to failed insulators, or to the accumulation of dirt/debris/contaminants in the bus duct. The key, however, is that the effects of the fault are manifested at transition points along the bus duct length. Fire scenarios for segmented bus ducts should, therefore, be postulated to occur at duct transition points (i.e., bolted connections)." The consideration of the 1977 testing and the NUREG-6850 guidance ties back to the SECY-77-439 statements above for considerations to be taken when analyzing for failures.Overall, inter-cable faults "between" medium voltage armored power cables and armored control (DC circuits) are not postulated.

The routing of these type cables includes physical separation (not in same tray or on same support) to mitigate the risk that both cables could be impacted by a common source. Also the cable intervening grounded shield/armor results in any fault being shorted to ground prior to affecting adjacent cables (power or control).

The non-credible failure mechanism Page 16 of 21 necessary to result in an inter-cable fault would involve a failure of the intervening armor of both cables.2. Within ONS Licensing Basis: a. Are medium voltage power cables that are intended to provide emergency power to the RPS/ESPS equipment as well as provide the motive force to the actuated ESPS equipment during a Chapter 15 event within the scope of IEEE 279-1971 ?See the ONS letter to the NRC dated May 1 3 th, 1976 for commitments to IEEE 279-1971.

The criterion in section 4.2 of IEEE 279 states "Any single failure within the protection system shall not prevent proper protective action at the system level when required".

In correspondence to the NRC dated May 13, 1976 Oconee stated that "The design of the Oconee onsite emergency AC and DC power systems conforms to the single failure requirements of IEEE 279-1971."" Must such power cables be considered under Section 3 "Design Basis" Item 7for transient conditions?

No, the May 1 3 th, 1976 letter committed to the "single failure requirements of IEEE 279-1971." The requirements are contained in IEEE 279-1971 Section 4 "Requirements" with the single failure portion being limited to Section 4.2 "Single Failure Criterion." The letter did not relate any other section of IEEE 279-1971 to the design of the Oconee onsite emergency AC and DC power systems.* Must potential multi-phase short circuits or ground faults from such power cables be considered under Section 3 "Design Basis" Item 8for unusual events, etc. ?No, the May 13th, 1976 letter committed to the "single failure requirements of IEEE 279-1971." The requirements are contained in IEEE 279-1971 Section 4 "Requirements" with the single failure portion being limited to Section 4.2 "Single Failure Criterion." The letter did not relate any other section of IEEE 279-1971 to the design of the Oconee onsite emergency AC and DC power systems.b. Does three-phase medium voltage power cables, intended to provide Class 1E emergency power to the RPS/ESPS equipment, represent "interconnecting signal or power cables" as discussed in 4.2 of IEEE 279?ONS committed in the May 13, 1976 letter to the NRC that the design of the onsite emergency power system meets section 4.2 of IEEE-279 and that a failure within the system would not prevent proper action at the system level. A failure of the underground path is analyzed and would be mitigated via the overhead path. UFSAR Table 8.4 documents the single failure analysis for the emergency electrical power system.c. Can the timing of electricalfailures in assumed analyses be limited to reduce the consequential damage as described in the "single failure memo to file"?The emergency power system and emergency power switching logic was designed based on failures occurring on initial demand. This design basis has been maintained throughout the Page 17 of 21 operating history of Oconee. The emergency power switching logic is power seeking in that it will transfer to an alternate source if it determines that power is not available.

The switching logic and the associated time delays in the Chapter 15 accident analysis are predicated on failures occurring on initial demand. The design basis selects the most conservative single failure to maximize the consequences of the associated design basis accident.* How is the single failure timing applied to the commercial Font power feeder and the QA-1 power feeders from the KHUs to PSW different than the Class 1E power feeders to the CT-4 transformer?

The single failure timing is applied consistently to both. The PSW system is designed as a defense in depth system for beyond design basis events.d. Can ONS Staff make any distinctions between passive and active electrical single failures as described in the "single failure memo to file"?ONS does not make a distinction between active and passive failures for the electrical portions of the emergency power system. As stated in UFSAR Section 8.3.1.2 "the basic design principle for the electrical portion of the emergency electric power system is that a single failure of any component, passive or active, will not preclude the system from supplying emergency power when required.

Special provisions have been employed to accomplish this which include...diverse protective relaying for each circuit breaker, physical separation and other features." e. Is the ONS Staff required to analyze for contributions of multi-phase short circuits as well as ground faults within trench 3 in order to be compliant with the regulations and/or the current licensing basis for ONS?As stated in UFSAR Section 8.3.1.2 a single failure of active and passive components within the system is required.

The level of analysis of a specific failure case is commensurate with the credibility of such a case as exemplified in NRC and industry guidance documents.

See the "Single Failure Scenarios" section above for a detailed explanation specific to the above examples.f. Is the licensee required to analyze for consequential damage for electricalfailures to adjacent Class 1E safety systems?* Is the licensee required to assume that AC circuits could short to DC circuits?UFSAR Section 8.3.1.2 requires analysis of single failures of passive and active components.

The failure mechanism of AC circuits shorting to DC circuits has been determined to be incredible.

Based on physical separation and intervening grounded armor, AC and DC cables are not assumed to short to each other.Page 18 of 21

  • If so, are the installed ONS 125 VDC protective devices sufficient to mitigate the effect of AC voltages ranging from 2.5 kVAC to 13.8 kVAC to prevent these voltages from propagating throughout the DC systems?The failure mechanism required to necessitate the need for 125 VDC protective devices to mitigate the effects of AC voltages has been deemed incredible for the emergency power system at ONS.g. Are all commercial non-quality related (i.e. not QA-1 or QA-5) electrical components assumed to fail in the most limiting way possible?The licensing basis for ONS with respect to failure analysis makes no distinction between commercial and "quality related' components.

A failure of a commercial component would be the single failure in that instance and not compounded with other single failures.

The credible failures of the component would then be assumed. See "Reliance on commercial equipment for protection" section above.* Does the failure of one of these commercial components represent a "single failure" in the context of the ONS licensing basis?Yes, Single failure analysis is done irrespective of QA classification of components.

h. Can unrestrained cable whip in Trench 3 be assumed to cause cable damage leading to secondary short circuits that could cause damage to the DC systems and should these effects of cable whip be analyzed?No, the analysis documented in the PDO for PIP 0-14-2965 states the following conclusions: "Based upon this evaluation, a postulated, credible fault of the 13.8 kV cables (both the Keowee Underground to CT4 or PSW feeder) as well as the 4kV cable (CX feeder from 1TC) would not cause collateral damage on nearby cables (referred to as I&C cables) that could either prevent the remaining Keowee unit aligned to the overhead path from a successful emergency start or disable operation of the Keowee overhead unit after an emergency start.The I&C cables in Trench #3 have sufficient mechanical protection such that interaction with the 750 kcmil cables will not adversely affect the insulation integrity or function of the armored cables due to the unrestrained cables having a terminal velocity of about 150 in/sec which corresponds to a drop height of only 30" with a fault current of 27kA (most bounding fault current case).The I&C cables in Trench #3 are shielded from the effects of the EMI or induced voltage if the 750 Kcmil cables are in close proximity or in direct contact. The multiple barriers (outer cable jacket, interlocked steel armor and shield) in the I&C cable design will protect the cable conductors from damage if an energized severed 750 kcmil cable end came in contact with the I&C cables until the fault is cleared in 181 milliseconds (most bounding fault clearing time) or less." Page 19 of 21 Are overload currents as well as short circuit currents required to be evaluated to determine the most limiting results from electricalfaults and component failures?* Do the results of such an analysis influence the required component separation to meet the regulatory requirements and the ONS licensing basis?An overloaded conductor on the 13.8kV Keowee Underground Path concentric power cable could, depending on the severity, lead to degraded insulation between the conductor and the shield. This could in turn lead to a ground fault between the conductor and the grounded shield. The ground fault on the Keowee Underground Path would be limited by the high impedance grounded system on the Keowee generator.

Also, the ground fault would be quickly detected by the ground fault relay(s) and interrupted by the underground path circuit breaker(s).

Therefore, an overloaded conductor would be bounded by the short circuit analysis.j. Can cable shielding or armor prevent short circuits or limit faulted currents or voltages?* Can the two wraps of bronze shielding tape in the licensee's current power cable configuration be considered equivalent to steel interlocked armored cable as described in test report MCM 1354.00-00-0029.001

?* Are the results of test report MCM 1354.00-00-0029 sufficient to demonstrate that electrical faults cannot propagate from one cable to another as described in the single failure DBD, Section 3.3.6.1 ?Yes, the intervening grounded armor provides a grounding plane that limits faults from propagating beyond phase-to-ground.

The "Cable Testing" section above describes how bronze shielded tape medium voltage cables of the design used in Trench 3 passed the performance requirements of UL 1569 'Metal Clad Cable' test sections 24 (impact testing), 25 (increasing crush), and 26 (direct burial crush). Also, see further discussion in the "Single Failure Scenarios" section above. The overall analysis supports that the bronze tape shield/armor provides a level of protection sufficient to preclude inter-cable shorts or faults.k. Does the interconnected nature of the Class 1E DC systems in the ONS KHU start panels and Keowee KHU start panels present vulnerabilities where DC to DC interaction could disable the Keowee emergency power system?Separation concerns were documented in PIP 0-14-3915 during the CDBI and resolved based on the following:

1. The mutually redundant safety related wiring has been separated/re-trained (or a barrier installed) to ensure compliance with OSS-0218.00-00-0019
2. The wiring identified in the Keowee Emergency Start Panels (KESP) that were identified as touching or in close proximity are not mutually redundant circuits and therefore do not need to meet separation criteria per OSS-0218.00-00-0019.

No additional actions will be taken to re-train or re-route wires in the KESPs.Page 20 of 21

5. Summary This submittal provides additional information to address the configuration of cabling in the underground concrete raceway and the associated unresolved item from the 2014 NRC CBDI.Duke Energy's position is that the underground power path meets the design and licensing requirements for Oconee Nuclear Site. However, Duke Energy agrees with feedback during the CDBI that the UFSAR supporting documentation does not explicitly cover bronze tape shielded cables. In response to the UFSAR concerns, the issue was entered into the corrective action program and Duke Energy initiated efforts immediately after the CDBI to conduct testing of these cables. Phase 1 of this testing was completed in February 2015 and confirmed that the bronze tape shielded cable design in use in the Keowee Underground Trench passed the performance requirements in UL 1569 'Metal Clad Cable' test sections 24 (impact testing), 25 (increasing crush), and 26 (direct burial crush) for mechanical protection.

The electrical testing performed subsequent to the mechanical tests validated that the medium voltage power cables would retain their functionality through the physical deformation specified by the testing. Phase 2 of the testing, anticipated for the fourth quarter of 2015, will perform fault testing of the medium voltage power cables. This testing will use additional sections of the concrete raceway to replicate the as-installed configuration of the underground trench. Given that the same separation will be used in this testing as exists in the plant, Duke Energy will use this testing to validate that the existing separation requirements will not result in any adverse interaction between the faulted medium voltage power cables and any non-faulted medium voltage power cables or low voltage control cables. The results of this testing will be used to update the Oconee UFSAR to specifically address the bronze tape shielded power cables. Duke Energy has also performed probabilistic risk analyses of the postulated cable fault scenario and has determined that the risk is exceedingly low. In conclusion, Duke Energy believes that the existing cable separation requirements at Oconee are sufficient.

If the fault testing provides new information that challenges the adequacy of the existing cable separation requirements at Oconee, this will be entered into and addressed through the corrective action program.Page 21 of 21

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